Speaker
Description
The effects of variable terrain within a SAR image often dominate the backscatter signature, as the phenomenon of radar foreshortening is much stronger than radiometric distortions seen in aerial photography or satellite images obtained with optical instruments. Radiometric terrain correction (RTC) makes use of a digital elevation model (DEM) to simulate the radar imaging geometry and correct for the modeled effects on radar backscatter. RTC backscatter products are therefore simpler to interpret across time, esp. in the presence of variable viewing geometries, beam-modes, or even sensors.
We combine multiple level 1 RTC products, by employing the image simulations originally put to use for the terrain corrections a second time, to enable the generation of multi-track wide-area backscatter composite images. The image simulations are “local imaged area” estimates in radar geometry. The reciprocal of the “local imaged area” is the local resolution. By weighing contributions to the composite by the local resolution, the observations made with the best geometry (i.e. down a mountain’s non-shadowed back slope) are given the highest weights. All observations made within a set date range are processed to RTC level and then combined with local resolution weighting into a single composite backscatter map. The process is then repeated over a series of sliding time-windows. The resulting seamless composites enable change detection over wide areas, unrestricted by swath-size.
Using Sentinel-1 data, we demonstrate application of the technique over multiple regions, from the Alps to the Arctic, at medium resolution (400m), and at full sensor resolution (20m). We illustrate multi-sensor integration with C-band composites generated by combining Radarsat-2 and Sentinel-1 data. We demonstrate wide-area wet snow mapping, sea ice melt-onset detection, and forest-type mapping, all using wide-area backscatter composites as their basis. We conclude with an outlook to upcoming possibilities given combination of Sentinel-1 with Radarsat-Constellation-Mission data.
Summary
Use of level 3 radar backscatter products with seamless wide-area coverage is demonstrated for multiple applications.
