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 158 of 350
4.5.4.10.4.1 Cloud Screening
For Cloud Screening, algorithms will be calibrated (i.e. threshold and parameters will be
defined) based on an empirical approach using an imagery dataset composed by a calibration
sub-set (for defining the algorithm parameters) and a validation sub-set (for algorithm and
products validation purposes).
Calibration and Validation will be performed based on the visual inspection of images and for
a set of test sites based on ground observation of atmosphere status (eventually also
supported by instrumental measurements of variables such as aerosol optical thickness).
4.5.4.10.4.2 Atmospheric Correction
For Atmospheric Correction, the calibration of the algorithms and the validation of the
obtained products (bottom-of-atmosphere reflectance, aerosol optical thickness and water
vapour content) will be performed using a set of test sites representative of main surfaceatmosphere
types.
For a quantitative validation, these sites will include the LANDNET sites which are a set of
Land Equipped Sites (LES) endorsed by CEOS as standard reference sites for the calibration
of space-based optical imaging sensors. In addition, ad-hoc validation campaigns will be
organized involving airborne, balloon and ground measurements.
4.5.5 X-BAND HKTM MISSION OPERATIONS
As outlined in section 4.3.7.3, HKTM data is required by the FOS for spacecraft health
monitoring with an update frequency of no less than once per orbit.
To this end, the PDGS will perform the following operations:
○ Through the mission-planning and scheduling loop (cf. 4.5.3.1.1), the MMFU HKTM
data-store will be systematically commanded for playback at every spacecraft
revolution coinciding with a downlink opportunity at a CGS, making sure that all HKTM
data buffered on-board since the last playback operation is downlinked and then freed
to start a new recording cycle.
○ On reception and as part of its systematic data-driven operations outlined in paragraph
4.5.6 the PDGS will package the data and forward it to the FOS no later than one hour
following downlink;
For sake of optimising this process, the PDGS generated mission-plan will concentrate as
much as possible all HKTM downlinks to a limited number of CGSs, in particular to the ones
pre-allocated for NRT processing at the station, such that HKTM delivery to the FOS is
performed in a reliable and deterministic manner at every orbit.
Although this is likely to result into a systematic scenario with one-orbit frequency and using
polar stations, the final HKTM mission scenario will be settled once the operational CGS
network has been selected.
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