AlpSAR 2012-13, a Field Experiment on Snow Observations and Parameter Retrievals with Ku- and X-Band Radar
Rott, Helmut1; Nagler, Thomas2; Prinz, Rainer2; Voglmeier, Karl2; Fromm, Reinhard3; Kleemayr, Karl3; Yueh, Simon4; Elder, Kelly5; Marshall, Hans-Peter6; Meta, Adriano7; Coccia, Alex7; Schüttemeyer, Dirk8; Kern, Michael8
1ENVEO IT GmbH, AUSTRIA; 2ENVEO IT, AUSTRIA; 3BFW, Department of Natural Hazards, AUSTRIA; 4JPL-CalTech, UNITED STATES; 5Forest Service, United States Department of Agriculture, UNITED STATES; 6Department of Geosciences, Boise State University, UNITED STATES; 7METASENSING, NETHERLANDS; 8ESA-ESTEC, NETHERLANDS

In order to support the development of observation techniques and inversion algorithms for the retrieval of physical snow parameters from high frequency radar backscatter data, field campaigns have been performed in previous winters in Northern Finland, Canada and United States. In winter 2012-13 additional field campaigns take place in the Austrian Alps within the AlpSAR experiment. AlpSAR is aimed at enhancing the experimental data base on radar backscatter by covering different snow regimes and terrain types than in previous campaigns. A main objective of the campaign is the testing and validation of algorithms for retrieval of the water equivalent (SWE) of winter snow cover over different land cover types in Alpine regions. The activities are contributing to feasibility studies for the ESA Earth Explorer Candidate Mission CoReH2O (Cold Regions Hydrology High-resolution Observatory). The proposed satellite sensor is a dual frequency SAR, operating at 17.2 GHz and 9.6 GHz, VV and VH polarizations. In the AlpSAR experiment backscatter data are collected with an airborne polarimetric SAR sensor (SnowSAR) which operates at the same frequencies as the CoReH2O SAR. Field measurements are performed at three test sites in different elevation zones in order to cover various snow regimes: Leutasch at 1200 m elevation, where the land cover is dominated by meadows and coniferous forest, Rotmoostal at about 2200 m elevation in the Alpine tundra region, and Mittelbergferner, an Alpine glacier. Measurement campaigns are carried out on three different dates during the winter period: mid-November to catch the start of the snow season, January in mid-winter, and late February before the start of the melting period. In autumn 2012 automated measurement stations were deployed in the test sites to record snow, soil and atmospheric parameters. During the flight campaigns intensive snow measurements are performed, including the measurement of vertical profiles of snow parameters in a network of snow pits, GPR transects on snow depth and stratification, terrestrial laser scanner measurements, and UAV imaging. The data analysis deals with the evaluation of backscatter properties in dependence of snow parameters to validate backscatter forward models, and with the inversion of the SnowSAR backscatter images to derive and validate maps of snow water equivalent.