An ultra-wideband radar for measurements of snow thickness over sea ice

Snow cover of variable thickness exists on sea ice with thickness fluctuations in the range from less than a few centimeters to several meters depending on snow drifts and ice type. Snow largely controls the thermal and electrical properties of a sea ice cover. Because of its low thermal conductivity, it effectively insulates the sea ice surface from cold polar air and modifies the heat flux between the atmosphere and ocean. It also changes the sea ice albedo. Additionally, thick snow cover acts as a mechanical load and can depress the ice surface below sea level, causing the ice floe to be flooded with sea water. Thus accurate knowledge of snow thickness on sea ice is essential for determining the overall heat budget in the polar regions, which in turn can impact global ocean circulation and climate. We developed an ultra-wideband radar for measuring snow thickness. It operates over the frequency range from 2-8 GHz in FM-CW mode. We used a phase-locked YIG oscillator to generate a very linear 2-8 GHz chirp by using a low-frequency (5-20 MHz) digital chirp generator as a reference signal for the phase detector. We also constructed a receiver with a large dynamic range and fast settling time. The received signal was digitized using a 12-bit A/D converter and stored for further processing. We also developed simple models to simulate radar performance. We modeled snow as a multi-layered media and sea ice as dielectric half-space, and performed extensive simulations using snow geophysical data collected during Antarctic cruises to optimize radar performance. We evaluated the radar´s performance by measuring its response to point targets such as a delay line and corner reflectors. With the Hanning window function, the measured radar range resolution is about 3.75 cm. We collected data on snow-covered ground in conjunction with measurements of snow parameters such as density, particle size, and roughness. The results from these measurements show that we can clearly delineate returns of the snow-air and snow-ground interfaces for 6-cm-thick dry snow.