Development and Optimization of Airborne FMCW Radars for High-Resolution Snow Depth Measurements

Over one-sixth of Earth's population relies on glaciers and seasonal snowpacks for freshwater supply. In the United States, the Colorado River Basin (CRB) gets 75% of its water from snow melt; it constitutes the water supply of 40 million people in seven states, two countries, and 5.5 million irrigated acres of land. An ultra-wideband (UWB) radar enabling snowpack information production in near-real-time would greatly aid in planning and effectively distributing this precious resource.The primary objective of this research is to design, develop, and optimize UWB FMCW (Frequency-Modulated Continuous-Wave) radar systems for airborne snow measurements to generate data products in near-real-time for operational applications. We need to address a few significant engineering challenges to do this. The first is to develop a high-sensitivity FMCW radar providing near-ideal response requiring minimal signal processing for a single and multi-channel configuration. These systems must overcome sensitivity limitations posed by the internal reflections, chirp and system non-linearities, and transmitter-receiver feedthrough signals and operate in thermal noise regions, ensuring optimal performance. We can employ coherent signal processing techniques with thermal noise-limited systems and keep the transmit power low. The second is to develop a Mills-Cross antenna array for the airborne platform for these radar systems to obtain a narrow transmit-receive beamwidth. Finally, we must demonstrate that we can provide near-real-time operational data products in the field with the improved UWB radar.We performed careful design, simulations, and optimization to reduce the effects of system non-linearities, internal reflections, and chirp-related non-linearities in the radar. We extensively used modern computer-aided design (CAD) tools to optimize the transmitter and receiver sub-sections of the radar to obtain a perfect point target response that does not need additional signal processing. The radar we developed operates over 2-11 GHz and uses only 10 mW of transmit power. We addressed the challenge of obtaining the high transmitter-receiver over ultra-wide bandwidth and accommodating two large nadir-looking antennas on medium-range aircraft with a T-shape Mills-Cross antenna array with narrow two-way beamwidth. We demonstrated that we could deliver snowpack results in near real-time for operational applications within a few hours after completing each survey flight.