Calibration system for ARM radars

The Atmospheric Radiation Measurement (ARM) Climate Research Facility is a U.S. Department of Energy (DOE) user facility for the study of global and regional climate by the research community. The ARM facility has established a cloud and precipitation radar facility to enable the observation of cloud and precipitation systems under various climate regimes. The purpose of the radars is to collect and maintain a comprehensive and continuous long-term data sets that provide observations of cloud and precipitation over a wide range of environmental conditions. Calibration and tracking the calibration state during long-term operations is critical. The modernized radar systems are designed with built-in test equipment (BITE) to calibrate, track and monitor each sub-system. However, for an end-to-end system calibration the antenna must be included because the antenna pattern has a significant impact on the observations. Solar observation has been used on research radars operating at S-band to evaluate the performance of the antenna. However, such techniques are not always viable for higher frequencies such as Ka-band and W-band. This paper presents a calibration system for the ARM radars that enable the calibration of the system using a trihedral corner reflector. A novel technique to counter the effect of receiver saturation from corner reflector is presented. The paper presents the calibration system in an operational framework. In addition, calibration results from the ARM radars will be presented highlighting the applicability of the method and its usefulness for unmanned radars deployed in in remote locations.