Microwave radiative transfer at frequencies of AMSU-B: Effects of uncertainties in ice permittivity on brightness temperatures

This paper presents the effects of uncertainties in ice permittivity on emerging brightness temperatures at three different zenith angles at the frequencies of Advanced Microwave Sounding Unit-B (AMSU-B), 89 GHz, 150 GHz and 183 GHz. The absolute error of brightness temperature, due to an uncertainty of ±20% in the imaginary part of ice permittivity and of ±5% in the real part, is explored with vector discrete ordinate radiative transfer (VDISORT) method at the zenith angle of 0°, 30° and 53° in this study. Particles in clouds are taken to be spheres, of which the diameters are uniformly distributed in the range of 40 μm to 4000 μm in Gamma-size distribution. We found that ±5% uncertainty in the real part of ice permittivity results in more than 1 K variation in upwelling brightness temperature, higher than ±20% uncertainty in the imaginary part when the effective diameter in Gamma-size distribution is 150 μm. And the absolute error of brightness temperature caused by uncertainties in ice permittivity is up to more than 2 K at the zenith angle of 53°, greater than the corresponding value at the other two zenith angles.