GSC Sentinel-2 PDGS OCD - Emits - ESA

GSC Sentinel-2 PDGS OCD
Issue 1 Revision 2 (draft) - 25.07.2010
GMES-GSEG-EOPG-TN-09-0008
page 142 of 350
4.5.4.5.3.3 Processing Margins
Considering that Level-1 image processing can be performed independently per-detector, the
required overall fore+aft margin amounts to twice the sum of the margins budgeted in
sections 4.3.9.1 (2/3 rd of a scene) and 4.3.9.2.2 (10% of a scene), resulting in 2 scenes
considering the granularity of the measurements.
For spatial registration (cf. section 4.3.9.2.3) it is introduced a margin of three MSI scenes
total overlap (fore+after margin overlap) at each discontinuity (cf. section 6.20.3Appendix-B -
MSI Scenes Overlap Analysis).
Hence, the compound processing will require a fore+aft margin of three MSI scenes to be
ensured as described in section 4.5.4.2.2.2.
4.5.4.5.3.4 Preliminary Quick-Look and Cloud Mask Processing
Since all data will be elaborated up to Level-1C, the final preview image (PVI) will be
computed over the Level-1C images. Nevertheless, a preliminary quick-look (PQL)
processing will be performed and will be used to derive a preliminary cloud-mask mapped on
the Level-1A and Level-1B geometry.
This preliminary quick-look generation requires coarse band registration (with at least 150m
accuracy) which is impaired by the Datastrip discontinuities (cf. previous paragraph). As such,
it will be implemented as a Level-0 consolidation processing sequence, deferring the
extraction steps specified for the GPP Level-0 inventory sequence.
In complement, the derived cloud-mask will be used to extract a coarse cloud-cover metadata
comprehensively summarising the cloudiness of each MSI scene and detector measurement.
This metadata will be appended as ground-generated ancillary data and processed as an
inventory item such that it can be used to selectively filter the data by simple threshold at
Level-0, Level-1A and Level-1B processing levels and with a spatial granularity of 23km x
25km.
During commissioning phase, the preliminary quick-look will be provided optionally as a
downloadable ground ancillary data of the Level-0/1A/1B products to provision for potential
problems in the higher level processing steps preventing final quicklook generation.
4.5.4.5.3.5 Spatial Registration
As outlined in paragraph 4.3.9.2.3, the stringent requirements of multi-temporal registration
lead to setup a specific processing to improve the location accuracy based on automatic
ground control point (GCP) selection and a geometric viewing model refinement algorithm. To
this end, a global reference image will be produced starting at commissioning phase of
Sentinel-2A as described in section 4.5.4.10.3.1. Any Sentinel-2 image will then be
geometrically refined thanks to automatic tie-point selections with respect to these reference
images.
Within the PDGS distributed context, the quality of this refinement will be ensured by means
of:
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