Accurate MERIS Ortho-Rectified Geo-location Operational Software (AMORGOS)Entry ID: ESA_AMORGOS
Abstract: The purpose of the AMORGOS (Accurate MERIS Ortho-Rectified Geo-location Operational Software) tool is to generate accurate geo-location information - longitude, latitude, altitude - for each MERIS pixel, starting from a MERIS Full Resolution product: either a Full Swath or a standard half-swath Scene product. The quarter-swath product is not managed.
If the input product is a Full ... Swath one, the current version accepts two modes. The first one preserves the organisation of the input product, namely the Level 1b product grid, it is referred to as the FSG (full swath geo-corrected) mode and generates a MER_FSG_1P product. The second one generate results re-organised in the instrument geometry, it is referred to as the FSO (full swath ortho-geolocated) mode and generates a MER_FSO_1P product.
The FSO mode first restores radiance samples and accompanying flags into Instrument Geometry, un-doing the spatial re-sampling of the Level1 processing, and computes accurate ortho-rectified geo-location using MERIS detectors individual pointing vectors, a High Resolution DEM and accurate spacecraft Orbit and Attitude files.
The FSG mode essentially skips the Instrument Geometry restoration step and computes the same geo-location information for each MERIS detector and each acquisition time but it affects these values to the corresponding MERIS L1B product pixels. It must be noted here that since the MERIS product grid is filled by a nearest neighbour method from the Instrument Acquisition grid with a slight spatial over-sampling, the same instrument sample can be found several times in the same Level 1b product (it is then identified as a DUPLICATE pixel within the Level 1b product flags). Since the additional geo-location information of the MER_FSG_1P product is linked to the source Instrument sample, it will be duplicated the same way than the radiance information.
Ortho-rectified geo-location must be understood as the computation of the intersection of a given sample line of sight with the Earth surface (as represented by the Digital Elevation Model) rather than with the reference ellipsoid as in Level 1b. However, it must be noted that image geometry is either the Instrument one (FSO mode) or the Level 1b one (FSG mode) and thus the output product is not ortho-rectified.
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Email: Tyler.B.Stevens at nasa.gov
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