Influence of forest disturbances on backscatter of the airborne L-band synthetic-aperture radar in a larch forest in northern Japan

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This paper is a case study on the detection of forest disturbances in airborne synthetic-aperture radar (SAR) data. We investigated changes in the L-band SAR backscattering coefficient (σ0) following thinning and a typhoon in a larch forest in northern Japan. The thinning caused changes of intermediate magnitude in the above-ground biomass (AGB), whereas the typhoon broke or uprooted most of the trees, thereby significantly changing the forest structure without changing the biomass. Thinning led to back-scattering coefficients change of less than about 1 dB; HV polarization was most sensitive to the change in AGB, and HH was insensitive to it. In the case of the typhoon, VV was sensitive to the change in forest structure, whereas HH and HV were insensitive to it, suggesting that the tree trunks, which were felled in one direction by the typhoon, enhanced the backscattering signal of the polarisation that accorded with the trunk direction.