Microwave Signatures of Defoliating Spruce Canopies

摘要

The results achieved from microwave radar backscattering measurements ofdefoliating spruces are presented. Individual spruces were measured in an unechoic chamber and in outdoor conditions using a look angle of 45 deg. Natural defoliation was simulated by gradually removing the needles of the trees. The measurements were carried out using 5/10 GHz and 35 GHz radar systems. The 5/10 GHz radar system is a ranging 8-channel scatterometer named 'HUTSCAT' and the 35 GHz radar system is a network analyzer based radar polarimeter. The influence of defoliation to the volume backscattering and extinction coefficients of spruce canopy has been determined from the measured data. The results show that defoliation has a considerable effect on radar backscattering at 10 GHz linear polarizations. At 35 GHz the achieved data indicate a rather complicated and controversial backscattering behavior with increasing defoliation. At 5 GHz and 10 GHz cross-polarized channels, the effect of defoliation on the backscattering coefficient is weak or negligible.