For the past several years, we have developed critical microwave component and receiver technologies to reduce the risk, cost, volume, mass, and development time for high-frequency microwave radiometers. First, we are designing and fabricating low-power, low-mass, small-volume high-frequency (90-170 GHz) radiometers with integrated calibration sources. 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 laboratory 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 studies of future altimetry missions, including SWOT.
To demonstrate higher technological readiness for space, we are producing an airborne instrument that combines high-frequency, high-sensitivity window and sounding channel radiometers with low-frequency Jason-class radiometers to provide substantially improved spatial resolution and the potential for multiple fields of view across the SWOT airborne radar's swath. The current airborne instrument development and flight demonstration will (1) assess wet-tropospheric path delay variability on 10-km and smaller spatial scales, (2) demonstrate high-frequency millimeter-wave radiometry using both window and sounding channels to improve both coastal and over-land retrievals of wet-tropospheric path delay, and (3) provide an instrument for calibration and validation in support of the SWOT mission. We will discuss the current status of these component and receiver technologies enabling the transition from research to operations.