Sigo Scharnholz
email: asigo.scharnholz@isl.eu

Ralf Hassdorf
email: bralf.hassdorf@isl.eu

Dirk Bauersfeld
email: cdirk.bauersfeld@isl.eu

Bertrand Vergne
email: dbertrand.vergne@isl.eu

Viêt Luong

Phung

Dominique Planson
email: fdominique.planson@insa-lyon.fr

Investigation of SiC thyristors with varying amplifying gate design

Keywords: Thyristor, Amplifying gate, Device fabrication, Etched JTE, Turn-on characteristic, Onstate characteristic

This paper presents experimental 1.2 kV, 10 A SiC thyristors with different amplifying gate design. In contrast to comparative devices (with simple gate) the amplifying gate thyristors show a characteristic snap-back and a higher gate current to trigger. Their gate-anode I-V characteristics comply with the underlying design constraint (RP > RM). Moreover, the turn-on waveforms of welldesigned amplifying gate thyristors reveal peak-shaped inversions in the gate current and voltage transients, providing clear evidence of the successive triggering of pilot and main thyristor.

Introduction

Due to their superior performance in terms of current density and blocking voltage, silicon carbide (SiC) thyristors are of particular interest for pulsed power applications [START_REF] Ryu | 15 kV n-GTOs in 4H-SiC[END_REF][START_REF] Agamy | A high speed SiC thyristor gate driver for pulse power applications[END_REF]. Furthermore, in view of the tremendous progress made in SiC crystal quality and wafer size, large-area SiC thyristors appear to be in reach today. In this context, both electrically and optically triggered SiC thyristors require adequate amplifying gate structures. With the aim to investigate this aspect, a mask set featuring numerous SiC thyristor devices with varying amplifying gate structures has been conceived [START_REF] Scharnholz | Conception de thyristors SiC permettant l'étude de l'amplification interne de l'allumage[END_REF]. And based thereon, a 100 mm epitaxial SiC wafer was processed recently. Resulting from this process run, the present paper reports on the electrical characteristics measured on-wafer as well as on singularized and encapsulated SiC thyristor devices with and without amplifying gate.

Device fabrication and structure

The fabricated devices are asymmetrically blocking, vertical SiC thyristors, of which the 10 µm thick p-base (drift) layer (5×10 15 cm -3 ) is separated by a 4 µm p-type buffer (5×10 17 cm -3 ) from the wafer substrate (> 1×10 19 cm -3 ). The n-base (gate) and the anode layers have a nominal thickness (and doping concentration) of 2 µm (1×10 17 cm -3 ) and 1 µm (1×10 19 cm -3 ), respectively. The gate and the single-step junction termination extension (JTE) are formed simultaneously by reactive ion etching (RIE). A second RIE step was used to define the JTE length and thus the device mesa. Following the etching, the primary metallization of gate/cathode (Ti/Ni) and anode (Ni/Ti/Al) was realized separately by e-beam evaporation, lift-off, and subsequent annealing. The surface was passivated with 1 µm thick, deposited SiO2. The over-metallization consists of 1 µm Al and 0.7 µm Ti/Ni/Au on the top-side (anode/gate) and the backside (cathode) contacts, respectively.

Fig. 1 shows a scheme of a circular SiC amplifying gate thyristor with characteristic dimensions (radii). All fabricated amplifying gate thyristors have a central, circular gate (G) with a radius of rEA = 160 µm and a main anode (A), expanding from an inner radius of rEM = 500 µm to a distance of rSM = 1200 µm. Therefore, all devices have the same size of the anode and thus the same resistance RM of the main thyristor (cf. cross-section in Fig. 1). At the distance of rSM, either ring-shaped or dotted anode shorts are situated for devices with a circular or a square-shaped anode, respectively. With a JTE length of 150 µm and a security margin to the cutting edge, the die size measures 3.2 mm × 3.2 mm (0.1 cm 2 ). Fig. 2 depicts one of the experimental amplifying gate thyristors with square-shaped anode and dotted anode shorts. In-between gate and main anode, the amplifying gate is located, consisting of the anode A' of the pilot thyristor and the auxiliary gate G'. The etch-step separating A' and G' forms a circle with varying radius of rSA. This way, the resulting thyristors meet the amplifying gate design criterion (RP > RM  rSA/rEA > rSM/rEM) [START_REF] Scharnholz | Conception de thyristors SiC permettant l'étude de l'amplification interne de l'allumage[END_REF][START_REF] Baliga | Fundamentals of Power Semiconductor Devices[END_REF] to different degrees:

 safe (rSA = 460 µm): the pilot thyristor always triggers the main thyristor  adequate (rSA = 400 µm): still ok, but susceptible to technological uncertainties  non-adequate (rSA = 300 µm): the pilot is less sensitive than the main thyristor, which may reverse the triggering order, negating the benefits of the pilot.

Electrical characterization

On-wafer (in a vacuum probing chamber), the best devices demonstrated stable blocking up to 2 kV. After dicing, bonding, and encapsulation they were repeatedly tested up to 1.2 kV, the nominal voltage they were conceived for. Fig. 3 exemplarily shows the blocking characteristics (on-wafer and encapsulated) of a square-shaped SiC thyristor with safely designed (rSA = 460 µm) amplifying gate and dotted anode shorts. The higher leakage current of encapsulated devices is due to the lower current resolution of the curve tracer. The real leakage current (measured using an SMU on an equivalent device) is in the order of some nanoamperes (not shown), and thus only slightly higher than that one measured on-wafer under vacuum. Fig. 4 shows on-state characteristics (at varying gate currents) of the same amplifying gate thyristor (bottom graph) as in Fig. 3 compared to a device without amplifying gate (top graph). As expected, the amplifying gate thyristor shows a characteristic snap-back. Note that the difference in the differential on-resistance is due to a spread between samples and not a characteristic difference between the two device types.

By contrast, the fact that the amplifying gate thyristor requires a higher gate current to trigger, means a characteristic difference. For comprehension, note that the amplifying gate thyristors under investigation are experimental devices with a small periphery (main thyristor). They have been conceived only for the purpose of examining the design constraint. Their amplifying gate has about the same size as the gate of the comparative thyristor (without amplifying gate), but due to the parallel current path formed by RP and RM, they require a larger gate current to trigger. In terms of a reduced gate current, the amplifying gate only takes advantage when it supplies the gate current via an interdigitated structure to a large area (main) thyristor. Fig. 5 shows the gate-anode I-V characteristics of three SiC thyristors with differently dimensioned amplifying gate (non-adequate, adequate and safe, cf. above), allowing to determine the characteristic resistances RP and RM of pilot and main thyristor, respectively. RP is directly derived from the slope of the I-V characteristic measured between the gate contact G (in the centre) and the ring shaped anode A' of the pilot thyristor (cf. Fig 1). In the same way, RP + RM (and thus RM) is determined from the slope of the I-V characteristic measured between G and the main anode A. Tab. 1 summarizes the extracted values which confirm the compliance to the above mentioned design rule (RP > RM).

Finally, Fig. 6 shows turn-on characteristics of circular and square SiC thyristors disposing of ringshaped and dotted anode-shorts, respectively. For each of these two types, the curves of three devices with differently dimensioned amplifying gate are shown. Note, that though giving the impression of a logical sequence, there is no coherence of the turn-on delay time with the individual device dimensions. It appears rather that devices with adequately and safely designed amplifying gate reveal a peak-shaped inversion in the gate current and voltage transients, while non-adequately designed devices do not. These peaks originate from the current passing through the anode A' of the pilot thyristor, delivering the gate current for the main thyristor. This way they prove evidence that the pilot thyristor is triggered in advance of the main thyristor, which obviously does not emerge for thyristors with non-adequately designed amplifying gate.

Conclusion

The results presented in this paper demonstrate that the experimental SiC amplifying gate thyristors under investigation can be triggered adequately fully compliant to the underlying design constraints. Furthermore, the measurements reveal relatively large resistances RP and RM of pilot and main thyristor, respectively, being causal for meeting these constraints. Anyway, the main part of the resistance, here quantitatively about 70%, is determined by the sheet resistance of the n-base layer (gate) underneath the two sub-thyristors. The rest, however, as calculations based on TLM measurements indicate, must be attributed to the contact resistance to the n-base layer. Nevertheless, this relatively high amount does not negatively affect the adherence to the design rule. In so far, the conceived amplifying gate structures can be used as design building blocks for larger area, electrically or optically triggered SiC thyristors.

Fig. 1 .

 1 Fig. 1. Scheme of an SiC amplifying gate thyristor, consisting of a pilot thyristor (index P) in the centre and a main thyristor (index M) with the characteristic resistances RP and RM.

Fig. 2 .

 2 Fig. 2. Micrograph of an experimental, 3.2 × 3.2 mm 2 SiC amplifying gate thyristor with square-shaped anode and dotted shorts (rSA = 400 µm). Gate (centre) and anode wedgebonded with 50 µm Al wires, cathode (backside) solder attached.

Fig. 3 .

 3 Fig. 3. Forward blocking characteristics of an SiC amplifying gate thyristor measured onwafer with an SMU (up to breakdown) and after bonding and encapsulation with a curve tracer (limited to 1.2 kV).

Fig. 4 .

 4 Fig. 4. On-state characteristics of SiC thyristors with and without amplifying gate (AG).

Fig. 5 .

 5 Fig. 5. Gate-anode characteristics of SiC thyristors with differently dimensioned amplifying gate (cf. Tab.1).

Acknowledgement

Financial support provided by the French DGA under the research program ASTRID, contract no. ANR-11-ASTR-0011, is gratefully acknowledged.


Meryem Marzouki

Andrea Calderaro

Minister Danish Foreign

Anders Samuelsen

Global Internet Governance An Uncharted Diplomacy Terrain?

announced his plan for Denmark to become the first nation ever to appoint a 'digital ambassador' (Jarlner and Koch 2017). Noting that giant US digital companies -such as the so-called GAFA (Google, Apple, Facebook and Amazon) -'affect Denmark just as much as entire countries', he concluded that 'these companies have become a type of new nations and [Denmark] need [s] to confront that'. With the cautious mention that '[Denmark] will, of course, maintain [its] old way of thinking in which [it] foster[s] [its] relationships with other countries. But [Denmark] simply need [s] to have closer ties to some of the companies that affect [it]', the minister claimed: 'We are sending a signal that includes that royal crown and our entire diplomacy' (Jarlner and Koch 2017).

This announcement was, at the same time, a pioneering move and an emblematic sign of the increased centrality of diplomacy to ease tensions around the transnational governance of digital challenges in foreign relations. However, given the peculiarity of the digital domain, characterized by the transnational nature of its infrastructure, the variety of actors beyond those of the state necessary to negotiate the technical, policy, economic, and security aspects of the internet (DeNardis 2018 1 ), the translation of this new dimension of diplomacy into a tangible concept and practice is still limited and vague.

Digital issues generate new spaces of conflicts as such, where new diplomatic practices take space to facilitate the negotiations among parties about the governance, policy developments and technical solutions of the internet (Calderaro and Kavada 2013; Radu 2019). As a result of this, in order to understand the shift of diplomatic practices engaging with the digital domain, we need to expand our understanding of the global governance of the internet ID_3pp.

and identify the tools, venues, and processes, so as to adequately address this new dimension of diplomacy (Broeders and van den Berg 2020b).

While digital diplomacy is traditionally referred to as the use of digital technologies to engage in diplomatic dialogues (Bjola and Zaiotti, 2021), the adoption of diplomatic practices to negotiate the variety of challenges related to the functioning of the digital domain is often framed as cyber diplomacy (Riordan 2019) which is defined as 'the use of diplomatic resources and the performance of diplomatic functions to secure national interests with regards to the cyberspace' (Barrinha and Renard 2017, 3). Given the focus on the role played by diplomats in ensuring the security of 'national interest', this definition mostly addresses practices performed by traditional diplomats representing the interest of state actors (Thomson 1995). However, it is crucial to take into account that state actors are only partially responsible for the functioning of the internet. If state actors do have the responsibility to provide the legal and policy framework facilitating citizen's online experience, industry traditionally leads the development of the internet infrastructure and most of its services (Powers and Jablonski 2015;Carr 2016). We argue that the concept of diplomacy in the global governance of the internet goes beyond traditional diplomatic practices solely performed by states' representatives. The stability, safety, and economy of the internet involve a variety of actors and expertise beyond state actors in the negotiations of technical protocols, international agreements, legislations, and forms of governance accountability in a new dimension of diplomacy (Calderaro 2021), that, with this book, we address as Internet Diplomacy.

Our approach to Internet Diplomacy extends to foreign affairs and international relations, and with regard to all emerging international tensions clustered around digital environments, including cybersecurity, internet governance, and the political economy of the internet. In other words, we refer to Internet Diplomacy as the adoption of diplomatic practices by both state and non-state actors, to negotiate any technical, legal, policy, economy, security issues, and practices related to the functioning of the internet.

THE MULTISTAKEHOLDERISM OF INTERNET DIPLOMACY

Given the increasing centrality of the governance of the digital field in global politics, we are witnessing a growing need to better understand recent transformations of international diplomacy in this context, their drivers and their nature, whether and how they might change European and transnational power relations and, ultimately, which values they carry and channel on the global scene. Since the UN World Summit on Information Society (WSIS 2 ) in 2003-2005, the United Nations has established that internet governance processes should be institutionalized in an open and inclusive manner through multistakeholder participation. This decision has extended the invitation at the table of diplomatic negotiations to actors beyond governments, including the business sector and civil society.

Since then, multistakeholder participation along this line has characterized several initiatives by the UN and its agencies in the internet governance field, as well as many thematic or regional international organizations (Levinson and Marzouki 2015). As part of recent moves, in July 2018, the United Nations secretary general appointed 'a High-Level Panel on Digital Cooperation', co-chaired by Melinda Gates, Co-Chair of the Bill & Melinda Gates Foundation, and Jack Ma, then Executive Chairman of Alibaba Group (UN 2018). In December 2018, the United Nations General Assembly (UNGA) adopted a multistakeholder approach by launching the Open-Ended Working Group (OEWG) to complement the process led by the Group of Governmental Experts (UN GGE 3 ) on 'advancing responsible State behaviour in cyberspace in the context of international security'. While the UN GGE only included diplomats representing 25 selected UN member states, the UN OEWG 4 in the 'field of information and telecommunications in the context of international security' welcomed all UN member states and representatives of civil society and the business sector to 'act on a consensus basis' to contribute to 'further develop the rules, norms and principles of responsible behavior of States listed [in the same resolution], and the ways for their implementation' (UNGA 2018). These UN initiatives and their outcomes offer additional evidence on how a multistakeholder approach adopted for the negotiation of internet related issues has set the standards for present and future development of Internet Diplomacy. All this has an impact on the broader field of global governance studies and has set important mutations in diplomatic practices beyond the cyber dimension (Scholte 2005).

Given also the variety of actors and experts engaged in the transnational governance of the digital domain, the definition of commonly shared solutions among stakeholders is particularly challenged by the fast-moving target of the negotiations. In particular, the capacity of stakeholders to make informed choices and agree on issues that go beyond the engineering dimension of the internet is challenged by the rapid developments of the technical, social, and market aspects of the internet. In other words, traditionally, technology evolves quicker than the capacity of policy makers to understand the implications of the technological shift, which is a major obstacle for diplomats and their role in negotiations taking place around digital policy making. As a result of this, technological developments regularly challenge national, regional, and global policy making, in terms of sovereignty and other Moreover, given the transnational nature of the internet, the implementation of digital policies at the national level might generate impacts on a global scale, with potential amplified consequences on global politics. For this reason, we are witnessing an increasing need to enhance international cooperation beyond national borders and national legislations in order to define a consistent and inclusive transnational governance approach to the cyber domain (Calderaro and Craig 2020).

By global internet governance, we intend not only the restricted issue of managing internet technical resources (infrastructure, protocols, and domain names) and technical standards setting (Harcourt, Christou, and Simpson 2020), but, as defined by the Working Group on Internet Governance (WGIG 2005) and adopted in 2005 by the United Nations at WSIS, an extensive set of issues ranging from the 'administration of the root zone files and system' to 'capacity building' and the 'meaningful participation in global policy development' as well as a whole set of human rights and consumer rights issues directly at stake in the governance of information and communication processes (Brousseau and Marzouki 2012).

Among the cross-cutting challenges that domestic and foreign policies are facing, we can identify the following (DeNardis 2018): The difficulty to keep pace with numerous internet innovations in order to make informed choices and decisions on issues that may appear only technical; the difficulty to understand and conciliate roles and positions of a great variety of actors and stakeholders; the need to identify the different exchanges and dialogues in regional and international fora and to navigate in these waters; and the requirement to be aware of their evolving strategies of transaction and coalition, while internet governance has proven to be much more than a public policy issue in light of the essential characteristics of this network (the interconnection is global; its management is distributed) and as it has historically been privately coordinated and operated. Finally, there is a need to channel and maintain democratic values in global internet governance processes, namely that of sustainability, participatory governance, openness and transparency in policies and markets, human rights, social justice, and social cohesion, as well as democracy and the rule of law. As recent discussions on European digital sovereignty are showing (Christakis 2020; Madiega 2020), this challenge is particularly difficult to address with private US firms, such as the GAFA and other internet giants, including the emerging role played by Chinese ones, dominating the innovation market.

This book stems from the observation of a number of mutations at the crossroads of globalization and digitalization. These mutations concern both the global governance of the online world, which has been facing several disruptions, and diplomacy itself, which has been experiencing important transformations. In our view, both categories of mutations must be addressed at the same time, analyzing and understanding the digital disruptive trends they create while exploring how Internet Diplomacy could be an effective mean to address such disruptive trends to keep channeling democratic values in global internet governance processes. Focusing on global internet governance allows exploring, in a consistent way, almost all issues related to globalization and, therefore, at the heart of foreign policy international relations discussions: sovereignty, security, trade, finance and taxation, economic and social transformations (including labor) as well as human rights, democracy and the rule of law. These particularly wide implications of global internet governance result, obviously, from the fact that the internet has become an integral part of the political, economic and social life in all their dimensions and from the fact that the network raises, by construction, cross-border issues.

UNDERSTANDING MULTIFACETED DIGITAL DISRUPTIONS

Since the internet reached a wide public in the mid-90s, technical, business, marketing, communication, and innovations have profoundly transformed power relations, in social, economic, normative, institutional, and geopolitical terms. Earlier controversies regarding human rights implications of internet use emerged at the national level, leading policy makers to address issues related to conflicts of rights and conflicts of jurisdictions 5 . Becoming even more prominent with the development of social media platforms and their centrality in society's online experience, these debates also led to procedural issues related to the role and liability of internet intermediaries and algorithms, in terms of legal, technical and economic aspects.

Ten years later, the United Nations held the WSIS with the ambition to define a globally recognized governance model for the internet, and how internet governance processes should be institutionalized in an open and inclusive manner through multistakeholder participation. One of the main outcomes of the Summit was the creation of the Internet Governance Forum (IGF 6 ), which, since 2006, has served as the main open forum for such dialogue among all interested stakeholders.

The launch of these initiatives has de facto institutionalized international cooperation in the digital domain. Consequently, all global actors, including the EU and its member states, have started engaging in these new global processes in accordance with their own foundational values and national priorities (Mueller 2010). At the same time, they had to face the transnational nature of the internet and, more specifically, the extraterritorial effect and other kinds of deliberate or serendipitous externalities of internet-related public or private policies and actions. Since this early stage, the global governance of the internet is still clustered around a series of contentious topics that have not yet found long-term solutions. Data protection, data trade, core functions of the internet architecture, intellectual property rights, electronic surveillance, net neutrality, human rights, and the digital divide have traditionally characterized negotiations in the domain of internet governance. Following decades of generalized optimism on the beneficial impact of the internet on society, politics, and economy, concerns emerged also on the potential threats of the internet, and, in recent years, the major emphasis has been on cybersecurity, artificial intelligence, algorithmic governance, platform regulation, and digital sovereignty. We classify these issues and the disruptions they create into four main categories:

Governance disruptions include all the transformations related to state and non-state agents involved in internet governance, including who they are, what is their nature and relevance, what are their strategies, how they coalesce or divide, what kind of relationships they establish among them, how they proceed to advance their views, and, ultimately, how power relations are transforming globally in political and institutional terms. Such agents include state and non-state (civil society, business sector) actors, as well as more inconspicuous actors in this field, such as technical or other epistemic communities, courts, parliaments, regulatory agencies, and intergovernmental organizations. Not only human, organizational, and institutional actors, but also artifactual agents need to be studied and understood, such as internet governance processes and instruments, including architectures, protocols, and algorithms.

Democracy disruptions relate to the transformation of national and international hard and soft law, regulation and private practices, and how they may impact, in the online environment: the substance of human rights and their balance in a democratic society; the rule of law principle; and the democratic values of legitimacy, transparency, accountability, participation, and fairness. This involves procedural as well as substantive transformations and includes, inter alia, the transfer of some states' responsibilities and prerogatives to private intermediaries, the practice of profiling (by private and public actors for marketing and security purposes, respectively) and the datafication trends.

Economy disruptions, where we include all transformations pertaining to trade, finance, and taxation, economy, as well as labor and working conditions, mostly relate to the challenges and opportunities of the 'Uberisation' or so-called sharing economy and its many business and marketing models (Marsden 2015). They also relate to the outsourcing of certain (not necessarily digital, such as after-sale services and various hotlines) economic activities when this is made possible by digitalization.

Geopolitics disruptions relate to the transformations of the global digital geopolitical order. Issues such as network neutrality and the so-called fragmentation of the internet need to be addressed here as a dialectic movement between globalization and renationalization of the digitized world. In addition, transformations in international development and international development aid (especially the emergence of private initiatives, alone or in coordination with state actors) are also part of this category: global internet access, zero-rating policies, their impact on public policies, and the transformed kinds of digital divides they may lead to need also to be studied from the point of view of the new (digital) world (dis)orders they may create. The multiple dimensions of cybersecurity also fall into the category of geopolitical disruptions, as do the provision, control, or prohibition of specific technologies and equipment, such as those used for surveillance, including biometrics.

Many aspects of these four categories of disruptions are the subjects of academic research, as part of profound mutations carrying important implications far beyond the sole online domain: platformization and datafication of the economic and social life, from social networks to the so-called sharing economy; multistakeholderisation of the institutional governance processes, where various categories of stakeholders are involved, together with nation states, in policy arenas and decision-making related to several diplomatic issues; renormativisation, or the reorganization and the reformulation of normative frameworks, following the increasing role of private actors; and fragmentation, the process by which access to the global internet becomes subject to barriers to entry, whether such barriers are of a technical, legal, economic, or social nature and whether their purpose is to discriminate access to infrastructure, software, applications, services, or usages. However, analyzing governance, democracy, economy, and geopolitics mutations to fully understand them in their systemic nature and to unfold their consequences requires a highly multidisciplinary approach, that we identify as the first component of an Internet Diplomacy research agenda.

THE CHANGING NATURE OF DIPLOMACY

These digital disruptions and their effects resonate with diplomatic transformations, as observed in the dedicated literature. Contemporary diplomacy has itself been facing multiple challenges due to the combination of globalization and, more recently, digitalization (Hocking and Melissen 2015). As analyzed by Pouliot and Cornut (2015), the very nature of diplomacy is changing, along different characteristics:

Diplomacy agents: diplomats are no longer only official governmental agents, but also different categories of state and non-state actors interacting with foreign affairs officials as well as among themselves. In this respect, Wiseman argues (2004) that polylateralism constitutes a third form or dimension of diplomacy, in addition to bilateralism and multilateralism. The internet governance world prefers the related concept of multistakeholderism (ITU 2013), coined in management circles, most notably the Davos World Economic Forum (WEF), with the stakeholder theory having been developed by Klaus Schwab in 1971 at the WEF foundation. The concept also found its way to the UN and its agencies and bodies, where it is centered on states as central agents, rather than on corporations, as initially envisioned by Schwab (Gleckman 2012). Multistakeholderism has now widely spread, as both a concept and a mechanism, in internet governance as well as in almost all global governance fields (Scholte 2020).

Diplomacy fields: diplomacy has developed over time, from strict foreign affairs negotiations as an alternative to war, into a myriad of formal and informal discussions on almost any matter, especially with globalization. While the initial raison d'état is often still the ultimate objective of diplomacy, it is no longer restricted to the security field and now encompasses many other components for the stability of a nation and the welfare of its (Cooper, Heine, and Thakur 2013a). Moreover, in addition to narrow nation-state objectives have now come global concerns regarding future generations, such as environmental issues and, in particular, global warming. One of the consequences of this evolution is that diplomacy now requires many more skills, particularly in science and technology, than foreign affairs personnel are taught in diplomatic academies (Mayer, Carpes, and Knoblich 2014).

Diplomacy processes, practices and means: Diplomacy as discourse, communication, and negotiation between professional diplomats in dedicated settings is now only part of the diplomatic activity. Huge varieties of practices and means exist (ITU 2013), which are in constant development as cultural and intercultural mediations, as well as interpersonal relationships, playing an increasingly important part in diplomacy, including cooking and hospitality (Neumann 2011), fine arts, music (Ramel and Prévost-Thomas, 2018), and sports (Frank 2012), and are considered as part of the full range of diplomacy processes. Among the many examples of such diversification, public diplomacy and humanitarianism must be highlighted as forms of direct reach to people of foreign nations, most notably when usual diplomatic discussions avenues are difficult or entirely cut (e.g., public diplomacy has been practiced by the United States since the beginning of the Cold War; international humanitarianism intensively developed since the 1970s and 1980s, after the 'foreign humanitarian intervention' doctrine was developed by the 'French doctors' during the war in Biafra, and USAID was created in 1961). In recent years, there have been two particular moments where both public diplomacy and humanitarianism (sometimes in the form of development aid directly targeting civil society groups) played a major role before, during and after the event: the collapse of the Berlin Wall leading to the end of Cold War in 1989, and the Arab uprisings in 2011. In both cases, communication means were especially addressed and used, such as radio in the former case (Cummings 2009), the internet and, particularly, social networks in the latter (Clinton 2010). More generally, after the Cold War, the European Union exerted a significant role in stabilizing and democratizing Europe's Neighborhood through the use of its soft power, becoming in the space of a few years, a magnet of security with strong attractive power.

The mutations described so far are at the center of discussions 7 and analyses trying to clarify the concepts characterizing contemporary diplomacy, which remains fuzzy and overlapping. For instance, 'public diplomacy', 'science diplomacy,' and 'digital diplomacy' are often used interchangeably, without having been clearly defined and delimited (Cooper, Heine, and Thakur 2013b). While digital diplomacy for some aims at specifically addressing diplomacy objectives and practices in an age characterized by numerous digital innovations, public diplomacy and science diplomacy have an older history not necessarily linked to the digital era. Science diplomacy, in particular, has recently received renewed interest, with various attempts to define and flesh out the concept by, most notably, The American Association for the Advancement of Science (AAAS) and The Royal Society -UK National Academy of Science, and, as some chapters in this volume show, global internet governance may also be analyzed as one of a 'science in diplomacy' issues, i.e. global issues with scientific basis and the scientific/ technical aspects of formal diplomatic processes (The Royal Society 2010; Turekian et al. 2015). This undoubtedly demonstrates a political will to give a new impetus to diplomacy in the contemporary context.

As part of its innovative nomination of a 'digital ambassador to the internet giants' in 2017, Denmark has been particularly creative when coining a new concept of contemporary diplomacy to deal with Internet Diplomacy beyond its instrumental dimension of the use of digital means by diplomats: that of 'technological diplomacy', or 'Techplomacy', to use the portmanteau branded as a banner by the forerunner in the field, Casper Klynge, the former Danish ambassador in charge of these matters. We identify this promise of innovative diplomatic practices, one could even say of rupture, as a further development of an Internet Diplomacy research agenda.

More specifically, while, since 2017, other countries have nominated ambassadors in charge of digital affairs, almost none of them follow the Danish model. Under the French model, for instance, the digital ambassador is one of the twenty-one (as of June 2021) thematic ambassadors appointed by the French Ministry of Foreign Affairs. His mission covers the full digital governance spectrum of issues, including participation in bilateral, multilateral, and multistakeholder discussions on digital affairs. Given the current ambassador's public entrepreneur profile, who theorized the notion of 'Platform State' (Pezziardi and Verdier 2017), Henri Verdier's mission has extended to the development of Gov/Civic Tech tools tackling global issues, such as the fight against disinformation. In the Australian model, also adopted by Estonia and Finland, the role of the digital ambassador sticks more to classic regalian diplomacy, with cybersecurity issues being at the heart of the mission. Such different visions, models and strategies of 'techplomacy' vary considerably with the underpinning political orientation of the government defining them and appointing the ambassador. The diplomatic style and practices are also shaped by the ambassador in place, and the person's own background and culture. As a matter of fact, the new Danish digital ambassador, Anne Marie Engtoft Larsen, took office in October 2020. One would think that Danish 'techplomacy' would continue on the same line, but, in the meantime, the Liberals have been replaced by the Social Democrats in the affairs of the country, and the words of the new Danish Foreign Minister, Jeppe Kofod, in the nomination press release dated 22 August, 2020, suggested that a political shift may be coming, promising a 'Techplomacy 2.0'. It remains to be seen whether the 'Tech for Democracy 2.0' initiative launched by the Danish government in June 2021 8 will indeed lead to a new strategy and a new start for the Danish technological diplomacy.

While possessing various strengths depending on the 'Techplomacy' model, polylateralism and the role of private players as a power in international relations remain an inexorable trend, to the extent that a strong 'porosity' exists between the tech giants and the diplomatic world: for instance, Nick Clegg, the UK Deputy Prime Minister 2010-2015, joined Facebook in 2018 as Vice President for Global Affairs and Communication, and Casper Klynge, the first Danish Tech ambassador 2017-2020, joined Microsoft in 2020 as Vice President for European Government Affairs. Exploring all such cases and identifying whether this trend is simply 'revolving doors' as usual or a true 'Techplomacy' and 'Diplotech' encounter leading to deep mutations of diplomacy practices and outcomes must become an important strand of an Internet Diplomacy research agenda.

ORGANIZATION AND CONTENTS OF THE BOOK

As a contribution to this overall research agenda, the main research questions that this volume aims to answer are: can we see an emerging Internet Diplomacy as a new diplomatic field? If so, what do we mean by Internet Diplomacy? What are the diplomatic challenges around the governance of the internet? Does Internet Diplomacy develop new models and practices in the context of diplomacy? With this book, we thus approach Internet Diplomacy beyond the instrumental use of digital technologies for diplomatic practices.

As already discussed, the book doesn't address the use of digital means by diplomats to practice a kind of 'Public Diplomacy 2.0', which is explored by scholars under 'digital diplomacy' studies (Manor 2019;Bjola and Zaiotti 2020). This volume contributes to both the scholarly conversation and the global policy developments in the field by addressing how global internet governance, including cybersecurity policies, could be framed as an Internet Diplomacy area. As a matter of fact, even beyond its cybersecurity dimension, global internet governance in all its dimensions and areas could be addressed, analyzed and assessed as a 'science diplomacy terrain' and means of 'soft power' (Nye 2004), where scientific and technical expertise join forces with political influence and diplomatic action to address global challenges. This is With this book-which is, to a large extent, the unfolding of a conversation that started in 2017 among a network of scholars interested in exploring global internet governance actors, regulations, transactions and strategies and gathered for the first edition of the GIG-ARTS conference 9 to address global internet governance as a diplomacy issue-we have the ambition to unfold the concept of Internet Diplomacy by taking into consideration both the above-mentioned peculiarities of the emerging diplomatic practices in the governance of the internet and their outcomes in terms of normative transformations at the global, regional, and national levels. In particular, with the goal to understand and formalize Internet Diplomacy across all its dimensions and from multiple interdisciplinary perspectives, this book includes contributions addressing diplomacy around the international debate on the governance of the internet. A special emphasis is given to the role of the European Union and its member states in a field historically dominated by the US voice in the debate, due to its crucial role in the history of the internet, but also because of the leading position of the US internet giants in the global digital market. This book approaches the topic from an interdisciplinary perspective, by including contributions from leading scholars in the field of internet governance, approaching the topics from multiple backgrounds and disciplines, combining complementary novel theoretical approaches and empirically grounded research in the field of the governance of the internet as a diplomacy issue. This volume is, therefore, composed of ten chapters organized into three parts.

Part 1 explores how internet governance may constitute a (new) diplomacy issue in its own right, with the first three chapters respectively putting internet governance in the long-term perspective of the historical developments of diplomacy (chapter 2 by Yves Schemeil); analyzing it in relation with the two concepts of global governance and diplomacy, while taking into account specifics of the internet governance field, first and foremost the technology aspect (chapter 3 by Katharina E. Höne); and tracing how it has been politically constructed with different definitions, scopes and visions by the various stakeholders participating in the ten-year review process of the United Nations World Summit on the Information Society (chapter 4 by Mauro Santaniello and Nicola Palladino).

Part 2 more specifically analyzes whether and to what extent internet governance could serve as a science diplomacy instrument, exploring its opportunities and pitfalls through the relationships between science and authority, showing how the latter characterizes internet governance arrangements (chapter 5 by Robin Mansell); the comparative perspective between the US and Europe cases is explored in detail, with a focus on public diplomacy (chapter 6 by Nanette S. Levinson) and on cybersecurity policies (chapter 7 by Francesco Amoretti and Domenico Fracchiolla).

Part 3 presents four case studies that address in deeper detail, through empirical research, how internet governance diplomacy may be a means for the diffusion of values, norms, and policies from some regions of the world to others where internet governance and other digital regulation is less developed, and to what extent this may impact national sovereignty. Provided cases studies cover transatlantic free trade agreements and data flows (chapter 8 by Maria Francesca De Tullio and Giuseppe Micciarelli), the liberalization of telecommunication markets and its impact on transnational surveillance (chapter 9 by Claire Peters), privacy and the right to be forgotten in Latin America (chapter 10 by Jean-Marie Chenou), and international policy diffusion in the fields of copyright and privacy (chapter 11 by Krisztina Rozgonyi and Katharine Sarikakis).

With his chapter on 'Undiplomatic Ties: When Internet Blocks Intermediation', Schemeil (2022) opens the first part with a historical approach to question whether, how and to what extent the internet and its governance might-if it has not already done so-transform diplomacy, seen as relying on intermediation. Considering the highly privatized character of the internet ordering and the diversity of non-state actors intervening in its multistakeholder governance, the questioning focuses on the evolution of two main aspects of diplomacy: its practice as a formal communication process conducted by professional ambassadors in conventional settings and following established rules; and its organization as a multilateral or bilateral negotiation process between states. The chapter then examines two hypotheses: (a) the internet as a shortcut to classical diplomacy; and (b) that internet governance could only be effective through professional intermediation. To explore these two extreme situations, the chapter provides historical developments of diplomacy and up-to-date analysis of internet governance processes, both of which are highly relevant for the reader to understand the dialectics of two apparently mutually exclusive processes and antagonistic concepts.

Then, in chapter 3, Höne (2022) digs deeper to conceptualize the relation between diplomacy and governance in the internet field while avoiding one concept subsuming the other. In terms of methodology, the chapter suggests thus to refer, under the governance concept, to institutions and the set of rules and norms they define and apply, and to consider diplomacy when dealing with actors and their practices. The approach particularly fits the internet field, where new categories of actors have gained a seat at the table ID_3pp Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers of negotiations, making multistakeholderism an especially prominent feature in the related discussions. These new blocks of actors include private ones, such as the business sector and civil society in the same way as in some other areas, as well as individuals who may bring their expertise to the discussions, but also artifactual ones, namely the internet infrastructure itself and its protocols, leading to a situation where technological developments transform both the nature, the substance and the outcomes of the debate. Here again, the dialectic relation between diplomacy and governance is highlighted, through several examples in the internet field.

With chapter 4, Santaniello and Palladino (2022) complete this first part by providing evidence that internet governance discussions are truly a diplomatic process that aims at making different definitions, scopes and visions from various stakeholders coexist, cooperate, and interoperate. The authors proceed through discourse analysis of different stakeholders' contributions to the WSIS+10 review process, ten years after the first World Summit on the Information Society held by the United Nations in 2005. The authors identify four coalitions ('neoliberal', 'sovereigntist', 'constitutional', and 'developmentalist'), providing the list of their members among the contributing stakeholders according to their own classification, and identifying the main contentious issues between them. These coalitions are, of course, ideal types defined for the sake of this analysis, and provide an empirical illustration of where main tensions and contentions lie in internet governance and how they are expressed by involved stakeholders. With this contribution, the authors shed light on the process by which actors coalesce around common narratives and eventually produce discursive orders.

Opening part 2 with her chapter on 'Science Diplomacy and Internet Governance: Opportunities and Pitfalls ', Mansell (2022) starts by exploring how internet governance might be a field where science diplomacy can be deployed, especially considering its highly technological features. To this end, in particular, she examines the relationships between science (and scientists) and authority, both constituted and adaptive, where the former is predominant in science diplomacy and the latter characterizes internet governance arrangements. Here again, controversies and conflicts are traced and tackled, and attention is particularly paid to situations where academic researchers in internet governance engage in tackling socio-political challenges associated with the digital environment, and to the authoritative status of research evidence in situations where it may affect the interests of certain stakeholders. Further, taking into account the political economy of digital markets and the increasing powers of digital platform companies and their influence on the regulation and governance of the field, the author highlights how challenging the protection of citizens' interests becomes in such an Still analyzing internet governance as a potential science diplomacy arena, Levinson (2022) focuses on the case of the United States with her chapter on 'Crafting Science Diplomacy In Comparative Perspective: The Case of US Internet Governance', in view of providing elements for a comparative perspective and paying particular attention to relevant cross-cultural communication and public diplomacy research and writings as well as to the public and science diplomacy practices of the United States. The author revisits, in the internet era, the US long-standing tradition of public diplomacy, arguing that the development of new media has transformed what she identifies as 'diplomacy places'. This resonates with the rise of new diplomacy actors in internet governance multistakeholder processes. Then, the chapter explores in which ways science diplomacy follows the same path, especially in the internet governance field. Comparative elements from Spanish public and science diplomacy are provided. The chapter concludes with some directions for the development of this research area.

Continuing the comparative approach, Amoretti and Fracchiolla (2022) address, in their chapter on 'Modes of Internet Governance as Science Diplomacy: What Might the EU Learn from the US Cybersecurity Policy?' more specifically cybersecurity as one of the most important issues in the internet governance field, and probably the one that most immediately illustrates how internet governance constitutes a (science) diplomacy issue. The chapter provides, with many examples, a thorough comparative analysis of US and EU cybersecurity policies, and examines common and diverging elements in their respective internet governance strategies and policies in this regard; it also analyzes the state of transatlantic cooperation in this field. In conclusion, the authors consider different scenarios on how the EU cybersecurity policy may develop in the future. Concluding the part on internet governance as a science diplomacy area, this chapter focusing on cybersecurity constitutes the perfect transition to part 3, which provides case studies on internet governance diplomacy.

The first case study proposed in part 3 deals with free trade agreements and their impact on internet governance. In chapter 8, De Tullio and Micciarelli (2022) analyze the role and position of the EU and other state and non-state actors involved in the negotiation of free trade agreements, that led to what they call 'free trade governance'. They also discuss how new publicprivate institutions created by the neoliberal design of free trade agreements may affect internet governance, in that they generate a shift of power on a transnational scale, since private subjects act as real negotiators, having an authoritative substance behind their formal corporate nature. The authors more specifically consider the Trade in Services Agreement (TiSA, whose negotiations were paused following the US presidential elections in November 2016) as a case study, to analyze how it affects crucially both political institutions and internet governance issues such as privacy and personal data protection, as well as network neutrality and transnational data flows. The study is framed in the broader theoretical background of constitutional law, governmentality studies, and a Foucauldian perspective.

In her chapter on 'National Sovereignty, Global Policy, and the Liberalization of Telecommunications Markets', Peters (2022) addresses, as a second case study, the consequences of the privatization of the telecom market on surveillance, with the evolution of the regime of lawful interception in Europe and of international cooperation of law enforcement authorities. By focusing on the issues of sovereignty, international cooperation, and publicprivate cooperation, the chapter analyzes it as an international relations issue, addressing inter alia the important cyber-normative field of international human rights. The author establishes a causality link between the privatization of the telecom sector and the evolution of surveillance legislation and shows how the globalization of private telecom operators led to problems with the enforcement of national laws that could only be solved through diplomacy and international standardization. An enlightening example of 'law enforcement authority diplomacy' is provided with the reported FBI initiative. The detailed analysis provided in this chapter constitutes an essential tool to understand the never-ending developments in national and transnational surveillance based on telecommunication data, and the increasing issues of national sovereignty in the field.

'In This Bright Future You Can't Forget your Past: Debating the "Right to Be Forgotten" in Latin America', says Chenou (2022), who presents in his chapter an example of law and policy diffusion, that of the EU 'Right To Be Forgotten' (RTBF) in Latin America. He analyses how the issue was debated and implemented in four large countries (Argentina, Brazil, Colombia and Mexico), with regard to two possible conceptions of the RTBF: that of the EU and that of the US. Tracing back to the 'Costeja' case that initiated the European Court of Justice's decision on the RTBF and the subsequent EU legislation, the chapter presents and discusses the US and EU's different approaches to internet intermediaries liability, and highlights the difference in the ways of approaching the role of search engines, in this case, that is at the heart of the two competing visions of the case (data controller in the ECJ decision vs. internet intermediary in the US vision contesting this decision) and, consequently, the different vision of the applicable law (EU data protection legislation vs. US-as the search engine country-intermediary liability Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers regulation). The chapter then discusses in detail the elements and tensions in this debate in the four considered Latin American countries, as regard the perspective to adopt in their legislation. Showing how these discussions were held in the shadow of EU and US (public) diplomacy and influenced by them, this chapter provides an important example of policy diffusion process and the role played by academic researchers and civil society actors in it.

In the closing chapter on 'Policy Diffusion and Internet Governance: Reflections on Copyright and Privacy', Rozgonyi and Sarikakis (2022) extend the elaboration of international policy diffusion processes in the field of internet governance, analyzing more specifically two case studies related to privacy (with the notion of informed consent) and copyright (with the concept of graduated response). The chapter focuses on policy transfer as a matter of foreign policy and investigates structural factors that influence this process, in particular the role of citizens' activism in international policy making. With these two selected case studies, the authors consider two emblematic 'sites of struggle' among the many characterizing internet governance contentions, that affect citizens' everyday life and their rights to access, use and generate internet content, impacting their very fundamental freedoms. As the authors argue, these cases entail policy principles that reflect ideological dispositions about the role of the state and the market, the role of the citizen as an actor and, ultimately, even the state of fundamental rights in a volatile world.

NOTES

1. As it is impossible to cite here all the relevant work in the internet governance field, this reference is provided as an anthology of such work by a number of authors covering almost all aspects of the global internet governance studies.

2. See UN WSIS related information on ITU website available at: https://www .itu .int/net/wsis/.

3. See UN GGE webpage at: https://www .un .org/disarmament/group -of -governmental-experts/.

4. See UN OEWG webpage at: https://www .un .org/disarmament/open -ended -working -group/.

5. Such as, for instance: illegal and harmful content vs. freedom of expression; state surveillance, private companies abuses, and various forms of cybercrime activities vs. the protection of privacy and personal data; intellectual property rights vs. a vision of internet content as commons to foster education, knowledge, innovation and global development.

6. See the IGF website at: https://www .intgovforum .org/. 7. See for instance discussions organized by The AAAS Center for Science Diplomacy (https://www .aaas .org/programs/center-science-diplomacy), The USC

  Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers political, legal, economic, social, cultural, and societal choices. The mutation of diplomatic practices in Internet Diplomacy reflects these challenges.Diplomacy in the transnational governance of the digital domain is called upon to tackle the deep and multifold mutation resulting from multifaceted digital disruptions that affect every aspect of current social, economic, and political life. Together with opportunities, these transformations generate challenges in terms of sovereignty, economic development, social cohesion,

	AT THE CROSSROADS OF GLOBALIZATION
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political and cultural values, and legal and policy frameworks (DeNardis 2018). The cross-field nature of the impact of the internet imposes diplomats to adopt a multidisciplinary understanding of the issues, by combining their representative role with scientific advice. Contrary to other fields of global governance clustered around the role of states and international organizations (Zürn 2018), in global internet governance scientific and technical expertise join forces with political influence and diplomatic action to address digital challenges (Kaltofen and Acuto 2018), channel democratic values, and share knowledge to build common visions (Scholte 2005).

  Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers

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  Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers citizens, including economic and social wealth, access to critical resources, and access to knowledge

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  Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers particularly true considering the importance of technical experts and technical organizations, recognized as a stakeholder on its own in the multistakeholder regime of global internet governance.

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  Internet Diplomacy: Shaping the Global Politics of Cyberspace / Marzouki and Calderaro / Open Access PDF from Rowman & Littlefield Publishers environment. Science diplomacy is then discussed as a potential means of influencing diplomacy, in order to channel respect for democratic values and fundamental rights in internet governance discussions.

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B Kalaiselvi

Amar Suputhra

M Lalitha

Rajendra Hegde

S K Singh

Philippe Lagacherie

DIGITAL SOIL MAPPING OF KEY GLOBALSOILMAP PROPERTIES IN NORTHERN KARNATAKA PLATEAU

Keywords: Digital soil mapping, Vertisols, Alfisols, Quantile Regression Forest, soil properties, Field capacity, Permanent wilting point

Accurate and quantitative information on soil properties of each and every location is essential for site specific sustainable management of land resources. A study was conducted to predict the different key soil properties of Northern Karnataka as per GlobalSoilMap specifications using Quantile Regression Forest (QRF) Model. Along with Sentinel-2 data, terrain attributes such as elevation, slope, aspect, topographic wetness index, topographic position index, plan and profile curvature, multi-resolution index of valley bottom flatness, multi-resolution ridge top flatness and vegetation factors like NDVI and EVI were used as covariates. Equal-area quadratic splines were fitted to soil profile datasets to estimate soil properties viz. pH, OC, CEC, clay, sand, silt, field capacity and permanent wilting point at six standard soil depths (0-5, 5-15, 15-30,30-60, 60-100 and 100-200 cm) as per GlobalSoilMap specifications. The coefficient of determination (R 2 ), mean error (ME) and root mean square error (RMSE) were calculated in order to assess model performance. Prediction interval coverage percentage (PICP) was calculated to evaluate the associated uncertainty predictions.

The predicted soil properties are reliable with minimum errors and the QRF model captured maximum variability for most of the soil properties.

Introduction

Soil properties are assessed through resource inventorisation with the main objective to delineate areas which need uniform management practices and provide users with information on soil properties. Assessment of spatial distribution of soil properties for each location is important for site-specific land management, land evaluation and land suitability analysis [START_REF] Gessler | Modeling soillandscape and ecosystem properties using terrain attributes[END_REF][START_REF] Jackson | Spatial soil information systems and spatial Soil inference systems: perspectives for digital soil mapping[END_REF]. Although several spatial soil databases are developed throughout the world, they are neither exhaustive nor precise enough for ensuring enlightened decisions. For example, though digitized soil maps are available for most of the world [START_REF] Grunwald | Digital soil mapping and modeling at continental scales: Finding solutions for global issues[END_REF], those information are at very small scale (1:1 million or coarser) for many areas and do not adequately represent soil variability in a format that is useful for a non-pedologists [START_REF] Sanchez | Digital soil map of the world[END_REF]. Digital soil mapping (DSM) represents a ground-breaking solution compared to conventional soil survey by its ability to exploit large sets of spatial data, to produce uncertainty estimates associated with soil predictions and can be revised once new data are collected [START_REF] Jackson | Spatial soil information systems and spatial Soil inference systems: perspectives for digital soil mapping[END_REF]. Soil database generated through field sampling and laboratory analysis are used to feed a DSM model that predicts soil properties in areas not sampled. Digital soil maps also provide the uncertainties associated with such predictions. The overall uncertainty of the prediction is estimated by combining uncertainties of input data, spatial inference, and soil functions (Dharumarajan et al., 2019a). Uncertainties are essential for understanding and dealing with risk in decision-making.

DSM has moved from a largely academic towards an operational activity through GlobalSoilMap project (http://www.globalsoilmap.net/). The project aims to map the several key soil properties of globe onto a three-dimensional grid at fine spatial resolution with local uncertainty estimates [START_REF] Arrouays | GlobalSoilMap: towards a fine-resolution global grid of soil properties[END_REF]. The first versions of GlobalSoilMap products have already been produced in various countries [START_REF] Mulder | National versus global modelling the 3D distribution of soil organic carbon in mainland France[END_REF][START_REF] Grundy | Soil and landscape grid of Australia[END_REF][START_REF] Adhikari | Constructing a soil class map of Denmark based on the FAO legend using digital techniques[END_REF][START_REF] Poggio | 3D mapping of soil texture in Scotland[END_REF] with spatial inference functions using globally available landscape parameters such as Digital Elevation Models, multispectral remote sensing, geology maps, and legacy soil maps as inputs.

In India, ICAR-National Bureau of Soil Survey and Land Use Planning (ICAR-NBSS&LUP), Nagpur has recently launched an ambitious program called "IndianSoilGrids" with the objective to develop soil properties map as per GlobalSoilMap Specifications. In recent past, effort has been made to compile the legacy soil data in the form of harmonized databases and stored in NBSS&LUP Geoportal. Besides pursuing the storage effort, IndianSoilGrids project paved the ways to exploit legacy soil data through DSM models. In this context, the present exploratory study was carried out to produce a fine resolution map of major GlobalSoilMap soil properties such as organic carbon, pH, CEC, clay, sand, silt, field capacity and permanent wilting point in part of Northern Karnataka Plateau region representing semi arid tropics of south India using Quantile Regression Forest Model techniques.

Materials and methods

Study area

The present study was carried out in part of Koppal and Gadag districts of Northern Karnataka Plateau (Fig. 1). The study area is located in 14° 56' to 15 ° 37' N latitude and 75 °23' to 76 ° 25' longitude with an area of 3655 km 2 . The study region represents hot-semi arid climate with rainfall range of 600-750 mm and potential evapo-transpiration (PET) of 1600-1700 mm. The average annual rainfall is 672 mm. This area includes mountainous, expansive plateau with substantial area is underlined by basalts with continuation of Deccan trap of Maharashtra. The major area comes under rainfed cultivation with crops like Sorghum, Pigeon pea and Pearl millet. The major soils represented by shallow to deep vertisols, alfisols and inceptisols.

Sampling methodology

The profiles studied under Sujala III (Karnataka Watershed Development Project II) project were used for mapping of soil properties. Sixty soil profiles were studied upto 2m or hard rock based on variability in landform and land use. The soil horizons were demarcated and from the representative soil horizons, soil samples were collected for laboratory analysis.

Collected soil samples were air dried in shade and passed through 2 mm sieve by gently ground with a wooden mallet. The samples were analysed for particle-size distribution following International Pipette method [START_REF] Richards | Diagnosis and improvement of saline and alkali soils[END_REF], pH and electrical conductivity (EC) in 1:2.5 soil:water suspension [START_REF] Jackson | Spatial soil information systems and spatial Soil inference systems: perspectives for digital soil mapping[END_REF]. Organic carbon was estimated by [START_REF] Walkley | An estimation of the method for determining soil organic matter and a proposed modification of the chromic acid titration method[END_REF] method. The cation exchange capacity (CEC) and exchangeable cations were determined as described by [START_REF] Jackson | Soil Chemical Analysis[END_REF]. Field capacity (FC) and permanent wilting point (PWP) were estimated using pressure plate apparatus [START_REF] Richards | Physical processes determining water loss from soil[END_REF]. The profile soil properties were pre-processed by harmonization of soil depth interval (GlobalSoilMap depth specification) predictions using equal-area spline functions [START_REF] Bishop | Modelling soil attribute depth functions with equal-area quadratic smoothing splines. A comparison of prediction methods for the creation of field-extent soil property maps[END_REF].

Environmental covariates and models used

A Digital elevation model (DEM) with 30 m resolution was obtained from SRTM and processed using ArcGIS10 data management tool box. The primary and secondary derivates of DEM like elevation, slope, aspect, curvatures (plan and profile), topographic wetness Index (TWI) and topographic position index (TPI), LS factor, Multi-resolution Ridge Top Flatness (MrRTF) and Multi-resolution Index of Valley Bottom Flatness (MrVBF) were derived by using Saga-GIS 6.3.0 version. Along with DEM attributes, all the bands of Sentinel-2 imagery (13 bands), Normalized Difference Vegetation Index (NDVI) and Enhanced vegetation index (EVI) (MOD13Q1) were used as covariates for prediction of soil properties (Table .1). The environmental variables were intersected for all the sampling points for prediction of soil properties.

Fig.1. Study area with profile locations

Table.1. Different covariates used in the model

Quantile regression forest (QRF) model was used for prediction of soil properties and uncertainty estimates in the study area. QRF is an extension of Random forest model and the advantage of QRF over Random Forest model (RFM) is for each node in each tree, RFM keeps only the mean of the observations that fall into this node and neglects all other information whereas QRF keeps the value of all observations in this node, and assesses the conditional distribution based on the information [START_REF] Meinshausen | Quantile regression forests[END_REF][START_REF] Vaysse | Using quantile regression forest to estimate uncertainty of digital soil mapping products[END_REF]Dharumarajan et al., 2019a). For the present study, ranger package was used for running the QRF algorithm in R environment. Ranger package helps to identify the best RF properties for running the model. Ten folds cross validation techniques with 20 times repetition was used to evaluate the performance of QRF model. The performance of QRF was evaluated using indicators such as Coefficient of determination (R 2 ), Root Mean Square Error (RMSE), mean error (ME). Prediction interval coverage percentage (PICP) was used to evaluate the uncertainty of prediction. Sentinel-2 13 bands of Sentinel 2 data 10-60m

Predictor

Results and Discussion

Summary statistics of soil properties

Summary of the soil properties are presented in Table . 2. The soil pH ranged from 4.7 to 9.9 with a mean and standard deviation of 8.2 and 1.1, respectively. The organic carbon content ranged between 0.11 and 1.16% with mean of 0.5 % and standard deviation of 0.23%.

The organic carbon skewed positively whereas pH skewed negatively showed that asymmetrical distribution. The higher variability in pH is mainly attributed to soil pedological factors and land management. The soil hydraulic properties such as field capacity and permanent wilting point were ranged from 6 to 60% and 1.5 to 43.7% with mean and standard deviation of 29.2, 18.5 and 12.2, 10.5 % respectively. Cation exchange capacity of the soil varied from 2.0 to 80.9 cmol(+) kg -1 with mean and SD of 32.3 and 20.5 cmol(+) kg Soil hydraulic properties are important for irrigation scheduling and proper landuse planning (Dharumarajan et al., 2019b). Soil hydraulic properties such as field capacity and permanent wilting point determines the availability and retention of the water for crop growth. Field capacity and permanent wilting point were well predicted by QRF model.

Compared to field capacity (R 2 =30-38%), permanent wilting point was predicted with high accuracy (R 2 =41-49%). [START_REF] Hong | Predicting and mapping soil available water capacity in Korea[END_REF] recorded digital soil mapping approach for prediction of soil hydraulic property with maximum accuracy (R 2 -61%) whereas Román Dobarco (2019) reported prediction accuracy (R 2 ) of FC and PWP were 21 and 29 % respectively.

Prediction interval coverage probability (PICP) is an indication of efficiency of uncertainty measurements. The present predictions found that the PICP values ranged from 83.2 to 92.2 %. Overall, the prediction performance of this model was high for soil hydraulic properties. Higher sample density is required for better results in tropical countries where soil pattern is complex due to the geological uplift than other regions [START_REF] Junior | A regional-scale assessment of digital mapping of soil attributes in a tropical hillslope environment[END_REF].

Importance of predictor variables for predicting soil properties

RFM model estimates the importance of covariates based on how best or worse the prediction would be if one or more variable is removed and also it protects elimination of good predictor variables which are important for the model [START_REF] Prasad | Newer classification and regression tree techniques: bagging and random forests for ecological prediction[END_REF]. Figures 3a-h shows the variable importance rankings of Random Forest model for pH, OC, clay, sand, silt, CEC, FC and PWP. Elevation is emerged as top predictor for prediction of clay and organic carbon.

MRVBF and TWI are ranked as most important predictor for prediction of pH and PWP.

Different bands of Sentinel -2 imagery occupies in the top position for prediction of majority of soil properties. Different researchers recorded usefulness of Sentinel-2 imageries in prediction of different soil properties [START_REF] Castaldi | Evaluating the capability of the Sentinel 2 data for soil organic carbon prediction in croplands[END_REF][START_REF] Gholizadeh | Soil organic carbon and texture retrieving and mapping using proximal, airborne and Sentinel-2 spectral imaging[END_REF][START_REF] Vaudour | Sentinel-2 image capacities to predict common topsoil properties of temperate and Mediterranean agroecosystems[END_REF]. Recently, [START_REF] Gomez | Use of Sentinel-2 Time-Series Images for Classification and Uncertainty Analysis of Inherent Biophysical Property: Case of Soil Texture Mapping[END_REF] showed good discrimination ability of time series

Sentinel-2 images in identifying different texture class and associated uncertainty. 32.6 % respectively. High sand content recorded in North-eastern part of study area and high clay and silt content recorded in north-western part. The high sand content of surface soils in North-eastern part might be due to severity of the erosion where finer particles are moved into the low lying areas. The predicted cation exchange capacity varied from 4.7 -62.3 % and recorded low CEC in north-eastern part. Predicted hydraulic properties viz., field capacity and permanent wilting point ranged from 9.1-41 % and 3.2-29.5% respectively. The spatial prediction of soil properties suggested that distribution of soil properties on the surface are highly variable due to variations in environmental factors, land management and land use. The spatial resolution of the maps helps to assess and monitor the soil health and preparation of proper land use plan.

Spatial prediction of soil properties

Conclusion

The prediction of soil properties and uncertainty by QRF model was reasonable and varied from 8-51% for surface and 0-56% for subsoil. Except pH and OC, the present model predicted better for most of the soil properties compared to previous studies. Weak variations in soil properties, mixed lithologic occurrence and sparse sample density are linked with performance of the model. The data augmentation certainly helps in reducing the uncertainty and over fitting and to improve model accuracy further. The prediction can also be improvised by increasing the environment covariates such as geology map and climatic datasets.

Laurent Ruiz, Indo-French Cell for Water Sciences, Bangalore for his guidance in Indian digital soil mapping programme.

Fig. 2

 2 Fig. 2(a-h). Observed soil properties Vs Predicted soil properties in 0-5 cm depth

Performance of Quantile Regression Forest Model in predicting soil properties

  The performance of Quantile Regression Forest model was evaluated by calculating statistical indicators viz., Coefficient of determination (R 2 ), Mean error (ME) and Root Mean Square Error (RMSE). The cross validation results (Table3and Fig.2a-h) showed that the combination of different covariates explained the variability's of predicted soil properties viz., pH, organic carbon, CEC, clay, sand, silt, FC and PWP. The model could capture low to medium variability (R 2 =0-56%) while predicting pH, Organic carbon and CEC for different

	Table2. Statistical results of soil properties Properties Mean Min pH 8.2 4.7 3.2 Dharumarajan et al., 2019a). The prediction of particle size quantities viz., clay, sand and silt Max Std dev. Skewness Kurtosis 9.9 1.1 -1.2 0.9
	OC (%)	0.5	0.11	1.16	0.23	0.5	-0.35
	Clay(%) content were fairly good. Prediction accuracy for sand is 41-49 % with RMSE of 15.4-42.6 4.1 75.8 18.2 -0.1	-0.8
	Sand(%)	41.3	8.7	87.6	22	0.3	-1
	Silt(%) 17.9%.R 2 of silt varied from 29 to 49 %for different depth intervals. Similar results were 16.1 4.7 40.7 6.9 0.6	0.3
	CEC (C mol(+) kg -1 ) FC(%) observed by Akpa et al. (2014) who recorded R 2 value of 16-56 % for prediction of particle 32.3 2 80.9 20.5 0.3 29.2 6 60 12.2 0.3	-1.1 -0.6
	PWP(%)	18.5	1.5	43.7	10.5	0.5	-0.6

-1

respectively. Except pH and silt content, all other soil properties had registered negative kurtosis. Similar way except, clay content and pH, all other properties showed positive skewness. The correlation analysis showed that field capacity and permanent wilting point has significant positive correlation with clay and silt and negative correlation with sand content. depth ranges. Among these soil properties, CEC prediction was good compared to pH and Organic carbon. The present model explained 31-56 % of variation for prediction of CEC in different depth intervals. Similar results were observed by different researchers

(Gallo et al.,

2018, R 2 =40%; Chagas et al., 2018, R 2 =47%;

[START_REF] Ghaemi | Using satellite data for soil cation exchange capacity studies[END_REF]

, R 2 =45-65%). In case of pH, only 8-23 % of variability was captured by the model. The poor prediction may be attributed to more variability in pH influenced by soil intrinsic (pedogneic) and extrinsic (land management) factors. Like, pH, the performance of the model for prediction of organic carbon is also very low (R 2 =0-27%). The poor performance may be related to the low levels of soil organic carbon compared to soils having high organic carbon

[START_REF] Lo Seen | Soil carbon stocks, deforestation and land-cover changes in the Western Ghats biodiversity hotspot (India)[END_REF][START_REF] Junior | A regional-scale assessment of digital mapping of soil attributes in a tropical hillslope environment[END_REF][START_REF] Gastaldi | Mapping the occurrence and thickness of soil horizons within soil profiles[END_REF][START_REF] Dharumarajan | Spatial prediction of major soil properties using Random Forest techniques -A case study in semi-arid tropics of South India[END_REF]

size fractions in Nigeria using RFM whereas

[START_REF] Santra | Digital soil mapping of sand content in arid western India through geostatistical approaches[END_REF]

found only 21-28 % of variation in sand content captured by Random forest algorithm.

Table . 3 Performance of Quantile Regression Forest model for prediction of soil

 .

		15-30 cm	-0.04 ± 0.2	7.79 ± 0.15	37 ± 3	86.0 ± 1.6
		30-60cm	0.26 ± 0.16	8.49 ± 0.15	38 ± 2	85.7 ± 2.1
		60-100 cm 0.66 ± 0.37	10.1 ± 0.41	38 ± 5	89.6 ± 1.5
		100-200cm -0.29 ± 0.31	10.7 ± 0.41	40 ± 5	84.6 ± 2.4
	PWP	0-5 cm	0.26 ± 0.21	6.8 ± 0.2	41 ± 3	92.0 ± 1.5
	(%)	5-15 cm	0.3 ± 0.21	6.74 ± 0.25	41 ± 4	91.9 ± 1.4
		15-30 cm	0.3 ± 0.16	6.31 ± 0.13	43 ± 2	89.9 ± 1.7
		30-60cm	0.50 ± 0.17	6.91 ± 0.16	47 ± 3	91.6 ± 2.1
		Mean error 60-100 cm 0.79 ± 0.19	RMSE 8.62 ± 0.39	R 2 (%) 42 ± 5	PICP 90.8 ± 1.8
	pH	0-5 cm 100-200cm 0.84 ± 0.37 -0.19± 0.02	0.96 ± 0.02 8.89 ± 0.53	10± 5 49 ± 6	88.7± 1.3 90.6 ± 2.7
		5-15 cm	-0.18± 0.02	0.94± 0.03	13± 6	89.0 ± 0.78
		15-30 cm	-0.18± 0.02	0.95± 0.03	8± 9	90.0± 1.1
		30-60cm	-0.14± 0.03	1.00± 0.03	9± 6	88.3 ± 2.0
		60-100 cm -0.3± 0.02	1.02± 0.02	23±3	89.3 ±2.1
		100-200cm -0.23± 0.01	0.88± 0.03	4±8	86.4 ± 3.2
	OC	0-5 cm	-0.02 ± 0.0	0.22 ± 0.01	08 ± 6	87.5 ± 1.7
	(%)	5-15 cm	-0.02± 0.01	0.22± 0.01	07 ± 5	86.2 ± 1.9
		15-30 cm	0.0 ± 0.00	0.21 ± 0.01	10 ± 4	86.8 ± 2.3
		30-60cm	0.02 ± 0.01	0.20± 0.01	27± 4	88.6 ± 1.5
		60-100 cm 0.03± 0.01	0.19± 0.00	0± 2	89.4 ± 1.7
		100-200cm 0.03± 0.00	0.20± 0.00	5± 3	84.8 ± 2.1
	Clay	0-5 cm	0.19 ± 0.2	6.10 ± 0.29	37 ± 6	88.4 ± 2.3
	(%)	5-15 cm	2 0.22 ± 0.17	6.04 ± 0.22	39 ± 5	88.3 ± 2.0
		15-30 cm	0.59 ± 0.16	6.09 ± 0.20	39 ± 4	88.2 ± 1.2
		30-60cm	-0.04 ± 0.51	12.39 ± 0.42 43 ± 4	87.2 ± 2.3
		60-100 cm 0.0 ± 0.09	4.95 ± 0.1	18 ± 3	88.3 ±2.1
		100-200cm 0.05 ± 0.21	5.2 ± 0.22	0 ± 8	83.2 ± 1.6
	Sand	0-5 cm	1.54 ± 0.56	17.24 ± 0.59 48 ± 4	86.6 ± 1.7
	(%)	5-15 cm	2.25 ± 0.56	16.92 ± 0.72 49 ±4	87.6 ± 2.0
		15-30 cm	1.37 ± 0.44	16.10 ± 0.34 45 ± 2	85.3 ± 1.4
		30-60cm	40.04 ± 0.45	17.86 ± 0.43 42 ± 3	92.2 ± 1.2
		60-100 cm -0.24 ± 0.52	15.43 ± 1.18 45 ± 9	93.6 ± 1.3
		100-200cm 0.1 ± 0.92	16.66 ± 0.94 41± 7	88 ± 0.0
	Silt	0-5 cm	-0.20 ± 0.39	13.47 ± 0.5	49 ± 4	91.8 ± 1.5
	(%)	5-15 cm	0.05 ± 0.32	13.90 ± 0.44 45 ± 4	90.8 ± 1.6
		15-30 cm	-0.08 ± 0.31	13.45 ± 0.40 40 ± 4	89.5 ± 1.2
		30-60cm	0.57± 0.17	6.30 ± 0.21	29 ± 5	84.0 ± 1.8
		60-100 cm 0.53 ± 0.49	11.78 ± 0.58 52± 5	90.8 ± 1.3
		100-200cm 0.57± 0.17	6.30 ± 0.21	29 ± 5	84.0 ± 1.8
	CEC	0-5 cm	1.26 ± 0.27	13.48 ± 0.66 51 ± 5	87.6 ± 1.2
	(C	5-15 cm	1.19 ± 0.51	13.47 ± 0.42 51 ± 3	86.9 ± 1.5
	mol	15-30 cm	1.03 ± 0.38	12.27 ± 0.37 56 ± 3	87.6 ± 1.9
	kg -1 )	30-60cm	1.19 ± 0.67	14.88 ± 0.55 43 ± 4	87.1 ± 2.3
		60-100 cm 1.52 ± 0.61	15.98 ± 0.66 40 ± 5	88.8 ± 2.3
		100-200cm 1.55 ± 0.69	17.1 ± 0.71	31 ±6	87.1 ± 2.3
	FC	0-5 cm	0.03 ± 0.25	8.42 ± 0.29	36 ± 4	88 ± 2.9
	(%)	5-15 cm	0.12 ± 0.28	8.69 ± 0.21	30 ± 3	88.0 ± 2.5

Table . 4. Summary statistics of predicted soil properties

 .

		15-30 cm	39.9	7.3	64.1	8.6	0.0	0.2
		30-60cm	45.7	8.5	66.5	8.6	0.1	0.6
		60-100 cm	15.2	8.0	19.0	2.4	-1.3	-0.2
		100-200cm	17.2	12.1	21.7	1.7	1.6	-0.5
	Sand	0-5 cm	45.5	17.8	82.6	15.4	-0.7	0.7
	(%)	5-15 cm	45.3	17.7	82.9	15.0	-0.8	0.7
		15-30 cm	41.7	15.5	76.5	13.5	-1.0	0.5
		30-60cm	36.1	13.4	80.5	11.9	-0.6	0.3
		60-100 cm	38.4	12.4	57.8	13.9	-1.3	-0.3
		100-200cm	38.0	11.2	62.6	15.6	-1.4	-0.4
	Silt	0-5 cm	36.5	7.7	61.9	12.0	-0.8	-0.2
	(%)	5-15 cm	16.7	6.2	32.6	5.6	-0.7	0.2
		15-30 cm	17.5	7.1	35.6	6.4	-1.0	0.3
		30-60cm	15.8	8.7	27.5	4.2	-0.4	0.3
		60-100 cm	46.9	20.2	69.0	10.7	-1.2	0.4
		100-200cm	45.0	24.1	71.4	12.9	-1.5	0.3
	CEC	0-5 cm	27.5	4.7	62.3	14.0	-1.3	0.1
	(C	5-15 cm	27.5	5.2	62.3	14.5	-1.3	0.2
	mol	15-30 cm	29.9	5.0	64.0	14.6	-1.3	0.2
	kg -1 )	30-60cm	32.9	7.0	62.3	13.3	-1.2	0.1
		60-100 cm	32.4	10.6	65.3	14.9	-1.6	0.1
		100-200cm	31.0	13.9	54.5	14.7	-1.5	0.3
	FC
	(%)
			Mean Min	Max		stdev	kurtosis	skewness
	pH	0-5 cm	8.1	5.5	9.2	0.6	2.2	-1.5
		5-15 cm	8.2	5.9	9.2	0.4	1.8	-0.8
		15-30 cm	8.2	6.0	9.2	0.3	5.7	-1.6
		30-60cm	8.2	6.4	9.3	0.4	3.8	-0.9
		60-100 cm	8.5	6.5	9.2	0.3	5.3	-1.5
		100-200cm	8.6	8.0	9.1	0.2	1.7	-1.4
	OC	0-5 cm	0.61	0.35	0.83	0.08	0.9	1.3
	(%)	5-15 cm	0.60	0.40	0.84	0.07	3.0	1.7
		15-30 cm	0.59	0.37	0.83	0.10	-0.5	0.5
		30-60cm	0.59	0.28	0.80	0.11	-0.7	0.0
		60-100 cm	0.4	0.3	0.6	0.1	-0.9	-0.1
		100-200cm	0.4	0.3	0.6	0.0	9.9	0.9
	Clay	0-5 cm	16.2	5.5	32.6	5.1	-1.0	0.0
	(%)	5-15 cm	36.6	7.7	62.1	11.3	-0.7	-0.2

Acknowledgements

The funding received from the project ATCHA, ANR-16-CE03-0006 to attend and present this paper in the 2019 digital soil mapping and GlobalSoilMap workshop held in The University of Chile, Santiago is highly acknowledged. The authors also acknowledge Dr.