Ka-band high-altitude precipitation radar with ground measurements: data processing and initial validations

Data processing, calibration, and quality evaluation are critical elements for successful airborne radar missions. For a downward-looking airborne radar, the usage of ground as a calibration target has been discussed before but not completely analyzed for precipitation measurement missions at Ka-band. In this study, the team performed data analysis and calibration modeling for the Millimeter-Wave Airborne Radar for Learning and Education (MARBLE), which was developed as a recent undergraduate team effort beginning in 2016. Millimeter-wave radar missions for MARBLE include precipitation measurement and terrain remote sensing through vertical profiling. To achieve these mission goals, the team used multiple time- and spectrum-domain processing methods on the ground return data collected from 2018 NASA ER- 2 engineering calibration flights. Some of the algorithms include spectrum analysis with various CPI arrangement and multi-lag processing to enhance signal-to-noise ratio (SNR). Doppler calibration based on aircraft platform motion and orientation is also considered. Useful results are obtained from ground power calibration as well as Doppler estimation. In addition, multiple ground calibration tests with actual weather results are incorporated to supplement the airborne measurements after some hardware checking and improvement. Based on the reasonable outcomes from the calibration measurements, a new high-altitude flight campaign for precipitation measurement is being planned for 2020.