POLARIZATION SIGNATURES OF FROZEN AND THAWED FORESTS OF VARYING ENVIRONMENTAL STATE

During the two different overflights of the Bonanza Creek Experimental Forest (near Fairbanks, Alaska) by the NASA/JPL radar polarimeter in March 1988, the environmental conditions over the region changed signi ficantly with temperatures ranging from unseasonably warm (1 to 9-degr ees-C) during one day to well below freezing (-8 to -15-degrees-C) dur ing the other. The moisture content of the snow and trees changed from a liquid to frozen state causing significant changes in the radiometr ic and polarimetric responses of the forest to the radar wave. The L-b and polarimetric observations are summarized in this paper. Up to a 6 dB change in the backscatter was observed in certain forest stands at L-band. Features extracted from the Stokes matrices of the same stands from the thawed and frozen days suggest the changes in the relative c ontribution of the different scattering mechanisms to the radar return . Comparison of the polarimetric signatures indicate relatively higher contribution from diffuse scatterers on the thawed day than on the fr ozen day. The sensitivity of the polarimetric signatures to changing e nvironmental conditions is clearly demonstrated.