Using deep learning to model elevation differences between 2 radar and laser altimetry

peer reviewedSatellite and airborne observations of surface elevation are critical in understanding climatic and glaciological processes and quantifying their impact on changes in ice masses and sea level contribution. With the growing number of dedicated airborne campaigns and experimental and operational satellite missions, the science community has access to unprecedented and ever-increasing data. Combining elevation datasets allows potentially greater spatial-temporal coverage and improved accuracy; however, combining data from different sensor types and acquisition modes is difficult by differences in intrinsic sensor properties and processing methods. This study focuses on the combination of elevation measurements derived from ICESat-2 and Operation IceBridge LIDAR instruments and from CryoSat-2’s novel interferometric radar altimeter over Greenland. We develop a deep neural network based on sub-waveform information from CryoSat-2, elevation differences between radar and LIDAR, and additional inputs representing local geophysical information. A time series of maps are created showing observed LIDAR-radar differences and neural network model predictions. Mean LIDAR vs. interferometric radar adjustments and the broad spatial and temporal trends thereof are recreated by the neural network. The neural network also predicts radar-LIDAR differences with respect to waveform parameters better than a simple linear model; however, point level adjustments and the magnitudes of the spatial and temporal trends are underestimated

Prise en charge et coûts de la bronchopneumopathie chronique obstructive en France en 2011

RésuméIntroductionCette étude vise à estimer une prévalence de la bronchopneumopathie chronique obstructive (BPCO) traitée et les coûts associés par degré de sévérité.MéthodeElle a été conduite sur les données 2011 de l’échantillon généraliste de bénéficiaires (EGB). Cet échantillon représente 1/97e des bénéficiaires des principaux régimes d’assurance maladie obligatoire. Les cas et leur sévérité ont été identifiés à partir d’algorithmes originaux. Les coûts ont été établis dans une perspective collective.RésultatsLe taux de prévalence minimale de la BPCO traitée a été estimé à 3,8 % dans la population âgée de 40ans et plus, et 1,9 % tous âges confondus. La population (58,2 % d’hommes) avait 68,8±12,7ans d’âge moyen. Au total, 6,2 % des patients ont eu des consommations de soins évocatrices d’un stade très sévère, 8,1 %, 13,8 % et 71,9 % d’un stade sévère, modéré ou peu sévère. Sur une année, 28,8 % ont consulté un pneumologue, 5,0 % ont été hospitalisés (≥24h) pour BPCO et 6,7 % sont décédés. En moyenne, les patients ont eu 1,7±1,5 exacerbations/an et seulement 61,4 % ont reçu un traitement médicamenteux spécifique. La consommation annuelle moyenne de soins d’un patient a été estimée à 9382€ dont 5516€ attribuable à la BPCO.ConclusionCette étude utilisant des bases de données médico-administratives confirme l’importance du fardeau épidémiologique et économique de la BPCO en France.SummaryObjectivesTo estimate the prevalence of treated chronic obstructive pulmonary disease (COPD) and its associated costs by stage of severity.MethodsThe study was conducted on the 2011 data of the french general beneficiary sample database (EGB). EGB is a 1/97th sample of the whole population of the beneficiaries of the main compulsory national health insurances. COPD cases and the level of severity of the disease have been identified using new algorithms established from the available parameters in EGB. Costs were estimated using a collective perspective.ResultsThe minimal prevalence of treated COPD was estimated at 3.8% in patients of 40 years and older and 1.9% regardless of the age of individuals. This population was predominantly male (58.2%) with a mean age of 68.8 years (±12.7). A total of 6.2% of patients had a health-care utilization suggestive of a very severe stage of COPD and 8.1%, 13.8% and 71.9% suggestive of severe, moderate and mild stages respectively. Over one year, 28.8% of patients visited a specialist respiratory physician, 5.0% were hospitalized (≥24h) for COPD and 6.7% died. Patients experienced an average of 1.7 (±1.5) exacerbations per year and only 61.4% received specific pharmacological treatment for COPD during the year. The average yearly health-care cost of a patient with COPD was estimated at €9382, with €5342 directly related to COPD.ConclusionThis study based on medico-administrative databases confirms the high epidemiological and economic burden of COPD in France

Estimating spring terminus submarine melt rates at a greenlandic tidewater glacier using satellite imagery

Oceanic forcing of the Greenland Ice Sheet is believed to promote widespread thinning at tidewater glaciers, with submarine melting proposed as a potential trigger of increased glacier calving, retreat, and subsequent acceleration. The precise mechanism(s) driving glacier instability, however, remain poorly understood, and while increasing evidence points to the importance of submarine melting, estimates of melt rates are uncertain. Here we estimate submarine melt rate by examining freeboard changes in the seasonal ice tongue of Kangiata Nunaata Sermia (KNS) at the head of Kangersuneq Fjord (KF), southwest Greenland. We calculate melt rates for March and May 2013 by differencing along-fjord surface elevation, derived from high-resolution TanDEM-X digital elevation models (DEMs), in combination with ice velocities derived from offset tracking applied to TerraSAR-X imagery. Estimated steady state melt rates reach up to 1.4 ± 0.5m d-1 near the glacier grounding line, with mean values of up to 0.8 ± 0.3 and 0.7 ± 0.3m d-1 for the eastern and western parts of the ice tongue, respectively. Melt rates decrease with distance from the ice front and vary across the fjord. This methodology reveals spatio-temporal variations in submarine melt rates (SMRs) at tidewater glaciers which develop floating termini, and can be used to improve our understanding of ice-ocean interactions and submarine melting in glacial fjords.Publisher PDFPeer reviewe

Evolution of supraglacial lakes on the Larsen B ice shelf in the decades before it collapsed

The Larsen B ice shelf collapsed in 2002 losing an area twice the size of Greater London to the sea (3,000 km 2), in an event associated with widespread supraglacial lake drainage. Here we use optical and radar satellite imagery to investigate the evolution of the ice shelf's lakes in the decades preceding collapse. We find (1) that lakes spread southward in the preceding decades at a rate commensurate with meltwater saturation of the shelf surface; (2) no trend in lake size, suggesting an active supraglacial drainage network which evacuated excess water off the shelf; and (3) lakes mostly refreeze in winter but the few lakes that do drain are associated with ice breakup 2–4 years later. Given the relative scale of lake drainage and shelf breakup, however, it is not clear from our data whether lake drainage is more likely a cause, or an effect, of ice shelf collapse

Assimilation of Antarctic velocity observations provides evidence for uncharted pinning points

International audienceIn ice flow modelling, the use of control methods to assimilate the dynamic and geometric state of an ice body has become common practice. These methods have primarily focussed on inverting for one of the two least known properties in glaciology, namely the basal friction coefficient or the ice viscosity parameter. Here, we present an approach to infer both properties simultaneously for the whole of the Antarctic ice sheet. After the assimilation, the root-mean-square deviation between modelled and observed surface velocities attains 8.7 m a −1 for the entire domain, with a slightly higher value of 14.0 m a −1 for the ice shelves. An exception in terms of the velocity mismatch is the Thwaites Glacier Ice Shelf, where the RMS value is almost 70 m a −1. The reason is that the underlying Bedmap2 geometry ignores the presence of an ice rise, which exerts major control on the dynamics of the eastern part of the ice shelf. On these grounds, we suggest an approach to account for pinning points not included in Bedmap2 by locally allowing an optimisation of basal friction during the inversion. In this way, the velocity mismatch on the ice shelf of Thwaites Glacier is more than halved. A characteristic velocity mismatch pattern emerges for unaccounted pinning points close to the marine shelf front. This pattern is exploited to manually identify seven uncharted features around Antarctica that exert significant resistance to the shelf flow. Potential pinning points are detected on Fimbul, West, Shackleton, Nickerson and Venable ice shelves. As pinning points can provide substantial resistance to shelf flow, with considerable consequences if they became ungrounded in the future, the model community is in need of detailed bathymetry there. Our data assimilation points to some of these dynamically important features not present in Bedmap2 and implicitly quantifies their relevance

d=2, N=2 Superconformal Symmetries and Models

We discuss the following aspects of two-dimensional N=2 supersymmetric theories defined on compact super Riemann surfaces: parametrization of (2,0) and (2,2) superconformal structures in terms of Beltrami coefficients and formulation of superconformal models on such surfaces (invariant actions, anomalies and compensating actions, Ward identities).Comment: 43 pages, late

Subglacial controls on dynamic thinning at Trinity-Wykeham Glacier, Prince of Wales Ice Field, Canadian Arctic

Mass loss from glaciers and ice caps represents the largest terrestrial component of current sea level rise. However, our understanding of how the processes governing mass loss will respond to climate warming remains incomplete. This study explores the relationship between surface elevation changes (dh/dt), glacier velocity changes (du/dt), and bedrock topography at the Trinity-Wykeham Glacier system (TWG), Canadian High Arctic, using a range of satellite and airborne datasets. We use measurements of dh/dt from ICESat (2003-2009) and CryoSat-2 (2010-2016) repeat observations to show that rates of surface lowering increased from 4 m yr-1 to 6 m yr-1 across the lowermost 10 km of the TWG. We show that surface flow rates at both Trinity Glacier and Wykeham Glacier doubled over 16 years, during which time the ice front retreated 4.45 km. The combination of thinning, acceleration and retreat of the TWG suggests that a dynamic thinning mechanism is responsible for the observed changes, and we suggest that both glaciers have transitioned from fully grounded to partially floating. Furthermore, by comparing the separate glacier troughs we suggest that the dynamic changes are modulated by both lateral friction from the valley sides and the complex geometry of the bed. Further, the presence of bedrock ridges induces crevassing on the surface and provides a direct link for surface meltwater to reach the bed. We observe supraglacial lakes that drain at the end of summer and are concurrent with a reduction in glacier velocity, suggesting hydrological connections between the surface and the bed significantly impact ice flow. The bedrock topography thus has a primary influence on the nature of the changes in ice dynamics observed over the last decade.</p

The Minimal Supersymmetric Standard Model: Group Summary Report

CONTENTS: 1. Synopsis, 2. The MSSM Spectrum, 3. The Physical Parameters, 4. Higgs Boson Production and Decays, 5. SUSY Particle Production and Decays, 6. Experimental Bounds on SUSY Particle Masses, 7. References.Comment: 121 pages, latex + epsfig, graphicx, axodraw, Report of the MSSM working group for the Workshop "GDR-Supersym\'etrie",France. Rep. PM/98-4