Describes all auxiliary information that will be used by the PDGS for the processing of MSI data. The auxiliary data required in MSI data generation are:
Calibration is the process applying a quantitative definition to the system responses with respect to known and controlled signal inputs.
Validation is the process of assessing, by independent means, the quality of the data products derived from the system.
The calibration and validation (cal/val) of the MSI instrument and acquisition chain is the process of updating and validating the on-board and on-ground sensor and associated algorithmic parameters in order to meet predetermined product data quality requirements, and to mitigate drift in responses over the lifetime of the mission.
The continuous acquisition of an image from one SENTINEL-2 satellite in a given imaging mode is called a "data-take". The maximum length of an imaging data-take is 15,000 km (continuous observation from northern Russia to southern Africa). However, this would require the potential for continuous acquisition by a single ground station and is currently unlikely. The future introduction of the European Data Relay Satellite (EDRS) geostationary system offers the potential for continuous acquisition of data-takes.
Within a given data-take, a portion of image downlinked during a pass to a given station is termed a "datastrip". If a particular orbit is acquired by more than one station, a data-take will consist of one or more datastrips. There may be several distinct segments of a data-take separated by gaps of whole granules (see below). This happens when the instrument is switched to a new operational mode, such as over oceans. It is expected that the maximum length of a datastrip downlinked to a ground station will be approximately 5000 km.
Granules and Tiles
The elementary level of MSI products are granules of a fixed size. The granule size is dependent on the product level.
Granules are sub-images of a given number of lines along track and detector-separated for Level-0, Level-1A and Level-1B products. A granule covers approximately 25 km across track and 23 km along track. Granules are defined further for each product level type.
For Level-1C , the granules, also called tiles, are 100 km squared orthoimages in UTM/WGS84 projection.
A medium that accompanies the data, and can be used to obtain information necessary to determine the suitability of a product for a certain use or application.
MSI image data is packaged in a set of Instrument Source Packets (ISPs) on-board the satellite. This set of ISPs is called an "on-board scene" or "scene", and corresponds to a simultaneous observation of all bands and all detectors of approximately 3.6 seconds in duration. During this time, the satellite has moved along track by approximately 23 km measured at the Earth's surface.
There are three categories of timeliness defined for SENTINEL-2 operation: