Passive microwave measurements of snow-covered forest areas in EMAC'95

Airborne passive-microwave signatures collected in Northern Finland during EMAC-95 are analyzed with the emphasis on forested areas and dry snow conditions, The microwave signatures cover the 6.8-18.7-GHz frequency range and were acquired at both vertical and horizontal polarizations. The analysis is carried out with respect to the forest-stem volume data and comprises three different snow-depth situations. Emissivities approach saturation limit with the increasing stem volume. At 10.65 GHz, the saturation level was found to be linearly related to the snow-water equivalent, On the basis of passive-microwave measurements, an empirical forest transmissivity model is developed, The model is valid at vertical polarization 50 degrees incidence angle, and it accounts for microwave frequency and forest-stem volume effects in the range of 6.8-94 GHz and 0-150 m(3)/ha, respectively.