GSC Sentinel-2 PDGS OCD - Emits - ESA

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ESA UNCLASSIFIED – For Official Use GSC Sentinel-2 PDGS OCD Issue 1 Revision 2 (draft) - 25.07.2010 GMES-GSEG-EOPG-TN-09-0008 page 132 of 350 whenever no data is fed by the MMFU, the satellite XBS will automatically transmit idle frames with an adequate noise pattern to make the modulated signal compatible with CCITT regulations. 4.5.4.2.3 Ancillary-Data Packet-Store Management As introduced in section 4.3.8.5, the asynchronous handling of the Ancillary and MSI data on board, each one routed to different packet stores separately operated for downlink, imposes a specific scenario to ensure that the ancillary data coinciding in time with the MSI data downlinked at a specific CGS or LGS is appended to the downlink. The ancillary data acquired along one orbit can be downlinked in a very short time at any given station pass unlike the corresponding MSI data which will necessarily be scattered throughout several station passes. It is hence required that the ancillary packet store is managed as a time-rolling buffer systematically ensuring via its complete playback the coverage in time of the MSI data timeline received at every CGS or LGS. To this aim, and coupled with the ancillary data acquisition scenario described in section 4.5.4.1.2, the ancillary-data circular buffer will be operated as follows for data recovery onground: ○ It will be minimally sized such as to hold at any given time the data down to a couple of orbits in the past corresponding to the maximum uncertainty inherent to the MSI data downlink strategy; ○ It will be managed as a time-rolling buffer (cf. 4.5.4.1.2) and downlinked entirely by playback to every CGS or LGS following the MSI downlink. This will ensure that the acquired ancillary-data covers entirely the MSI timeline recovered at the station. Playback commanding of the Ancillary memory will be driven by the PDGS through the mission-planning loop with the FOS. Adequate sizing of the packet store can be performed in-flight via a specific telecommand. The PDGS will manage this parameter as part of its mission planning activities such that it can be re-adapted at will following changes on the overall data downlink scenario. 4.5.4.2.4 On-Ground Data Reception At every CGS, the PDGS will acquire the mission data downlinked from the spacecrafts as driven by the CGS schedules derived from the downlink plan (cf. section 4.5.4.2.1.4). According to the downlink agenda, the reception activities will be activated shortly before the planned AOS event and include the following real-time operations: o The antenna selected for acquisition will be moved to the AOS position and signal search will be activated enabling tracking on the RF carrier signal with the associated antenna movement until the planned LOS; o Bit synchronisation, locking on the Sentinel-2 signal and demodulation from AOS to LOS will be autonomously performed by the demodulation hardware. For Ka-Band acquisitions via EDRS, a dedicated EDRS compatible hardware will perform the demodulation; o Front-end processing activities will be performed in parallel according to the front-end processing schedule including frame synchronisation, decoding (descrambling and © ESA The copyright of this document is the property of ESA. It is supplied in confidence and shall not be reproduced, copied or communicated to any third party without written permission from ESA.
GSC Sentinel-2 PDGS OCD Issue 1 Revision 2 (draft) - 25.07.2010 GMES-GSEG-EOPG-TN-09-0008 page 133 of 350 Reed Solomon FEC), time annotation of telemetry data and real-time storage.. In parallel, the acquired raw data will be supplied in real-time to downstream PDGS functions for further elaboration. Demodulation and front-end processing will be performed in parallel onto two redundant equipments to provide for reliability. A single equipment will be configured for nominal autonomous downstream data-supply operations to the Level-0 processing chain. The second unit will be used on contingency (cf. section 4.5.4.3.2). 4.5.4.3 Real-Time Data Downlinks to Local Stations As anticipated in section 4.2.7, the PDGS will accommodate LGS real-time downlinks in the mission plan. This operation will be based on a predefined network of LGS granted through HLOP for direct-downlink access. 4.5.4.3.1 Planning Strategy At each mission-planning session (cf. 4.5.3.1.1) and after the preliminary downlink plan to the CGS network has been settled, additional opportunities for real-time transmission left in the X-Band downlink budget (cf. section 4.3.8.4) will be computed. An ancillary data playback will systematically be appended at the term of each RT opportunity as described in paragraph 4.5.4.2.3 and further detailed in [AD-03]. The resulting plan will be merged in the nominal mission-plan fed to the FOS. As mentioned earlier, the prospects of a core mission data-recovery scenario to a CGS network including X-Band ground-stations appointed to receive RT data (e.g. over Europe) will enhance the possibility to serve a coinciding LGS network. In this case, the Ancillary packet store enabling MSI processing might require two successive downlinks: ○ A first one at the term of the core RT downlink in such a way that it can be received by the coinciding LGS network; ○ A second one placed immediately after a possibly trailing NRT/Nominal playback commanded following the RT segment to take benefit of the remains of the core station visibility. Figure 4-22 depicts an example of this scenario whereby a core RT downlink over a CGS located in Europe is received in parallel by two coinciding LGSs, LGS1 and LGS2. It successively features: ○ One continuous RT segment covering the European zone acquired entirely in the CGS and in parts by LGS1 and LGS2; ○ One Ancillary-Data playback at the term of the European coverage RT acquisition dedicated to enabling MSI data-processing in LGS stations; ○ One playback segment of on-board recorded MSI data (NRT, Nominal or both) taking benefit of the remaining CGS visibility whilst RT is no more required; ○ One trailing Ancillary-Data playback at the end of the CGS visibility to enable MSI data-processing at the CGS. ESA UNCLASSIFIED – For Official Use © ESA The copyright of this document is the property of ESA. It is supplied in confidence and shall not be reproduced, copied or communicated to any third party without written permission from ESA.
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[RD-33] Sentinel-2 MSI - Level 2A A
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LES LGS Land Equipped Sites Local G
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3.5.2 MULTI-SPECTRAL INSTRUMENT CHA
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5 PDGS DESIGN GSC Sentinel-2 PDGS O
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○ Effective processing resources
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o preserving integrity of exchanged
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6 DETAILED OPERATIONS CONCEPTS GSC
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o Report generation frequency and c
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○ MSI L1A, L1B, L1C and TCI produ
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Some relevant use cases are present
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Two main mapping services have been
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The requirement on the cloud covera
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GSC Sentinel-2 PDGS OCD - Emits - ESA

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