SSM/I-based surface temperature retrieval methods for boreal forest zone

Novel inversion methods for the retrieval of surface temperature (air temperature at ground level) in forested areas using space-borne multi-channel microwave radiometer data are presented and analyzed. The first technique is an inversion method based on the use of a semi-empirical emission model. The other methods discussed are empirical approaches: multiple linear regression and polarization difference formulas. The methods are evaluated in the case of Finnish boreal forests. The results show that for conifer dominated boreal forests the surface temperature can be estimated reliably from SSM/I measurements during snow-free conditions. The highest test site-wise correlation coefficients (r) between the ground-based reference values and the SSM/I-based estimates are above 0.97 and the corresponding unbiased rms errors are smaller than 1.3°C