Attenuation of Radar Signal by a Boreal Forest Canopy in Winter

An investigation of boreal forest attenuation of a radar signal in winter is presented, applying a multifrequency (1&#x2013;10 GHz) ground-based synthetic aperture radar (GB-SAR). As stable targets, corner reflectors (CRs) with known radar cross section (RCS) were used under the forest canopy. This enabled to relate changes in observed wideband backscattering from the reflectors to attenuation of the radar signal in forest vegetation, eliminating the influence of the background, such as snow and soil. We found that ambient temperature affected the observed attenuation of the radar signal in the entire 1&#x2013;10-GHz frequency range. For temperatures <inline-formula> <tex-math notation="LaTeX">$T &lt; 0 ~^{\circ }\text{C}$ </tex-math></inline-formula>, attenuation was found to decrease by up to 4.3 dB at the lowest observed temperatures of &#x2212;36 &#x00B0;C, with peak attenuation occurring at <inline-formula> <tex-math notation="LaTeX">$T \approx 0 ~^{\circ }\text{C}$ </tex-math></inline-formula>. The overall apparent two-way attenuation increased by up to 18 dB from L- to X-band. The presence of snow on the canopy was found to increase attenuation by 1&#x2013;4 dB, the effect increasing with frequency while having only negligible effects on vegetation backscatter.