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 87 of 350
Those processing steps are theoretically applied on a continuous input image flow
corresponding to the data generation process performed on-board. As such, they require
small portions of image data acquired along-track before and after the data to be processed
hereafter referred to as “radiometric processing margins”.
The overall processing margin is computed by adding up the different contributions needed
corresponding to slightly more than 10% of a scene as reported in [RD-30]:
○ For the decompression step (Level-1A), 32 lines of each band are required before and
after. The worst-case corresponds to 1/12 th of a scene for 60m bands.
○ For the deconvolution of 10m bands (Level-1B) 50 image lines are required before and
after. This corresponds to slightly less than 1/46 th of a scene.
4.3.9.2 Geometry Processing Constraints
4.3.9.2.1 Image Datation
The image datation model is a key element for the geolocation accuracy of the final products.
Referring to the datation process performed on-board as summarised in paragraph 3.5.2.3.3,
a global error-budget was computed (cf. Table 4-1 below) based on Bias (B) and Rate (R)
error-budget figures inherited from the instrument design.
The first column represents the overall accuracy obtained with raw time stamp information
(CUCM_s), and the second one represents the one corrected though the MSI internal
correction (Δ_s).
Contributor Type Budget based on MSI CUC time taking
into account internal time correction (Δ s)
Scene start time B
R
+/- 0.119 µs
+/- 0.09 µs
Scene duration B
R
+/- 0.428 µs
+/- 0.06 µs
Integration period B
R
+/- 0.001 µs
+/- 0.01 µs
Total
B
R
+/- 0.548 µs
+/- 0.109 µs
B+R +/- 0.657 µs
Table 4-1 Datation Accuracy Budgets
This ±0.657μs datation error resulting from the enhanced time correction performed on-board
is expected to contribute to less than 0.5 cm on-ground when reported on the geolocation
error budget, which is negligible.
As return of experience from previous missions, a refinement of the datation model was
nevertheless recommended and will be implemented in the GPP as an optional processing
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