The newest innovation to passive microwave remote sensing technology is the inclusion of noise diodes for radiometric calibration of total power radiometers. Instead of the usual two-point calibration using passive black body sources, now there are four-calibration noise levels, which allow system nonlinearities to be corrected. Conventional approaches linearize the radiometer output "rad_counts" (using the four-point calibration correction) and use a linear transfer function to calculate the antenna temperature (TA) at the radiometer input. This paper presents a novel approach of using a quadratic radiometer transfer function (with nonlinear rad_counts) to derive (TA). This algorithm is tested using on-orbit satellite measurements from the Global Precipitation Measurement (GPM) Microwave Imager (GMI). Empirical results are presented, which show only mille-Kelvin differences between this TA algorithm and the standard TA product provided by NASA.
展开▼
