The Ocean Surface Vector Winds (OSVW) project is part of the NASA Making Earth System Data Records for Use in Research Environments (MEaSUREs) Program. MEaSUREs develops consistent global- and continental-scale Earth System Data Records by supporting projects that produce data using proven algorithms and input.
The OSVW project aims to produce a consistent record of wind vector, wind stress, and their spatial derivatives for a period of over two decades by cross-calibrating the retrievals from four scatterometers deployed during previous projects. This includes the Metop-A ASCAT, Metop-B ASCAT, QUIKSCAT SeaWinds, and SCATSAT-1 scatterometers, which together provide an unbroken record from October 1999 to May 2022.
The importance of having a consistent record of wind and wind stress, as well as their derivatives, is the motivation behind the MEaSUREs OSVW Project. Ocean surface wind and wind stress are key components of the Earth system and understanding these interactions is critical for improving weather forecasting on a variety of spatial and temporal scales – from air-sea interactions, to isolated convective cores, to the organized mesoscale systems, to hurricanes and typhoons, to the seasonal and intraseasonal phenomena such as Madden-Julian Oscillation (MJO), El Niño, and the trends and variability in the large-scale Hadley cell. Furthermore, while wind estimates have been routinely produced and used in weather forecasting and ocean modeling, there has not been a systematic effort to produce the dynamically-significant derived products – the wind stress and the spatial derivatives of the wind and stress (their curl and the divergence). Yet, the atmospheric circulation is strongly affected by the wind convergence, while the oceanic circulation is driven by the curl of the stress.
Rigorous details of intercalibration between the instruments can be found in accompanying documentation and publications and is described briefly here. For this project, inter-calibration refers to the following: The ASCAT-A and ASCAT-B wind retrievals have been cross-calibrated with the QuikSCAT and ScatSat-1 data such that when coincident observations exist the wind retrievals are consistent between all instruments. The IOVWST Ku-band Geophysical Model Function (GMF) was adopted since it was developed to perform equally well across multiple incidence angles, providing consistent wind estimates from the multitude of Ku-band scatterometers from NASA and ISRO missions. Then, collocated observations between Ku-Band instruments (SCATSAT-1 and QUIKSCAT) and C-Band (Metop-A ASCAT and Metop-B ASCAT) are used to modify the existing C-band GMF such that remaining small differences between the estimates are eliminated. Lastly, the JPL wind retrieval system is used to produce winds from the entire set of observations from the four scatterometers.
Provided here are brief introductions and basic characteristics of each scatterometer. Detailed information can be found in the references / documentation and elsewhere (note that these instruments are part of separate projects that predate this one).
Metop-A and Metop-B Advanced Scatterometers (ASCAT-A and ASCAT-B): Scatterometers aboard the Metop-A and Metop-B satellites, launched by the ESA (European Space Agency) and operated by EUMETSAT (European Organization for the Exploitation of Meteorological Satellites). The instruments are real aperture, C-band, vertically polarized radars with three fan beam antennas pointing to the left-hand side of the subsatellite track and three fan beam antennas pointing to the right-hand side.
Scatterometer Satellite-1 (SCATSAT-1): ScatSat-1 was launched by the Indian Space Research Organisation (ISRO) and carries the Ku-band OSCAT instrument. The OSCAT instrument is a conically scanning pencil-beam scatterometer. It uses a 1-meter dish antenna rotating at 20 rpm with two “spot” beams (a horizontal polarisation beam and a vertical polarisation beam). The beams sweep the surface in a circular pattern.
QuikScat SeaWinds (QUIKSCAT): The SeaWinds on QuikSCAT is a Ku-band (13.4 GHz) Scatterometer featuring a circular dish antenna, which provides pencil-beam radar backscatter measurements. The mission was a “quick recovery” mission to fill the data gap created when the ADEOS-1 satellite carrying the NASA Scatterometer (NSCAT) lost power in June 1997. QuikSCAT was launched from California’s Vandenberg Air Force Base aboard a Titan II vehicle.
JPL user guide for QuikSCAT, produced for the data sets associated with the original mission (not the MEaSUREs OSVW data sets). It is included here because it contains sections on the engineering and operational characteristics of the instrument and background information on the satellite.
