Toward improved sea ice freeboard observation with SAR altimetry using the physical retracker SAMOSA+

International audienceSince 2010, the CryoSat-2 satellite mission has enabled to largely improve sea ice freeboard estimations. But due to the complexity of radar echoes over sea ice, freeboard retrieval from altimetry still presents some errors and biases that further limit the potential of these observations for climate studies or for assimilation into models. Various methods have been explored, producing a large range of freeboard estimations. In this study, we analyze the main steps of the radar freeboard computation developed as part of the Cryo-SeaNice Project. The objective is to quantify the impacts of each processing method and to identify optimal strategies to improve freeboard estimations from SAR altimetry measurements. We consider two SAR processing options: the Hamming Window (HW) and with the Zero-Padding (ZP), and 2 retrackers: the Threshold First Maximum Retracker Algorithm (TFMRA) based on heuristic measurements and SAMOSA+ a retracker declined from model based analysis of the surface back-scatter. Four freeboard solutions are generated from combinations of the 2 processing options (HW and ZP or ZP only) and the 2 types of retrackers. In addition, an alternative to the Hamming Window method to filter out side-lobes errors is presented. The impacts of the different approaches to estimate freeboard are quantified from comparisons with Operation Ice Bridge (OIB) and the Beaufort Gyre Exploration project (BGEP) in situ data. Our results show that SAMOSA+ provides more precise freeboard estimations. This new time-series is available on CTOH website. We also identified some impacts of the Hamming Window for both retrackers. Finally, we present the potential of using the simpler threshold retracker but with a correction to account for the surface roughness that is calibrated against SAMOSA+

Effective channel and ungauged braided river discharge estimation by assimilation of multi-satellite water heights of different spatial sparsity

Multi-satellite sensing of continental water surfaces (WS) represents an unprecedented and increasing potential for studying ungauged hydrological and hydraulic processes from their signatures, especially on complex ow zones such as multichannel rivers. However the estimation of discharge from WS observations only is a very challenging inverse problem due to unknown bathymetry and friction in ungauged rivers, measurements nature, quality and spatio-temporal resolutions regarding the flow (model) scales. This paper proposes an effective hydraulic modeling approach of sufficient complexity to describe braided river flows from sparse multisatellite observations using the HiVDI inverse method presented in Larnier et al. [42] with an augmented control vector including a spatially distributed friction law depending on ow depth. It is shown on 71km of the Xingu River (braided, Amazon basin) with altimetric water height time series that a fairly accurate upstream discharge hydrograph and effective patterns of channel bathymetry and friction can be infered simultaneously. The coherence between the sparse observation grid and the ne hydraulic model grid is ensured in the optimization process by imposing a piecewise linear bathymetry prole b(x), which is consistent with the hydraulic visibility of WS signatures (Garambois et al. [27], Montazem et al. [46]). The discharge hydrograph and effective bathymetry-friction patterns are retrieved from 8 years of satellite altimetry (ENVISAT) at 6 virtual stations (VS) along flow. Next, the potential of the forthcoming SWOT data, dense in space, is highlighted by infering a discharge hydrograph and dense patterns of effective river bathymetry and friction; a physically consistent definition of friction by reaches enabling to consider more dense bathymetry controls. Finally a numerical analysis of the friction term shows clear signatures of river bottom slope break in low flows and width variations in high flows which is consistent with the findings of Montazem et al. [46] from WS curvature analysis

Variational estimation of effective channel and ungauged anabranching river discharge from multi-satellite water heights of different spatial sparsity

International audienceMulti-satellite sensing of continental water surfaces (WS) represents an un precedented and increasing potential for studying ungauged hydrological and hydraulic processes from their signatures, especially on complex flow zones such as anabranching rivers. However the estimation of discharge from WS observations only is a very challenging, ill-posed, inverse problem due to unknown bathymetry and friction in ungauged rivers, measurements nature, quality and spatio-temporal resolutions regarding the flow (model) scales. This paper proposes an effective 1D hydraulic modelling approach of sufficient complexity to describe anabranching river flows from sparse multisatellite observations using the HiVDI inverse method presented in Larnier et al. (2019) with an augmented control vector including a spatially distributed friction law depending on the flow depth h. It is shown on 71 km of the Xingu River (anabranching, Amazon basin) with altimetric water height timeseries that a fairly accurate upstream discharge hydrograph and effective patterns of channel bathymetry and friction can be inferred simultaneously. The coherence between the sparse observation grid and the fine hydraulic model grid is ensured in the optimization process by imposing a piecewise linear bathymetry profile , which is consistent with the hydraulic visibility ofWS signatures (Garambois et al., 2017; Montazem et al., 2019). The discharge hydrograph Q(t) at observation times and effective bathymetry-friction patterns are retrieved from 8 years of satellite altimetry (ENVISAT) at 6 virtual stations (VS) along flow. Next, the potential of the forthcoming SWOT data, dense in space, is highlighted by inferring a discharge hydrograph and dense patterns of effective river bathymetry and friction; a physically consistent scaling of friction by reaches enables to consider more dense bathymetry controls. Finally a numerical analysis shows: (i) the importance of an unbiased prior information in the inference of a triplet from WS observations; (ii) the clear signatures of river bottom slope break in low flows and width variations in high flows, through the analysis of the friction slope term, which is consistent with the findings of Montazem et al. (2019) from WS curvature analysis

Inference of complex river channels parameters and distributed discharges from historical altimetric time series and forthcoming SWOT data

International audienc

Origins, Developments and Future of the Concept of Innovation: Opening the Economic Framing of Innovation to Social, Ethical, Political Parameters to Achieve Responsibility: Strengths and Limits

Part 1: Society, Social Responsibility, Ethics and ICTInternational audienceThe concept of innovation is making a successful comeback in philosophy, particularly with the qualifier “responsible” attached. This attachment of the qualification “responsible” reflects the idea that the concept of innovation has to be opened to new considerations, namely social, political and ethical concerns. Since the 18th century, innovation has been the object of economics and science of business and growth. This paper aims at testing the legitimacy of these attempts to open the concept and redefine it in terms other than those of economics. We start with a contextualization of the use of the term innovation, to see why it has been so strongly associated with the market, growth and business then we see what is at stake in opening it up to other considerations. We consider the limits of this opening and look at possible ways to attach other meanings to the concept, without losing significance by too much inclusion. The solution proposed is that instead of imposing new parameters and trying to shift the concept, we could keep the economic bias of the term, but challenge it with concerns expressed by people coming from the field of economics who are trying to propose an alternative framework for economics that would take into account other concerns, and in which responsible innovation could find a place