Long-term Scatterometer Wind Climate Data Records

A wind scatterometer is a radar instrument mounted on a weather or research satellite that sends pulses of energy (centimeter radio waves) to the sea surface and then measures the energy scattered by centimeter waves on the sea surface.

Wind speed and direction can be derived from this backscatter signal.

Since several decades scatterometer wind measurements over sea are available and these winds are more and more often used in climate studies, addressing air-sea interaction, tropical dynamics and moist convective processes, among others.  Moreover, long-term wind Essential Climate Variable (ECV) Data Records (CDR) are useful to obtain estimates of the accuracy of re-analyses obtained with General Circulation Models (GCM) in representing, for example, extreme events. Several wind data sets of past and current missions are being reprocessed in order to create homogeneous wind ECV CDRs.

The scatterometer wind data records are compared to model winds from the ECMWF ERA-Interim reanalysis, which are used by many downstream CDR users.  The project focusses on  how to compare and calibrate winds measured by different instruments and GCMs.

Several scatterometer CDRs are available, e.g. 10 years (1999-2009) of winds from the SeaWinds scatterometer  (on board the US polar orbiting QuikSCAT satellite) and the ASCAT (Advanced Scatterometer) winds from the polar orbiting European Metop-A satellite, available since 2007.  The ASCAT coastal product has enhanced resolution and provides wind information on a 12.5 km grid spacing[1].  The winds are produced in the scope of the EUMETSAT OSI SAF (Ocean and Sea Ice Satellite Application Facility).

Validation Reports and Product User Manuals are available for all data sets. For an overview of the currently available data, please see http://www.knmi.nl/scatterometer/archived_prod/. For a general overview of scatterometer activities at KNMI, see http://www.knmi.nl/scatterometer/.

Scatterometer winds are used operationally and have undergone extensive calibration and validation against measurements made by buoys and model winds using advanced methods. Moreover, they are  routinely monitored for quality assurance[2]. KNMI has produced near-real time scatterometer ocean vector winds for almost 20 years now (near-real time means that winds are computed and distributed as soon as the raw satellite data are received).  These data sets are not always homogeneous, because wind retrieval algorithms have been continuously improved over the years and the creation of homogeneous wind ECV CDRs is thus eminent.

L3 (regridded) data for this project is also availabe through the CMEMS project website: http://marine.copernicus.eu/ (search for wind in the online catalogue). The L3 reprocessing product now contains data from 1992 upto 2016, including ERS1, ERS2, Quikscat, ASCAT-A and ASCAT-B winds. In addition wind stress and stress equivalent model wind, as well as curl and divergence for both wind and wind stress is provided in these data sets.

 

 

Reference:  A. Verhoef, J. Vogelzang, J. Verspeek and A. Stoffelen, Long-term Scatterometer Wind Climate Data Records, accepted for publication in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, doi: 10.1109/JSTARS.2016.2615873.

[1] http://www.knmi.nl/scatterometer/ascat_osi_co_prod/ascat_app.cgi

[2] www.knmi.nl/scatterometer/ascat_osi_co_prod/ascat_app.cgi and http://nwpsaf.eu/site/monitoring/winds-quality-evaluation/scatterometer-mon/

Stability of the calibration coefficients of the six ASCAT scatterometer radar beams on board the EUMETSAT Metop-A satellite. The stability in dB corresponds approximately to an accuracy in m/s. The calibration is relative to the mean values over 2013.
Stability of the calibration coefficients of the six ASCAT scatterometer radar beams on board the EUMETSAT Metop-A satellite. The stability in dB corresponds approximately to an accuracy in m/s. The calibration is relative to the mean values over 2013.
ASCAT-B wind field retrieved in the Caribbean (around Cuba) on 6 October 2016, approximately 2:00 UTC, overlaid on a GOES infrared satellite image.  © EUMETSAT/KNMI.
ASCAT-B wind field retrieved in the Caribbean (around Cuba) on 6 October 2016, approximately 2:00 UTC, overlaid on a GOES infrared satellite image. The circular wind field of tropical hurricane Matthew is clearly visible. © EUMETSAT/KNMI.

A. Verhoef, J. Vogelzang, J. Verspeek and A. Stoffelen, Long-term Scatterometer Wind Climate Data Records, accepted for publication in IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing, doi: 10.1109/JSTARS.2016.2615873.