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2.8.3 Datation

To derive the surface height the RA measures, very precisely, the range to the surface. It is also necessary to locate the time and position on the surface where the measurement was taken. This is called the Datation. As the RA is a high-precision instrument the Datation must also be know to a high precision.

 

A single RA-2 measurement is actually an average of 100 pulses reflected from the surface and we define Datation as:-

The exact time when the averaged waveform is reflected from the surface,and hence,when the middle of the 100 averaged waveform is at the surface.

It is important to remember that a Range measurement and its Datation must be consistent. This consistency is ensured in the RA-2 data products due to processing at Level 1. The computation takes into account all the important factors including:-

  • Location of the mid point of the averaged waveform
  • Time when the value of the datation is actually generated by the hardware
  • The rate of change of the time delay (Window Delay) during a measurement
  • Propagation time delay from satellite to surface
  • Time when the value of the range is taken from the on-board hardware

 

Full details of the Datation computation are documented in an ESA Tec-note PO-TN-ESA-GS-00588


Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry