Ice Sheets and Landsat

1、Ice Sheets and LandsatRobert BindschadlerNASA Goddard SFCSome Cold Hard Facts Ice Sheets 10% of land area is ice covered Sea Level Ice sheets hold 70 meters of sea level equivalent Variation of Sea Level -125 meters to +5 meters Rate of Sea Level Change 3 mm/yr. (50% rate increase in last decade)Lan

2、dsat Image Mosaic of Antarctica1131 Landsat scenes (+ 2 ASTER)circa 2000Summer 2007 completion dateLandsat tells Glaciologists about: Coastal change Calving Surface velocity Elevation Change in elevationIce Measurements with Landsat Coastal change Calving Surface velocity Elevation Change in elevati

3、onElevation? Ice sheet surface: Nearly constant albedo Diffusive reflector Image brightness becomes a slope map (in direction of solar illumination) +1 DN = + 8 cm across a 15-m pixel Slopes used to interpolate elevations between control elevation profilesChecking Digital Elevation Models with Shade

4、d Relief Images100 kmICESat elevation precision = +20 cmICESat Digital Elevation ModelLandsat gives the “right” answer30 kmLandsat-730 kmICESat DEMImage-based slopes can provide an accurate interpolationICESat tracksNew ScienceConway RidgeEngelhardt RidgeWhillans Ice Stream (B)Mercer Ice Stream (A)M

5、OA (NSIDC)Repeat-pass elevation changes are revealing subglacial water movementElevation range 2003-06 (m) 0 9mSubglacial Lake EngelhardtImage Contributions to New Science of Subglacial Hydrology1. Image-derived slopes to adjust elevation to reference trackRepeat tracks are close and parallel, but N

6、OT exact repeatsSpatial (cross-track) elevation differences can be confused with temporal elevation differences2. Image differencing to show spatial extentObserved Ground Track Footprint Location:Reference Ground Track:1. Image-based Profile Adjustment30oreference profilemeasured profilesSunNo adjus

7、tmentLatitudeElevation (m)Adjusted profiles shifted along trackLatitudeElevation (m)Adjustment to Reference TrackElevation Difference (m)2. Image DifferencingImagesImage DifferencesRadiometric resolution is critical to success8-bit data wont suffice Conclusions Landsat data continue to be used in new, innovative ways by glaciologists The most important