Airborne UWB FMCW Radar for Snow Depth Measurements

We developed and deployed a high sensitivity and low transmit power airborne ultra wide band (UWB) frequency-modulated continuous-wave (FMCW) radar for snow depth measurements. The radar has a near-ideal point target response so that we can produce near-real-time snow thickness maps after each survey flight. The improved performance is achieved by carefully designing the radar hardware to reduce internal reflections between various components, third-order products generated by mixers, higher order harmonics generated in multipliers and nonlinear devices, and amplitude and phase errors in transmitted chirp signals. In addition, we performed extensive linear and nonlinear system simulations to predict degradations in the radar hardware in advance and applied the remedies to correct them. These improvements allowed for near-real-time data products to be generated by reducing the need for advanced signal processing techniques. We also developed a T-shape Mills-Cross antenna array to obtain a small overlapped footprint of transmit and receive antennas. We performed measurements over snow in Grand Mesa, CO, USA, from March to April 2022, and the radar mapped the top and bottom interfaces and density changes of 1.2-2.1 m of snow. We generated a snow thickness map from the data collected over the grid flown and compared results with in situ measurements. The comparison between radar estimates and in situ measurements shows that the average snow depths obtained from the radar data are within a standard deviation from the mean of in situ measurements.