Abstract
RPG (Radiometer Physics GmbH) has developed a 7 channel radiometer (18.7 GHz vertical and horizontal polarization, 23.8 GHz vertical polarization, 36.5 GHz vertical and horizontal polarization, 90 GHz vertical and horizontal polarization) for environmental research with a high absolute stability of 0.5 K and a sensitivity of better than 0.2 K rms. The system uses an internal radiometric autocalibration technique to precisely adjust for overall gain and system noise temperature variations without the need for external calibration loads or inaccurate sky tip calibration procedures. In addition nonlinearity errors caused by the non ideal responses of detector diodes which are always present in radiometers are eliminated by using a four point fit noise injection method. The radiometer's housing is mounted to a positioner system and can be accurately scanned in elevation (±90°) and azimuth (0-360°) for atmospheric or ground observations. The antenna beams have a FWHM (Full Width at Half Power Maximum) of 10°with a -40 dB sidelobe level. The system is designed to be used under outdoor conditions (rain protected, temp. range : -20°C to 40°C). Data aquisition, calibration, system diagnostics, position scanning etc. are automatically controlled by a versatile computer software.
