Observation and Characterization of Radar Backscatter Over Greenland.

Characterization of the microwave signature of the Greenland snow surface enables delineation of the different snow facies and is a tool for tracking the effects of climate change. A new empirical observation model is introduced that uses a limited number of parameters to characterize the snow surface based on the dependence of radar backscatter on incidence angle, azimuth angle, spatial gradient, and temporal rate of change. The individual model parameters are discussed in depth with examples using data from the NASA Scatterometer (NSCEF) and from the C-band European Remote Sensing satellite (ERS) Advanced Microwave Instrument in scatterometer mode. The contribution of each model term to the overall accuracy of the model is evaluated. The relative contributions of the modeled dependencies vary by region. Two studies illustrating applications of the model are included. First, interannual changes over the Greenland ice sheet are investigated using nine years of ERS data. Surface changes are observed as anomalies in the σ° model parameters. Second, intra- annual variations of the surface are investigated. These changes are observed in the average backscatter normalized to a given observation geometry. The results indièate that the model can be used to obtain a more complete understanding of multiyear change and to obtain low-variance high temporal resolution Observations of intraannual changes. The model may be applied for increased accuracy in scatterometer, synthetic aperture radar (SAR), and wide- angle SAR studies. [ABSTRACT FROM AUTHOR]