The Compact Ocean Wind Vector Radiometer: A New Class of Low-Cost Conically Scanning Satellite Microwave Radiometer System

The paper describes the design and development of the Compact Ocean Wind Vector Radiometer (COWVR) which is currently being designed, built and tested by the Jet Propulsion Laboratory for an Air Force proof-of-concept technology demonstration mission planned for launch no earlier than 2016. COWVR is a low-cost, low-mass, low-power fully-polarimetric imaging radiometer system operating at 18.7, 23.8 and 34.5 GHz and based on the Jason-2/3 Advanced Microwave Radiometer (AMR) design. The fully-polarimetric observations enable retrieval of ocean surface wind vector, as well as other key environmental parameters such as precipitable water vapor, cloud liquid water, precipitation rate and sea ice. The measurement of ocean surface vector winds using a polarimetric microwave radiometer was first demonstrated by the Naval Research Laboratory WindSat radiometer (launched in 2003). Because this was a first-of-its-kind measurement, the system minimized use of new technology to ensure successful demonstration of the new measurement technique (Gaiser et al., TGRS, 2005) and consequently had a large mass and power (380 kg and 350 W). The COWVR system utilizes a novel design to reduce the system complexity which in turn significantly reduces the cost, mass, power and volume from the heritage WindSat sensor, yet is predicted to maintain the same wind vector retrieval accuracy.

The enabling features include the use of a single multi-frequency feed horn permitting a simple antenna rotating about the feed axis, as opposed to having to spin the entire radiometer system; internal calibration sources which enable fully polarimetric calibration and eliminate the need for an external warm load and cold sky reflector simplifying the mechanical design and enabling a complete 360 degree scan; and a compact highly integrated MMIC polarimetric combining receiver implementation, lowering the system mass and power which in turn makes the system well suited for deployment on smaller class, lower cost satellites.

This paper will give a description of the COWVR system and an overview of the technology demonstration mission. We will discuss the unique processing techniques required for this system, including Electronic Polarization Basis Rotation to transfer the polarimetric measurements from the instrument frame to the Earth frame and describe how this actually improves the sensor calibration compared to the more traditional sensor design approach. We will also discuss the wind vector retrieval performance improvement enabled by the two-look (fore and aft) observations from the 360 degree scan. Finally, we will discuss how the COWVR design is scalable to a wider range of frequencies from 6-183 GHz enabling a class of low-cost operational sensors that match the current capability provided by sensors such as SSMI/S, AMSR-2, WindSat and GMI.