Minimize Geophysical Measurements

The main geophysical parameters to be measured by the SENTINEL-3 topography mission are:

  • Surface Height (SSH)
  • Significant Wave Height (SWH)
  • Wind speed over ocean surface.

These parameters are retrieved from the physical characteristics of the altimeter waveforms received by the SRAL instrument.

Figure 1: Physical Characteristics of the Altimetry Waveforms (Credit: isardSAT)


  • Epoch: this is related to the range. SSH is computed from it.
  • P: power of the useful signal. This power, with respect to the emitted power, gives the backscatter coefficient, sigma0. Sigma0 (together with the SWH) is used to estimate wind speed.
  • Leading edge slope: this can be related to the Significant Wave Height (SWH).
  • Trailing edge slope: this is linked to antenna mis-pointing and Significant Wave Height (SWH).


Parameter Range NRT delivery NTC delivery
SSH - 10 cm 3.5 cm
SWH 0.5 - 20 m 4% 1%
Wind Speed 0-20 m/s  2 m/s  1.5 m/s 

Table 1: Measurement requirements for altimetry specified for 1 Hz averaged along track samples