Radar Observations of Snowpack Changes from the Second Cold Land Processes Experiment

To support the NASA Snow and Cold Land Processes (SCLP) and the ESA Cold Regions High-Resolution Hydrologic Observatory (CoRe-H2O) missions and advance observation of the global water cycle, NASA is supporting the second Cold Land Processes Experiment (CLPX-II). The experiment is being conducted in two parts over two winter seasons (Colorado 2006-2007, and Alaska 2007-2008). The focus of CLPX-II is on testing and development of advanced snow measurement using high-frequency radar through repeat observations of changing snow conditions using airborne and spaceborne radars and intensive in situ measurements. During 2006-2007 three field campaigns were conducted in a 90-km x 9-km study area in north-central Colorado. The campaigns were carried out in December, January and February to observe significant changes in snowpack characteristics. In each campaign, the Jet Propulsion Laboratory's conically scanning Ku- band polarimetric scatterometer (POLSCAT) was flown on a Twin Otter aircraft to collect radar data over the study area. Multiple complete images of the entire study area were acquired during each campaign, enabling examination of short-term changes in radar response as well as long-term changes between campaigns. In each campaign, intensive in situ observations of snow depth, water equivalent, stratigraphy, and grain size were made in each of 16 target sites. All of the target sites shared similar backgrounds (flat terrain with a ground cover of grasses and sedges) but exhibited a wide range of snowpack characteristics. Preliminary analyses of the POLSCAT data acquired from the CLPX-II in winter 2006-2007 are described. The data showed response of the Ku-band radar echoes to snowpack changes for various types of background vegetation. There was about 0.4 dB increase in backscatter for every 1 cm SWE accumulation for sage brush and pasture fields. The data also showed the impact of freeze/thaw cycles, which appeared to create depth hoar and ice lenses with large snow grain size, and consequently increased the radar signals by a few dBs.