An Airborne Mission Simulator at X- and Ku-bands driven by SnowEx 2017 Data

Extensive airborne and ground measurements were deployed in February 2017 in Grand Mesa, Colorado supported by NASA Terrestrial Hydrology Program, entitled with NASA SnowEx - a multi-year airborne campaign for SWE retrieval. To meet one of the objectives lied on SnowEx Year 1 campaign with 'evaluating SWE retrieval performances in a vegetated region', it is imperative to characterize the entire year of the snow evolutions associated with microwave observations. Recent developments regarding microwave volume scattering approach suggest a promise to retrieve a relevant SWE estimation by using both active and passive microwave observations. To evaluate this optimism in SnowEx 2017, ESA (European Space Agency) SnowSAR was mounted in one of the aircrafts in February 2017. Owing to limitations on technical and managerial issues on airborne managements, SnowSAR scanned the Grand Mesa only one single day. To fill this gap of the single flight line, and to provide data to validate and improve SWE retrieval algorithms, this paper constructs SnowSAR backscattering coefficients at X- and Ku bands during the entire snow season along dedicated flight lines in Grand Mesa CO.

The simulator starts from a snow physics model driven by weather forcing dataset at Grand Mesa. Then, the outputs of the snow physics model drive DMRT, one of the representative microwave forward simulator to produce both Tb and backscattering coefficient, forming snowpack-microwave signatures along the snow year. Modeling calibrations will be simultaneously conducted by using abundant ancillary datasets from SnowEx including JPL Airborne Observatory, a set of ground-based terrestrial lidar measurements, and satellite observations including JAXA AMSR2 and PALSAR. The simulation results from DMRT will be validated against both snow physics against snowpit measurements and microwave observations from a variety of ground-based microwave sensors equipped in SnowEx 2017.

A single flight line is tested to apply the forward simulator and it is extended to cover an entire flight box. Also, non-vegetated regions is first assumed and extended to the vegetation coverage to evaluate the influence of vegetation toward microwave signatures. A comprehensive set of simulations both for snow physics and microwave signatures thus serves a virtual mission of SnowSAR to fill the gap associated with the limited deployments of the airborne campaign in SnowEx 2017.