2012 AGU Chapman Conference on Remote Sensing of the ...

grain size evolution and implications for remote sensing ofsnow mass will be discussed.SANTOS DA SILVA, JoecilaALTIMETRY OF THE AMAZON BASIN RIVERSSANTOS DA SILVA, Joecila 1 ; Calmant, Stéphane 2 ; Seyler,Frédérique 3 ; Moreira, Daniel M. 2, 41. Centro de Estudos do Trópico Úmido – CESTU,Universidade do Estado do Amazonas – UEA, Manaus,Brazil2. UMR 5566 LEGOS CNES/CNRS/IRD/UT3, Institut deRecherche pour le Développement – IRD, Toulouse,France3. UMR ESPACE-DEV, Institut de Recherche pour leDéveloppement – IRD, Montpellier, France4. Universidade Federal do Rio de Janeiro - UFRJ, Rio deJaneiro, BrazilAltimetry of rivers all along their course is majorinformation in hydrology, whatever it is for runninghydrological model, determine the amount of surface waterstored, and predict the consequences of extreme events.Satellite altimetry can be used in many ways to retrieveconsistent altimetry information throughout the course ofrivers. Now, it is now well known as a useful tool to retrievethe space and time variations of the water surface. Besidesthis basic use of satellite altimetry, it can also be used to: 1/level gauges, so making a consistent dataset merging hightemporal sampling from gauges and dense sampling fromthe crossings between satellite tracks and river network; 2/densify climatic series (mean value per month of the year) allalong the river course when series are long enough and, bycomparison with time series, evidence extreme events; 3/detail the altitudinal changes of the river course which, whencompared to a DTM, inform over the basin hypsometry; 4/level bathymetric profiles in order to obtain altitudinalchanges of the river bed; 4/ check for errors in the gaugeseries or in the metadata information related to a gauge. Inthe present study, we present examples of such applicationsof satellite altimetry for the major contributors of theAmazon basins. In this basin, more than 500 series havebeen computed from the ERS2 & ENVISAT missions in theone hand (1995-2010) and from the T/P & JASON2 missionsin the other hand (1992-2002 / 2008-). All series have beencarefully checked manually and we present statistics ofcomparison with ground-truth, i.e. water levels from GPSleveledgauges. Rivers of very different widths have beensampled, ranging from several km wide to less than 100mwide. For some of the rivers, altimetry series are the onlypossibility to get stage and slope information since theserivers are devoid of in-situ measurement or themeasurements are not available, in particular out of Brazil.Schroeder, Dustin M.Remote Sensing of Subglacial Water Networks withIce Penetrating RadarSchroeder, Dustin M. 1 ; Blankenship, Donald D. 1 ; Young,Duncan A. 11. University of Texas Institute for Geophysics, Austin, TX,USAThe subglacial water systems beneath outlet glaciers ofcontinental marine ices sheets is an important and difficultto constrain control on ice sheet mass balance and sea levelrise estimates and their role in the global hydrologic cycle.The net subglacial water flux is the dominant unknown inreconciling satellite gravity and inSAR derived surfacevelocity measurements of ice sheet mass balance. It is also akey parameter in predicting sub-ice-shelf circulation andcollapse as well as glacial surge and retreat initiated by thedynamics of subglacial lakes. Successfully modeling thesephenomena and their effects requires understanding notonly the locations of individual subglacial lakes andconduits but the entire subglacial hydrologic network. Sincedirect observations of the basal hydrology of ice sheets areboth extremely limited in area and prohibitively expensive(e.g. drilling, seismic), airborne radar sounding is the onlypractical means of acquiring basin-scale observations ofsubglacial water systems. Airborne ice penetrating radarsounding has been used with variable success to identify andcharacterize basal water systems and their sedimentarycontext by the strength of the return from the basalinterface. Specularity is a parameterization of the angularitydependent echo intensity that measures how tightly or“mirror-like” the energy is distributed with observing angle.The specularity of the basal return can indicate the presence,extent, and configuration of subglacial water and sedimentindependent of the temperature profile and impurityconcentration of the ice column, which complicatetraditional amplitude based interpretations. We use multipleradar focusing windows to produce a basal specularity mapfrom a gridded aerogeophysical survey of West Antarctica’sThwaites Glacier catchment (over 150,000 square kilometers)using a 60 MHz coherent ice penetrating radar with a 15MHz bandwidth linear frequency modulated waveform. Wefind that regions of high specularity correlate with modeledhydrologic pathways and indicate an extensive water networkbetween the ice and bed. We demonstrate how variations inthe strength of the specularity signal with the survey-line towater-flow-path angle can be used to constrain the size,geometry and flow-regime of the water system using physicaloptics.Using these results, we present an interpretation ofthe basal hydrology and morphology of Thwaites Glacier inthe context of the hydrologic gradient, surface slope,inferred basal melt, and inferred basal shear stress. Thisinterpretation provides insights into the current andpotential role of subglacial water in the Thwaites Glaciersystem and demonstrates the ability of specularity analysisto provide information about the basal boundary conditionat a scale that is inaccessible to traditional amplitude basedradio echo sounding analysis.130