Correlator Array-Fed Microwave Radiometer Component Technologies

Multiband passive microwave imagery in X to W Bands (e.g., 10, 18 or 19, 22 or 24, 37, 86 or 89 GHz) has a nearly 40-year history of utilization for measurement of multiple geophysical parameters. For example, quantities retrieved include precipitation rate, integrated water vapor, integrated cloud liquid water and ice, ocean surface wind speed, snow water equivalent, sea ice concentration, and land surface temperature (for evapotranspiration). Spatial resolution is limited by aperture size, and although aperture sizes have grown to 1-2 meters, current capability will not meet future science spatial resolution needs. As geophysical models have improved, the need has emerged to improve spatial resolution further to < 5 km. Improved spatial resolution in turn leads to a need to populate the antenna with additional radiometer elements to preserve noise performance (NEDT) and to provide adequate spatial sampling of Earth's surface. We propose to develop key building blocks of a multi-band correlator array that would feed a large reflector antenna to generate multiple radiometer beams on Earth. The envisioned system (relevancy scenario) would image Earth at 36.5 and 89.0 GHz with 2 to 3 km spatial resolution and at 10.65, 18.7 and 23.8 GHz with 5 to 10 km resolution from 700 km altitude with approximately 0.5 to 1 K NEDT. At 36.5 GHz, the proposed spatial resolution is a 10X improvement over the legacy polar-orbiting capability SSM/I and SSMIS and a 3X improvement over the modern AMSR2 radiometer. The correlator array feed will also enable a conical scanning radiometer to image with 50% overlap between footprints (complete Nyquist sampling). Today's state-of-the-art radiometers do not provide spatial Nyquist sampling in all of these microwave bands. The key proposed development is a broadband line array covering 10-90 GHz appropriate for illuminating a large deployable reflector and will be developed by industry partner Nuvotronics Inc. A trade-study and design will be performed for integrating calibration noise coupling, frequency multiplexing, and low noise amplification into the beam forming structures. A brassboard sub-scale correlator array-fed radiometer will be developed at 36.5 GHz and elevation scanning of the main beam will be demonstrated. We will enter at TRL 2, mature the technology during a two-year period of performance (Jan. 2018 to Dec. 2019), and exit at TRL 3.

Accelerate mission development and reduce risk by developing critical components and subsystems for advanced instruments and observing systems

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