Deployment of the ASCAT calibration transponders

The METOP-A Advanced Scatterometer Radar has stringent radiometric requirements requiring regular, accurate, calibration. The specified stability of 0.2 dB or better is too demanding for targets such as rain forest or simple corner reflectors, so three highly stable return signal sources have been precisely sited to give accurate measures of the beam patterns over the satellite repeat cycle. The Scatterometer is required to provide full coverage over all the oceans, so the three calibration transponders have been installed in Turkey, as the Black Sea and Eastern Mediterranean are not used in the ASCAT programme.