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Scatterometers

Introduction


Scatterometers are radar instruments that measure the radar backscatter from a part of the ocean surface. The radar backscatter depends on wind speed, wind direction, and observation geometry. This relation is described by a so-called Geophysical Model Function (GMF). When the radar backscatter is measured from three or more directions, numerical inversion of the GMF yields the wind speed and direction at the ocean surface.

In general, such a procedure does not have a unique solution locally. Sophisticated software is needed to find the possible solutions by local inversion, control the quality of these solutions, and find the best unique solution for the spatial wind field.

Scatterometer data processors for SeaWinds (SDP), ASCAT (AWDP) and OSCAT (OWDP) are supplied and maintained by the NWP SAF. These packages process radar backscatter data to wind vector field solutions featuring:

  • Local representation of the full wind vector PDF based on the radar backscatter measurement input (Multiple Solution Scheme);
  • State of the art quality control procedures;
  • Two-dimensional variational ambiguity removal.

The wind processing packages are written in Fortran 90. SDP generates surface winds from data obtained by the SeaWinds scatterometer on board QuikSCAT, AWDP from data obtained by the Advanced Scatterometer (ASCAT) and European Remote Sensing satellite (ERS) scatterometer instruments. OWDP generates surface winds from data obtained by the OSCAT scatterometer on board Oceansat-2. All processors allow the use of ambiguity removal with the Two-dimensional Variational Ambiguity Removal (2DVAR) method and they support the Multiple Solution Scheme (MSS). Their output consists of wind vectors which represent surface winds within the ground swath of the scatterometer. Normalized Radar Cross Section (NRCS) data is input by AWDP, SDP and OWDP.

The input files of SDP are in BUFR using the BUFR templates for SeaWinds that already contain Numerical Weather Prediction (NWP) wind fields needed as a first guess for Ambiguity Removal. The output is written in BUFR using the SeaWinds and /or the KNMI BUFR templates.

The input files of AWDP are in BUFR or Product Format Specification (PFS, native MetOp) format. BUFR input may be provided using the BUFR templates for ERS or ASCAT; output is always written using the ASCAT BUFR template. Moreover, AWDP needs Numerical Weather Prediction (NWP) model winds as a first guess for the Ambiguity Removal step. These data must be provided in GRIB format.

The input files of OWDP are BUFR or Level 2A data by ISRO in HDF5 format. BUFR input may be provided from OWDP output files in case of reprocessing. The output is written in BUFR using the SeaWinds and /or the KNMI BUFR templates. Moreover, OWDP needs Numerical Weather Prediction (NWP) model winds as a first guess for the Ambiguity Removal step. These data must be provided in GRIB format.

The SeaWinds Data Processor (SDP) and ASCAT Wind Data Processor (AWDP) have been fully operational since January 2009. The OSCAT Wind Data Processor (OWDP) is fully operational since April 2013. SDP, AWDP and OWDP are available free of charge under licence, and are distributed by the Met Office.

The current version of AWDP is v2.1 and it is available using the link at the bottom of this page. Compared to the previous version 2.0, the backscatter correction used in the wind processing is adapted to the new level 1 processor version 7.4. Moreover, some bugs and other issues have been solved.

The current version of SDP is v2.1, and is available using the link at the bottom of this page. The main difference with the previous version is that the OSI SAF sea ice model and screening are now operational. Note that this model needs a few days of data before it produces reliable sea ice discrimination. Since SeaWinds on QuikSCAT ended its mission in November 2009, the SDP package is only maintained. Bugs will be fixed, but adjustments or extensions will only be made on user request.

The current version of OWDP is v1.1 and it is available using the link at the bottom of this page. It is the first publicly released version.

See the links at the bottom of the page for instructions on how to request a copy of SDP, AWDP or OWDP. Copies of the user manuals can be downloaded below.

 
Latest News and releases 03-08-2011

 

  1. OWDP v1.1 was publicly released on ?? April 2013, and is available using the link at the bottom of this page.
  2. New versions of the Technical Reports Two-dimensional variational ambiguity removal (2DVAR) and How to calculate wind spectra were released on 4 April 2013.
  3. AWDP v2.1 was publicly released on 2 August 2011, and is available using the link at the bottom of this page.
  4. A workshop on scatterometer data assimilation was organized by the NWP SAF on 14 April 2011 at EUMETSAT premises in Darmstadt (registration deadline 15 March 2011). The goal of the workshop was to provide NWP data assimilation colleagues with insight into the main relevant characteristics of the scatterometer data, provide guidance for data assimilation and collect NWP user requirements for the scatterometer wind observation operator. For further details including workshop presentations, click here.
  5. SDP v2.1 was publicly released on 24 November 2010, and is available using the link at the bottom of this page.

 
Detailed Information

 

  • Development Plans
    • SDP: Since SeaWinds on QuikSCAT has ended its mission in Nov. 2009, the SDP code will only be maintained. Bugs will be fixed but extensions or improvements will only be made upon user request.
    • AWDP: AWDP 3.0 will include improved wind retrieval, mainly connected to Geophysical Model Function improvements (CMOD6).

 
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