SWE Retrieval Performance from X and Ku-Band Airborne SAR During SnowEx 2017

NASA’s SnowEx campaigns were initiated to provide multi-sensor snow data for algorithm development and satellite mission concept development. Since half of the seasonally snow covered world is forested, the first SnowEx campaign in 2017 was designed to collect multi-sensor observations to enable evaluation of snow water equivalent (SWE) retrieval accuracy in an environment that included the confounding effects of forest cover. The primary Grand Mesa site in Colorado was selected for the 2017 SnowEx campaign to challenge the sensing techniques with varying amounts of forest canopy conditions and for the general lack of other confounding factors, such as complex terrain.

This study focuses on the ability of the airborne SnowSAR observations at X- and Ku-bands to retrieve SWE. SnowSAR is a European sensor, flown on a US P-3 aircraft to collect radar backscatter observations. Extensive snow ground truth was also collected both in forested areas and in clearings to enable the evaluation of SWE retrieval accuracy. In addition to providing valuable field data, the unexpected relatively high-SWE conditions (450-750 mm) encountered in 2017 led to the demonstration that X and Ku-band sensitivity to SWE remained even for such high values. Recent results have also shown that retrieval accuracy degrades gradually with increasing forest cover. Together, this means the X/Ku retrievals should work over a wider range of snow and denser forest cover conditions than previously expected—a plus for a global satellite mission concept.

We will show detailed examples of SnowSAR data for varying forest cover areas, non-forested areas, and for dry vs. non-dry snow conditions. Combined with snow ground truth data and high-resolution optical imagery, this will highlight the sensor capabilities and limitations across the conditions experienced during SnowEx 2017. SWE retrieval performance will be examined in relation to the conditions to further explore the strengths and limitations of volume scattering-based retrievals in the context of a satellite mission that addresses the global snow observation goals of the 2017 Earth Science Decadal Survey.