Monitoring continental surfaces by satellite altimetry

Welcome to the CTOH (Centre de Topographie des Océans et de l’Hydrosphère) web page dedicated to applications of satellite altimetry overs continental surfaces and for hydrology.


A technology initially developed for the determination of marine geoid undulations and monitoring dynamic ocean topography, satellite altimetry has demonstrated strong potential in the study of the polar ice caps and continental surfaces.

The Centre of Topography of the Oceans and the Hydrosphere (CTOH) is a French observation service for the National Institute for Earth Sciences and Astronomy (INSU) and the French Institute for Development Research (IRD). Based at the Laboratory of Studies in Spatial Geophysics and Oceanography (LEGOS), at the Midi-Pyrénées Observatory (OMP), the CTOH is specialised in the processing and distribution of radar satellite altimetry data.

Motivated by the importance of better understanding the water cycle on the continents, the CTOH offers new tools and products for specialists in earth observation from space who want to develop new applications in the field of space hydrology, water cycle modellers looking for data to validate or force hydrologic and hydrodynamic models, and hydrologists working on the scale of a catchment area who would like additional sources of data to use with the measurements they rely on traditionally



Differences, in metres, between minimum surface water levels in 2005 and the average minimum of this level for the period from 2003 to 2007, obtained by combining the extension of flooded surface areas determined using satellite images and the water levels given by satellite altimetry.

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