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GSC Sentinel-2 PDGS OCD - Emits - ESA

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6.4 On-line Quality Control (OLQC) Operations<br />

6.4.1 PRINCIPLES<br />

6.4.1.1 Systematic Quality Control Concept<br />

<strong>ESA</strong> UNCLASSIFIED – For Official Use<br />

<strong>GSC</strong> <strong>Sentinel</strong>-2 <strong>PDGS</strong> <strong>OCD</strong><br />

Issue 1 Revision 2 (draft) - 25.07.2010<br />

GMES-GSEG-EOPG-TN-09-0008<br />

page 258 of 350<br />

Systematic quality control consists in performing essential quality checks on all MSI data<br />

generated by the <strong>PDGS</strong> in an entirely autonomous manner (operator unattended). The<br />

checks include basic consistency verification of the format and value ranges, and more<br />

complex and specific control algorithms over the quality indicators associated to the<br />

radiometry and geometry properties of the images (e.g. histograms statistics, GCP residuals,<br />

etc).<br />

The result of the systematic quality-control activity is the annotation of Quality Indicators (QI)<br />

that will be embedded in the product metadata for:<br />

○ Monitoring and investigation purposes;<br />

○ Overall traceability under the form of one or several “quality-reports” linked to the<br />

product.<br />

In addition specific expert QIs will be computed for short to long term monitoring purposes<br />

through the <strong>PDGS</strong>/MPA complementary function.<br />

6.4.1.2 Quality Indicators (QI) Generation & Usage<br />

Depending on the product level, several on-line quality indicators have been identified.<br />

Examples of envisaged on-line quality check are described in [RD-07].<br />

Most of them can directly be derived from the product quality indicators generated by the<br />

<strong>PDGS</strong>/IDP function during the products processing; others are derived by the OLQC function<br />

through simple operations on the product.<br />

Every QI generated by the OLQC function will be appended to the relevant data products.<br />

Most QIs will be used for off-line (i.e. not real time) monitoring activities (by the Off-line<br />

Quality Control sub-function of the MPA) in order to control products performance and<br />

accuracy trends, as well as to extrapolate instrument performances.<br />

6.4.1.3 Quality Indicators (QI) Scope<br />

The OLQC function quality checks are autonomously applied on the MSI product data and<br />

metadata according to the logic breakdown as defined in the <strong>Sentinel</strong>-2 Product Definition<br />

Document (cf. [RD-07]) and the physical layout modelled for the archiving purposes (i.e. the<br />

product data items – PDIs).<br />

Accordingly the OLQC operations are performed at different levels according to the<br />

production breakdown:<br />

PDI-level: this is the general case of processing the product data and metadata in<br />

order to retrieve and verify the quality information detected/contained at single PDI<br />

© <strong>ESA</strong><br />

The copyright of this document is the property of <strong>ESA</strong>. It is supplied in confidence and shall not be reproduced, copied or<br />

communicated to any third party without written permission from <strong>ESA</strong>.

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