Raphael Mathevet

Pascal Marty

come

Can Environmental and Conservation Research Do without Social Scientists? A Comment on Victoria Y. Martin (2019)

In her recent Viewpoint article, Victoria Y. [START_REF] Martin | Four common problems in environmental social research undertaken by natural scientists[END_REF] questions why natural scientists conduct social science research without specific training or experience in the social sciences and calls for more collaboration between natural and social scientists. As two geographers with years of experience of working with ecologists, we concur and, furthermore, ask why many environmental studies deploy social research tools or collaborative approaches with local stakeholders without enrolling social scientists. In our experience, one of the main factors underpinning these failures in the collaborative process is the high diversity of approaches in social sciences. For too long, natural scientists have considered social scientists to be facilitators for implementing conservation solutions, unaware that the latter have a different understanding and vision of what a society is and of what nature is, based on different theoretical frameworks. In the present letter, we distinguish three different approaches in environmental social science and recommend that natural scientists discuss them with prospective collaborators when building joint projects, to minimize misunderstandings [START_REF] Mathevet | Peut-on faire de la biologie de la conservation sans les sciences de l'homme et de la société? État des lieux. [Can conservation biology do without social and human sciences? Current situation[END_REF]. A first group includes social scientists who focus on specific questions from the social sciences and implement their research without consideration for the natural scientists' work, even if their outcomes might be of interest to conservation biology (e.g., surveys on environmental attitudes and values). A second group includes researchers focused on the social-ecological community made of humans and nonhumans (e.g., plants, animals, objects). They describe how the members of this community interact and live together and address the plurality of values and legitimacies of actions [START_REF] Latour | An Inquiry into Modes of Existence An Anthropology of the Moderns[END_REF]. A last group of social scientists is engaged in power relationships between stakeholders and can be further split in two subgroups. Members of the first subgroup focus on people, considering environmental problems to be mainly socially constructed. They critically analyze the power relationships, being particularly attentive to the most vulnerable and marginalized social groups [START_REF] Robbins | Political Ecology: A Critical Introduction[END_REF]. Researchers in the second subgroup focus on the environmental problem itself and look for ways of solving it. They too analyze power relationships but are particularly sensitive to impacts on sustainability, wildlife, and biodiversity, supporting key strategic stakeholders in decision-making processes [START_REF] Stern | Social Science Theory for Environmental Sustainability[END_REF]. Some social scientists may move across groups according their interactions with natural scientists, whereas others are stable in their position. If natural scientists aim to implement action research, only the last subgroup of social scientists fully aligns with their approach. If they are instead attempting to understand general or specific social processes, the other groups fit better. While recognizing that disciplinary knowledge is important in environmental research, we argue that the lack of environmental social scientists trained in interdisciplinarity and action research may help to explain why some natural scientists implement social research by their own means. Acknowledging the need for mutual learning and joint problem-solving, we invite the conservation community to move beyond shallow engagement with the environmental social sciences [START_REF] Bennett | Conservation social science: Understanding and integrating human dimensions to improve conservation[END_REF]) and social scientists to increase their familiarity with conservation biology.

  doi:10.1093/biosci/biaa016 BioScience 2020 RAPHAËL MATHEVET AND PASCAL MARTY Raphaël Mathevet (raphael.mathevet@cefe.cnrs.fr) is affiliated with the Centre d'Écologie Fonctionnelle et Évolutive, CNRS, Université de Montpellier, Université Paul Valéry Montpellier 3, EPHE, IRD, in Montpellier, France. He is also affiliated with IFP UMIFRE 21 CNRS/MAEE, in Pondicherry, India. Pascal Marty is affiliated with UMR 7733 CNRS, Université de Paris 1 Panthéon-Sorbonne, LADYSS, Campus Condorcet, in Paris and Aubervilliers, France.


Kevin Jacq
email: jacq.kevin@hotmail.fr

Estelle Ployon

William Rapuc

Claire Blanchet

Cécile Pignol

Didier Coquin

Bernard Fanget

Kévin Jacq

Kévin Jacq

Structure-from-motion, multi-view stereo photogrammetry applied to line-scan sediment core images

Keywords: Structure from motion photogrammetry, High-resolution image, Automatic image assembly, Orthorectification, Sediment cores, Agisoft Metashape

Introduction

Paleoclimate and paleoenvironmental conditions are frequently inferred from natural archives such as lake and marine sediment cores, tree rings, corals and speleothems (PAGES2k Consortium 2017).

These archives are often sampled for multiple physical, chemical and biological analyses. Prior to sampling, the archives are sometimes imaged with an RGB camera, a process that is rapid, cheap and simple, and used to preserve primary information, e.g. about color and structure. Such images are, however, rarely exploited to extract relevant environmental information, which can be accomplished using image processing techniques. Characterization of structures such as laminae or instantaneous deposits enables creation of spatial landmarks that can be matched with other analyses, but requires high-resolution images.

Structure-from-Motion, Multi-View-Stereo (SfM-MVS) photogrammetry is gaining interest in the Geosciences, as a method to model object surfaces at high resolution. It enables use of 2D images, taken at different orientations and positions, for construction of a 3D structure in color. SfM-MVS is widely used to reconstruct topography in contexts where other methods, such as LiDAR, cannot be used [START_REF] Smith | Structure from motion photogrammetry in physical geography[END_REF][START_REF] James | Guidelines on the use of structure-from-motion photogrammetry in geomorphic research[END_REF]. [START_REF] Eltner | Image-based surface reconstruction in geomorphometry-merits, limits and developments[END_REF] summarized articles on SfM-MVS published between 2012 and 2016, and noted an increase in numbers of papers across all disciplines, e.g. soil science, volcanology, glaciology, fluvial and coastal morphology. Objects such as bones or archaeological artifacts can also be reconstructed with SfM-MVS [START_REF] Falkingham | Low cost 3D scanning using off-the-shelf video gaming peripherals[END_REF][START_REF] Marchal | The Microsoft Kinect: validation of a robust and low-cost 3D scanner for biological science[END_REF], as can trees, for forest monitoring and management [START_REF] Piermattei | Terrestrial structure from motion photogrammetry for deriving forest inventory data[END_REF]. SfM-MVS has proven itself in the laboratory, with results similar to a scanner. Airborne SfM-MVS has been shown to provide better reconstruction quality than other methods, at much lower cost [START_REF] Cawood | LiDAR, UAV or compass-clinometer? Accuracy, coverage and the effects on structural models[END_REF][START_REF] Bilmes | Digital outcrop modelling using "structure-from-motion" photogrammetry: Acquisition strategies, validation and interpretations to different sedimentary environments[END_REF]. Some environmental samples possess periodic structures associated with natural cycles (seasonal, annual, or multi-annual) or instantaneous events (e.g. floods, avalanches, volcanic eruptions). Several studies have attempted to identify and count such periodic structures using imaging techniques [START_REF] Meyer | The WinGeol Lamination Tool: new software for rapid, semi -automated analysis of laminated climate archives[END_REF][START_REF] Weber | BMPix and PEAK tools: New methods for automated laminae recognition and counting -application to glacial varves from Antarctic marine sediment[END_REF][START_REF] Ndiaye | A semi automated method for laminated sediments analysis[END_REF][START_REF] Vannière | Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy[END_REF][START_REF] Ebert | Semi-automated detection of annual laminae (varves) in lake sediments using a fuzzy logic algorithm[END_REF][START_REF] Zolitschka | Varves in lake sediments, a review[END_REF], but have run into problems because the resolution of images is insufficient, i.e. they have too few pixels to distinguish structures. Structural and spatial variations along the lengths of sediment cores are reflected in laminae discontinuities, changing shapes, and heterogeneous colors. Sample texture can sometimes be determined by detecting particle edges under a microscope [START_REF] Francus | An algorithm to aid varve counting and measurement from thin-sections[END_REF][START_REF] Lewis | An automated system for the statistical analysis of sediment texture and structure at the micro scale Li S[END_REF] or by using a standard photographic image [START_REF] Rubin | A simple autocorrelation algorithm for determining grain size from digital images of sediment[END_REF][START_REF] Baptista | A new and practical method to obtain grain size measurements in sandy shores based on digital image acquisition and processing[END_REF]. The main challenge for detecting structures is image resolution.

High-resolution images have application for fusion of data related to: (1) laboratory destructive analyses and (2) non-destructive sensors. Multiple images of a sample, collected at various dates, enable estimation of sample deformation, which can be corrected with image registration [START_REF] Liu | SIFT flow: dense correspondence across scenes and its applications[END_REF]. Creating a time-independent spatial landmark permits comparison of multiple analyses (e.g. organic matter, mineralogy, spectroscopy), or fusion of such measures to infer paleoclimate or paleoenvironment conditions more accurately.

Studies were conducted in remote sensing to improve the spatial resolution (nD with n<100) of multispectral sensors, using a high-resolution 2D image. This approach is called pansharpening. It essentially merges high-resolution panchromatic and low-resolution multispectral imagery to create a single, high-resolution color image [START_REF] Alparone | Comparison of pansharpening algorithms: outcome of the 2006 GRS-S data-fusion contest[END_REF][START_REF] Vivone | A Critical comparison among pansharpening algorithms[END_REF]. Recently, in remote sensing that utilizes hyperspectral sensors (nD with n>100), pansharpening methods were improved to fuse panchromatic, multi-and hyper-spectral images, in a new method called hypersharpening [START_REF] Selva | Hyper-sharpening of hyperspectral data: A first approach[END_REF][START_REF] Yokoya | Hyperspectral and multispectral data fusion: a comparative review of the recent literature[END_REF]. Based on these studies, it was shown that an environmental sample's high-resolution image can be the basis for fusion with other laboratory sensors (hyperspectral images from several spectroscopic ranges, CT-scans).

Recent improvements of standard RGB cameras have enabled acquisition of high-resolution core images at low cost, with micrometric pixel size for small core samples. For longer core samples, the straightforward way to acquire images is to raise the camera, but this reduces resolution.

Alternatively, one can take multiple close-up images along the length of a core and then assemble them. This method, however, requires several steps that can be time-consuming and create measurement uncertainties. We propose a semi-automatized method to create a high-resolution orthorectified image, sometimes called an orthomosaic image or ortho-image, from several close-up images. This method is based on the recent development of Structure-from-Motion Multi-View-Stereo (SfM-MVS) methods and uses metrically calibrated markers to estimate and correct distortions. This simple, low-cost method was used in this study to generate sediment core images.

Acquired images were then processed for sediment strata determinations and fusion of data. We discuss how the approach can be employed in the field, where images are obtained with a smartphone.

Materials and methods

The ortho-image is a metrically calibrated image, corrected for three main deformations [START_REF] Chandler | Metric capabilities of low-cost digital cameras for close range surface measurement[END_REF]. The first results from the sensor causing optical distortion, the second is caused by the sensor position around the sample for each image, and the third by characteristics of "relief" on the sample surface (e.g. holes, fissures). The proposed method estimates these deformations and corrects them to create the ortho-image (Fig. 1a).

Image acquisition

Core images were acquired with a 2.5-m-long, manually moved tray and a Nikon D80, 10.2-megapixel camera with an AF Nikkor 35-mm lens (Fig. 2). The camera was fixed at a height of 32 cm above the core sample, providing a nadir viewing angle and enabling imaging of its entire width. Under these conditions, the depth of field was 3 cm. Each image spans a sediment length of 16 cm, with a ground sampling distance (GSD) of 50 µm. The tray was moved ~4 cm between photographs, to achieve 75% overlap recovery, such that each section is present in four images. Camera acquisition parameters were the same for all the images. Two halogen bulbs (GE Polylux XL, F18W/860) were used to illuminate the sample and all other light sources were eliminated. The lights were fixed at a height of 20 cm and calibrated to have maximum light in the center and the same light dispersion at the core's two ends. Light calibration enables recording of sample colors and is necessary for high-resolution image creation. Rulers were placed on both sides along the length of the core to estimate the positions of sediment structures.

Reference markers

Coded targets are printed markers from the software, which are placed on the rulers (Fig. 2c). Each is different (Fig. 2d) and is used as a ground control point (GCP). They are metrically calibrated by georeferencing their positions on the rulers. We assumed that the rulers and sediment cores were horizontal, to create a plane coordinate system (z = 0), which was used as a projection plane to create the ortho-image. By using different markers along the bench, the software can automatically detect them, thereby avoiding confusion and enabling automatic processing of the images. A Python script was then developed to find the GCP coordinates in an Excel sheet.

Coded targets must be printed on material that remains clean and is not damaged by exposure to sediment and water. They must not reflect excessive light because that will confound the algorithm. For these reasons, we selected an adhesive matte paper. Targets must also be of a size comparable to the sample. The image should capture the entire marker, especially the central black circle. Markers we used had a diameter of 1 cm. Agisoft Metashape tutorials recommend that the radius of the central black circle should be ≤ 30 pixels. These targets need to be square cut, keeping in mind that the targets are black circles on a white background. They must be placed flat, with at least three markers per raw image, i.e. 10 cm apart on our bench. Reproducible conditions during image acquisition enable semi-automatized image registration.

Automatic assembly and orthorectification

Images are processed according to the four steps below, using Agisoft Photoscan, (recently renamed Metashape) software [START_REF] Agisoft | Agisoft PhotoScan User Manual[END_REF] and Python scripts, a procedure that can be accomplished in < 15 minutes. This software is simple to use and has many automatic functionalities that do not require advanced photogrammetry skills. It can be used for different objects, which vary in size and number, and has scripts to automate processing. The four steps of the proposed method (Fig. 3) are described below.

Image correction

Camera images possess optical and geometrical aberrations and deformations, which result in pixels that are not truly square. This is caused by lens distortion. Camera calibration is done to estimate geometric corrections that must be made to obtain the true shape of the sample. Such distortions are estimated using Brown's distortion model [START_REF] Brown | Decentering distortion of lenses -the prism effect encountered in metric cameras can be overcome through analytic calibration[END_REF]). To accomplish the correction, a chessboard was imaged from different angles, and Agisoft Lens software was used at all corners of the squares to estimate radial and tangential distortions (Agisoft LCC 2011). Under our laboratory conditions, the images also presented barrel distortion. The camera calibration was then fixed in the software and applied to all subsequent images. White balance was established to obtain colors and calibrate them for the multi-view stereo image matching step.

Registration and assembly

First, thousands of features were automatically selected within each image and the GCPs were detected. Then, image and feature matching were undertaken with the structure-from-motion (SfM) process. It enables estimation of the features, GCPs, and camera positions for each image, and creation of a "sparse" 3D tie-point cloud. The GCPs create spatial landmarks to georeferenced the model and optimize the optical distortion and sensor position estimates. Finally, a dense cloud was estimated with multi-view-stereo (MVS) matching of the pixels between images acquired at the different camera positions.

In the case of images that do not use GCPs, a curved shape, i.e. the well-known "dome or arc effect" can appear [START_REF] James | Mitigating systematic error in topographic models derived from UAV and ground-based image networks[END_REF], caused by misestimation of pixel positions in the x, y, and z dimensions (background axis of Fig. 4.a), and typical of linear image acquisition [START_REF] Faure | Métrologie par photogrammétrie aéroportée légère appliquée aux digues[END_REF]. Initial qualitative evaluation consists of visually verifying the absence of these effects. Marker position errors (as root mean square errors, RMSE) in the three dimensions (x,y,z) were also estimated using the distance between marker coordinates on several images [START_REF] Verma | A method based structure-from-motion photogrammetry to generate sub-millimetre-resolution digital elevation models for investigating rock breakdown features[END_REF]. It is recommended that the model's accuracy be evaluated with checkpoints that were not used for model estimation [START_REF] Sanz-Ablanedo | Accuracy of unmanned aerial vehicle (UAV) and SfM photogrammetry survey as a function of the number and location of ground control points used[END_REF]). If the image alignment and dense cloud quality are not sufficient, some manual optimizations are required, e.g. image corrections and added manual reference points, calibrated or not.

Mesh and orthorectification

Micro-relief was modeled to obtain a digital surface model. The algorithm uses the dense cloud points to generate a closed surface with triangle surfaces called mesh. These enables modeling of sample micro-relief, like grains, holes, agglomerates and bumps. Finally, the orthorectified image was estimated from the colorized mesh projection in a 2D space to correct the image from perspective and projective distortions. Thus, an ortho-image is a mosaic of orthorectified original images, and the essential step in its creation is white balance to detect relevant color variations.

Properties and validation of the created ortho-image

The proposed method enables creation of an orthomosaic image that is 9 cm wide and 150 cm long, with a GSD of 59 µm for our example. If a single image were made for the same sample, the GSD would be 590 µm. Two main properties need to be assessed to validate the model, error of the measurements and radiometric quality. The first corresponds to pixel adjustment succession. In an unsuitable case, such as a false camera position estimate in surface model reconstruction, shears can appear in the sample structures. As noted earlier, Photoscan estimates the reconstructed RMSE of the marker positions, which are usually ≤ millimeters. We recommend use of additional checkpoints whose positions are known, in areas without markers, or use of objects of known dimensions to validate the RMSE (Sanz-Ablanedo et al. 2018). For our example, the control points RMSE is 17.43 µm and that of the check points is 15.26 µm. Radiometric quality must be checked to see if color throughout the image is consistent or if color differences and aberrations can be seen between successive images. Verification in areas where the color is known, such as for markers, rulers, or reference objects, enables validation of this criterion. It is also possible to place spatial resolution and radiometric reference targets at the sample's extremities to validate these two properties [START_REF] Honkavaara | Digital airborne photogrammetry-a new tool for quantitative remote sensing?-a state-of-the-art review on radiometric aspects of digital photogrammetric images[END_REF].

Discussion

Using this method with manual targets and other types of image acquisition This method can also be applied to images acquired by other means, for example those taken with a smartphone. Generally, in such cases, the metrically calibrated markers are not available, but rulers are used to measure the sample. The user must manually place control points for all raw images and estimate their depths using the rulers. This process will take more time than with georeferenced markers, and is user-dependent. Nevertheless, the method follows the same steps presented in Fig. 1b, using tie points and dense cloud assembly, followed by application of the mesh to create the ortho-image. Image acquisition parameters in the field, however, cannot be entirely controlled, as in the laboratory, with respect to illumination, camera height, focus, tray position, etc., so biases can be introduced into the resulting ortho-images (precision, resolution, quality, spatial and color aberrations). The camera calibration step is not performed in the field, but the software performs estimates to correct some geometric aberrations. Spatial aberrations can be reduced with images taken at multiple distances (i.e. closer or farther) and multiple angles, but this requires that more images be processed manually, with control points to avoid "dome or arc effects." In such cases, the proposed method will be less automatized. Under non-laboratory conditions, it is sometimes necessary to make radiometric corrections in the ortho-image estimation step, to achieve consistent color along the ortho-image and correct color aberrations. It is also necessary to define precisely the selected marker positions manually or have rulers with coded markers. For this example, the RMSE is similar to those of laboratory, here the control points RMSE is 7.17 µm and that of the check points is 9.22 µm.

When an ortho-image can be estimated, it has been corrected for spatial deformations and reveals surface variations that were not visible in a single image, a consequence of the lack of perspective. This is seen in a comparison of the orange boxes in Figs. 5a and5d. In the raw image, the surface seems to be smooth, but in the assembled one, some relief is evident. Correction for reflection, as seen in a comparison between the red boxes of Figs. 5b and 5e, illustrates another post-acquisition process. Some biases, however, will persist, for example the shadow on the left end of the core in Fig. 5c, which cannot be corrected by the proposed approach.

Applications with ortho-images

The ortho-image produced at low cost and without a specific metric camera, can be used for many applications. Metric calibration and high resolution are advantages compared to standard images.

We present three potential applications for such ortho-images, from the simplest and most common to the most advanced and pioneering.

Stratigraphic log with true metrics

The ortho-image can be used in applications intended for initial core description. The following example, presented in Fig. 6, was made with the PSICAT open-source application (https://csdco.umn.edu/resources/software/psicat). The image was imported, after which the top and bottom (length) were defined to fix the metric, which was confirmed by the rulers. The user can then manually select the main units to be photographed, describe the stratigraphic lithology and textural information, and capture images of specific, local areas. The images can be used to describe the core and make suggestions about sampling for future analyses. Comparison of several sections from the same study site, or cross-comparison of geochemical analyses, are more efficient with well measured spatial landmarks. All structures are characterized by their true depth in the profile, thanks to the metrically calibrated image. All such sediment measures and depth information can be saved in multiple data formats to be processed using other software.

Ortho-image for image processing

Metric calibration is useful to quantify the exact dimensions of structures (flood deposits, laminae, stratigraphic units) with image processing, if the resolution is sufficient. For example, the orthoimage with the 59 µm GSD makes it is possible to discriminate sediment structures with classification or image processing methods, and then estimate a mean length using pixel size, and study their variations through time [START_REF] Meyer | The WinGeol Lamination Tool: new software for rapid, semi -automated analysis of laminated climate archives[END_REF][START_REF] Weber | BMPix and PEAK tools: New methods for automated laminae recognition and counting -application to glacial varves from Antarctic marine sediment[END_REF][START_REF] Ndiaye | A semi automated method for laminated sediments analysis[END_REF][START_REF] Vannière | Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy[END_REF][START_REF] Ebert | Semi-automated detection of annual laminae (varves) in lake sediments using a fuzzy logic algorithm[END_REF][START_REF] Zolitschka | Varves in lake sediments, a review[END_REF]. If particles are coarse, it may be possible to estimate particle size distributions along the length of the core [START_REF] Lewis | An automated system for the statistical analysis of sediment texture and structure at the micro scale Li S[END_REF].

Figure 7 shows an image of a laminated sediment core segment that is 1 cm x 9 cm. RGB is a color space designed for the human eye, but some studies have shown that L*A*B* (Luminance) or HSV (Hue Saturation Value) color spaces are more appropriate for classification purposes [START_REF] Bora | Comparing the performance of L*A*B* and HSV color spaces with respect to color image segmentation[END_REF][START_REF] Hernández-Hernández | Optimal color space selection method for plant/soil segmentation in agriculture[END_REF]. We selected an RGB image for this example because the two sediment structures on which we focused are different enough to be discriminated. Machine learning was used to separate two types of laminae, based on previous studies by [START_REF] Aymerich | Detection of tephra layers in Antarctic sediment cores with hyperspectral imaging[END_REF] to detect tephra layers, and [START_REF] Jacq | Sedimentary structures discriminations with hyperspectral imaging on sediment cores[END_REF] to discriminate instantaneous deposition events from continuous sedimentation. Creation of a classification model with Matlab (R2017a, MathWorks) was accomplished by selection of a few areas and their association to one of two classes of laminae, a step called labeling (Fig. 7b). Then, pattern recognition, with an artificial neural network, was used to develop a model that discriminates between the two classes. 70% of the labeled pixels were used in calibration and 30% in validation, the latter to test the accuracy of discrimination (percent classification accuracy). One hidden layer was used for the neural network, with two neurons. The validation accuracy of the model was 97.8%. Then, the model was used to classify each pixel in the image (Fig. 7c). We assumed that the laminae were horizontal and parallel to create a composite image (Fig. 7d). The sum of each column was calculated, and a threshold was fixed at the half-width.

If the value was greater than the half-width, the column corresponds to a light lamina, and if the value was lesser than the half-width, it corresponds to a dark lamina. It was also possible to estimate the approximate lamina thickness, in pixels and/or mm, given the resolution of the ortho-image (Fig. 7e). If the image is not calibrated, the pixels and laminae will be distorted, and the thickness will be misestimated. Advanced image processing methods, such as segmentation, can be used to study the whole width of the lamina to determine their true orientation and shape, and estimate the thickness range for each. There are two types of segmentation methods, those that take a "region approach," which group together neighboring pixels with similar properties, and those that take a "frontier approach," which look for transitions between regions. These methods, when applied to the classification map, can be used to discretize individual laminae.

Orthomosaic image for image registration and data fusion

RGB image acquisition was done as a first step to preserve a record of sample structure. Then destructive analyses were conducted. The position of samples is referenced at that moment and is dependent on core deformation. For instance, the core may have dried and contracted since it was first opened/extruded. Thus, sample positions (depths) must be compared with the initial orthorectified image. Image registration between the first image and others acquired after sampling, enables creation of a spatial reference, independent of time and deformation [START_REF] Liu | SIFT flow: dense correspondence across scenes and its applications[END_REF].

Images can be used to compare results from different analyses or fuse them to make more precise inferences about paleoclimate and paleoenvironment.

Similarly, image registration and data fusion approaches can combine the RGB image with results from other high-resolution, non-destructive sensors. For example, hyperspectral images are surface analyses that provide us with spatial and structural information, and tomography is a volume analysis that can estimate the size and shape of particles. All these sources of information can be combined to improve our knowledge of the sample [START_REF] Selva | Hyper-sharpening: a first approach on SIM-GA data[END_REF]Li et al. 2017;[START_REF] Yokoya | Hyperspectral and multispectral data fusion: a comparative review of the recent literature[END_REF]). An RGB image can play an important role in this fusion process, given its high spatial resolution.

Free open function

Photoscan can use Python scripts to automatize processes. For example, to calibrate the markers, a calibration Excel sheet is opened to find core depths and associated marker codes. The Photoscan algorithm finds the markers, with their code on each image, and a comparison is made to find the depth associated with each marker on the raw images. Another script can be used to automatize all the proposed steps (tie point, dense cloud, mesh, and orthorectification). These scripts can be found at https://github.com/JacqKevin/RGB_PhotoScanOrthorectification (last accessed september 12, 2020). This method can be carried out using other software or programming language, which may be free for many users, but may require advanced skills in photogrammetry, image processing, and programming. Among them are VisualSFM, MicMac, COLMAP and GRAPHOS (Gonzalez-Aguilera et al. 2018). According to the structure-from-motion community, each of these software packages has its own advantages/disadvantages and capabilities, but is essentially an alternative to Agisoft Photoscan/Metashape.

Marker recommendations

Markers are the most important tool used in the automatic method. If they are not printed on appropriate material, some steps can be compromised, for instance if the marker is not detected or is confused with another marker. Standard paper does not work because it is easily damaged and gets dirty quickly. Adding polypropylene-based tape is also unsuitable. Metal stickers can be used, but are prone to being scratched. Additional ideas that remain untested include use of 3D printed plastic markers, or entire plastic rulers printed with markers. For the moment, we use adhesive matte paper. We note that the method can still be carried out if some markers are damaged. It is essential, however, to check the tie points and see if some do not work and hence compromise the model. In such cases they must be replaced.

Conclusions

Creation of high-resolution images of sediment cores is essential to preserve primary information about characteristics such as color, surface topography and grain size. Acquisition of images is the first step after core collection/extrusion, and the images must be processed further to better characterize the sample. The proposed method enables rapid creation of an ortho-image from several images, via an automated process (GSD: 59 µm, RMSE: 7-18 µm). The procedure only requires metrically calibrated markers that are recognized by Agisoft Photoscan/Metashape software. A Python script can be used to automatize all steps required to obtain the ortho-image. It may be possible to use this method with open-free tools or with a stand-alone executable program, but those may need some adaptation steps.

The orthorectified image shows great possibilities with data processing. Image processing enables classification of patterns in the sediment core, which can be used to analyze coarse (flood deposits, laminae) or fine (grain size) characteristics of the sediment. It can create a spatial landmark with other images captured on several dates, with image registration used to estimate deformations and correct them, to register all analyses conducted on the core. This new image can also be combined with information from other high-resolution, non-destructive sensors (hyperspectral image, CT-scan) to add other dimensions (volume, spectral, temporal) to stratigraphic study of the sample. An orthomosaic-image can enable better high-resolution study of sediment cores and other environmental samples.

Figure legends

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 7

 1234567 Fig. 1 Creation of an ortho-image with camera, under (a) laboratory and (b) field conditions

  Figure 2

Acknowledgements

Cores used in this study are stored at the Environnements, Dynamiques et Territoires de la Montagne EDYTEM laboratory. We are grateful to Charline Giguet-Covex and Stéphane Guédron for the smartphone images of the Lake Huacacarpay sediment core. We also thank Pierre Sabatier, Fabien Arnaud, and Erwan Messager for the Lake Bourget (method steps) and Aiguebelette (lamination application) sediment cores. Furthermore, we thank the anonymous reviewers and Mark Brenner (Editor-in-Chief) for their helpful comments.


Monika Stern

Getting Our Voices Heard: Radio Broadcasting and Secrecy in Vanuatu 1

Introduction

When in May 2018 I returned to Mota Lava in the Banks Islands in the far north of the Vanuatu archipelago, after being away more than ten years, I was struck by something new: several groups who played music wanted to be recorded and told me of their dream of making an album. The local journalist Edgar Howard Woleg also asked me to record a few pieces of music there so he could include them in his radio programmes. All I could offer was to record a few of their songs on my little Zoom H4, not professionally, and then leave them the recording on an SD card from one of their phones so that they could exchange, distribute and broadcast them as they saw fit.

Vanuatu is a Melanesian archipelago made up of more than 80 islands, whose inhabitants, called ni-Vanuatu since independence, speak more than 130 vernacular languages, thus holding the world record for linguistic density. As well as these Austronesian languages, there are three official ones (French, English and the lingua franca pidgin English, locally called Bislama). These three languages stem from the joint Anglo-French colonial history, known as the Condominium of the New Hebrides from 1906 to 1980. Mirroring this linguistic diversity, traditional (kastom) forms of music are many and various according to the different islands, regions and even villages. Other music genres also exist: string band music, Christian religious music and pop, essentially reggae and hip-hop. For technical reasons, pop music is played mostly in towns but also widely listened to in rural areas.

Apart from the two islands on which Vanuatu's two towns (Port-Vila and Luganville) are to be found, the other islands are isolated, with poor transport services and, for most of them, no electricity grid. For all these reasons, it is not always easy for their inhabitants to be part of national and international news networks, nor to make their voices heard.

The national radio can sometimes be more or less picked up; FM radio stations, like television, do not reach most of the islands and mainly broadcast in the two urban centres.

Since the opening up of the telecommunications market to competition in 2007, mobile phone services have developed considerably. The networks, and more recently 3G, have been reaching all the archipelago's islands for several years. However, these new means are expensive and in some islands the network seldom works, in others it is only accessible at certain times and in certain places. Thus the role of radio is seen by the population as an essential public service, although the infrastructure does not always sufficiently meet this demand.

This then makes one wonder how the recording technologies and radio which enable music to be broadcast have been used. This chapter will not include digital technologies, as it is essentially devoted to music considered as "traditional" which is not greatly broadcast on the Web and seldom exchanged by individuals on their SD cards and, on the other, because I have already discussed the circulation of music by digital means in another publication [START_REF] Stern | Digital developments, copyright and music circulation in Port-Vila, Vanuatu[END_REF].

The official media broadcast music as diverse as traditional music from the archipelago's different islands and other musical genres. How are choices made in the media's treatment of repertoires? Are distinctions made, competition created? Is all music equally accessible to everyone? These questions are also connected to the understanding of the more general notions of culture and democracy commonly understood in what we call democratic states as the possibility for everyone to access all knowledge. Here we will not go into the debates on cultural democratization and democracy specific to notions of class in the West, but will retain the vocabulary used by Harrison (1995): "openness" and "freedom of access" to knowledge. For Melanesia is known for its secretsin the form of secret societies, secret spirit voices, secret instruments and secret songs described in many classic anthropological works on the region. 2 A great deal of specific knowledge and practices are reserved for a kin group, whether hierarchical or residential, or a secret society, and only the initiated or people belonging to these groups have access to it. Moreover, publicly showing one's knowledge (in the form of public dances for example) brings prestige. Thus, as Harrison notes (1995: 12), in some cases: "(…) knowledge increases in value by being shared. In the other approach, (…) it decreases in value by being shared. There seem to be two contradictory models here for managing knowledge, and two incompatible theories of its value."

We shall be drawing on Harrison (1995) and [START_REF] Lindstrom | Knowledge and Power in a South Pacific Society[END_REF] works which demonstrate that here it is not a question of a simple dichotomy (secrets/open knowledge), but of strategies and political stakes put in place in order to conceal or reveal secret knowledge (or some of its elements). This knowledge which is both restricted and circulated through the large exchange systems has often been described in Melanesia since Malinowski. However, what appears to be a regional particularity can be found in other forms, less explicit perhaps, in other parts of the world. Foucault therefore questions this opposition between the secret knowledge of certain cultures and the supposedly free circulation of knowledge in the West, "one of the great myths of European culture (…)": "[t]o the monopolistic, secret knowledge of oriental tyranny, Europe opposed the universal communication of knowledge and the infinitely free exchange of discourse. This notion does not, in fact, stand up to close examination. Exchange and communication are positive forces at play within complex, but restrictive systems; it is probable that they cannot operate independently of these." (Foucault 1971 : 17, 18).

He thus demonstrates that these forms of "secret-appropriation and non-interchangeability at work" exist in numerous contexts in European societies. We shall therefore follow Lindstrom who has suggested that Foucault's theories have "considerable relevance for making sense of systems of knowledge and power in Melanesia" (Lindstrom 1990: IX).

Radio which provides the technological means of cultural broadcasting is directly connected to these questions of secrecy and disclosure.

Looking at radio and recording technology, I will thus examine how the ni-Vanuatu use these technical means in their practices of listening to, broadcasting and producing music. Rather than analysing the media as transformative cultural elements [START_REF] Bull | No Dead air! The iPod and the Culture of Mobile Listening[END_REF], we will follow the trend which studies how specific historical, social and cultural contexts deploy technologies [START_REF] Miller | The digital and the human: A prospectus for digital anthropology[END_REF]Wall and Weber 2014, etc.).

We will begin with a historical panorama of the national radio and the role it played at the time of independence. The second part will consider the constraints in uses of kastom music. Afterwards I will describe the emergence of the music industry which favoured the development of music for entertainment and its link to radio broadcasting. A final part will then return to the attempts to restructure the national media, based again on local knowledge.

Radio, kastom and national identity

In order to make my remarks easier to understand, let us first put the notion of kastom (in Bislama, the local lingua franca), which is at times too rapidly translated by "custom" in English, into context. In fact, in Vanuatu, kastom has a more complex meaning especially because of the political role it played in the history of gaining independence in 1980.

Jolly has explained the double meaning of kastom and its revival: on a national level it represents a means of distinguishing the ni-Vanuatu as a whole from the former European colonizers. On a local level, the particular practices of kastom (marriage, birth or rank-taking ceremonies, myths, dance and music) are claimed by distinct communities and sometimes passed down in the form of secret/restricted knowledge, to which explicit ownership rules are attached. This does not preclude the possibility of loaning or exchanging [START_REF] Jolly | Custom and the way of the land : past and present in Vanuatu and Fiji[END_REF]: 341-344, Stern 2013).

In her well-known article entitled "Radio and the Redefinition of Kastom in Vanuatu", Lissant [START_REF] Bolton | Radio and the Redefinition of Kastom in Vanuatu[END_REF] retraces the history of the national radio and the role it played at the time of pre-independence in 1970 to 80's. She notably demonstrates how it contributed to the valorization and broadcasting of the archipelago's different oral traditions (traditional stories and music). The history of radio in the New Hebrides began in the 60s. Its interactive programmes (personal messages, feedbacks, sending of recordings, etc.) were inward-looking, focusing on national issues: "Rather than seeing the radio as a way of gaining access to the 'world-out-there', the ni-Vanuatu response was concerned mainly with programs that engaged with their own world, the knowledge and practice that arose out of the place itself, and with their own concerns." (Bolton 1999: 346) Contrary to the fears mentioned in many works at the beginning of radio in industrialized countries (Johnson 2017(Johnson [1998]]: 172) that it would prevent people from talking to each other, in this island context it was quite the opposite: radio enabled the inhabitants of different islands to communicate among themselves. It was used (and still is to a certain extent) to send not only collective messages such as information on the circulation of copra boats (which also transport other goods and passengers), but also very diverse family and personal ones: information about a death or birth, a parcel to collect at the boat, a letter carried by someone to be collected at the airport, or to announce a forthcoming arrival on the island. In addition, as we shall see in this chapter, radio's beginnings in Vanuatu represented an example of a highly participative tool. Bolton (1999: 345) writes: « Service messages have always been the most listened-to program. » According to Bolton (1999: 347), when in the early 70s the journalists Godwin Ligo (ni-Vanuatu) and Paul Gardissat (French) launched their respective programmes broadcasting local music and oral histories, people reacted actively all over the archipelago. The journalists received a great deal of listener correspondence. Gardissat, it is said, could receive fifty or so letters a day. He even set up a system of "travelling cassettes" by sending a Dictaphone and cassettes to people on remote islands to enable them to send in their recordings. Ligo concentrated on the competitiveness of his listeners' reactions:

"The program generated a form of competitiveness. People would hear a story from another island, or another village on their island, or even from another clan in their own area, that was similar to one they also told themselves, and would write to the radio requesting that their version be broadcast. Sometimes, Ligo said, they would write to say that the version first broadcast had been stolen from them. Or they might write to say that they had the same story in their own island, but that it went further than the story that had been broadcast. (…)" (Bolton 1999: 346) This bears witness to the way in which the inhabitants took advantage of the technical means radio offered in order to extend their possibilities for using the power and prestige surrounding their knowledge to broadcasting. Ligo also states that "This did not happen so frequently with songs, which were sung in local languages, and therefore not accessible to the majority of listeners". For, in Vanuatu, knowledge circulates in different ways: "[S]ome knowledge circulates secretly, narrowcast along lineal roads that snake through the forest, or in the private conversations between a knower and his heir. Other knowledge circulates publicly, broadcast from open clearings to surrounding audience." (Lindstrom 1990 : 130) In some situations, as in land disputes for example, continues Lindstrom, secret knowledge can be divulged in order to testify to the legitimacy of one's claim to this property. Certain secret songs, containing genealogies and geographical names, can also be revealed in this context. Thus technical devices exist in the creating or performing of songs and dances in order to protect/hide their secret content. For example, some songs were often in a specific vernacular language [START_REF] François | Musiques du Vanuatu : Fêtes et Mystères/Music of Vanuatu: Celebrations and Mysteries[END_REF], difficult to understand even for the speakers in question and not easy to pass on. In other cases, as for instance the Newēt dances of the Torres Islands, the songs are performed by a soloist placed in the middle of the other singers and musicians who cover his song with a vocal and instrumental ostinato: "While stamping the board, the musicians sing a hocket "O ho, Ohé o -O ho, Ohéo"… Once this setting is created, the soloist can finally begin to sing the newēt song proper. Its melody and rhythm seem independent from the main rhythm, and is [sic] largely drowned out by the latter. This is in fact deliberate: most newēt poems are secret (toq "sacred"), and must remain inaudible to the non-initiated crowdfor fear that the song, which belongs to the singer and his family, be stolen from him. In the Lo-Toga language, the verb gupe "hide" designates the way in which the choristers, with their loud panting ("O ho, Ohé-o"), conceal the voice of the soloist." (François/Stern 2013: 123) Thus, in a language incomprehensible to the uninitiated, some songs, although secret, can be broadcast on the radio without divulging their secret aspects. As we have already stated, kastom music more generally, in the form of particular dances, musical instruments or songs known to be part of reserved/restricted repertoires could belong to a family, an island, a village community or a hierarchical group and require payment in traditional money [START_REF] Stern | Music in Traditional Exchanges in North Vanuatu[END_REF], Leach/Stern forthcoming). These special repertoires, even on a very local scale, regularly give rise to property claims when performed publicly. At times the inhabitants of neighbouring communities still accuse each other in ceremonial or festival contexts of stealing a particular song, dance, instrument or element of a dance or even a whole genre, like water or bamboo band music. This competitiveness and these "arguments" on the radio, described by Ligo, are nothing more than an extension of the usual strategies established in order to control the circulation of knowledge.

As for radio, although it was reported that programmes on kastom were those that made people react most, at the time other forms of music were also being broadcast: string band music, pop music from other Pacific islands, Anglophone and Francophone light music, pop, rock, etc.

We could therefore describe these early days of radio as a sort of "cultural democracy", in the classic sense of being open to all cultural forms, opinions, criticism and discussions, through the possibility of active individual participation in culture, underlined by [START_REF] Zask | De la démocratisation à la démocratie Culturelle[END_REF]: "This participation is the democratic ideal par excellence: a society which does not make available to its members the resources necessary for their fulfillment as distinctive individuals and as fully participative members can be neither just nor democratic." (Zask 2016 : 44) Radio broadcasting created a space where everyone 3 (whatever their status in society), could express themselves, share their knowledge, discuss things, criticize and reply to criticisms about this knowledge, the way of presenting it and the legitimacy of owning and broadcasting it. Let us remember what Foucault's words about the "(…) ambiguous interplay of secrecy and disclosure" (Foucault 1971 : 18). We are in exactly this situation where through selfcontrolled disclosure and restriction of information, radio broadcasting has enabled individuals themselves to make their voices heard.

Kastom: between broadcasting and secrecy

The first known recording of the archipelago's music were those of Layard in 1914, then a few recordings made in the following years by various researchers and travellers. Most of these early sound documents long remained in the obscurity of archives, scattered all over the world, even if some copies were later sent back to the archives of the Vanuatu Cultural Centre (Vanuatu Kaljoral Senta: VKS) and the digitalization of archives is now making an increasing number of these documents accessible online 4 . In parallel to the radio programmes which began to broadcast traditional oral cultures, another project has played an important, perennial part in the future of this local knowledge and its valorization and dissemination in the archipelago: The Vanuatu Oral Traditions Project. In order to solve the problems of the New Hebrides Cultural Centre (founded in the late 1950s by the two colonial governments), which had difficulty attracting local inhabitants, in 1976 the ethnomusicologist Peter Crowe and the linguist Jean-Michel Charpentier launched a project for recording oral traditions financed by UNESCO and the South Pacific Commission. Their aim was to train the local inhabitants in recording and archiving techniques, in an attempt to involve them in the production of the material conserved at the Centre. In particular, the ethnomusicologist Peter Crowe trained the ni-Vanuatu living in rural areas and involved in kastom practices on a daily basis to make recordings which were then broadcast on radio programmes [START_REF] Crowe | After the Ethnomusicological Salvage Operation -What?[END_REF][START_REF] Crowe | The Vanuatu Oral Traditions Project[END_REF]. Crowe notably describes how in 1977, during a very rare ceremony on Maewo Island, two of his disciples made recordings which were broadcast on the radio. This training project in making recordings was at the root of the Vanuatu Cultural Centre's specificity, which thus developed a local fieldworkers' programme [START_REF] Bolton | The museum as cultural agent: the Vanuatu Cultural Centre extension worker program[END_REF]. With a view to involving ni-Vanuatu inhabitants in the preservation and valorization of their traditions, researchers like Crowe and Charpentier, then Tryon, Huffman and Bolton, developed this project by training a network of fieldworkers in most of the archipelago's islands 5 . When Gardissat decided to stop his radio programmes, various employees of the Vanuatu Cultural Centre (and some fieldworkers) produced their own which they gave the radio to broadcast. These programmes took a great deal of their material from the Centre's sound archives, containing recordings made by local fieldworkers and foreign researchers. A lasting link was thus established between radio programmes on kastom and the Vanuatu Cultural Centre. However, in 1994, the Vanuatu Broadcasting and Television Corporation (VBTC) was created, with two national stations (Radio Vanuatu and Nambawan FM 98) and began to adopt a more commercial policy: "(…) FM98, a music station modeled on commercial FM popular music stations in western countries, was founded, broadcasting to Port Vila and to Luganville. Both stations increasingly assume a hearing rather than listening model in radio, a development that is far from welcome in the islands, as rural Ni-Vanuatu depend on the radio as the source of all kinds of information." (Bolton 1999: 354) Fees were due for all content broadcast (on both National and FM98 radios) thus reducing broadcasting opportunities for many organizations and associations, including the VKS. The broadcasting of local programmes decreased dramatically, replaced by numerous replays of foreign films, series, news, music, programmes etc. (Bolton 2010 : 8). Today however the VKS is once again producing cultural programmes broadcast on Vanuatu's radio and television, as well as by a private Telsat channel owned by an expatriate living in Vanuatu.

The legitimacy of the VKS, a government body, as the guarantor of respect for the broadcasting of traditional repertoires is widely recognized by the ni-Vanuatu. Therefore the other institutions perhaps feel they have less right to venture into this field. As Moses Cakau, a television programme producer born in the capital yet with an utterly Western education, told me, broadcasting kastom repertoires is not always easy:

"Another problem, is the secret aspect of kastom music. Many people from elsewhere like this music, tourists adore it, but for us … the definition is different, so to go and record music like that. The VKS does it, but we are aware that these are kastom practices (…). You know, the reactions of our ancestors' spirits might be feared if we broadcast it. People might not sufficiently respect this music (…). There are ways of paying 6 for these kastom songs. Also, because if we play these kastom songs on the air, the value of these songs decreases, (…) if you listen to them at a certain time, in an appropriate situation you will feel a power (…) but if you listen to them on the air, some young people might lack respect, because they would be more exposed to mockery" (Interview with Moses Cakau, 29 May 2018).

Melanesians often mention the precautions needed in the different uses of this singular repertoire and in this can be seen a desire to protect it against the risk of disrespect and inappropriate uses: "Within Papua New Guinea, concerns had been raised from around 1996 onwards that certain aspects of local cultures, particularly traditional songs, music and dances, were increasingly used without authorisation and outside traditional contextsseen by many Papua New Guineans to be unacceptable. A former Chief Ombudsman of Papua New Guinea is reported as saying: 'In many ways, our traditional music and dances are unique. They must be recognised and accepted as such, encouraged and promoted, and above all must be protected… I must admit that introducing traditional music and dances into modern music using modern instruments can become mockery'." (Kalinoe 2004 :41) For the spiritual nature and the connections of this music with its places of origin and kinship, make it at the same time sacred, intimate and precious. The bulk of Vanuatu's musical repertoires is closely linked to the ancestors. The songs and dances are not considered to be compositions by living individuals, but to be brought to humans by spirits, in dreams.

Moreover, some songs containing geographical and historical knowledge capable of bearing witness to land ownership are strictly secret (Ammann 2012 : 44 ;Lindstrom 1990 : 109, 110). They may also possess magic powers. Therefore, those who possess knowledge constantly waver between secrecy and disclosure. For this knowledge giving them a certain power: "[a] person is empowered by his public revelation of knowledge" (Lindstrom 1990 : 113). Deep knowledge of local rules is necessary to know if and how these pieces of music can be broadcast. Some elements are strictly secret, 'taboo' and dangerous while others, on the contrary, are public and need to be revealed in order to confirm one's prestige. Thus Peter Crowe (1981: 171, 172) explains that, among secret knowledge, some parts of the repertoires can be heard by all and this public listening brings prestige to those who possess the right to perform them: "Secret knowledge is repeated and transmitted during the Qat Baruqu rites. The material performed and recorded from the final and 10 th night was, however, largely public and suitable for broadcast. Indeed, it is customary for women and children and non-initiated men to listen at this time outside the ghamali 'men's house' and to be spectators for the dances and audience for the music."

I have often encountered this kind of caution regarding the broadcasting of kastom music and dance in Vanuatu. I experienced it with my colleague Alexandre François [START_REF] François | Musiques du Vanuatu : Fêtes et Mystères/Music of Vanuatu: Celebrations and Mysteries[END_REF] when our CD "Music of Vanuatu. Celebrations and Mysteries" was released: the necessary steps and discussions with the VKS and the communities concerned took several years. While some repertoires, particularly those for children or forms recreated recently like water or bamboo band music, pose no major problems (except when they become commercial 7 ). For others, conflictual ownership, spiritual aspects and presupposed origins may occasionally make their production/broadcasting difficult, even when non-commercial.

At the same time, this spirituality gives kastom music a kind of "aura" that could be compared to that evoked by Benjamin for 'authentic' art work 8 or Adorno for the live performance of 'serious' music 9 at the beginning of recording industry. For some or in certain conditions, the ni-Vanuatu's spirituality also makes performance outside its context or media broadcasting (as for Moses) inappropriate. For all these reasons, although, as we have seen, it was broadcast in the early days of radio in Vanuatu and today essentially by the staff of the Cultural Centre, up until now kastom music has not been part of the recording industry.

The recording industry and radio broadcasting

The impact of the first years of national radio was not however without echoes in local musical creation. Parallel to the broadcasting of kastom during the 1960s and 70s, the radio recorded and broadcast another style of music, string band music, and thus launched a national music industry. It was Gardissat, the French journalist, who in the 70s created the archipelago's first recording studio, Vanuata Productions, and up until 1988 made some 150 albums on cassettes, mostly by string band groups.

String band music is a musical genre played by mostly male groups, sung in falsetto, in responsorial form and accompanied by acoustic string instrumentsguitars, ukuleles and a string bush bassand some percussion like bamboos and/or congas, bongos, etc. Initially inspired by country music and American light music, spread by American soldiers based in the archipelago during the second world war, and pan-Pacific pop strongly influenced by Polynesian music, Vanuatu string band music strictly speaking was created under the influence of the owners of the first tourist hotels and developed in the 70s around the capital Port Vila [START_REF] Ammann | String Bands in Vanuatu: Pop or Ethno?[END_REF]. For Ammann, string band music was the first real music for entertainment, as traditional and Christian music had spiritual functions [START_REF] Ammann | String Bands in Vanuatu: Pop or Ethno?[END_REF]. It was also the first local music recorded and sold on cassettes in the town's shops. However, according to Bolton, a French producer of one of the first radio programmes recorded in the New Hebrides around 1960 is said to have approached local employees of Vila Town Council, who formed a string band broadcast during the programme. This programme which tended to play mostly ni-Vanuatu productions (kastom music and stories and string band music) is said to have left a strong mark on the memory of the local population (Bolton 1999 : 339).

As the recording studios were almost exclusively based in Port Vila, it was mostly groups from the islands nearest the capital which made recordings and became known on a national level. However, string band music rapidly spread to all the archipelago's islands. In an informal conversation with Ralph Regenvanu, the former director of the Cultural Centre and currently a minister, he suggested to me that while kastom music was a form which reflected the local identities of particular islands and villages, string band music, because it was present on all the islands and used Bislama amongst other languages, might represent national music.

Nonetheless the community aspect is usually kept, for the groups are often made up of musicians from the same islands, interpreting their original songs in the lingua franca, Bislama, and sometimes re-using their community's traditional (kastom) songs.

The commercialization of string band music marked the 80s when tape recorder technology developed and spread all over the archipelago. While radio could no longer always be picked up, some people in the islands could afford the luxury of listening to music on batterypowered tape recorders. As with radio, people usually listened to cassettes in groups. Like elsewhere in the world (Manuel 1993: 3), cassettes also gave rise to a parallel distribution circuit, whether through certain shops which copied albums and sold them with no scruples or through exchanges between private individuals (Stern 2014).

At the time, the archipelago was not concerned by copyright laws. A Copyright Act was written in 2002, but it remained unpublished for more than ten years. It was only in 2011, in preparation for joining the World Trade Organization (WTO), that the act was ratified and that the country became part of the World Intellectual Property Organization (WIPO) 10 .

After Vanuata Productions, the growing number of recording studios enabled the development of a music industry with local string bands and imported musical styles (reggae, foreign pop music, remixes, etc.) released first on cassettes, then on CDs. Because of its links with the spiritual world and its secret, identity aspects (links to a place and a group of people), kastom music is generally seen as unsuitable for commercial recordings. 11 With the development of these studios, radio no longer needed to continue doing a large amount of recordings itself, especially as the studios left them copies of their creations For being broadcast on the radio was the only means of getting known. Even copies of music albums imported from abroad for commercialization were left at the radio station for publicity purposes. Thus, the first recording studios had contracts with the national radio so that neither the radio nor the studio would have anything to pay and both of them would reap advantages:

for the radio, material to broadcast and for the studios publicity (interview with Ambong Thompson, former programming director at Radio Vanuatu and currently in charge of the audiovisual section of the VKS, 29 May 2018).

As everywhere else (Malm and Wallis 1984: 241), recording industries and broadcasting are closely linked. The former provide the latter with material and the latter publicize it so boosting sales. However in Vanuatu, not only does broadcasting in the media not generate royalties, but moreover, bearing in mind the limited size of the market, the sale of albums does not bring in much either. On the other hand, having an album and getting it broadcast on the media, brings renown and prestige, as was the case when in the early days of radio kastom oral traditions were broadcast. This relationship between the local music industry and broadcasting on the media has not always been rosy. For, at the same time as payment was introduced for airtime thus reducing the number of VKS programmes broadcast other forms of local music came up against the same problem. Musicians or producers wanting to be broadcast had to pay: "(…) it must be remembered that only two or three years ago, when a group wanted its clip to be on TV, it had to pay, as if it were an advertising space, that's it, so that, that has changed, precisely thanks to, to the pressure group in fact musicians, this has changed, so clips are broadcast without paying rights, let's say, but on the other hand, there is no remuneration" (Interview with Georges Cumbo, director of local branch of Alliance Française 8 November 2012).

Since then it has become relatively easy today to be broadcast on the radio when you have made a single or an album: for political and cultural discourses valorize the broadcasting of local musicians and this lack of payment (on both sides) enables a fairly easy exchange between the musicians who offer their recordings and the radio which plays them. However if the majority of this music is broadcast when an album is released, not very many continue to be played repetitively for any longer than a few days.

Nonetheless, the official media do not have a monopoly on broadcasting. As Wallis and Malm have also mentioned for other small countries (Malm and Wallis 1984: 255, 256), music can become better known by being played in buses and taxis and at concerts and festivals where during a group's performance, announcements are made and the album can be sold directly on the festival stands. Moreover, today with digital technology, broadcasts on channels like You Tube, Vimeo, Daily Motion or Face Book are also very widespread.

Even if studios and recordings are on the increase, there are hardly any musicians making a living from their musical activities in Vanuatu (apart from a few individuals playing in the capital's bars and restaurants). Despite this, in town as in rural areas (as mentioned at the beginning of this chapter), all groups dream of having an album. One of my musician friends in the capital told me how after years of effort, approaches, fund-raising and work, once the album had been released, they completely messed up advertising and marketing it. Finally the CDs were distributed to friends and family. He realized that in fact they had just wanted to fulfill this old collective dream of making an album, even if it was not sold. Having an album is a way of speaking out, a possibility to express oneself and to be heard. For musicians, it legitimizes their status in a sense. As in the early days of radio having one's story or song on the air helped to assert one's existence or proclaim one's island belonging, nowadays having an album means being heard outside one's own island or marginal condition and gaining prestige [START_REF] Stern | Is music a "Safe Place"? The Creative and Reactive Construction of Urban Youth through Reggae Music (Port-Vila, Vanuatu)[END_REF]). However, despite this prestige and flourishing local music production, the radio and television programmes broadcast today play mostly foreign music [START_REF] Hayward | Local interpretation: Music video, heritage and community in contemporary Vanuatu[END_REF](Hayward : 63, 2012: 65): 65). The few programmes still broadcasting kastom music are prepared beforehand by the VKS, which may also agree to broadcast recordings made by inhabitants in the islands. But these are rare cases and the interactive programmes in which inhabitants of the remotest islands could send their own recordings directly to the station are no longer possible. The only way to be heard therefore is to make an album or take part in a programme made by local journalists of the official media.

New cultural policies: kastom back on the air

According to Ambong Thomson 12 , listeners' demand for kastom programmes is enormous and the feedback after their broadcast always very positive. Some programmes are even re-run on public demand. However the VKS does not have sufficient staff able to devote themselves exclusively to the production of such programmes. For his part, Moses Cakau underlines the necessity for the VBTC to work in closer collaboration with the VKS, but he mentions too the lack of staff competent for such topics on national radio and television, who are also restricted by marketing considerations. In 2007, the first private radio station, FM 107, was created, though according to A. Thompson, the FM stations do not sufficiently valorize kastom music.

M. Cakau stresses the fact that the national stations, Radio Vanuatu and Paradise FM 98 (which since 2009 has replaced Nambawan FM98) have a particular responsibility, more so than the private radio stations, to broadcast local music. Indeed, for the new management in place since 2017: "(…) the focus is on man Vanuatu, the focus is on promoting the development of Vanuatu culture. So you're going to see that every day you can hear at least an hour of local music (…). Radio Vanuatu and Paradise FM are Vanuatu stations, they're run by the government and intended for "people from Vanuatu", so we want to broadcast stories about people from Vanuatu, the music of Vanuatu people, so the OC (Organization Committee) has given more advice about this point" (Interview with Moses Cakau, 29 May 2018). Indeed, the VBTC has been the subject of various development and restructuration operations, not only on a national scale but also with Pacific regional aid.

The VBTC, linked to national politicians, has always had problems and been involved in scandals: unpaid salaries, frequent dismissals of directors and staff, misappropriation of funds, etc. After the golden age of the beginnings of national radio, for a long time radio could not be picked up in the islands far from the capital. To solve these problems, important reforms were implemented with considerable international aid including the Australian public agency The importance of radio on the most remote islands was particularly underlined following Cyclone Pam (classed 5 on the Richter scale) which devastated the archipelago in 2015 and helped to make people aware of the importance of a public service which could have brought radio coverage to all the islands. The valorization of local broadcasts is thus part of a broader context of regional media policies with common objectives.

Entitled Vois Blong Yumi ("Our voices"), one of the goals of this new project was to give a voice to those who could not make themselves heard like women, the young or inhabitants of the most remote islands. As stated in one of the reports on the project, it was about "Building the nation by linking its past to its future and connecting people to knowledge and to each other" (VBY Review 2012: 7). In this way, its initiators wanted to introduce educational aspects by valorizing both local knowledge and development. Following government policies aimed at reducing the lack of local knowledge among urban youth, television programmes such as "Art Kalja" (Art Culture) tried to encourage the young to turn to traditional knowledge in order to help them be creative.

Moses Cakau emphasizes the importance of local music broadcasts: "even if it is true that many international stars (including African ones) are very well-known in Vanuatu, and this is inevitable particularly because of easy access to You Tube and the Internet", but he continues: "our position is that of also playing Vanuatu music so that though the young listen to all this foreign music, they also " have to be rooted". (Interview with Moses Cakau, 29 May 2018) In addition, broadcasts like talk back shows and programmes produced in rural areas were created to generate an interactive spirit. Again in this context, a series of programmes was started to train journalists in the archipelago's six provinces in order to make Vois Blong Provins heard, a weekly half-hour programme including provincial news, interviews and public comments (VBY Review 2012: 19). What is important in this action is that production be in the hands of local people, (journalists from the provinces) who know (or are close to those who know) what can and cannot be divulged. This, in a way, has certain similarities with Peter Crowe's idea in the 1970s when he trained fieldworkers. Perhaps a link between these local journalists and fieldworkers (Edgar Woleg, a Banks Islands journalist is the brother of a VKS fieldworker for example 13 ), could improve this project even more.

For Edgar Woleg, a local journalist of Torba Province, the northernmost in the archipelago, his province had long been forgotten. The people there had no access to news as even today the national radio can only be picked up very badly during the day and a bit better at night: "(…) despite this, for me it is important to be able to transmit government news. Thus, even if our islands are far away, this service enables news to reach Vila where government departments, NGOs and the representatives of other countries are and perhaps draw their attention to our problems so they come to help us here." (Interview with Edgar Howard Woleg, 18 May 2018) With these words, Edgar makes the point that, in an island context, being able to make oneself heard in the national media in a sense makes it possible to be part of the nation and provides the opportunity to seek development aid. Unlike in the 1970s to 80s, the broadcasters, here island journalists, and the local people interviewed are not necessarily the same as the listeners, who tend to be town dwellers. In order to make his province (Torba) voice better heard and to stand out, Edgar uses a form of identification in the content he broadcasts: I interview people (…), I only play music with the unique sound of Torba (…) when the music is over, I move on to an interview (…). Throughout the 30 minute programme I only use music from the island talked about, I never use music from elsewhere, not just elsewhere outside Vanuatu but even elsewhere outside Torba, like Santo, Vila, Efate." (Interview with Edgar Howard Woleg, 18 May 2018).

The radio and tv programmes Edgar produces bring the voices of his province back on the air.

In his determination to only broadcast music from Torba, Edgar is again giving a strong identity to the cultural forms of expression of certain regions in the archipelago. However when there are kastom forms among this local music, these are repertoires which are partly accessible, with no notion of secrecy, interpreted by legitimate people (the music's owners).

The interplay between what must be kept secret and what can be disclosed, in order to gain recognition and prestige, is thus once again on the air.

Conclusion

Using examples of broadcasting oral knowledge, particularly kastom music, on Vanuatu radio, I have endeavoured to show how the inhabitants constantly reconsider and manipulate what can be shared and what must remain unshared. For nothing is fixed and our words have here confirmed Harrison and Lindstrom's theories on the strategies used by the population to manipulate knowledge: "(…) it tries to maintain a delicate balance between restricting it and circulating it. (…) The 'management' of knowledge seems therefore to consist in a sort of balancing act, in an attempt to function with some combination of two equally credible, but contradictory, models of the value of knowledge at the same time." (Harrison 1995 : 13, 14) The competitiveness which developed around the radio broadcasts of the times bears witness to the way in which the population appropriated this technology in order to continue to use the interplay between these two models. Revealing part or all of a piece of knowledge, making it known that one possesses a more complete version or proclaiming exclusive ownership of it, all this shows the importance accorded to this knowledge and to the manner in which it is preserved and disseminated. Free radio broadcasting enabled everyone to become part of this dual system, directly on the air and therefore on a national scale. The classic borders between listeners and receivers thus in a way became less distinct and radio then belonged democratically (in the sense that everyone could make their voice heard) to all Vanuatu's inhabitants. However, this participative aspect of radio kastom programmes has gradually disappeared. On the one hand, for several years a media marketing policy has impeded the broadcasting of local knowledge. On the other, the creation of the Vanuatu Cultural Centre's network of fieldworkers and its legitimization to spread kastom knowledge has in a sense institutionalized this broadcasting. As formerly for the fieldworkers trained to enable the inhabitants themselves to become involved in the Cultural Centre's actions, today in the effort to train local journalists living in their villages and in direct communication with the population the remotest provinces have been given a voice. These journalists have been trained to connect local knowledge with current development problems, by following the more general policies of the Pacific region. What is happening here amounts to an institutionalization of the broadcast word. A second layer of decision-making power in the form of institutions is establishing itself alongside the power stakes "traditionally" in the hands of "customary" representatives.

Whether it be in a direct system (individuals-radio) or through these new intermediaries, strategies concerning knowledge are not peculiar to Melanesia alone, even if particularly explicit cases are characteristic of this region. Foucault's work also reveals these models in European societies despite the democratic circulation of knowledge they claim: "(…) none may enter into discourse on a specific subject unless he has satisfied certain conditions or if he is not, from the outset, qualified to do so. More exactly, not all areas of discourse are equally open and penetrable; some are forbidden territory (differentiated and differentiating) while others are virtually open to the winds and stand, without any prior restrictions, open to all » (Foucault 1971 : 17).

However, the fact of limiting one of the means available, inevitably causes other means to emerge at some time or another. Thus, if in Vanuatu today this institutionalization has in a sense reduced individual control of kastom knowledge circulation and listeners' interactivity present in the first radio programmes 14 , the population is appropriating other technological means (Facebook and its forums for example) in order to discuss this knowledge (sometimes in a very lively fashion), the way it circulates and the legitimacy and manner of broadcasting it 15 .

5 Fieldworkers are volunteers who live in their village of origin and come once a year to take part in workshops at the Vanuatu Cultural Centre in Port-Vila. During the year, their aim is to do awareness-raising, preservation and transmission work among their community, concerning practices on the theme chosen at the VKS workshop. A hundred or so men and women living on different islands in the archipelago are part of the Vanuatu's fieldworkers' network. 6 This is not payment in the commercial sense, but a "traditional" form connected to ceremonial exchanges which use such moneys as shells, mats or exchanges of food or pigs. 7 For issues concerning conflicting notions of music value due of commoditization and international copyrights imposition, see Leach and Stern, Oxford Handbook, forthcoming. 8 Benjamin, ([1936] 1969) 9 Borrowing from Benjamin's idea which deplores the disappearance of the "aura" in art when it can be reproduced in several copies, Adorno considers that music which is not performed in live but reproduced by mechanical devices, is not "authentic" and loses its "aura" and "spirituality" (2009 -2006 for first edition), he also criticizes in his several works music as commodity and distinguishes "light" and "serious" music. [START_REF] Adorno | On the Fetish-Character in Music and the Regression of Listening[END_REF]. 10 For more information on copyright laws in Vanuatu see for example [START_REF] Forsyth | The Developmental Ramifications of Vanuatu's Intellectual Property Commitments on Joining the World Trade Organization[END_REF] and Forsyth and Haggart (2014). 11 Even if in tourism contexts, live performances of kastom dances are given. 12 Interview with Ambong Thompson 29 May 2018. 13 According to fieldwork feedback, it would seem that among the programmes of the Vois blong Torba project, the ones from the Banks Islands made by Edgar Howard Woleg were those which met with the most success. The fact that Edgar has considerable experience of working on kastom through his collaboration with his brother, a VKS fieldworker, as well as with foreign researchers is probably not without these results. 14 Even if feedback on these programmes is still present as Ambong Thompson shows. 15 Here I am thinking of a discussion after the Melanesian Festival of Arts in Honiara in 2018, where the performances presented by the Vanuatu delegation gave rise to a great deal of online discussion (Facebook) about the proper manner to present kastom, authenticity /inauthenticity of presentation and legitimation of this presentations.

  AUSAID which organized an aid programme (Vois blong Yumi) from 2007 to 2013 and PACMAS (Pacific Media Assistance Scheme) in the context of ABC (Australian Broadcasting Corporation) International Development from 2008 to 2019. The staff has also been largely renewed. A new General Manager has been chosen in the person of Francis Herman who has considerable experience in the region's media (Fiji and Australia in particular). Broadcasting policies have been aligned with broader ones on a Pacific scale:"For Herman, the power of the media rests in its ability to 'look beyond today's news and look at tomorrow's news. This quality is essential to address key issues in the Pacific such as poverty, climate change and gender inequality. (…) The media can and should play a very pivotal role in development."[START_REF] Anderson | Vanuatu's radio's active decay[END_REF]


Lorena Acuña

M Deleuil

Olivier Mousis

Sergio Hoyer

Théo Lopez

Emmanuel Marcq

Thierry Morel

Alexandre Santerne

Davide Gandolfi

David J Armstrong

Characterising the interior structures and atmospheres of transiting super-Earths and sub-Neptunes

Introduction

Low-mass planets such as super-Earths and sub-Neptunes might be composed of a Fe core, a silicate mantle and a volatile layer. Together with H and He, water is the second most abundant volatile, whose density depends strongly on the planetary conditions and its phase. Therefore, interior structure models of low-mass planets need to take into account the dependency of density on the phases of water and the planetary surface conditions, which are defined by their atmosphere, if present.

In this work, we present a self-consistent interioratmosphere model, that includes all possible water phases in low-mass planets. We apply this model to several multiplanetary systems to explore their compositional trends.

Interior-atmosphere model

1 use a 1D interior structure model with a Fe-rich core, a silicate mantle and a water layer. For planets with liquid and ice surface conditions, we include liquid and ice Ih-VII in our water layer, whereas for highly-irradiated planets we implement a supercritical water layer with a steam atmosphere on top.

2 In all water phases, we employ Equations of State (EOSs) that are based on experimental and theoretical data and are valid within the pressure and temperature ranges they are applied to.

3 The surface temperature and thickness of the steam atmosphere is computed with a 1D, radiative-convective (RC) atmosphere model.

The atmosphere model estimates the surface temperature at which the atmosphere is in RC equilibrium via the computation of the outgoing longwave radiation (OLR) and the Bond albedo (A B ). The atmosphere is coupled with the interior in a self-consistent algorithm (Fig. 1).

4 We adopt a Markov-chain Monte Carlo (MCMC) Bayesian framework to obtain the planetary core mass fraction (CMF), water mass fraction (WMF), surface pressure and temperature, and other atmospheric properties such as the atmospheric mass M atm , with their associated uncertainties.

Figure 1:Interior-atmosphere coupling algorithm. T base is the temperature at the bottom of the steam atmosphere. z denotes the atmospheric thickness. R bulk and M bulk correspond to the planet bulk radius and mass, respectively. R guess refers to the initial guess of the bulk radius, while R interior is the output bulk radius of the interior structure model in each iteration. See [START_REF] Acuña | Characterisation of the hydrospheres of TRAPPIST-1 planets[END_REF] for more details.

Results

1 The water mass fraction shows a global trend with incident flux, which consists of an increasing gradient for the inner planets, followed by a plateau of constant water content for the outer planets (Fig. 2)

2 Highly-irradiated planets, such as TOI-220 b, can present WMFs up to 60%, (Fig. 3), while the outer planets might present H/He atmospheres since their densities are significantly lower than those of a planet with a water-dominated atmosphere (Fig. 4).

3 This trend might result from the combination of planetary formation in ice-rich regions of the protoplanetary disk, followed by a later inward migration in the case of the outer planets, while the increasing water mass fraction trend for the inner planets could be shaped by atmospheric escape.

Take-home message

1 We present a homogeneous analysis of the compositional trends of several multiplanetary systems with a self-consistent interior-atmosphere model.

2 Multiplanetary systems allow us to study both super-Earths and sub-Neptunes that have formed within the same protoplanetary disk simultaneously, making them suitable distant laboratories to explore the diversity of small planets, and their formation and evolution pathways.

Figure 2 :MFigure 3 :

 23 Figure 2:Water mass fraction as a function of received flux, normalised to the flux of the innermost planet for the TRAPPIST-1, K2-138 and TOI-178 multiplanetary systems.

Figure 4 :

 4 Figure 4:Retrieved CMF and WMF of planets in the multiplanetary systems. Low significance levels indicate that the assumption of a water-dominated atmosphere is adequate for a particular planet.

We use as input data the planetary radii, masses and Fe/Si mole ratio derived from their estimated host stellar abundances.

Contact Information

Email: lorena.acuna@lam.fr