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

Cherry, Jessica E.Advances in Airborne Remote Sensing ofHydrologic Change in Cold RegionsCherry, Jessica E. 11. IARC 408, University of Alaska Fairbanks and NorthernScience Services, Fairbanks, AK, USASeveral challenges face the study of hydrologic change incold regions from remote sensing, including the relativelylow-resolution of commonly used satellite products such asMODIS snow covered area. Higher resolution products, inthe case of TerraSAR, are costly—in part because there is nocurrent U.S. Synthetic Aperture Radar (SAR) satellitemission. Airborne remote sensing can lower costs andincrease resolution, relative to current satellite products.This presentation will review advances made possible by thefalling costs of high quality airborne sensors, as well as newcapabilities of automated software. Examples will be shownfrom different cold region hydrologic applications usingairborne techniques: use of forward-looking infrared todetect ground water contributions to runoff, use of opticalimagery for snow melt and water equivalent estimates,multispectral imagery for wetland delineation, and use ofoptical and SAR for estimating liquid water resources duringthe cold season.Chew, ClaraUSING GPS INTERFEROMETRICREFLECTOMETRY TO ESTIMATE SOILMOISTURE FLUCTUATIONSChew, Clara 1 ; Small, Eric 1 ; Larson, Kristine 2 ; Zavorotny,Valery 31. Geological Sciences, University of Colorado Boulder,Boulder, CO, USA2. Aerospace Engineering, University of Colorado Boulder,Boulder, CO, USA3. NOAA, Boulder, CO, USAHigh-precision GPS receivers can be used to estimatefluctuations in near surface soil moisture. This approach,referred to as GPS-Interferometric Reflectometry (GPS-IR),relates precise changes in the geometry of reflected GPSsignals to estimate soil moisture. Standard GPS antennaconfigurations, for example that used in NSF’s PlateBoundary Observatory network, yield sensing footprints of~1000 m2. Previous remote sensing research has shown thatmicrowave signals (e.g., L-band) are optimal for measuringhydrologic variables, such as soil moisture. GPS satellitestransmit similar signals and therefore are useful for sensingwater in the environment. Given this sensitivity, hundreds ofGPS receivers that exist in the U.S. could be used to providenear-real time estimates of soil moisture for satellitevalidation, drought monitoring and related studies. We haveestablished nine research sites with identical GPS andhydrologic infrastructure to study this problem. These sitesspan a wide range of soil, vegetation, and climate types. Inaddition to daily GPS and hourly soil moisture data, we havecollected weekly vegetation water content samples at all sites.Our data demonstrate that soil moisture fluctuations can beestimated from GPS-IR records with RMSE < 0.04. GPS-IRmetrics are best correlated with soil moisture data from thetop of the soil column (2.5 cm). Soil moisture estimates areless reliable when vegetation water content exceeds 2 kg m-2.A similar problem exists when using other L-band signals forremote sensing of soil moisture. Results from a forwardmodel show that the phase, amplitude, and frequency of thereflected signal are sensitive to soil moisture regardless ofsoil type. The same model suggests that the L-band signal ismost strongly affected by the surface soil moisture. Weoutline different approaches for separating the soil moistureand vegetation signals and quantifying errors in our retrievalalgorithm.Cohen, SagyCalibration of Orbital Microwave Measurements ofRiver Discharge Using a Global Hydrology ModelCohen, Sagy 1 ; Brakenridge, G. R. 1 ; Kettner, Albert J. 1 ;Syvitski, James P. 1 ; Fekete, Balázs M. 2 ; De Groeve, Tom 31. CSDMS, INSTAAR, University of Colorado, Boulder, CO,USA2. CUNY Environmental CrossRoads Initiative, NOAA-CREST Center, The City College of New York, CityUniversity of New York, New York, NY, USA3. Joint Research Centre of the European Commission,Ispra, ItalyReliable and continuous measurement of river dischargeis crucial for calculating terrestrial water cycle budgets(including surface water storage) and flux of water andsediment to the oceans. It also has numerous practicalapplications in addressing the increasingly urgent waterneeds for the expanding global population. Previous workdemonstrates that orbital passive microwave instruments(such as AMSR-E – now out of operation – and TMI) havethe capability to measure river discharge variation on a dailybasis, and thereby help address major limitations in groundbasedgaging of global rivers. Its potential is largelyuntapped. While future satellite missions are being plannedto retrieve less frequent discharge measurements, viaaltimetry, on an experimental basis, for a limited missionduration, the data from the present internationalconstellation of sensors that provide sustained observationshould be more fully utilized. Our strategy is to use existingdata streams that directly monitor discharge, and to couplesuch data to increasingly sophisticated global runoff models.This allows the needed calibration of remote sensing signalto (m3/s) discharge units (or catchment runoff in mm), andalso the possibility to improve the models. In many regions,ground-based discharge data are non-existing, or not freelyshared, or have only intermittent periods of record. Inothers, abundant ground-based data are available to providerigorous tests of the accuracy and precision of orbitalmeasurements and our calibration methods. In the latterlocations (e.g. within the U.S.), the use of modeling tocalibrate remote sensing discharge measurements is47