The first Geostationary Earth Radiation Budget (GERB) experiment was launched on the Meteostat Second Generation (MSG-1) satellite in August 2002. GERB exists to make high accuracy measurements from geostationary orbit of the outgoing components of the Earth radiation budget at high temporal resolution. The GERB pixel size is approximately 44 km at the sub-satellite point, but in the GERB processing the position of each pixel must be located to an accuracy of about one tenth of this. This is because of the need in the level 2 processing to co-locate the GERB data with data from the Spinning Enhanced Visible and Infra-Red Imager (SEVIRI) instrument on MSG. MSG is a spin-stabilised satellite, and since the time constant of the GERB detectors is relatively long, of order 4 milliseconds, a de-spin mirror is used to obtain a constant scene over the detector integration time. As a consequence, issues of timing, pointing and alignment all have to be taken into account when geolocating the GERB data. This paper will explain the geolocation method devised to meet the required accuracy, the problems encountered in the initial data from GERB and the solutions being employed to overcome these problems.
分享
引用
