Digitally Enhanced Meta-surface Radar/Radiometer for Snow Remote Sensing

We propose to develop a Ku-band active and passive (radiometer/radar) microwave wavelength instrument capable of measuring the spatial distribution of snow-water-equivalent (SWE) from a space-borne platform using CMOS radar combined with metasurface antenna technology to overcome the isolation and dynamic range challenges associated with snow sensing. Traditionally remote sensing of SWE from a space-borne is prohibitive as it demands both a large aperture (>1m diameter) to maintain resolution in terms of ground footprint, and high dynamic range radar system (beyond 60dB) to accommodate the vast difference in reflectivity between the snowpack's top surface and the underlying ground. This dynamic range in particular requires that a radar have a very low transmit-to-receiver leakage (again beyond 60dB). Airborne remote sensing of snow addresses this leakage by employing bi-static radars where the transmitter and receiver operate using separate antennas. The separation of the two signals with separate antennas allows these systems to easily achieve the required transmit-to-receive isolation as the two are not required to share an aperture. While suitable for large airborne campaigns, the bi-static approach is prohibitive for spaceborne platforms as needing two large antennas (as opposed to a single antenna) makes the instrument prohibitively large. To overcome this we propose an instrument which employs a new metasurface antenna which enables simultaneous transmitting and receiving using the same antenna aperture and frequency, while still providing the high isolation required for sensing SWE from a spaceborne platform. This high isolation is achieved through a combination of the antenna's native design (approx. 20dB isolation), as well as a leakage cancelling pre-distortion technique where signals leaking between the two ports are digitally cancelled to provide an additional 50dB. Using this high dynamic range, the proposed instrument can provide critical information about snowpack features (depth, density, liquid water content) used to estimate and constrain SWE, but unlike ground-based or airborne measurements, can provide global coverage as it targets a spaceborne approach. The instrument also offers a passive radiometer mode (where the radar transmitter is disabled) which is an important measurement in constraining the amount of liquid water pooled at the bottom of the snowpack. To achieve the high level of signal processing performance required to enhance the isolation of the metasurface antenna, we employ CMOS system-on-chip (SoCs) technology (the same electronics technology used in modern smartphones) for all radar and radiometer electronics. CMOS SoCs offers approximately a factor of 100X in performance over FPGA platforms implemented with the same transistor size.

Increase scientific understanding of natural phenomena using remote sensing

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