Calibration of millimeter-wave radiometers with application to clear-air remote sensing of the atmosphere

Research on the development of an absolute calibration methodology for microwave and millimeter-wave radiometers, and subsequently, on the results of clear-air brightness temperature comparisons performed between calibrated radiometer measurements and radiative transfer calculations is presented. The scattered, transmitted, and internal fields of a typical radiometer calibration target (lossy periodic absorber), illuminated in the principal direction by a plane wave, are analyzed using the coupled-wave (CW) algorithm. The field solution is facilitated by a formulation in which each layer of the discretized periodic structure is considered to be a linear multiport network with an associated generalized scattering matrix. Thermal analysis of the radiometer calibration targets is performed using a finite element algorithm. The electromagnetic and thermal analyses presented herein for calibration targets quantify the interrelationship between the nonuniform local emissivity and the nonuniform temperature field calculated for materials comprising these targets. A novel antenna calibration model is presented for a state-of-the-art cross-track scanning radiometer, the NASA Millimeter-Wave Imaging Radiometer (MIR). The MIRs antenna temperature calibration is validated through several diagnostic experiments, thermal-vacuum chamber experiments, and detailed clear-air brightness temperature comparisons. The comparisons are between MIR calibrated measurements and atmospheric radiative transfer theory calculations. The MIR was operated concurrently with supporting meteorological instruments (radiosonde and Raman lidar) to construct a paired set of both spatially- and temporally-coincident calibrated brightness temperatures and atmospheric profile parameters. Calculated brightness temperatures were obtained from the radiative transfer equation, based on the measured atmospheric profile parameters. The comparisons use the first atmospheric observations made with the wideband MIR channel set and include unique observations at 220 GHz.; The calibration methodology developed herein is significant to the general area of microwave and millimeter-wave remote sensing and will guide radiometer developers in their assessment of the principal sources of radiometer error: calibration target performance, mixer performance, and antenna-to-calibration target coupling. The calibration target analyses in this thesis provide a significant tool to augment the typically sparse experimental data available for radiometer targets through straightforward interpolation and extrapolation of the numerical and measured data presented.