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Altimeter measurements | Orbit Determination | Geophysical corrections | Instrumental errors | Reference surface | Flags | Retracking | High-level processing

3.2.2.3. Geophysical corrections

The following corrections are computed:

Geophysical corrections

• Ocean tides
  Corrections for solid earth and sea surface height variations due to the attraction of the Sun and Moon. Calculated by models.
  Order of magnitude: 1 m in mid-ocean, up to 15-20 m near some shorelines.
   
• Solid earth tides
  Corrections for solid earth variations due to the attraction of the Sun and Moon. Calculated by models.
  Order of magnitude: 50 cm.
   
• Pole tides
  Corrections for variations due to the attraction of the Sun and Moon. Calculated by models.
  Order of magnitude: 2 cm.
   
• Tidal loading
  Corrections for height variations due to changes in tide-induced forces acting on the Earth's surface. Calculated by models.
  Order of magnitude: 30 cm
   

Propagation corrections

• Ionosphere
  Correction for the path delay in the radar return signal due to the atmosphere's electron content. Calculated by combining radar altimeter measurements acquired at two separate frequencies (C-band and K_u-band for Topex and Jason-1, K_u-band and S-band for Envisat).
  Order of magnitude: 0 to 50 cm
   
• Wet troposphere
  CCorrection for the path delay in the radar return signal due to liquid water in the atmosphere. Calculated from radiometer measurements and/or meteorological models.
  Order of magnitude: 0 to 50 cm
   
• Dry troposphere
  Correction for the path delay in the radar return signal due to the atmosphere. Calculated from meteorological models.
  Order of magnitude: 2.3 m
   

Surface corrections

• Inverse barometer
  Correction for variations in sea surface height due to atmospheric pressure variations (atmospheric loading). Calculated from meteorological models.
  Order of magnitude: about 15 cm, depending on atmospheric pressure
   
• Electromagnetic bias
  Correction for bias in measurements introduced by varying reflectivity of wave crests and troughs. Correction calculated from models. Bias uncertainty is currently the biggest factor in altimeter error budgets.
  Order of magnitude: from 0 to 50 cm, depending on wave heights