6.9, 19 and 36 GHz brightness observations of cold lands hydrology in alpine and Arctic terrains.

Abstract

Cold land regions are crucial components of the Earth system because of their sensitivity to global change and the subsequent feedbacks to global climate system. The cold land processes, including precipitation, snow melting and refreezing, soil thawing and freezing, change of active layer thickness, play important roles in water and energy balance of cold land regions. Low frequency microwave radiometry is sensitive to liquid water content and offers a means of monitoring the cold land hydrology. Both satellite microwave observation and ground based microwave observations over alpine and arctic terrains are studied. Advanced Microwave Scanning Radiometer-EOS (AMSR-E) satellite brightness temperature observations are synthesized using an improved Backus-Gilbert algorithm and compared to the standard brightness temperature product for AMSR-E. This algorithm improves the spatial resolution for the 6.925 GHz and 10.65 GHz channels by taking advantage of the oversampling of these two frequencies, which allows a tradeoff between noise and spatial resolution. Nearly circular synthesized footprints for all channels are achieved by using a circular Gaussian reference footprint. The synthesized observations are compared with ground based data collected during the Ninth Radiobrightness Energy Balance Experiment (REBEX-9) and the Tenth Radiobrightness Energy Balance Experiment (REBEX-10). REBEX-9 is a part of Cold Land Processes Field Experiment (CLPX) conducted in Central Rocky Mountain during February and March, 2003, representing alpine cold lands. REBEX-10 is conducted in North Slope, Alaska during May and June, 2004, representing arctic cold lands. The comparison shows that the potential usefulness of spatial aggregation of brightness temperature from a few land types within satellite footprint to explain the satellite brightness temperature. The sensitivity study shows that tree temperature and emissivity are the most sensitive parameters in aggregation for alpine cold land, and area fractions of water is the most critical component in aggregation for arctic tundra region.