Monitoring ice shelf velocities from repeat MODIS and Landsat data – a method study on the Larsen C ice shelf, Antarctic Peninsula, and 10 other ice shelves around Antarctica

摘要

We investigate the velocity field of the Larsen C ice shelf, AntarcticPeninsula, over the periods 2002–2006 and 2006–2009 based on repeat opticalsatellite data. The velocity field of the entire ice shelf is measured usingrepeat low resolution MODIS data (250 m spatial resolution). Themeasurements are validated for two ice shelf sections against repeat mediumresolution Landsat 7 ETM + pan data (15 m spatial resolution).Horizontal surface velocities are obtained through image matchingusing both orientation correlation operated in the frequency domain and normalized crosscorrelationoperated in the spatial domain, and the two methods compared. The uncertainty in thedisplacement measurements turns out to be about one fourth of the pixel size for the MODISderived data, and about one pixel for the Landsat derived data. Thedifference between MODIS and Landsat based speeds is −15.4 m a−1and 13.0 m a−1, respectively, for the first period for the twodifferent validation sections on the ice shelf, and −26.7 m a−1 and27.9 m a−1 for the second period for the same sections. This leadsus to conclude that repeat MODIS images are well suited to measure ice shelfvelocity fields and monitor their changes over time. Orientationcorrelation seems better suited for this purpose because itproduces fewer mismatches, is able to match images with regularnoise and data voids, and is faster. Since it can match imageswith regular data voids it is possible to match Landsat 7 ETM+images even after the 2003 failure of the Scan Line Corrector (SLC off) thatleaves significant image stripes with no data. Image matching based on theoriginal 12-bit radiometric resolution MODIS data produced slightly betterresults than using the 8-bit version of the same images. Streamlineinterpolation from the obtained surface velocity field on Larsen C indicatesice travel times of up to 450 to 550 years between the inland boundary and theice shelf edge. In a second step of the study we test our method successfullyon 10 other ice shelves around Antarctica demonstrating that the approachpresented could in fact be used for large scale monitoring of ice shelfdynamics.