Datation and Geolocation

The algorithms used to compute the time-tag of the measurements will:
  • convert the on-board time counters (coarse and fine) of ISPs to a GPS time
  • reference the time-tag of the measurements to the time when the pulse is reflected from the over-flown surface
  • reference the time-tag of the measurements to the middle of the tracking cycle
  • convert to Universal Time Code (UTC) time. Internally, the Global Positioning System (GPS) format is used but it is converted to UTC time with reference date January 1st 2000 (this conversion also includes handling of leap seconds).
The geo-position parameters (latitude, longitude, altitude and altitude rate) are calculated using the orbit file generated by the Precision Orbit Determination (POD) team at ESOC and the input date and time of each measurement generated . The POD file links the satellite position to the UTC time of the satellite platform. The Level-1 processing chain calculates the precise position of the measurements, interpolating the position in the precise date/time of the measurement. The library used to compute these locations is a Custom Furnished Item (CFI) provided by ESA.
The Sentinel-3 mission CFI software version 4.X.

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