Altimetry measures the range, which is the distance between the satellite and the sampled surface. This distance minus the satellite position (altitude) gives the surface height above the reference ellipsoid. Therefore, the surface height field is computed via the following equation:

Surface Height = altitude – Corrected Range

Where: Corrected Range = Range + all necessary corrections

In Level 1B products the geophysical corrections are not applied to the range or time delay. All corrections are included in the data products and therefore the range can be calculated by taking into account the surface type.

In Level 2 products the surface height is fully corrected for instrumental effects, propagation delays, measurement geometry and additional geophysical effects. The L2 Correction Applied flags inform users which corrections have been applied in each mode.