Western US Time Series (TS)
Rather than only one focused multi-week effort in one small area, as was done in the 2017 SnowEx Campaign (SnowEx17), SnowEx2020 activities encompass Winter 2019-2020 over the western United States. The time series approach leverages local experienced field observers and sites with ongoing snow measurements, allowing for increased temporal and expansive investigation within the constraints of a smaller budget than SnowEx17. SnowEx2020’s campaign incorporated over 100 scientists from over 20 government organizations and universities. Moreover, several data collection participants were trained during the 6th NASA/CUAHSI Snow School.
The Time Series campaign will focus on calibration and validation of a new SWE retrieval approach using L-band InSAR, leveraging the NASA JPL airborne UAVSAR. While this NASA asset has been used primarily for studying vegetation structure, and surface deformation due to earthquakes and volcanic activity, the change in phase from this sensor can be related to changes in snow depth and SWE. There have been few studies using L-band InSAR for measuring snow depth and SWE [e.g. Deeb et al, 2013; Gunnerison et al, 2001], largely due to the dynamics of the seasonal snow cover, which require repeat intervals on the order of weeks. Current spaceborne InSAR systems have repeat frequencies of 90 days, however the upcoming 2022 launch of NISAR provides an exciting opportunity for snow monitoring (11-day repeat globally).
The L-band InSAR technique will be tested under a wider range of snow conditions, for larger changes in SWE, and during the transition from dry to wet conditions, in order to understand the limitations, and evaluate the potential to leverage the upcoming NISAR mission for global snow monitoring.
From December 2019 through May 2020, UAVSAR will fly 13 flight paths across five states, at weekly to biweekly temporal resolution. These sites span a range of snow climates and conditions, elevations, aspects, and vegetation. Flight paths were designed to include sites with ongoing snow research projects, existing ground-based remote sensing infrastructure (e.g., radar and LiDAR), snow-off and planned snow-on aerial LiDAR, scheduled ground snow measurement campaigns, and locations with experienced local field observers performing regular observations coincident with UAVSAR (weekly to biweekly temporal resolution). To aid modeling activities, sites with energy balance observations were chosen.
Grand Mesa Intensive Observation Period (IOP)
Grand Mesa will be used as a Time Series site with bi-weekly UAVSAR and two airborne LiDAR data collections, and it will also host an Intensive Observation Period (IOP). The primary objectives of the Grand Mesa IOP are to test and validate SWE retrieval from active and passive microwave sensors, and to quantify subpixel variability in thermal IR signatures to assess the value of kilometer-scale satellite IR observations (e.g., GOES-16) for snow energy balance modeling. This component of SnowEx2020 primarily addresses airborne experiments with the NASA GSFC SWE Synthetic Aperture Radar and Radiometer (SWESARR) and the University of Washington Thermal IR sensor package.
The Grand Mesa IOP is scheduled for 27 January 2020 – 12 February 2020. The experiment will be performed across the range of vegetation and snow conditions that exist on the western part of Grand Mesa. A field team of approximately 40 scientists is planned for the 16-day IOP. This site was chosen for this component of the experiment because it provides gradients in vegetation and snow depth with minimal topography, is high elevation with abundant drier snow, and is conveniently located 25-35 km from Twin Otter International (TOI) at Grand Junction Regional Airport. Thanks to experience gained and local relationships developed during past campaigns, detailed knowledge of the required logistics and resources ease the implementation and execution of a safe campaign. Grand Mesa has four meteorological stations (three installed September 2016, and one existing site that was upgraded) and three SNOTEL sites. These continuous observations provide a relatively high density of available forcing data for snow models, compared to most areas in the mountains in the western U.S. Two large radar calibration targets have been permitted and maintained since 2015.
Coincident acquisitions will include the University of Alabama SnowRadar and NOAA’s National Operational Hydrological Remote Sensing Center (NOHRSC) gamma sensor, and these will be coordinated with SnowEx2020 activities on Grand Mesa; for this particular experiment these will take place at no cost to SnowEx2020. Coordination is mutually beneficial, as these groups will all share the data acquired during the Grand Mesa IOP.
Learn more by reading the 2020 Experimental Plan