A Ka/W-band dual-frequency millimeter-wave radar–thermal infrared radiometer system for cloud and precipitation observations over the Tibetan Plateau: design, performance evaluation, and preliminary observations

Abstract. Continuous observations of cloud and precipitation structure are important for characterizing atmospheric processes over the Tibetan Plateau, where long-term measurements remain challenging to obtain. We present a Ka/W-band dualfrequency millimeter-wave radar–thermal infrared radiometer system (KaW-TIR), developed by the Institute of Atmospheric Physics, Chinese Academy of Sciences, and Sun Create Electronics Co., Ltd., and deployed at the Yangbajing Atmospheric Observatory in Tibet. The system integrates all-solid-state frequency-modulated continuous-wave (FMCW) radars, sharedaperture dual-frequency Cassegrain antennas, separate transmit and receive assemblies, and a thermal infrared channel on a common scanning platform. A common time reference supports synchronized observations with approximately aligned viewing directions. We evaluated system performance using internal monitoring, UAV-suspended metal-sphere calibration, weak cold-cloud consistency analysis, and long-term observation statistics. The metal-sphere calibration yielded mean apparent reflectivity biases of −0.75 dB for the Ka band and +0.32 dB for the W band, which were used to correct the corresponding radar constants. Selected weak cold-cloud samples had a median Ka–W dual-wavelength ratio of 0.34 dB. In the routine observing mode, the nominal range resolution is 30 m, and the product update interval is approximately 0.92 s. At 10 km above radar level, the observed statistical detection boundaries are approximately −44.43 dBZ for the Ka band and −43.20 dBZ for the W band. A representative case illustrates concurrent radar-observed cloud and precipitation structure and thermal infrared brightness temperature. These results demonstrate the KaW-TIR system's capability for continuous, synchronous observations of cloud and precipitation at a high-altitude site on the Tibetan Plateau.