|
Aboard the next generation of EUMETSAT geostationary satellites, the Flexible Combined Imager (FCI) will continue the current SEVIRI (Spinning Enhanced Visible and Infrared Imager) mission with enhanced temporal, spatial, and spectral capabilities. For monitoring the radiometric stability of the FCI reflective solar bands ranging from 0.4 to 2.2 μm, the Moon acquisitions are planned to be used. The Moon will cross the FCI field-of-view on a regular basis, under different illumination conditions and elevations. The FCI scan mechanism will allow the acquisition of the Moon with two or three consecutive swaths at the most. Two challenges must be resolved to make use of Moon observations. First, consecutive swaths include an overlap region to avoid coverage gaps. It means that some Moon areas are observed twice. Second, the swaths make an angle with respect to the equatorial plane that varies with the elevation. Consequently, it is necessary to reconstruct the full Moon disc from those consecutive swaths before the total lunar irradiance can be calculated and compared to the current lunar calibration reference, the GIRO (GSICS Implementation of the ROLO) model. This paper presents the prototype developed to make use of Moon observations with FCI. It has two components: i) a Moon transit simulator that generates equivalent Level 1b data using Himawari-8/AHI data as an input, and ii) a Moon image-stitching algorithm, which re-builds the Moon image from the simulated Level 1b swaths. In order to assess the efficiency of the stitching algorithm, two methods to reconstruct the Moon image are implemented and compared. The first one makes full use of the information available from the Moon transit simulator. The second one is the stitching method that will be deployed during operations, i.e. using exclusively information from the Level 1b swaths.
|
