Al Developing Sustainability

Dr Samuel Depraz
email: samuel.depraz@univ-lyon3.fr

DEPRAZ, S. (2012), "Are Protected Areas really sustainable? How to develop sustainibility within Nature conservation". In

Keywords: Protected Areas, Nature Conservation, Integrated Management, Territorial Governance

The management of Protected Areas, once mainly devoted to ecosystems conservation and driven by a rather radical ecologic approach, has been significantly unsettled by the paradigm of sustainable development for a decade or two. The sector of Nature conservation has now to be socially responsible and shall take in account, in its policy, the ecological, economical and cultural fields at the same time. However, the global shift towards sustainability in the management practices of Protected Areas is not always obvious, and several examples of this reservation will be successively developed here, in the three above mentioned fields. Therefore a comprehensive assessment of Protected Areas effectiveness is needed in order to legitimate the role of nature conservation in the local development prospects, with the broader aim to foster a more integrated territorial governance at the local level.

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The sustainability of Protected Areas has not really been questioned before recent times: as long as protected areas have been solely considered from an ecological point of view, there was no point at asking whether they were carrying any socio-economic added value, or were at least socially and financially bearable for human societies. They were but considered as a necessary expense in the eyes of Nature conservation, as they were the most obvious and proud evidence of the achievement of public policies in the matter of environmental action i . Moreover, it was not questioned whether they were a good way of protecting Nature or not, even from an ecological point of view: based on an inherited conception of Nature conservation that protected the most remarkable places and species, and embedded with many representations on wilderness, natural landscapes and aesthetic sites [START_REF] Larrère | Les philosophies de l'environnement[END_REF], they were far beyond any rational criticism regarding their scientific legitimacy.

However, sustainability does not only mean nature conservation; neither is it a pure aesthetic and emotional approach of environmental questions in our contemporary world. At least, the paradigm of sustainabilityif one refers to the most widely acknowledged definition of the term after Brundtland (1987)leads to consider that any environmental action has also to be assessed in the scope of its social and economic function. In other words, conservation policies have to be scrutinized under a more integrated, socio-economic approach. In return, a more comprehensive planning of territorial development and regional governance, that includes environmental protection, will help conservation projects to gain more efficiency and legitimacy. This new paradigm of sustainability is consequently redefining the way how Nature protection has to be lead in the three fields of a sustainable management environment, economy and societyin order to reach a difficult optimal balance between a higher social acceptance without compromising the initial ecological goals.

Are protected Areas really protecting Nature?

From an ecological point of view, the answer to that first question is not obvious anymore. If one refers, in the history of nature sciences [START_REF] Acot | Histoire de l'écologie[END_REF][START_REF] Deléage | Histoire de l'écologie[END_REF][START_REF] Drouin | L'écologie et son histoire -réinventer la nature[END_REF] to the fundamentals of ecology (Odum & Odum, 1953), the analysis of natural areas seems to be mainly based on static principles that show the homeostasis of ecosystems, fighting against changes in order to maintain or re-reach their idealistic state, the climax (after [START_REF] Clements | Plant Succession. An Analysis of the Development of Vegetation[END_REF]. This nature is mainly considered apart thenecessarily badinfluence of human societies. Protected areas are thus a spatial response to this theoretic dichotomy, since they draw a clear line between human and natural areas, so as to protect the most exceptional species from any destruction. The very strict level of protection in many National parks or Reserves in the world has indeed to do with this inherited radical approach in the history of the scientific ecology.

However, the introduction of the key-concept of biodiversity in the 80's [START_REF] Soule | Conservation Biology: An Evolutionary-Ecological Approach[END_REF][START_REF] Pickett | The Ecology of Natural Disturbance and Patch Dynamics[END_REF] has had unexpected side-effects on the way to protect nature. First of all, a more dynamic vision of natural areas has developed, focusing on the capacity of adaptation of ecosystems, regardless to their initial state. Moreover, the climax theory has been criticized, in so far as biodiversity is not always at the highest level in quasi-natural areasif not a myth, since there is no more "natural areas", but always different evolutions of secondary vegetations because of permanent disturbances on every ecosystem. Therefore, human influence can sometimes even increase the scope of species, since some agricultural practices, such as the selective cutting of woods, the maintenance of natural hedges or terraced cultures for instance, create specific transitional areas that constitute unexpected resources for pioneer species, heliophytes, etc.

Most of all, biodiversity is not only a question of protecting the most valuable areas and species; it is also including an "ordinary nature" [START_REF] Mougenot | Prendre soin de la nature ordinaire, Paris: éditions de la Maison des sciences de l[END_REF], made of small, common species for which a lack of recognition has long existed, but which appear to have a key-role in the functioning of nature. Those species are identified as "target species" and can serve as strong indicators of the state of conservation for a whole ecologic series. Conservation is therefore not that much a question of spaces anymore, but rather a question of species: a global protection, considering group of species and their circulation, their symbiotic relationships, that is ecological processes more than the current location of valuable items, has become very relevant and is making the protection beyond protected areas also very important.

In this regard, protected areas cannot work as a closed laboratory, sealing the most valuable ecosystems behind a tight wall: they need to be included in a more global approach, they have to be interconnected in order to constitute a coherent network, with biological corridors, buffer zones or even areas of sustainable human activities [START_REF] Langhammer | Identification and Gap Analysis of Key Biodiversity Areas. Targets for Comprehensive Protected Area Systems[END_REF]. They are not protecting necessarily a nice nature, but mostly a significant level of biodiversity. There is also not a single type of protected area, but different degrees and ways of protection, with specific management levels, sometimes tolerating adapted human activities, or even asking for specific intervention on ecosystems: monitoring, measures for the restoration of degraded milieus, management or regulation of species, etc. [START_REF] Larrère | Du « principe de naturalité » à la « gestion de la diversité biologique[END_REF]. However, this new integrative approach of Nature management in Protected Areas is not always easy to develop, especially when management authorities have been built for decades in a radical state of mind, only with biologists and without specific considerations for local development and neighbouring societiesif not in opposition with the latter. One has to take in account the weight of institutional routines, that is a "path dependency" that makes changes in the field of conservation policies even harder.

Protected Areas, up to which financial expense?

The integration of nature conservation in a broader approach of human territories and spatial planning, mainly based on sustainable development, has also raised new economic challenges in the management of protected areas. The shrinking of public financing in a global neo-liberal context, added to a new contractual and co-operative approach in regional and rural planning, has also impacted on the way protected areas are managed. Those structures have now to justify their ecological action and to struggle for financial means by establishing projects and explaining their managementin a word, by proving their legitimacy in the field of the "economics of sustainable development" [START_REF] Bürgenmeier | Économie du développement durable[END_REF].

However, this legitimacy, if transformed in raw financial data and pure economic considerations, can be seriously questioned. In a narrow sense indeed, a costs-benefits analysis will always show that the costs for establishing, managing or developing a protected area are always much higher that the socio-economic benefits of it, since the expenses for a protected area are precisely located in the budget of the Authority in charge of the protected areaoften a public institution, with a specific budgetand will mostly account as direct expenses. In contrary, the benefits are spatially and socially diluted, shared among a broad number of stakeholders (Authority, private enterprises living from tourism around the protected area, etc.), that is, they mostly account as indirect expenses. This spatial and social dilution of the economic benefits generated by protected areas makes their evaluation uneasy. How far does the influence of the protected areas go, and what share of the benefits can be explained by the protected areas? There is indeed a large span in the possible answers, and consequently in the financial assessment of the impact of the protected areas on the local economy.

The balance often appears to be negative, making economic criticism against the cost of Nature protection easier.

In a broader sense, the principle itself of the economic valuation of protected areas appears however to be highly questionable, since the added socio-economic value of a protected area is not only a monetary one (see figure 1). The "optional" costs and benefits caused by protected areas has also to be assessed (costs : diminution of economic opportunities in the protected areas; benefits : increase of biodiversity and future natural resources, protection against some pollutions and risks, etc.), which is a difficult exercise since one has to measure virtual data that have not occurred yet [START_REF] Dixon | Economics of Protected Areas: A New Look at Benefits and Costs[END_REF][START_REF] Balmford | Economic Reasons for Conserving Wild Nature[END_REF].

Last, but not least, there is also a strictly social value of protected areas, that is the increase of knowledge, of well-being and the legacy that will be maintained for future generation. This is the key answer to economic criticism against protected areas, but the evaluation is against very difficult, not to say impossible. Many economic models are trying to convert this non-monetary, non-use value into a financial equivalent, such as the hedonic prices method, the cost of travel method, the renouncement cost method, or the most recent choice experiment or contingent valuation methods [START_REF] Hanley | Using Choice Experiments to Value the Environment: Design Issues, Current experiences and Future Prospects[END_REF][START_REF] Hanemann | Valuing the Environment Through Contingent Valuation[END_REF]. But, fundamentally, this "existence value", mostly based on moral and ideological considerations, is turning every macro-economic analysis into a nonsense: indeed, if one considers that the preservation of ecosystems and biodiversity is a key action for the perpetuation of humanity itself, then the economic value of protected areas will tend to infinite. [START_REF] Depraz | Géographie des espaces naturels protégés[END_REF].

In this regard, the economic sustainability of protected areas cannot be correctly assessed in a sole macro-economic valuation of costs and benefits. The question has to be laid on the political field; the cost of nature protection is rather a question of socio-economic priorities, and a relevant assessment of protected areas would rather consist in a costs-efficiency analysis [START_REF] Hockings | Evaluating management of protected areas: integrated planning and evaluation[END_REF][START_REF] Hockings | Evaluating Effectiveness: A Framework for Assessing the Management of Protected Areas[END_REF]: are the financial investments put in protected areas correctly translated into ecological improvements? Are the ecological goals of the protected areas socially relevant? Are the results reflecting properly the initial goals of the protected areas? Many NGOs working in the field of nature conservation have thus introduced new tools for the evaluation of the stage of nature conservation and the assessment of the efficiency of nature protection institutionsthe RAPPAM methodology by the WWF ( 2003) for tropical forests, the Forest Management Effectiveness Tracking tool by the WWF and the World Bank, the Threat-Ranking System by TNC ( 2007), etc.so that protected areas managers are now developing a new professional culture, clearly deriving from the private sector field.

Such questions were actually raised during the world commission of protected areas congress of the IUCN in Caracas (1992), where a task force about conservation effectiveness assessment had been launched at an international level. The Convention on Biological Diversity (CBD), in a 2004 meeting, also asked all Member States to act for a better management in existing protected areas. On a socio-economic point of view, it would be indeed irrelevant to raise the number of protected areas without securing the existing ones, and checking their action in regard to the new ecological objectives of the planet. Thus, 30% of protected areas had to be endowed with a management plan before 2010, and should strive for new financial resources by making the best possible projects, or even raising funds with public-private partnership, as any other territorial development project [START_REF] Emerton | Sustainable financing of protected areas: A global review of challenges and options[END_REF]Stolton & Dudley, 1999). Developing the economic sustainability of protected areas has definitely turned them towards managerial considerations.

The social disservices of Protected Areas

On the social point of view, one can consider that there is a rather broad acceptance of the idea of protected areas, since it is easily bound to the contemporaneous "categorical imperative" that intimates modern societies to protect Nature. Many NGOs are now acting in the field of Nature protection, especially in English-speaking countries, and their action is considered as a charity one, since the well-being of the future generations is at stake. However, are protected areas, and the action of their promoters, always socially sustainable? There is actually a strong debate in the conservation field between rather radical approaches, that claim for a nature conservation that has to be considered above any individual interests, since it is a universal priorityalso the general interest has to overwhelm any local consideration. But other conservationist circles will point out the social cost of establishing protected areas, especially in poor or developing countries. Is the ecological expense socially bearable, when compared to the question of reducing poverty or fighting against hunger [START_REF] Brunel | A qui profite le développement durable?[END_REF]? Shall most vulnerable people pay for others, when a protected area is created on their usual hunting territory, depriving them from natural resources? Environmental NGOs have now enough power to secure land by purchasing lots in poor countries, or intervene on national policies by the "debt or nature swap" method, making them a real global stakeholder of conservation [START_REF] Dumoulin | Les ONG, au centre du secteur mondial de la conservation de la biodiversité[END_REF].

In the 80's, political contests have arisen among local societies in eastern Africa, in South America or South-Eastern Asia against the "green imperialism" of western NGOs and their ecologic influence on poor countries [START_REF] Crosby | Ecological imperialism: the biological expansion of Europe, 900-1900[END_REF][START_REF] Rossi | L'ingérence écologique[END_REF]. The social impact of protected areas has now been taken into consideration at an international level. The IUCN, after the Nairobi summit on protected areas, has developed a more participative approach of nature conservation [START_REF] Kamstra | Protected areas: towards a participatory approach[END_REF][START_REF] Borrini-Feyerabend | Indigenous and Local Communities and Protected Areas: Towards Equity and Enhanced Conservation[END_REF], followed by most of the biggest NGOs since it was the best way to get more social acceptance of nature conservation. In Australia for instance, the establishment of Indigenous Protected Areas in the 80's was the first tangible experience of a real devolution of nature conservation on a voluntary and contractual basis. Other co-management programmes are currently implemented in most protected areas, with the idea of linking nature protection and local development by a promotion of sustainable tourism or new local resources [START_REF] Scherl | Can Protected Areas Contribute to Poverty Reduction? Opportunities and Limitations[END_REF].

However, such a policy needs strong local communities and the recognition of their collective rights to be successful. In many cases, the implementation of conservation policies remain actually very conflicting on the field. In India for instance, a very radical approach of nature conservation is still applying. Living in a national park is forbidden, as is the hunting or the use of any natural resource. However, the strong social pressure for firewood, for game or even for place to stay make these rules difficult to observe. The situation around national parks leads to a "shoot on sight" policy against poaching, and forced evictions occur, concerning not only informal housing, but also against Adivasis, which are the indigenous people traditionally living in mostly natural areas [START_REF] Mathews | Imperial Imperatives and the Global Financing of Protected Areas Ecodevelopment and the Resistance of Adivasis of Nagarhole National Park, India, Law, Social Justice & Global Development Journal[END_REF][START_REF] Zérah | Conflict between green space preservation and housing needs: the case of the Sanjay Gandhi National Park in Mumbai[END_REF]. Violent cases of forced evictions are also frequently recorded in Africa [START_REF] Brockington | Protected Areas and Resettlement: what scope for voluntary relocation?[END_REF][START_REF] Brockington | Eviction for Conservation: a Global Overview[END_REF]. After [START_REF] Geisler | A New Kind of Trouble: Evictions in Eden[END_REF], this could be the case of 14 million people around the world, constituting a new category of "refugees of the conservation". Even if this number remains highly questionable, and has even been attacked by some NGOs that raised severe doubts about the scientific value of those calculations [START_REF] Redford | Protected Areas and Human Displacement: a Conservation Perspective[END_REF], the case has to be at least taken in account, as some programs financed by the World Environmental Fund of the World Bank are still openly planning some "voluntary resettlement" or "soft evictions" policies.

The case of forced evictions is the most evident case of the possible gap between protected areas and sustainability, making the need for participatory and socially policies even more urgent.

Conclusion

A French defender of Nature Protection in the Northern Alps, Jean Eyerhalde, had these words, as he campaigned for the creation of Nature reserves in the 60's in Savoyen: "Nature reserves are conceived to disappear" (quoted in [START_REF] Mauz | Les Alpes, de la société de la vache au parc animalier[END_REF]. He was right in a certain way, for protected areas, since their creation at the end of the 19 th Century, are carrying some principles that might go in the reverse direction of sustainability. If they still lay on a radical vision of a preserved wilderness, especially in populated areas, they create economic, social disservices and might even have no grasp on biodiversity losses at a broader scale; however, if they are cleverly managed in a way that makes their goals merge into local development prospects, they can contribute to a better understanding of the goals of nature conservation, and bring an improvement of nature management even out of their borders, so that the principles of nature conservation could apply without differences in and out of protected areas.

But as long as protected areas are necessary, they will surprisingly enough prove that a sustainable development has not been reached yet, since human societies have not been able to completely integrate the ecological imperatives in their management of territories.

Figure 1 :

 1 Figure 1: the economic valuation of the spatial impact of protected areas[START_REF] Depraz | Géographie des espaces naturels protégés[END_REF].

i For a broader analysis of the historical and geographic context of Protected Areas, as well as more developed explanations about the main concepts that are mentioned throughout this chapter, see more generally[START_REF] Depraz | Géographie des espaces naturels protégés[END_REF]


Interviewing elites. Perspectives from medical tourism sector in India and in Thailand.

Audrey Bochaton1 , Bertrand Lefebvre2

In Fieldwork in Tourism: Methods, Issues and Reflections, Edited by Michael Hall, Routledge1. Introduction From culture, to cookery, to eco -tourism, the holiday experience is becoming more and more diverse. Since the Asian financial crisis of 1997, medical tourism has increasingly contributed to this trend, particularly in Thailand and India. The main motivation of our project is to engage a research study on medical tourism which has been almost exclusively approached from the point of view of the media today. Medical tourism has been indeed widely commented by the press, which presents the 'sea, sun, sand and surgery' [START_REF] Connell | Medical Tourism: Sea, Sun, sand and… surgery[END_REF] phenomenon as 'the' answer for patients living in developed countries and having to deal with long consultation waiting lists, and high medical costs. Until now, few articles are putting medical tourism in perspective and therefore we wanted to go a little further than the headline story that the media and the medical tourism stakeholders keep selling. Through a comparison between India and Thailand, our objective was to better assess medical tourism, its development, its impacts. Medical tourism takes place in different parts of the world today and emphasises well the globalization in the field of health care. In this context, we thought that the mirroring effect between the two countries would be very effective to deepen our understanding of the phenomenon, and to bring out the main elements constituting this trend.

During our research project we had to conduct many interviews with medical professionals, marketing and operation managers of corporate hospitals, and key members of different ministers or professional organisations in India and Thailand. Following Herod (1999: 313) in his effort to define foreign elite, we can identify our interviewees as "foreign nationals who hold positions of power within organizations such as corporations, governments". In India and Thailand, the corporate hospitals, the professional organisations (e.g. the Confederation of Indian Industry) and the ministry of health and the ministry of tourism are instrumental in the growth of medical tourism. There is a growing literature about the specificity of elite interview (e.g. [START_REF] Sabot | Dr Jekyl, Mr H(i)de: the contrasting face of elites at interview[END_REF][START_REF] Desmond | Methodological challenges posed in studying an elite in the field[END_REF][START_REF] Herod | Reflections on interviewing foreign elites: Praxis, positionality, validity, and the cult of the insider[END_REF][START_REF] Smith | Problematising power relations in 'elite' interviews[END_REF][START_REF] Welch | Corporate elites as informants in qualitative international business research[END_REF]. Though not exclusive, interviewing elites raises various methodological issues like the access to the informers, the unbalanced power relations during the interview, the reliability of information. [START_REF] Herod | Reflections on interviewing foreign elites: Praxis, positionality, validity, and the cult of the insider[END_REF] even considers that conducting research on foreign elites bring very specific issues of cultural positionality that do not exist in the case of study on non-foreign elites.

The objective of this article is to address the methodological issues we faced as French PhD students interviewing foreign elite. How did we interact with the main actors of medical tourism both in India and Thailand? How did we deal with interviewees who are mastering the art of communication and marketing? What strategies were adopted to get the right information during the interview?

In the following section of this paper, we will discuss the preparation of our field work and remind how it is essential before interviewing elite's members. Then, we will present the different strategies we used to access our interviewees. In a third section, we will document the process of interviewing and the related power-relation issue. In conclusion, we would like to discuss the interest of cross-border field works.

Preparing the fieldwork

Approaching a global phenomenon: medical tourism

In order for the comparison to become both useful and effective, we needed to choose some methods which could be applied in Thailand and India. With a common framework taking place in two different contexts, we would thus be able to discern similarities and differences in the way medical tourism has emerged in Thailand as well as in India. The first phase of our research relied heavily on secondary quantitative and qualitative sources. It involved the collection of many figures, articles, public speeches and interviews on medical tourism in the research reviews, the news magazines, the daily press and the professional magazines from both countries. We extended this work to the international and western media. These different sources of information gave us a broad perspective on a topic which was not that familiar to us.

We quickly found out that if we talk about medical tourism generally, it takes different forms through the context. For example, India receives among 'its medical tourists' nearly only Non-Resident Indians (NRI) living abroad who travel for medical treatment to their 'homeland' during their holidays. In Thailand, there is no typical medical tourist but a mix of nationalities among the patients and later the interviewees there were cautious in separating medical tourists from foreign patients. The private hospitals in India, have more difficulties in drawing such distinction. The medical tourist and the expatriate can be counted as foreigner patients, while the NRI coming for a health check-up can be counted as a local patient. As already mentioned by [START_REF] Connell | Medical Tourism: Sea, Sun, sand and… surgery[END_REF], measuring and assessing the exact number of patients involved in medical tourism is rather tricky. How differentiate a patient coming especially for care in Thailand or India from an expatriate or from a tourist using local health infrastructure further following an illness? And then among medical tourists, how differentiate those who have no quality hospital in their countries from those who are looking for cheaper treatments? The problem of the definition of 'a medical tourist' and the dissimilarities between Thai and Indian systems of counting brought us to be careful with the figures that we used and called into question the appellation of 'medical tourism' itself. The further we advanced, our look became more and more sceptical to this stock phrase as 'medical tourist' expression refers today to a reality which can not be precisely measured.

We also collected and analysed in a more detailed manner, the communication of the corporate hospitals involved in medical tourism. We collected brochures and visited their websites on various occasions. The concept of the brochures and the websites is similar for both countries: they are a well thought out mix of reassuring pictures, texts, patients' testimonials and international certifications. The ultimate purpose is to seduce the potential medical tourist into going to this particular facility in the same way as a classic tourist would choose this or that resort from a holiday brochure. This information gave us an idea of the manner the patients are perceived and medical tourism is heralded. All this documentation and the information previously collected in the media was analysed in order to outline the discourses produced by the various stakeholders of medical tourism and to identify the key arguments pro or against medical tourism, their variation from one country to another. We then realised that discourses on medical tourism, particularly in mass media, are coming from a limited number of sources and are controlled by certain groups, organisations.

In defence of medical tourism

In an enlightening paper about the development of biotechnology in Ireland, Desmond wrote (2004: 267): "During this early period the industry was embroiled in a society-wide discourse regarding its general safety and appropriateness. To counter these accusations, the sector actively attempted to discursively re-construct this image around claims of sound science and the national economic interest." In a similar manner, medical tourism's stakeholders are producing discourses and ready-to-think ideas to justify and reassess their activity. This group of actors can be identified as elite as they have a great control over medical tourism, from its creation to the discourses pertaining the sector. In India, most of them are affiliated to the Healthcare branch of the Confederation of Indian Industry (CII). In Thailand they are affiliated to The Private Hospital Association (PHA). These lobbies are instrumental in the implementation of medical tourism and in the interactions with the public authorities and political sphere. In 2002 the release by the CII of a joint report with the audit agency McKinsey on the future of Indian healthcare ("Indian Healthcare: the road ahead"), gave them the opportunity to market the idea that medical tourism was paving the way for a profitable future for the all nation. The information on Indian healthcare being often fragmented and out-dated, this report has been praised as a thorough attempt to fill such gap. This report has been heavily over-quoted and is now at the base of many articles or figures on medical tourism in Indian and international media. It is on the evidence of this report that Indian central government gave more support to medical tourism and began to work with the corporate hospitals to frame and market medical tourism. In its National Health Policy 2002 (NHP-2002) paper (GOI, 2002) the government stated that: "To capitalize on the comparative cost advantage enjoyed by domestic health facilities in the secondary and tertiary sectors, NHP-2002 strongly encourages the providing of such health services on a payment basis to service seekers from overseas".

Interestingly, the arguments supporting medical tourism used in India and Thailand were slightly different. We noticed that Indian communication is well focused on the benefits of medical tourism for the whole nation as a mean to justify this trend in their country and also to prevent criticism of the phenomenon. As one brochure of the Indraprastha Apollo Hospital of Delhi claims after the hospital received the Joint Commission International accreditation, they are: "Carrying the Indian Flame High". This nationalist aspect does not appear at all in Thailand. Thai communication lays more stress on the medical hub, gentleness of Thai people, the leisure infrastructure and the good time you can get after your treatment. The Thai Authority of Tourism is creating confusion, mixing medical tourism and wellness tourism (spa, traditional Thai massage) in its communication campaigns, and thus concealing the medical procedures that made the reputation of Thailand at the international level (plastic surgery, sex change).

Who? What? How? Preparing the interview

After assimilating all these different information, it was time for us to prepare for interviews. We first identified three different types of interviewees: the hospital managers, the medical staff and the public authorities. We were interested in tracing the history of medical tourism, the diffusion of this concept and the network of actors involved in the birth of medical tourism. The most important thing for us was to collect their views on medical tourism, on the future of medical tourism, on the impact on local healthcare systems, on their marketing strategies, on the links between private and public players, on the architectural design and on the way the hospital as a place is envisioned. Like in any elite or organisation, the official voice, heavily reproduced in the media, may be undermined by some clashing voices from the inside. We were then very much interested by collecting the views of the medical staff.

We used a semi-structured questionnaire and designed a list of all the issues we wanted to discuss. Doing so, our objective was to create a confident climate based on a discussion more than simply ask direct questions from a ten pages questionnaire. It was the best way to adapt to the, sometimes, limited time that the interviewees could give to us. It was also a way to stay close to the interviewees' vision of medical tourism. The issues were structured according to their importance for us. We did not ask too much detailed information on the hospital or the quality of the offer (i.e. medical equipment, staff) when the time was limited as it was available in the brochures and the annual reports that the corporate hospitals publish for their shareholders. Doing so, we have been able to extract the main elements constituting the medical tourism trend globally but also to underline differences in the way of broaching the phenomenon.

Accessing the elite

As seen previously, hospitals, ministries, professional organisations are highly visible and promote explicitly the medical tourism. It was of great interest as we could analyse at a preinterview stage the discourses they produced and their agenda. Through selected examples, we will present the different ways we accessed the elite constituted by the managers, the medical practioners and the ministries' representatives.

Thai fieldwork

We conducted a fieldwork in Bangkok over a period of two weeks in June 2006. Bangkok is the common gateway for international tourists to South-East Asia. And, as the representatives of the main private hospitals based in the city used to repeat, Bangkok is now 'the health care hub' for South-East Asia: this is where all the biggest health care facilities, the best standards, the best skilled and trained staff of the country are concentrated. We conducted interviews in the hospital sector and in the public authorities.

We interviewed a doctor working in the International Patient building of the Bangkok Hospital (BH). Audrey previously met him for her own PhD research and arranged a meeting with him at the Bangkok Hospital. At the end of the interview we asked him how we could access and interview somebody from the marketing department. He called the marketing department and managed to arrange an appointment for us. Half an hour later, to our own surprise and without any prior appointment, we were having a long and in-depth interview with the head of the marketing department.

Audrey contacted through email the head of the marketing division of the Bumrungrad Hospital on various occasion but never get any reply from his side. Once we were together in Bangkok, we just decided to go the hospital, and try to get an appointment with this person. We briefly introduced ourselves and our project at the reception office of the hospital and asked if it was possible for us to meet somebody from the marketing department. An employee asked us to wait and went for enquiry. She came back to us saying it was not possible for us to meet somebody from the marketing as they were all in a meeting. We insisted, saying that we were ready to wait or to come back later. We reminded her that Audrey tried to contact the head of marketing division on many occasions without receiving any reply. We told her that Bertrand was coming directly from India. We also pointed out that we already had an interview with their concurrent from the Bangkok Hospital. The employee went again with all this new information to check from the marketing division. Surprisingly, she came back to us, cheerful, saying the head of the marketing was ready to meet us at the end of the meeting.

Indian fieldwork

The interviews in Delhi, conducted by Bertrand only, were slightly different. The choice of Delhi was well justified other than practical advantages. With its international airport, a mushrooming corporate hospital sector (Apollo, Max, Fortis), the rather good level of infrastructure (compared to the rest of India), Delhi is a hot spot for medical tourism in the country.

In the case of this research on medical tourism he mostly interviewed contacts he had already met on previous occasions for his own PhD research. Since 2004, Bertrand is conducting a PhD research on the corporate hospitals in India. When he started, some Indian scholars were pessimistic on his chances to get information and interviews with the marketing and operation managers from the corporate hospitals of Delhi. Apparently, an M.Phil student from the Jawaharlal Nehru University had tried to work with Apollo Hospitals for six months, till she realised it was not possible, due to their lack of cooperation. He faced the same kind of difficulties during his first fieldwork. It took a long time to get an appointment in hospitals or at the Confederation of India Industry. Some people simply did not want to bother with a junior student in geography ("Why are you studying the hospital sector? Geographers should study relief and landscape" as one person said to him once on the phone) coming from an unknown university and struggling while speaking English. He shared then these difficulties with one of the heads of the Economic Mission of the French Embassy, who kindly prepared a letter of introduction for him, requesting the interviewees to be kind enough to cooperate as Bertrand was supposedly preparing a report on the corporate hospitals for the Economic Mission. Thanks to this letter and this faked identity, people were suddenly keener on taking some of their precious time to answer to his questions. It gave more credibility to his study. With this experience in mind, he is now emphasizing his affiliation not to his research centre in India which is a division of the French Embassy, nor his remote French university, but simply to the French Embassy in India, to gain an easier access to any new contact he wants to meet.

Is accessing the elite so difficult?

With regards to these experiences, it seems difficult to assess which method is better than another. From being introduced by an insider to the use of a letter of introduction, there are various possibilities to access the interviewees. We can thus consider two important issues out of our own limited experiences.

As Desmond state (2004), the question of time to access elite is extremely important. Medical tourism is actually a booming sector and the managers are ready to open their doors to herald the story of their success. As the marketing manager of the Bumrungrad Hospital told us, we were not the first students to visit him. His hospital is actually receiving a great interest from the media (e.g. CBS 60 minutes). We have been able to access sometimes very easily some top managers, because we are now at a deciding moment for medical tourism. It is no more a marginal phenomenon, be it by the number of patients involved or by the potential impact on the local healthcare sector. The use of marketing and branding is indeed a double edge sword. Bumrungrad Hospital or Apollo Hospitals position their brand at the international level in order to attract more international patients. It also positions them as potential target for public campaigns against medical tourism. There is an urgent need for the actors of this sector to legitimate their activity in face of the local and international public opinion. In an international activity like medical tourism, researchers, even juniors, can also be used to herald the medical tourism success and to disseminate the information abroad. Audrey was in contact last year with a TV journalist preparing reportage on medical tourism in Thailand. In 2005, Bertrand has been interviewed for a French travel magazine (Match du Monde) on medical tourism in India. It is somehow flattering for the managers to receive some interest from abroad.

Another important issue, was our positionality. We sometimes manipulated our identity to gain an easier access to the interviewees. For example we never insisted too much on the fact we were both geographers, in order to avoid the confusion and the reservation that goes with the typical question on "why geographers are studying medical tourism?". In the case of Bertrand we can see how his status improved drastically, in the eye of its potential interviewees, thanks to the French Embassy's label. The researcher's position is not only defined by what he is (e.g. a white, French, female researcher in geography) but also by what he represents in the eyes of the interviewees. This position evolves with the time and there is space for revealing more of your identity later. Befriend with your contacts can become beneficial on the long term. The interview is a defining moment in the evolution of your identity.

The moment of the interview

Foreigners, junior researchers… the different faces of the interviewers

Being a foreigner was certainly of great help to conduct our interviews. A foreigner is probably perceived as being less threatening than the local researcher by any elite. At the local level medical tourism raises some controversy, on the increasing inequality in term of access to healthcare. A foreign researcher is not here to stay. Because he did such a long way, coming from abroad, the foreign researcher is often welcome by the interviewees with lot of curiosity. "How long have you been in Thailand?" "Do you like Indian food?" "My daughter is going to study in France." This empathy helped on many occasions to engage the interview in a positive and warm atmosphere. We faced also on certain occasions, particularly with Western managers, a rather cold welcome, probably because there was a sense of disappointment at the view of two junior scholars. We could feel from start that the interview would require a lot of patience and humility from our side because our interviewee was making us understand that he was busy and that he was doing us a favour by receiving us.

One clear advantage of being a foreigner and a junior scholar is that you are allowed to ask stupid questions. You are not aware of the local situation or all the details. You can genuinely ask challenging questions or pointing some contradictions in the discourse but without too much damage because at the end "I did not know". Our experience was rather similar to what Sabot describes [START_REF] Sabot | Dr Jekyl, Mr H(i)de: the contrasting face of elites at interview[END_REF] when write about the foreign researcher: "S/he is also able to circumnavigate cultural taboos whereas the local researcher is tied by his/her own culture. In effect, the reception given to foreign researchers becomes a sort of public relations exercise at an international level; thus the foreigner researcher is allowed to ask almost anything."

Who is controlling the interview?

During an interview the power balance between the interviewee and the interviewers is evolving. This issue is very much important while interviewing an elite group. Elites have a strong consciousness of their importance [START_REF] Richards | Elite interviewing: Approaches and Pitfalls[END_REF]. In our case we were interviewing marketing directors, operation managers who are trained for this type of exercise. During our interviews in both countries, the message delivered was that medical tourism is positive for the country, its economy and its healthcare system. Whoever is doubtful of this positive impact, is "an outsider who has misconceptions on what is really medical tourism" as one of the interviewees explained to us. It was important for the managers of the corporate hospitals we interviewed to deliver the proper message, to emphasize certain points, and to legitimise their opinion. As the marketing director of Bumrungrad Hospital put it "Regarding Medical Tourism, I am THE source." It gives them more power over the interviewer who always has to be extremely careful if he wants some rewarding information. We had our own agenda for the interview, but so had our interviewees.

In face of such specialists, it was sometimes difficult for us to keep control over the interview. Some interviews were somehow turning into a Public Relation operation. Probably because we were junior researchers, some of them took even a paternalistic attitude, trying to advice us on what we should write and think or what part of their report is "particularly important to understand our activity" and that all the information we needed "is in the report". Because we prepared our interviews well before, studying the marketing discourses, we were able during the interview to segregate original information from communication material. If we remained extremely humble during every interview, we also tried to make our interviewees understand that we were not that new in the field of healthcare.

Being together during our fieldwork in Bangkok was indeed of great help to gain more information from our interviewees. If one forgot to ask a question, the other can carry on the interview. Facing the same answer, we could have different interpretation and thus push in the interview in different directions. During this fieldwork, Audrey was familiar to the Thai healthcare system and affiliated to a Thai university, while Bertrand coming straight from India was a complete alien to the local context. We had different level of foreignness to the situation. We experienced what [START_REF] Herod | Reflections on interviewing foreign elites: Praxis, positionality, validity, and the cult of the insider[END_REF] describes as different degrees of "outsiderness". The interviews were ultimately very rich. Doing her PhD between Laos and Thailand, Audrey was very much aware of the local context. Coming from India, without any prior knowledge about the local trends, Bertrand was asking very naïve questions. This strange combination was probably confusing for the interviewees and thus helped us at regaining more control over the interview.

Of decentring and reciprocity

Because we felt our position during the interview was fragile, we tried to broad the perspective of the interview. Instead of addressing certain sensitive issues too directly, we used such formula as "some people are saying that…" "We read on your website that… can you tell us more" or "The X hospital is doing that. What about you in Y hospital?" That way we gain not only information on certain sensitive issues (or we perceived as sensitive) but also on their perception of their concurrent or the medical tourism. While in Bangkok, the general atmosphere at least in the talk was more of "the medical tourism cake is big enough to be shared" or "their hospital is very different from ours. They are working their ways, we are working ours", in Delhi we could feel a strong sense of concurrence from every side: "We will always remain first because we invented everything in the field of hospital care in India. They are just followers and had previously nothing to do with this sector. They are just considering health as a business"; or "In this hospital, they are talking too much about medical tourism. What about the Indian patients? They are my real concern."

An interesting aspect from our fieldwork in Bangkok, was the use of India as decentring point. "In India, they are doing this…" Or "it is the same in India". It was again a way to avoid frontal and brutal questions on the use and misuse of marketing, for example. By relating some information collected previously in India or about the Indian experience, we have been able to build a confident exchange. Bertrand explained to some of our interviewees, what was the situation of the Indian hospital sector. The interview became then more like of an exchange of information. The reciprocity of information, the exchange of opinion, was of great help to build confidence among the interviewees. As the interviews were going on, the interviewees in Thailand were becoming franker, even sometimes very straightforward. The charitable activity being merely cosmetic, and a tool for communication, has been clearly explained to us. It was the same frankness regarding the surprising lack of cooperation between private players and the public authorities in Thailand. Similarly in India, interviewees were very keen on learning something about European or French healthcare. They were very curious about the French or other European health systems and were asking rather precise questions on the insurance systems, the public-private partnership or the potential for India to attract medical tourists. It was not rare that an interview that was supposed to last only 15 minutes at start lasted finally more than an hour.

Conclusion

We broach medical tourism from different points of view: main private actors in the hospitals and some important public actors in both countries. As it is a first step in the running of this study, we tried to focus the approach on the way the medical tourism phenomenon was setting up in the both countries, the political aspects of the trend, the levels of implications of different actors. But during this first stage, we didn't have the chance and the time to examine the point of view of the medical tourists themselves; how do they perceive the treatment and the global experience in these 'Five Star Hospitals'? What about their satisfaction? Of course, some comments of these patients are available in media, hospitals' websites or brochures but they are embedded in the discourse built on medical tourism as the 'perfect answer' today in the field of health care. It will be very necessary to interview the medical tourists in order to balance the discourse from the main actors and to get a less polished vision of medical tourism.

In the face of such recent and over commented phenomenon, like medical tourism the use of comparison allowed us to go beyond the description of the trend and put into perspective the phenomenon. The comparison between India and Thailand sheds light for example on the misconceptions of the "Thai model" as it is perceived and explained by the Indian medical tourism stakeholders. Thailand is seen as the country ahead of the rest regarding the various aspect of medical tourism (marketing strategy, infrastructure, management of the medical staff). In India, during the professional summits on medical tourism or in the interviews given to the media, Thailand is praised as the model to follow and to beat. What is particularly stressed is the strong joint action between public authorities and private actors to market medical tourism abroad and to develop this activity (e.g. http://www.expresshealthcaremgmt.com/20050215/interview01.shtml). The interviews in Thailand have qualified this vision as idealistic. The managers met at the Bangkok Hospital (BH) and at the Bumrungrad Hospital have both stressed that the connections with Thai public authorities were very recent and still very weak. They both agreed that on this point Thailand was lagging behind Singapore and even India. Indian stakeholders of medical tourism seem to use Thailand as an idealistic model to pressure Indian public authorities to get more support. During the 2004 Health Summit organised by the Confederation of Indian Industry, the managers of the main corporate hospitals were requesting the central government to create a medical visa, like in Thailand. At the next Health Summit in 2005, the same managers were proud to announce that the medical visa has been launched couple of months ago. It seems also that always referring to the successful medical tourism in Thailand is a good mean to convince the public opinion, justify the development of this trend in India and prevent possible criticism. Comparison, and the necessary multi-sited fieldwork we conducted, gave us some interesting information on medical tourism. It also showed us on the way how a global phenomenon imbed in local societies and how certain elites are manipulating facts and discourses in their own interest. Bochaton A., Lefebvre B. 2006, 'Interviewing elites. Perspectives from medical tourism sector in India and in Thailand', paper presented during the graduate workshop on questions of methodology: researching in Asia, 5-6 September 2006, Asia Research Institute at National University of Singapore.

University of Paris X-Nanterre (France), Institut de Recherche pour le Développement (Laos)

University of Rouen (France), Centre de Sciences Humaines (India)


Xiaoran Jiang

Mikaël Le Pendu

Christine Guillemot

DEPTH ESTIMATION WITH OCCLUSION HANDLING FROM A SPARSE SET OF LIGHT FIELD VIEWS

Keywords: depth estimation, light field, stereo matching, optical flow, low rank approximation

This paper addresses the problem of depth estimation for every viewpoint of a dense light field, exploiting information from only a sparse set of views. This problem is particularly relevant for applications such as light field reconstruction from a subset of views, for view synthesis and for compression. Unlike most existing methods for scene depth estimation from light fields, the proposed algorithm computes disparity (or equivalently depth) for every viewpoint taking into account occlusions. In addition, it preserves the continuity of the depth space and does not require prior knowledge on the depth range. The experiments show that, both for synthetic and real light fields, our algorithm achieves competitive performance to state-of-the-art algorithms which exploit the entire light field and usually generate the depth map for the center viewpoint only.

INTRODUCTION

Light fields, by capturing light rays emitted by a 3D scene along different orientations, give a very rich description of the scene enabling a variety of computer vision applications. The recorded 4D light field can also be regarded as an arrays of views giving information about the parallax and depth of the scene. Existing methods for depth estimation from light fields can be classified into several main categories: methods based on sub-aperture images (SAI), on epipolar plane images (EPI) or on refocused images. The methods based on SAI compute matches between the extracted views, assuming that they are well rectified with a constant baseline [START_REF] Heber | Shape from light field meets robust PCA[END_REF][START_REF] Jeon | Accurate depth map estimation from a lenslet light field camera[END_REF]. The authors in [START_REF] Heber | Shape from light field meets robust PCA[END_REF] use robust PCA to estimate the disparity which will minimize the rank of the matrix containing all the views warped on the center one. A method is described in [START_REF] Jeon | Accurate depth map estimation from a lenslet light field camera[END_REF] which instead computes a cost volume based on the similarity between sub-aperture images and the center view shifted at sub-pixel locations to evaluate the matching cost of different disparity labels. The authors in [START_REF] Chen | Fast and accurate optical flow based depth map estimation from light fields[END_REF] apply an optical flow estimator on a sequence of light field views along an angular dimension to estimate several disparity maps which are then aggregated to create a single disparity map which is then converted into a depth map.

Another type of methods for plenoptic depth estimation uses EPIs [START_REF] Wanner | Variational light field analysis for disparity estimation and super-resolution[END_REF][START_REF] Zhang | Robust depth estimation for light field via spinning parallelogram operator[END_REF]. Indeed, the slope of the line composed of the corresponding pixel in an EPI is proportional to the depth of the pixel [START_REF] Bolles | Epipolarplane image analysis: An approach to determining structure from motion[END_REF]. The authors in [START_REF] Wanner | Variational light field analysis for disparity estimation and super-resolution[END_REF] use structure tensors to estimate the local slopes which are then regularized using a variational labeling framework for global consistency, while a spinning parallelogram operator is proposed in [START_REF] Zhang | Robust depth estimation for light field via spinning parallelogram operator[END_REF] to estimate the slopes of these structures. A third category of methods uses images in a focal stack and use defocus cues, possibly combined with other measures, to estimate depth [START_REF] Tao | Depth from combining defocus and correspondence using light-field cameras[END_REF][START_REF] Ting-Chun | Occlusion-aware depth estimation using light-field cameras[END_REF]. This relies on the assumption that in-focus points are projected at the same spatial position in the different views.

However, most of these methods require that the light field is densely sampled. Furthermore, the methods using cost volumes or those that consider depth estimation as a multi-labelling problem require discretizing the depth space. In order to keep the computational cost within a manageable limit, the number of discretization levels in these methods should be kept low at the expense of accuracy. Finally, most methods only compute the depth map of the center view, hence do not give geometry information on pixels which are not visible from this viewpoint, yet this information may be required for problems such as light field reconstruction, or view synthesis.

In this paper, we propose a novel depth estimation algorithm exploiting only a sparse subset of light field views. The method computes a disparity (or equivalently depth) map for any light field viewpoint, hence is particularly interesting for applications such as light field reconstruction or view synthesis from a subset of views and for compression [START_REF] Jiang | Light field compression using depth image based view synthesis[END_REF]. Unlike [START_REF] Jeon | Accurate depth map estimation from a lenslet light field camera[END_REF][START_REF] Zhang | Robust depth estimation for light field via spinning parallelogram operator[END_REF][START_REF] Tao | Depth from combining defocus and correspondence using light-field cameras[END_REF][START_REF] Ting-Chun | Occlusion-aware depth estimation using light-field cameras[END_REF], the proposed method does not demand discretization of the disparity space, nor prior knowledge about the disparity range. According to the metrics defined in [START_REF] Honauer | A dataset and evaluation methodology for depth estimation on 4d light fields[END_REF][START_REF] Johannsen | A taxonomy and evaluation of dense light field depth estimation algorithms[END_REF], the experiments show that our approach achieves competitive performance compared to state-of-the-art methods that make use of the whole set of light field views.

ALGORITHM OVERVIEW

We consider the 4D representation of light fields defined by a function L(x, y, u, v) of 4 parameters at the intersection of the light rays with 2 parallel planes. The light field can be seen as capturing an array of viewpoints (called sub-aperture images and denoted by Lu,v) of the scene with varying angular coordinates u ∈ 1 . . U and v ∈ 1 . . V . In this paper, we propose to estimate one consistent and accurate disparity map per position (u, v), given only a sparse subset of light field views. This disparity map can then be easily converted into a depth map.

The algorithm proceeds as follows (cf. Fig. 1). The four corner views L 1,1 , L U,1 , L 1,V and L U,V are taken as input, since these views contain the geometry of the whole scene, accounting for disocclusions. Multiple rough disparity estimates for these input views are first computed using an optical flow estimator. These candidates are then aggregated by using an energy minimization and the resulting map per input view is further enhanced by using a novel superpixel-based bilateral filtering. These refined disparity maps are warped to novel viewpoints and a global inpainting using low rank approximation is performed to fill the holes. Finally, at each novel viewpoint, warped candidates are merged with respect to their disparity uncertainty via a winnertake-all process.

DISPARITY ON REFERENCE VIEWS

Optical flow-based initialization

Let R = {r} denote the set of input viewpoints, with r = (ur, vr). Horizontal and vertical disparity maps are computed between each input view Lr and each of the other views L r , with r ∈ R r, using an optical flow estimator,

d r→r = d X r→r d Y r→r = OpticalF low(Lr, L r ).
(1)

d X
r→r and d Y r→r are respectively the horizontal and vertical disparity from the view Lr to L r . In the experiments, we used Epicflow [START_REF] Revaud | EpicFlow: Edge-Preserving Interpolation of Correspondences for Optical Flow[END_REF], however, any state-of-the-art optical flow estimator can be used.

Assuming that the light field views are well rectified, a scene point moves only horizontally from position (1, 1) to (U, 1), and only vertically from position [START_REF] Heber | Shape from light field meets robust PCA[END_REF][START_REF] Heber | Shape from light field meets robust PCA[END_REF]

to (1, V ): d X (1,1)→(1,V ) = 0 and d Y (1,1)→(U,1) = 0.
For simplicity and without loss of generality, we also suppose the 4D light field is a square grid of regularly spaced views, i.e. U = V and the horizontal and vertical baseline between views is uniform. Therefore, a set of 4 estimates that reveal the same disparity information is obtained at view L 1,1 :

C 1,1 = {d X (1,1)→(U,1) , d Y (1,1)→(1,V ) , d X (1,1)→(U,V ) , d Y (1,1)→(U,V ) }.
These maps are normalized by dividing them by (U -1) (where U is the number of views in each dimension) such that they represent disparity between adjacent views, assuming a constant baseline. The sets of estimated maps C U,1 , C 1,V , C U,V for the other input views are computed in a similar manner. In the sequel, we let d i r denote the i th estimated disparity map in the set Cr.

Energy minimization

As optical flow estimators only work on pairs of images, which do not fully exploit angular diversity of all input views, each pair gives a rough disparity estimate. To have a more reliable estimate Dr, r ∈ R, at each pixel p, one disparity value is selected among all candidates d i r (p) by minimizing the energy E

Dr(p) = argmin d i r (p) E(d i r , p), (2)
where E(d i r , p) denotes the energy value at pixel p computed using d i r . These energy values for all pixels form a so-called energy map E(d i r ) expressed as

E(d i r ) = Ec(d i r ) + λ 1 Eg(d i r ) + λ 2 Es(d i r ), (3)
The energy term Ec is a color consistency term computed between Lr and the projected views as

Ec(d i r ) = r ∈R r M r ,i r E 1 (Lr, L r ,i r ) r ∈R r M r ,i r , (4)
where E 1 (I, I ) is defined as the pixel-wise sum of square errors for the three color components:

E 1 (I, I ) = C∈{R,G,B} (I C - I C ) 2 .
The symbols and denote respectively pixel-wise division and Hadamard product. L r ,i r stands for the warped image from position r to r by using the i th disparity candidate d i r . Here, backward warping is applied, and horizontal and vertical disparities between r and r are obtained by multiplying the normalized disparity d i r by the angular position offset rr. M r ,i r is the corresponding binary mask discarding the disoccluded pixels from the energy summation. If one pixel p falls into holes of all the warped images using one candidate disparity map d i r , (i.e.

r ∈R r M r ,i r (p) = 0) the candidate is discarded for that pixel by setting Ec(d i r , p) to infinity. The second term Eg is a gradient consistency term computed between the reference view and the warped views:

Eg(d i r ) = r ∈R r M r ,i r E 2 (Lr, L r ,i r ) r ∈R r M r ,i r , (5)
where E 2 denotes the pixel-wise square error on the gradients:

E 2 (I, I ) = (∇xI -∇xI ) 2 + (∇yI -∇yI ) 2 . Finally, the smoothness term Es Es(d i r ) = r ∈R r E 2 (d i r , Lr) |∇xd i r | 2 + |∇yd i r | 2 (6)
helps preserving edges. In fact, if an edge (large gradient) in the disparity map is misaligned with the corresponding one in the color image, the term E 2 (d i r , Lr) should be high. Otherwise, when the two edges are aligned, Es does not penalize the energy in spite of the large gradient of the disparity. In practice, to bring the disparity map and the color image to the same scale, their values are both normalized between 0 and 1.

A confidence measure of the selected disparity values can be deduced based on the minimum energy:

Fr = exp - min i E(d i r ) 2σ 2 e (7)
where σe controls the "width" of the distribution.

Superpixel-based edge-preserving filtering

The previous energy-based voting approach is fast and efficient to select the most likely disparity value among all candidates. Nevertheless, the resulting map may benefit from further enhancement due to the fact that: 1/-none of the candidate values may be correct; 2/-the disocclusion masks used in the energy computation (Eq. 4-5) may be erroneously estimated due to disparity inaccuracy.

To enhance the disparity estimate for each input view, we propose a novel superpixel-based edge-preserving filtering. We first identify the pixels with the lowest 5% confidence measure as the set of pixels Ωr for which the disparity is potentially wrong. A filtering of these unreliable disparities is performed by computing a weighted average of reliable nearby values:

∀p ∈ Ωr, Dr(p) = 1 Zp q∈Np∩Ωr wp,q Dr(q), (8)
where Zp is a normalization factor

Zp = q∈Np∩Ωr wp,q. (9)
As for the bilateral filter, the weights wp,q are defined as a function of a spatial Gσ s and photometric Gσ c kernel as:

wp,q = Gσ s ( p -q ).Gσ c ( L(p) -L(q) ) = exp(- p -q 2σ 2 s - L(p) -L(q) 2σ 2 c
).

(10)

However, unlike classical image-guided bilateral filtering for which the pixel neighborhood Np is usually a square window centered in p, in the proposed filter, the neighborhood is defined by superpixels assuming that pixels inside a superpixel are likely to have close depth. In our experiments, SLIC [START_REF] Achanta | SLIC Superpixels compared to state-of-the-art superpixel methods[END_REF] implementation is used. To best adapt the size of the neighborhood to the reliability of disparity values, a fine over-segmentation in superpixels is first performed and if a superpixel s i contains less than 50% of reliable disparity values, then it is merged to the most similar neighbor superpixel ss ∈ Ns i , Ns i being the neighborhood of s i . The most similar superpixel is chosen by the following minimization ss = argmin sj ∈Ns i µ(s i ) -µ(s j ) + var(s i ) -var(s j ) , [START_REF] Johannsen | A taxonomy and evaluation of dense light field depth estimation algorithms[END_REF] where the mean color µ and the variance var are both calculated in the CIELAB color space. An example showing the effectiveness of our superpixel-based filtering is given in Fig. 2.

DISPARITY PROPAGATION

The refined disparity map Dr (r ∈ R) thus obtained for each input view Lr is projected (forward warping) to the novel position s ∈ 1 . . U × 1 . . V by using the disparity information itself. Thus, at each position s, there are four pairs of warped maps and corresponding inpainting masks ( Dr s , M r s ). We thus construct the matrix H of 4 × U × V columns, each column being a vectorized warped disparity map with holes:

H = vec( Dr1 s1 ) |. .| vec( Dr4 s1 ) |. .| vec( Dr1 s N ) |. .| vec( Dr4 s N ) (N = U × V ).
The mask matrix is defined in the similar way:

M = vec( M r1 s1 ) |. .| vec( M r4 s1 ) |. .| vec( M r1 s N ) |. .| vec( M r4 s N )
. Given that the warped disparity maps are highly correlated, H can be efficiently inpainted using a matrix completion method which formalizes the problem as min Ĥ rank( Ĥ) s.t. P M ( Ĥ) = P M ( H), [START_REF] Revaud | EpicFlow: Edge-Preserving Interpolation of Correspondences for Optical Flow[END_REF] where P M is the sampling operator such that P M (H) i,j is equal to H i,j if Mi,j = 1, and zero otherwise.

The low rank matrix completion is solved using the Inexact ALM (IALM) method [START_REF] Lin | Linearized alternating direction method with adaptive penalty for low rank representation[END_REF]. The inpainting works well in practice because the disocclusions in the different warped views are unlikely to overlap. The inpainting is globally performed by processing all the view positions at the same time. While the superpixel-based filtering enhances spatial coherence in the disparity of the input views, angular correlation is exploited here.

After inpainting, four disparity maps ( Dr s , r ∈ R) per view are extracted from the matrix Ĥ. In order to obtain a unique disparity map Ds per view, a pixel-wise winner-take-all selection is performed based on the confidence values

Contrary to the reference view where the color information can be exploited to measure the confidence (cf. Section 3.2), here F r s is inferred by projecting (forward warping) the confidence Fr from the reference view r to the target view s.

Finally, a step of total variation regularization (TV-L1) using the primal-dual algorithm [START_REF] Chambolle | An introduction to Total Variation for Image Analysis[END_REF] is applied on the different epipolar slice images of the resulting disparity maps in order to enforce view consistency.

Table 1: Quality evaluation of the estimated disparity maps on center view. Our method (4 corner views input) is compared against two state-of-the-art methods (4D full LF input), namely *LF [START_REF] Jeon | Accurate depth map estimation from a lenslet light field camera[END_REF] and SPO [START_REF] Zhang | Robust depth estimation for light field via spinning parallelogram operator[END_REF] Fig. 3: Visual comparison of the estimated disparity maps on center view. The first 2 rows are synthetic LFs "Buddha" and "Cotton", the last 2 rows are Illum real LFs "Stone Pillars Outside" and "Fruits".

PERFORMANCE ASSESSMENT

The performance of our method has been assessed using different datasets: both the synthetic LFs from the HCI datasets [START_REF] Honauer | A dataset and evaluation methodology for depth estimation on 4d light fields[END_REF][START_REF] Wanner | Datasets and benchmarks for densely sampled 4D light fields[END_REF] and the real ones captured by Lytro Illum cameras [START_REF]INRIA Lytro image dataset[END_REF][START_REF]ICME 2016 Grand Challenge dataset[END_REF] are considered. In our experiments, the center 7 × 7 sub-aperture views are considered for all test LFs. We have set the parameters as follows: λ 1 = 2, λ 2 = 2, σe = 0.1, σs = 2 and σc = 1. Synthetic data. Ground truth disparity on center view is available for HCI synthetic light fields. Using the evaluation metrics defined in [START_REF] Honauer | A dataset and evaluation methodology for depth estimation on 4d light fields[END_REF][START_REF] Johannsen | A taxonomy and evaluation of dense light field depth estimation algorithms[END_REF], we compare in Table 1 our scheme against two state-of-the-art methods, namely *LF [START_REF] Jeon | Accurate depth map estimation from a lenslet light field camera[END_REF] and SPO [START_REF] Zhang | Robust depth estimation for light field via spinning parallelogram operator[END_REF]. In our experiments, the number of discretized disparity levels is kept the same as in [START_REF] Johannsen | A taxonomy and evaluation of dense light field depth estimation algorithms[END_REF], i.e. 100 for *LF and 256 for SPO. In order to achieve satisfying results, both methods require a high sampling rate on the angular dimension. Despite the fact that our method is disadvantaged as we only exploit the corner views and infer the disparity for other views, our method achieves significantly better performance than *LF, and comparable results to SPO. Espe-cially, our method is the best among the three evaluated methods for BadPix(0.01), BadPix(0.03) and Q25 which indicates "the best case accuracy" of a given algorithm. One of the main reasons for this gain is that our algorithm preserves continuity of the disparity space. Nevertheless, for scenes with very fine details, such as "Sideboard", the sampling rate (4 input views out of 49 of the light field) turns out to be too low. Real data. Limited by current technology, real light fields captured by plenoptic imaging devices are often prone to noise and distortion, which significantly compromises the accuracy of many depth estimation algorithms. In Fig. 3, we observe that SPO performs best on object boundary, but fails to provide consistent estimates on noisy homogenous zones. Our algorithm achieves a good balancing between accuracy and robustness. Readers are invited to view more simulation results and animations (estimation on every viewpoint) on the web page https://www.irisa.fr/temics/demos/ lightField/DepthEstim/DepthEstimXR.html. Our method has been also used to compute disparity maps from video light fields captured with a Raytrix camera [START_REF] Guillo | Light field video dataset captured by a R8 Raytrix camera (with disparity maps)[END_REF] (http:// clim.inria.fr/Datasets/RaytrixR8Dataset-5x5/ index.html).

Runtime. Thanks to the low sampling rate, our algorithm is comparatively efficient. Simulations have been carried out on a Macbook Pro with a 2.8GHz Intel Core i7 processor and 16G RAM. For a light field of resolution 7×7×512×512, it takes approximately 13 mins to estimate scene depth using our method, against 63 mins for SPO and 16 mins for *LF. Moreover, our method generates 49 disparity maps at a time. Note that the code is written in Matlab and could be further optimized in the future.

CONCLUSIONS

In this paper, we have proposed a light field depth estimation algorithm using only a small subset of light field views and inferring the depth for other views without exploiting the color information of all the views. The experiments show that, both for synthetic and real light fields, our algorithm achieves competitive performance compared with state-of-the-art algorithms, despite the fact that the algorithm uses much less light field information.

Fig. 1 :

 1 Fig. 1: Algorithm pipeline.

Fig. 2 :

 2 Fig. 2: An example of superpixel-based edge-preserving filtering. (a) Superpixel over-segmentation; (b) Uncertainty (1 -F ) measured on the unfiltered map; (c) Error on the unfiltered disparity map with respect to the ground truth; (d) Error after filtering with respect to the ground truth.

  F

  . The best results are marked in bold. Ours [2] [5] Ours StillLife 2.02 1.72 2.56 81.2 76.2 71.3 51.0 32.1 25.0 20.9 6.8 9.2 1.36 1.02 0.87 Buddha 1.13 0.97 0.82 57.7 41.2 34.9 24.4 14.8 12.3 10.1 6.7 5.4 0.51 0.34 0.31 MonasRoom 0.76 0.58 0.53 46.0 42.5 38.6 22.1 17.8 18.6 11.7 7.8 8.2 0.38 0.34 0.33 Butterfly 4.79 0.74 1.84 82.5 78.9 70.8 49.1 48.5 36.0 15.4 14.1 6.7 1.47 1.22 0.85 Boxes 14.15 8.23 12.71 72.7 62.3 65.8 45.5 28.1 37.7 26.4 15.8 23.9 0.89 0.62 0.68 Cotton 9.98 1.44 1.18 60.5 41.7 42.6 23.3 11.1 10.7 8.9 2.7 4.1 0.59 0.36 0.42 Dino 1.23 0.29 0.88 76.6 57.5 49.1 48.4 17.9 20.0 20.9 3.4 9.5 1.08 0.55 0.43 Sideboard 4.16 0.92 10.31 67.8 64.3 61.7 39.3 31.0 37.5 23.0 10.4 19.6 0.73 0.66 0.51 Average 4.78 1.86 3.85 68.1 58.1 54.4 37.9 25.2 24.7 17.2 8.5 10.8 0.88 0.64 0.55

		MSE*100	BadPix(0.01)	BadPix(0.03)	BadPix(0.07)	Q25
	Light fields [5] Ours [2] [5] Ours [2] [5] Ours [2] [5] Ours [2] *LF [2] SPO [5] GT / Image
	(4 views input)	(4D LF input)	(4D LF input)

* Mikaël Le Pendu is now with Trinity College Dublin. This work has been funded by the EU H2020 Research and Innovation Programme under grant agreement No 694122 (ERC advanced grant CLIM).


Frédérique Guillamot

Virgile Calvert

Marie-Virginie Millot

Stéven Criquet
email: steven.criquet@univ-amu.fr

Does antimony affect microbial respiration in Mediterranean soils? A microcosm experiment

Keywords:

a b s t r a c t

The aim of this study was to determine the effects of antimony on soil microbial respiration. Two Mediterranean calcareous soils were sampled: a contaminated soil close to an abandoned lead and silver smelter and a soil far from the pollution source and considered not to be contaminated. Two forms of antimony, antimony trioxide (Sb 2 O 3 ) and potassium antimonyl tartrate trihydrate (C 8 H 4 K 2 O 12 Sb 12 •3H 2 O), were tested at three concentrations (50, 500 and 5000 ppm) in controlled conditions under short-(3 days) and medium-(3 months) term incubation. Modifications in the substrate-induced respiration (SIR) were assessed by gas chromatography respirometric measurements. Results clearly showed that SIR was immediately and significantly more affected by Sb input in a non-contaminated soil than in a long-term contaminated soil, especially since the concentration was high and Sb was added to a more soluble and available form (tartrate instead of mineral oxide). Antimony (Sb), a metalloid of the same periodic group as arsenic (As), is known to present toxicological properties, but its effect on the environment and on human health is little documented. Worldwide production of Sb is considerably greater than of As, Sb having a wide range of uses (manufacture of semiconductors, diodes, flameproof retardants, lead hardener, etc.) [START_REF] Filella | Antimony in the environment: a review focused on natural waters: I. Occurrence[END_REF]. As a consequence of its extensive use, many soils have been contaminated by this metalloid worldwide, through geogenic sources or anthropogenic pollution from activities such as mining, smelting, industry and agriculture [START_REF] Douay | Contamination of urban soils in an area of Northern France polluted by dust emissions of two smelters[END_REF].

Sb bioavailability and toxicity depends on speciation. Sb exists at 4 degrees of oxidation: -3 and 0, which correspond to the metallic forms abundant in the soil of shooting ranges; +3 (or Sb (III)), the most toxic form and +5 (or Sb (V)), the most oxidised form [START_REF] Wilson | The chemistry and behaviour of antimony in the soil environment with comparisons to arsenic: a critical review[END_REF]. Although Sb and As share some chemical properties, e.g. they both occur in soils as oxides, hydroxides and oxoanions, they have so far not been shown to act in the same way. In fact, the typology of the mechanisms of Sb transport and accumulation via adsorption/desorption processes remains relatively unknown [START_REF] Wilson | The chemistry and behaviour of antimony in the soil environment with comparisons to arsenic: a critical review[END_REF]. Microbial communities can play a role in Sb mobility, and thus in its availability and toxicity, via oxidation, reduction and biomethylation mechanisms [START_REF] Frohne | Controlled variation of redox conditions in a floodplain soil: impact on metal mobilization and biomethylation of arsenic and antimony[END_REF]. Surprisingly, to date very few attempts have been made to determine Sb effects on soil microbial communities. Thus, the toxicity of Sb for soil microorganisms is relatively unknown, but appears to vary with the degree of Sb oxidation. Sb (III) appears to be ten times more toxic than Sb (V), while methylated Sb appears to be the least toxic [START_REF] Wilson | The chemistry and behaviour of antimony in the soil environment with comparisons to arsenic: a critical review[END_REF].

Here, therefore, we set out to determine using microcosms the effects of various Sb molecules and concentrations on soil microbial respiration. The Sb (III) oxidation degree was chosen, since this form is putatively the most toxic. Two poorly vegetated soils (calcosoil with surface colluvia) were sampled on the Mediterranean coast in the Marseilleveyre Massif, Marseilles (Bouches-du-Rhône, France). The first is a contaminated soil, herein called SC, located at the former Escalette metallurgical site, which extracted lead and silver from galena until the beginning of the last century, and close to an old horizontal smokestack running up a hillside to evacuate toxic fumes (43 • 13 30 N, 5 • 20 54 E Southeast of Marseilles). This smelting spread smoke, aerial deposits and metallurgical slag around the buildings, resulting in heavy metal and metalloid contamination (mainly Pb, Zn, As, Sb, Cd and Cr). The second soil was sampled near the Sormiou creek (43 • 12 47 N, 5 • 24 58 E), a site far from Escalette and thus considered non-contaminated (SNC). For each station, soil samples were collected from the surface layer (0-5 cm) in April 2011, sieved through a 2 mm mesh and stored at 4 • C before use. The main physico-chemical characteristics of these soils, as well as their metal and metalloid contents, are given in Table 1.

Microcosms were prepared in plastic boxes 5 cm × 5 cm × 5 cm, each containing 50 g of dry weight equivalent soil. Sb was supplied either as potassium antimonyl tartrate trihydrate (C 8 H 4 K 2 O 12 Sb 12 •3H 2 O, an organic highly soluble Sb form), herein called SbT, or as antimony trioxide Sb 2 O 3 (a mineral poorly After 3-day incubation (Fig. 1), SIR was more significantly affected by Sb input in a non-contaminated soil than in a longterm contaminated soil, especially since the concentration was high and Sb was added to a more soluble and available form (tartrate instead of mineral oxide). In both soils and for both Sb forms, SIR decrease can be explained by several physiological disturbances occurring at the cell level. Sb toxicity is known to induce oxidative stress resulting in lipid peroxidation, increased membrane permeability and cell lysis by loss of cytosolic constituents. Moreover, Sb has the ability to substitute to P in biological reactions and it can also more directly affect the respiration of soil microorganisms, since it can combine with certain thiol groups of respiratory enzymes (e.g. dehydrogenases) and thus inhibit cellular energy supply [START_REF] Tirmenstein | Antimony-induced oxidative stress and toxicity in cultured cardiac myocytes[END_REF][START_REF] Shtangeeva | Bioavailability and toxicity of antimony[END_REF]. Adding the poorly soluble form of Sb, Sb 2 O 3 , resulted, over a short-term incubation (3d), in lower SIR activities in the non-contaminated soil. This inhibition increased with the Sb dose applied, but the relation between the two variables was not proportional. Such results are consistent with those of [START_REF] Oorts | Solubility and toxicity of antimony trioxide (Sb2O3) in soil[END_REF] who reported that: (i) the dissolution rate of Sb increased almost three-fold when the applied dose of Sb 2 O 3 was increased from 50 to 10,000 mg Sb kg -1 ; (ii) inhibition of soil respiration processes (i.e. nitrifying aerobic respiration) also occurred only at the higher dose.

After a 3-month incubation, positive effects of Sb 2 O 3 occurred on SIR and remained for us unexplained. Despite this atypical response, the inhibitive effects of both Sb 2 O 3 and Sb-tartrate observed at 3-d were, in most cases, nil or greatly reduced at 3-m. This could be explained by the establishment of resistance responses by microbial communities such as ATPase pumps, chemo-osmotic antiports, oxydoreduction mechanisms and intracellular or membranar retention [START_REF] Rosen | Transport and detoxification systems for transition metals, heavy metals and metalloids in eukaryotic and prokaryotic microbes[END_REF]. Surprisingly, SIR was still decreased by SbT with regards to NaT in the contaminated soil, whereas it was not in the non-contaminated. Since the contaminated soil had far lower clay content and CEC, another reason for the pattern observed may be due to lower Sb immobilisation on soil particles resulting in higher availability and toxicity towards microorganisms [START_REF] Flynn | Antimony bioavailability in mine soils[END_REF]). Despite it was not possible for us to quantify the different Sb forms, a further explanation for the decrease in toxic effects observed during our experiments could be a modification in the speciation of Sb. Sb (III) is known to be instable in oxic soils, and is rapidly oxidised by Fe-Mn-oxihydroxides and humic acids in its Sb (V) form, which is less toxic than the Sb (III) form [START_REF] Oorts | Solubility and toxicity of antimony trioxide (Sb2O3) in soil[END_REF]).

Acknowledgements

Financial support was provided by the French National Agency for Research (ANR) for the Marseco project headed by Isabelle Laffont-Schwob. We greatly thank the General Council of Bouchesdu-Rhône for authorising us to perform this study in the Marseilleveyre hills.