Estimating Snow Accumulation Of Dry Snow Zone Of Greenland From InSAR Correlation Observations
Abstract
In remote regions such as Greenland and Antarctica snow accumulation is a key factor and is often estimated from radar brightness or reflectivity. ~Because ice is semi-transparent to microwave radiation, radar observations of the ice sheets reveal the structure of the top 10's of meters of firn when interpreted using electromagnetic scattering models. ~Previous microwave approaches have used radar reflectivity or emissivity measurements to obtain snow grain sizes, which are then related to accumulation rate.~But reflectivity and emissivity depend not only on grain size, but also on the thickness of annual layers in the top few meters of firn.~A radar image may appear bright because grain size is large, implying slow accumulation, or because the annual layers are thick, implying high accumulation. ~Using InSAR measurements of both reflectivity and correlation permits solution for both the layer thickness and the grain size at depth, hence the ambiguity in the brightness measurements is avoided. In situ ice core stations are sparse in these areas and maps derived by these data are not completely accurate. We have developed an interferometric ice scattering model that relates InSAR correlation and reflectivity to ice grain size and layer spacing, and can be used to invert the radar observations. Our model is a buried layer model including volume scatter and the incoherent addition of echoes from hoar layer interfaces, in which the scattering from a single layer is found by small-perturbation methods. Accumulation rates derived by our improved method showed superior agreement with in situ core measurements for a small area in the dry snow zone of Greenland, while other models using only reflectivity data match poorly. Here we apply our method for estimating snow accumulation rates to a larger area of Greenland. We need to estimate both surface and volume scattering to predict the accumulation rate in the dry snow zone of Greenland more accurately. Examining the variation of the backscattered power with range, we note a 2-3dB variation for ERS data. For larger incidence angles, as for these RADARSAT-1 data surface scatter is less and the variation is less. Since volume scattering does not change significantly for different incidence angles, we conclude that surface scattering affects the backscattered power for ERS data. New data sets are ordered to cover each base station with two different incidence angles in order to get a better estimate of the surface scattering of that area. Raw ERS1-2 tandem pair data acquired from the European Space Agency, collected between January and February of 1996, has been processed. Accumulation rates for the dry snow zone are derived by applying our new model to radar reflectivity and correlation of these C-band ERS1-2 data. The high resolution map derived from insar remote sensing data leads to an accurate and detailed map of accumulation. Comparison of our model inversion results and in situ core measurements for this large area will show whether our new method is applicable to the entire Greenland dry snow zone.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2006
- Bibcode:
- 2006AGUFM.C41E..06O
- Keywords:
-
- 0736 Snow (1827;
- 1863);
- 0758 Remote sensing;
- 0768 Thermal regime;
- 0798 Modeling;
- 1827 Glaciology (0736;
- 0776;
- 1863)