L-band InSAR SWE retrievals over Northern Colorado

During the NASA SnowEx Time Series campaigns, NASA UAVSAR was tasked to acquire weekly to bi-weekly SAR imagery over the Never Summer Mountains and Medicine Bow Mountains of northern Colorado, near Cameron Pass. In 2020, three InSAR pairs were collected spanning 12 February to 12 March, coinciding with 117 mm of snow water equivalent (SWE) accumulation at the Joe Wright SNOTEL station (ID = 551) or about 18% of peak SWE. In 2021, eight InSAR pairs were collected from 15 January to 22 March, coinciding with 282 mm of SWE accumulation at the SNOTEL station or about 48% of peak SWE. The UAVSAR flightline was ~40 km long with a swath width of 16 km. The primary flight heading was southeast (141°), with a secondary northwest heading (321°) flown when time allowed. To produce this dataset, we used the 141° heading for all InSAR pairs except the 27 January to 3 February 2021 interval, which used the 321° heading. Associated NASA UAVSAR interferograms are archived with the Alaska Satellite Facility (Flight ID = Rocky Mountains NP, Colorado). This data set contains derived changes in SWE (ΔSWE), calculated using methods following Guneriussen et al. (2001), from the associated UAVSAR flights.

Methods
Detailed methods can be found in the associated publication (Bonnell et al., 2024). Changes in SWE (ΔSWE) were calculated following Guneriussen et al. (2001), which requires phase changes, local incidence angles, and relative permittivity. Phase changes were obtained from the UAVSAR unwrapped interferograms, local incidence angles were calculated in uavsar_pytools from the Copernicus DEM and UAVSAR look vectors, and relative permittivity was calculated from the mean snow surface density measured on snow accumulation boards. Finally, interferograms were calibrated to absoluate ΔSWE by subtracting the median difference between UAVSAR ΔSWE and ΔSWE calculated from a group of ground observations.