Airborne measurements of forest and agricultural land surface emissivity at millimeter wavelengths

Passive microwave radiometers have been operated on an aircraft over the same (N OPEX) area of Sweden, near Uppsala in September 1995 and March 1907. Their measurements have allowed the calculation of the emissivity of boreal forest and agricultural land surfaces at 24, 50, 89 and 157 GHz over a range of incidence angles and polarisations. These results show consistent differences between dense forestry, where the emissivity is close to 1 and open land, where it is approximately 0.96. These differences are examined and a model is presented to parameterise these surfaces by use of a Debye-like effective permittivity and Fresnel’s reflection coefficients.