Effect of the Tree Canopies in Microwave Radiometric Remote Sensing of Snowpack

Effective management of the freshwater reservoir requires almost daily monitoring the spatial and temporal
distribution of the snow water equivalent (SWE) and snowpack wetness. Both microwave radar and radiometers
systems have long been proposed and implemented as powerful remote sensing tools in retrieving the physical
parameters of interest due to their all-weather operation capability. In case of microwave radiometry, microwave
remote sensing of dry snowpack is based on frequency-dependent differential scattering by the ice grains in the
snowpack, referred to as scatter darkening. Scatter darkening has been developed as a SWE remote sensing
technology over the last three decades. However, the presence of tree canopies in a given scene can affect the SWE
estimation of snowpack. Hence, the knowledge of the brightness temperature of tree canopies is important in order
to better predict and recover the SWE of the snowpack. We have used the microwave radiometers at three different
frequencies; namely, 1.4 GHz, 19 GHz, and 37 GHz, mounted on our boom truck to look at the snowpack. The
measurements have been done in Grand Mesa National Forest in Colorado as the NASA SnowEx campaign in Feb
2017. In this paper, the effect of the snow on tree canopies on their brightness temperature is discussed. Moreover,
the elevation angular dependence of the brightness temperature of the tree canopies is investigated.