Advanced Component Development to Enable Low-Mass, Low-Power High-Frequency Microwave Radiometers for Coastal Wet-Tropospheric Correction on SWOT

Critical microwave component and receiver technologies are under development to reduce the risk, cost, volume, mass, and development time for a high-frequency microwave radiometer needed to enable wet-tropospheric correction in the coastal zone and over land as part of the NRC Decadal Survey-recommended Surface Water and Ocean Topography (SWOT) Mission. Current satellite ocean altimeters include a nadir-viewing, co-located 18-37 GHz multi-channel microwave radiometer to measure wet-tropospheric path delay. However, due to the area of the instantaneous fields of view on the surface at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. Addition of higher-frequency microwave channels to the Jason-class radiometers on the recommended SWOT mission will improve retrievals in coastal regions and enable retrievals over land. 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. This work focuses on the design and fabrication of a prototype system consisting of: (1) a low-power, low-mass and small-volume direct-detection millimeter-wave radiometer with integrated calibration sources covering frequencies from 90 to 170 GHz that fits within the overall SWOT mission constraints, and (2) a multi-frequency feed horn covering the same frequency range. Three key component technologies are under development to scale the design of the Advanced Microwave Radiometer (AMR) on the OSTM/Jason-2 altimetry mission from 18-34 GHz to 90-170 GHz, i.e. a PIN-diode switch for calibration that can be integrated into the receiver front end, a high-Excess Noise Ratio (ENR) noise source and a single, tri-frequency feed horn. These new components are currently in the process of fabrication and testing, after which they will be integrated into a MMIC-based low-mass, low-power, small-volume radiometer 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 mission concept study. The current technology readiness level (TRL) of the antenna and RF components is 2, and the project is intended to raise the TRL to 4.