Comparison of Experimental Brightness Temperatures for Snow on Lake Ice with Those for Snow on Terrain

We have conducted a multiyear (2011-2014) airborne microwave radiometer measurement program of snow on lake ice, regularly using our HUTRAD instrument (6.9 to 36.5 GHz, vertical and horizontal polarization). Occasionally, we have also used our interferometric 1.4 GHz HUT-2D radiometer. Our data consist of observations along a 4-km test line over two lakes in southern Finland, and include data also for adjacent land areas, whose land-cover types range from forest to short vegetation. A wide variety of snow and ice conditions were encountered, covering early winter, mid-winter and late winter conditions, and the melting season. In this paper we focus on the comparison of brightness temperatures observed for snow on lake ice and snow on terrain.

1. Introduction

Satellite microwave radiometry has proved to be the best remote sensing tool for retrieval of dry snow characteristics, especially the terrestrial snow water equivalent (SWE). A review of advanced algorithms developed and validated for this purpose has been recently published [1]. The two main land-cover types reducing accuracy of SWE retrieval are forest cover and ice-covered lakes. The physical characteristics of snow on lake ice may differ substantially from those for snow on terrain. Consequently, the emission behavior of the snow/ice/water system is different from that of the snow/soil system and, additionally, existence of water on top of ice strongly affects brightness temperatures (TB) especially at low microwave frequencies. Due to abundance of lakes in northern regions their effect to satellite-derived brightness temperatures must be accounted for in order to obtain good SWE retrieval accuracy [2].