Miniaturized s-UAS-Based Ultra-Wideband Radar for Snow Water Equivalent Map Synthesis

This paper presents a miniaturized, small unmanned aerial system (sUAS)-based ultra-wideband (UWB) radar system and results from measurements on snow over Grand Mesa, Colorado, during Spring 2024. The system was developed to estimate snow water equivalent (SWE) directly from radar data without extensive in-situ snow density measurements. The system can operate both as a monostatic and bistatic pulsed-radar over the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$0.7-2.1 \text{GHz}$</tex> frequency range. The bistatic operation utilized two drones, with their radars synchronized via GPS-disciplined oscillators. The transmit signal is generated through direct synthesis of a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1-\mu$</tex> s chirp using an RF-SoC platform. Received signals are directly digitized and pulse-compressed. A Synthetic Aperture Radar (SAR) algorithm was applied to obtain fine resolution in the along-track direction. The radar successfully measured snow depths ranging from 0.5 to 2.5 meters, even in forested areas with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">${1 5}-{2 5}$</tex> meter tall trees, showing strong agreement with in-situ measurements, with errors within a few centimeters. Using the bistatic radar mode, we measured snow permittivity and estimated snow density. We generated high-resolution SWE and snow depth maps and compared these with in-situ measurements.