Title: Advanced Component Development to Enable Low-Mass, Low-Power High-Frequency Microwave Radiometers for Coastal Wet-Tropospheric Correction on SWOT
Primary Author: Reising, Steven
Organization: Colorado State University
Co-Author(s): Shannon T. Brown, Todd C. Gaier, Daniel J. Hoppe, Douglas E. Dawson, Pekka Kangaslahti, Oliver Montes, Beyrouz Khayatian, Alexander Lee and Darrin Albers

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 on 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 surface instantaneous fields of view (IFOV) at these frequencies, the accuracy of wet path retrievals begins to degrade at approximately 50 km from the coasts. In order to meet the needs of the recommended SWOT mission, higher-frequency microwave channels will need to be added to the JASON-class radiometers in order to improve retrievals of wet-tropospheric delay in coastal areas and to increase the potential for over-land retrievals.

Development of a new high-frequency radiometer measurement technique for SWOT requires technology developments in the following two key areas: (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. To accomplish these objectives, one can start by scaling the design of the Advanced Microwave Radiometer (AMR) that is currently flying on the OSTM/Jason-2 altimetry mission. The MMIC-based AMR receiver combines three channels at 18.7, 23.8 and 34.0 GHz into a single unit with a single multi-frequency feed horn. This project focuses on developing the following three key component technologies in order to scale the AMR receiver design: 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 three-frequency feed horn. These new components 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, 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.