Calibration issues for a three-band microwave radiometric system with background noise compensation

Abstract

For microwave radiometric remote sensing systems in natural environments, the important issue is calibration, i.e. determination-one correspondence of values of the output signal value of the brightness temperature of the sensed region, the largest of which evaluated physical parameters. Microwave radiometric systems operate under the influence of external interference, for example, background noise – radiothermal radiation of the space surrounding the system, received through the scattering region of the antenna pattern. This article examines the influence of background noise on the external calibration of a microwave radiometric system (based on an external “deterministic” noise source) and analyzes the conditions for performing such calibration in a system with compensation for the influence of background noise. The analysis of the output signal of the microwave radiometric system showed a significant influence of background noise on the parameter determined during calibration of the system – the beginning of the receiver scale, due to a change in the value of the contribution of background noise to the output signal when forming two reference levels during calibration from two angular directions. The possibility of reducing the interference effect of background noise on the results of measurements in a microwave radiometric system with a special two-channel antenna operating on two modes of a circular waveguide, with the formation of an additional compensation signal at the antenna output, is shown. The proposed version of the analytical evaluation of the degree of compensation of the influence of background noise on the output differential signal of the system and presents results of its application to numerical analysis of error in external calibration a tri-band microwave radiometric system with compensation of background noise when receiving thermal radiation onthe total aperture of the antenna.