Extended Study of Natural Calibration for the Cloud Profiling Radar of EarthCARE

Contract with ESA ESTEC, in collaboration with CETP Centre d'Etude des Environments Terrestre et Planetaires and Novimet (France)

This project is a continuation of a successful initial study, in preparation for the future EarthCARE mission, which will carry the Cloud Profiling Radar (CPR). This radar will operate on W band, a frequency not used previously for active radar in Earth Observation Satellites, and for which calibration protocols must be designed. The frequency (94Ghz) was chosen as the most suitable for providing a profile of clouds.

Over land surfaces, altimeter sigma0 (σ⁰) is found to vary rapidly, both spatially and temporally, in response to changes in surface texture, terrain variations, and surface moisture (Bramer et al 2004). However, certain desert surfaces exhibit a coherent response, which allows the development of a sigma0 (σ⁰) model. Instrument offsets and drift may be determined by the comparison of satellite data with these models.

This study has identified and rated a number of possible calibration zones. In April 2006 NASA launched CloudSat, an Earth Observation Satellite that carries its own CPR, also a W band radar. Examination of the CloudSat data confirms that the approach taken in this project is correct and that it will be possible to calibrate the EarthCARE CPR by use of sigma0 (σ⁰) models tuned to W band.

ERS-1/2 Sigma0 (σ⁰) model (dB) of the Eastern Sahara, 15-30N 15-30E.

CloudSat repeat data over the Eastern Sahara, displaying variation due to cross-track drift and a small data anomaly.