Although most requirements for the CarbonSat phase A are defined over spatially homogeneous scenes, it is known from previous missions and studies that the observation of real, spatially heterogeneous scenes create specific measurement errors. One obvious mechanism is a distortion of the instrument spectral response function (ISRF) induced by a non-uniform slit illumination in the along-track (ALT) direction. This error has been analysed for several missions (OMI, Sentinel-4, Sentinel-5). The combination of spectrometer smile with across-track (ACT) scene non-uniformities induces similar errors. In this paper, we report about the analysis efforts carried out during CarbonSat preliminary phases to evaluate and mitigate these effects. In a first section, we introduce common concepts and notations for heterogeneous scenes analysis. An exhaustive list of known error mechanisms is presented. In section 2 we discuss the effect of inhomogeneous slit illumination, and describe hardware mitigation with a slit homogeniser. The combination of spectrometer smile and ACT heterogeneities is studied in section 3. |
Distortion
Spectrometers
Point spread functions
Telescopes
Diffraction
Astronomical imaging
Sensors