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 55 of 350
3.5.2.3.2 Scene Packaging
The on-board mission data is packaged in “Scenes” ensuring the consistency of a selfcontained
data set including all data from the 12 detectors and the 13 spectral bands.
A “Scene” is composed of 13 scene channels (one scene channel corresponds to one
spectral band), each one compiling the compressed data aggregated along a distance of
approximately 23km along-track by the 12 detectors.
The 23 km along-track is synchronised between channels of different relative pixel sizes by
an appropriate selection of the number of compressed blocks aggregated per scene channel.
This results into 144 blocks (resp. 72 and 24) for the 10m (resp. 20m and 60m) channel.
Considering 12 bits per pixel, the volume of each scene will amount to 4Gbits of
uncompressed data leading to about 1.4 Gbits after compression.
Overall, each compressed block inside one scene will be packaged into one CCSDS
Instrument Source Packet (ISP), resulting into a scene assembly of exactly 12960 packets.
3.5.2.3.3 Measurement Datation
The satellite clock, synchronised by the GPS measurements at 1Hz (TBC), in turn enslaves
the master-clock of the MSI. Within the MSI, an accurate datation process strongly linked to
the data generation process is then carried-out down to the actual time-stamping in the
generated ISPs. This process is summarised as follows:
○ At the start of acquisition of a new scene, the mater-clock time is stored. During the
processing period, this time information is reported in all source packets of the scene
(referred to as the CUCM_s tag);
○ During the scene acquisition period, the master-clock drift is estimated and a
correction value (referred to as Δ_s) is reported in all ISPs of the scene.
3.5.2.4 On-Board Configuration
The MSI imaging characteristics are configurable by way of parameter tables held on-board
and which can be altered by ground commanding. The SOCD [AD-03] details the contents of
each table and associated uplink strategy.
These tables allow the configuration of:
○ Image processing parameter sets (IPS), allowing to swiftly switch instrument imaging
characteristics along the orbit from seven different configurations. Those configurations
will be mapped to each operational mode of the instrument including nominal imaging
or specific calibration modes required for performance assessment and Cal/Val
activities. In particular the WICOM compression ratios are configurable though the IPS
tables;
○ The Non-Uniformity Coefficients (NUC), allowing the detector responses to be
equalised independently at pixel-level before on-board compression of the image. NUC
equalisation can be deactivated for calibration activities by way of an IPS switch;
○ Thermal Control Module (TCM) configuration data, allowing to fine-tune the thermal
control of the instrument;
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