Wind speed over water (ASCAT)


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Data access via file system: /data/icdc/atmosphere/ascat_surfacewind



Radar backscatter data measured by the EUMETSAT MetOP-ASCAT sensor are used to compute the wind vector over ice-free open water surfaces. The ASCAT sensor is a C-Band scatterometer which measures the surface radar backscatter along two about 500 km wide swaths parallel to its orbit with about 25 km spatial resolution at the Earths's surface. The ocean surface radar backscatter is a function of the ocean surface roughness which is in turn a function of the wind speed.

Remote Sensing Systems (REMSS, http://www.remss.com) used the EUMETSAT MetOP-ASCAT data to compute the surface wind vector at 10 m height above the ocean surface. This is done by using a so-called Geophysical Model Function (GMF) which has been developed specifically for MetOp-ASCAT (C-2015 GMF) paying special attention to extend the ocean surface wind speed data set produced from QuikSCAT Ku-Band data which ends in 2009. We refer to data set web page at REMSS: http://www.remss.com/missions/ascat and the references section for details. We refer further to the section about the data quality to learn more about potential limitations.

The product offered here is a modified version of the daily EUMETSAT MetOp-ASCAT ocean surface wind vector product v02.1 released by REMSS in April, 2016. The modification applied by ICDC is the conversion from flat binary into netCDF file format, the computation of the u- and v-wind vector components from wind speed and direction, and translation of the bit-wise to be read rain flag / rate information into two separate layers: a rain flag and a rain rate.

Last data set update at ICDC: May 10, 2019.

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Name Units Comment
wind speed m/s all variables separately for ascending and descending overpasses
wind direction degrees (0 ... 360°) direction into which the wind blows
u-component m/s  
v-component m/s  
rain flag -- 0, 1
rain rate mm/h 0 ... 31
quality flag -- 0 ... 5, Sum-of-Squares, the higher the number the lower the data quality
decimal time hours since 0 UTC every swath pair has different overpass time

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Coverage, spatial and temporal resolution

Period and temporal resolution:

  • 2007-03-01 to 2019-03-31
  • Daily (2 times, ascending & descending overpasses)

Missing days: 2017: Jan. 2-4 & 12-19

Coverage and spatial resolution:

  • Global, over open water
  • Spatial resolution: 0.25° x 0.25°, cartesian grid
  • Geographic longitude: 0°E to 360°E
  • Geographic latitude: -90°N to 90°N
  • Dimension: 1440 columns x 720 rows
  • Altitude: 0.0 m


  • netCDF

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Data quality

The data set offered here does not include any explicit uncertainty estimates for the variables themselves but a quality flag is included which allows to judge how successful the retrieval was.

Precipitation influences the measured radar backscatter intensity either directly by scattering of the microwave radiation by the precipitation particles or indirectly by adding to the water surface roughness due to precipitation particles impinging on the water surface. These areas are flagged invalid in this data set. The rain flag relies directly on ASCAT measurements while the precipitation rate is computed from brightness temperature measurements of other satellites taken within 3 hours to the ASCAT overpass. We note that ASCAT is less sensitive to precipitation and/or attenuation of RADAR radiation in the atmosphere / clouds than QuikSCAT because it uses C-Band instead of Ku-Band.

We refer to the section references for further information.

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Remote Sensing Systems
Santa Rosa, CA, U.S.A.
email: support (at) remss.com

Stefan Kern
ICDC / CEN / University of Hamburg
email: stefan.kern (at) uni-hamburg.de

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  • REMSS Data User Guide
  • Figa-Saldaña, J., J. J. W. Wilson, E. Attema, R. V. Gelsthorpe, M. R. Drinkwater and A. Stoffelen (2002), The Advanced Scatterometer (ASCAT) on the Meteorological Operational (MetOp) Platform:  A Follow on for European Wind Scatterometers, Canadian Journal Remote Sensing, 28(3), 404-412.
  • Ricciardulli, L. and F. J. Wentz (2014), Integrating Multiple Scatterometer Observations into a Climate Data Record of Ocean Vector Winds, paper presented at 2014 Ocean Sciences Meeting, held in Honolulu, Hawaii, USA.
  • Ricciardulli, L. and F. J. Wentz (2012), Development of Consistent Geophysical Model Functions for Different Scatterometer Missions: Ku and C-band, paper presented at the NASA IOVWST meeting held in Utrecht, Netherlands.
  • Ricciardulli, L., T. Meissner and F. J. Wentz (2012), Towards a Climate Data Record of Satellite Ocean Vector Winds, in Proceedings of the International Geoscience and Remote Sensing Symposium, Munich, Germany,  2067-2069.

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Data citation

When using the data please cite as follows:

Ricciardulli, L., Wentz, F.J., April 2016. Remote Sensing Systems ASCAT C-2015 Daily Ocean Vector Winds on 0.25 deg grid, Version 02.1, Santa Rosa, CA: Remote Sensing Systems.  Available at www.remss.com/missions/ascat.  Accessed from www.remss.com:, last access date: 2019-05-02. Downloaded in netCDF file format from the Integrated Climate Data Center (ICDC, icdc.cen.uni-hamburg.de) University of Hamburg, Hamburg, Germany.

In addition please add to the acknowledgements:

C-2015 ASCAT data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Vector Winds Science Team. Data are available at www.remss.com.

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