Compact Ocean Wind Vector Radiometer Performance After Three-years On-orbit: From Tech Demo to Operations

The Compact Ocean Wind Vector Radiometer (COWVR) is the first space demonstration of a low-cost, small-sat compatible conical microwave imager for atmospheric and surface observation, specializing in ocean vector winds. Heritage conical microwave imagers, such as SSM/I, AMSR, WindSat, GMI and WSF-M have been providing important Earth observations for over 45 years, including but not limited to surface wind vector, atmospheric and surface temperature, water vapor, clouds, precipitation, snow and sea ice. However, due to the cost and complexity of these legacy systems, the ad hoc international constellation is dwindling, extending re-visit times, impacting weather forecasting. The objective of the COWVR mission is to demonstrate that a new, lower-cost radiometer architecture can perform as well as the legacy systems.

COWVR has been operating on the International Space Station (ISS) since January 2022 along with the TEMPEST-H8 microwave sounder. COWVR provides measurements of ocean vector winds, precipitable water vapor, clouds and precipitation while TEMPEST-H8 provides retrievals of vertical water vapor profiles and ice cloud properties, including convective intensity. We present the detailed in-flight performance characterization from 3-years of operation of COWVR and TEMPEST-H8, focusing on the wind vector, water vapor, precipitation and cloud water products, demonstrating a compact sensor can perform as well as current generation operational sensors. The 3+year mission permits very detailed quantification of the magnitude of residual systematic errors in the sensor calibration and retrieval products, including long-term stability. We will summarize the results from this detailed in-flight characterization, including highlights of data assimilation impact studies.

We show that COWVR is performing significantly better wind vector retrievals than the WindSat legacy sensor. This is because COWVR has the advantage of an un-blocked conical scan, observing each spot in the swath at two different azimuth angles relative to the wind direction. This viewing geometry has the advantage of reducing ambiguous wind vector solutions and improving overall performance. We also compare the COWVR wind vector products to those produced from the operational ASCAT scatterometer system, showing nearly equivalent performance (with wind direction differences < 10 degrees at wind speeds > 10m/s). The COWVR data products are available with 1-2 hour latency and are in operational use by the Naval Research Laboratory. Data assimilation studies have shown positive impact, equivalent to legacy imagers with common channels. The brightness temperature and retrieval products are distributed publicly via the NASA PO.DAAC and as of August 2024 are available without any access restrictions.

COWVR has demonstrated a new sensor architecture suitable for deployment in a small-satellite constellation. We will describe a follow-on imager/sounder concept derived from the COWVR architecture that is a software defined digital system operating over a wide spectrum enabling new measurements of air-sea heat and moisture exchange as well as the traditional product suite derived from microwave imagers and sounders.