The ERS-1 Wind Scatterometer calibration and validation activities are summarised in the following document:

• Ad Stoffelen and David Anderson, 1995: The Ecmwf Contribution to the Characterisation, Interpretation, Calibration and Validation of ERS-1 Scatterometer Backscatter Measurements and Winds: Their Use in Numerical Weather Prediction Models

The ERS-2 Wind Scatterometer calibration and validation activities are summarised in the following document:

• Pascal Lecomte, Guy Brooker, 1996: ERS Wind Scatterometer Commissioning and in-flight Calibration

Calibration Activities

The aim of the absolute calibration is to ensure that the σ° value measured from a target is correct for all incidence angles. To achieve this, the absolute gain and the pointing of each antenna need to be established in flight, and this is done with the help of ground transponders. Transponders are active devices that, after receiving a pulse from the Scatterometer instrument, send a delayed and shifted in frequency pulse back. The Wind Scatterometer received and detected the transponder pulses from within its receiver and stored data on board.

Once data was downloaded, the measured transponder echo from the sensor and the measured pulse from the transponders device were processed by a calibration algorithm to derive a gain correction value for each antenna and a set of mispointing angles. This allowed a reference calibrated system to be established, against which the system performance can be evaluated and monitored. The accuracy that can be reached by this methodology with the ERS-2 transponders was about 0.5 dB.

The aim of the relative calibration was to asses the values of the σ° measured by the instrument for all incidences by comparing σ° measured at another time and/or location. This calibration was typically based on the usage of a natural target with specific geophysical properties like: isotropy, homogeneity and relative constant in time. For the ERS-2 relative calibration the Amazon rain forest was used to compute the gain correction and to monitor the system performances. The accuracy that can be reached by this methodology was about 0.2 dB. Other natural target (like sea-ice) or model (ocean calibration) was also used to perform the relative calibration.

More details related to the routine calibration activities and results for both ERS-1 and ERS-2 Wind Scatterometer can be found in the following papers:

• R. Crapolicchio and P. Lecomte, The ERS Wind Scatterometer mission: routine monitoring activities and results
• Calibration and long-loop performances since launch

More details focussed on the ERS Wind Scatterometer mission and the calibration activities for the mission reprocessing can be found in the following papers:

• R. Crapolicchio et al. ERS-2 Scatterometer: Mission Performances and Current Reprocessing Achievements
• Calibration strategy for ERS scatterometer data reprocessing
• ERS-1 Scatterometer Full Mission Reprocessing Verification Report

Further information is available on the SCIRoCCO page.

Validation Activities

There are Validation Reports related to the new ASPS products, both the Nominal (25 km) and High Resolution (12.5 km). The assessment of the ERS-2 Wind Scatterometer ASPS 20 product winds is based on the comparison with ECMWF short-range forecast 10 m wind fields.

• Final Validation Report: Saleh Abdalla, Giovanna De Chiara and Hans Hersbach, 2011: The technical support for global validation of ERS wind and wave products at ECMWF (July 2008 – July 2011)

A summary of the quality assessment, calibration and validation of ERS-1 Wind Scatterometer data can be found in the following report:

• D. LeMeur et al., 1998: Global validation of ERS Wind and Wave Products.