The rectification quality of EUMETSAT´s Meteosat Second Generation (MSG) level 1.5 imagery is routinely monitored for geometrical performance, summarily referred to as geometric quality assessment (GQA). The monitoring includes the absolute navigation error, image-to-image relative geometric accuracy and the inter-channel relative geometric accuracy. Recently, an inquiry from the user community indicated a structured residual error for certain channel pairs, when measuring the inter-channel relative accuracy using direct correlation of image channels. The residual relative interchannel geometrical accuracy shows a clear spatial banding structure in North -South direction. Within each band (i.e. in East-West direction), the measured value of the relative inter-channel geometric accuracy is not changing much, but when going from one band to the next the residual errors change more significantly. The effect is only measurable when comparing a channel located on the one focal plane with a channel on the other focal plane of MSG SEVIRI instrument. Channel - pairs located on the same focal plane do not show the effect. It has therefore been hypothesized that this effect could be associated with a problem in the ground-characterised pointing table for the SEVIRI instrument that associates a scan step with a look angle. Any error in the look angle characterisation would have the same effect on channels of one focal plane, but have a different effect on channels of different located focal planes. While the overall quality of the image is still within specification, an improvement to the processing could be achieved by updating the pointing table with in-flight measurements.
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