What most people are interest in about the sea is mostly at the beach level (especially in Summer), or at the furthest, just abroad the harbors and river mouthes, than at the open sea level. For a long time, those coastal areas have been put aside by altimetry. Now, with knowledge increase and 15 years of conitunous experience in radar altimetry, altimetry data enhancement near the coasts is under study in several scientific teams around the world.

This shortage of altimetry data (or their lower quality) near the coasts is due to several things:
   - to the technique in itself, since the radar echoes reflected over water or over water and land mixed are not identical, and only the former are processed, basically, by the ground segments. Other altimetry satellite measurements have also the same problem, like the radiometer (at a distance of about 50 km from the coast)
   - to the fact that the basic distributed data (GDR) are mainly average over one second, thus covering about 7 km (data averaged over 1/20 s exist, however).
   - To the computation of some corrections. Tides, in particular, are much more complex near the shores than in the open sea, and request a high precision on the coastal geography to be accurately computed. Moreover, rapid variations ("high frequency") must be taken into account in those areas (for the tides as well as for the atmospheric pressure). Wet tropospheric corrections, computed from radiometer measurements are also less precise, or even missing, near the coasts.

See also:

• Applications: Tides
• Data: Regional products

Websites on this subject:

• Symposium "15 Years of Progress in Radar Altimetry", Coastal Oceanography session and posters
• Coastal Oceanography (Observatoire Midi-Pyrénées)