Initial results from the NASA SnowEx 2020 L-Band campaign at Cameron Pass, Colorado

Abstract:

A principal component of the NASA SnowEx 2020 project was an airborne UAVSAR L-band InSAR time-series campaign at 13 sites across five states in the western United States. The primary objective was to evaluate the use of repeat SAR acquisitions to measure changes in snow water equivalent (SWE). Here, we present initial results for one of these 13 sites: Cameron Pass, a ~3100 m pass in north-central Colorado. Ground-based validation efforts included snow pits (stratigraphy, depth, density, grain size, temperature) and snow depth derived from manual probes along pre-determined ~300 m transects that crossed both open meadows and dense forests. In addition to these core observations, we collected repeat 1 GHz (L-Band) ground-penetrating radar (GPR) surveys to measure changes in travel-time (and SWE), and repeat drone-based Structure from Motion (SfM) and terrestrial lidar surveys for changes in distributed snow depth between flight intervals. Initial results show strong agreement between the various in situ methods, including probe-GPR (Figure 1a) and SfM-GPR derived snow depths (Figure 1b; snow depths shown for March 12, 2020). This analysis specifically focuses on the change in SWE between each of the five UAVSAR flights (Feb. 1, Feb. 12, Feb. 19, Feb. 26, and March 12, 2020), which coincided with a ~25 cm cumulative increase in SWE along our transects (Figure 1c). Preliminary UAVSAR results demonstrate that coherence was maintained at both 7- and 22-day intervals, particularly in open meadows. The unwrapped phase change showed positive correlation with GPR-observed SWE changes, with the best agreement at HV polarization.