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 84 of 350
Orbit N-1 descending part
Orbit N descending part
`CGS-A
CGS-B
MMFU MSI packet store playback timeline
Explicit playback
interruptions
MSI imaging timeline
NRT NRT Nominal
ocean
NRT
RT
CGS-A
CGS-B
Spurious data discontinuities
introduced in the station RX timeline
Figure 4-5: MSI Timeline Discontinuities after Downlink
It shows that as seen from the two distinct timelines received at each ground-station three
kinds of discontinuities have been added to the overall MSI acquisition timeline:
○ Discontinuities introduced due to the playback being explicitly suspended at the term of
CGS-A and CGS-B visibilities at orbit N (green bullets).
To be noted that is not always the case as it may happen that the packet store is
actually emptied at the end of a station pass in which case the playback is stopped
naturally and no artificial discontinuity is introduced;
○ Discontinuities introduced by the NRT partitioning leaving orphan segments and
corresponding gaps in the MSI timeline (orange bullets);
○ Discontinuities introduced by the RT direct-downlink segments having similar impact
(red bullets).
It is assumed that the discontinuities will be introduced with a granularity of exactly one MSI
on-board scene acquisition (corresponding to 3.48 seconds of instrument operation and about
23km on ground along-track) as corresponding to the minimum indivisible packet size of the
MSI.
These discontinuities coupled with the MSI observation parallax described in the previous
paragraph would induce a specific complexity in the timeline reconstruction required onground
to ensure band co-registration in the final products.
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