Development of Low-Mass, Low-Power High-Frequency Microwave Radiometers to Improve Coastal and Enable Over-Land Wet-Tropospheric Correction for SWOT

Current satellite ocean altimeters include nadir-viewing, co-located 18-37 GHz multi-channel microwave radiometers to measure wet-tropospheric path delay. Due to the area of the surface instantaneous fields of view (IFOV) at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 40 km from the coasts. Higher-frequency radiometers with internal calibration are under development to assess their suitability as part of the Surface Water and Ocean Topography (SWOT) accelerated Tier-2 mission recommended by the National Research Council's Earth Science Decadal Survey and planned for launch in 2020. The addition of these high-frequency radiometers to current Jason-class radiometers is expected to improve retrievals of wet-tropospheric delay in coastal areas and to increase the potential for over-land retrievals. Specifically, high-frequency window channels at 92, 130 and 166 GHz are optimum for wet path delay retrievals in coastal regions. New, high-sensitivity, wide-bandwidth mm-wave radiometers using both window and sounding channels show good potential for over-land wet-path delay retrievals. Critical microwave component and receiver technologies are under development to reduce the risk, cost, volume, mass, and development time for high-frequency microwave radiometers. This project focuses on the design and fabrication of a prototype system consisting of : (1) low-power, low-mass and small-volume direct-detection millimeter-wave radiometers with integrated calibration sources operating from 90 to 170 GHz that fit within the overall SWOT mission constraints, and (2) a multi-frequency feed horn covering the same frequency range. The three key component technologies under development to achieve these objectives are PIN-diode switches for internal calibration that can be integrated into the receiver front end, high-Excess Noise Ratio (ENR) noise sources and a single, tri-frequency feed horn. These new components are being integrated into a MMIC-based low-mass, low-power, small-volume technology-demonstration radiometer with channels centered at 92, 130 and 166 GHz. This radiometer will serve as a breadboard demonstration by providing realistic mass, volume and power estimates to feed into the SWOT mission concept study.