LEGOS

The member of the CNES/LEGOS have been involved in the development and design of space altimetry applications for around 20 years, as PI of Topex/Poseidon, ERS-1/2, Jason-1/2, Envisat, and the future Altika/Saral and SWOT missions. Many papers have been published, initially about the study of mean sea level variations, at global and regional scale. Since 10 years the team members have also been involved in studying Lake Rivers and flooplains from altimetry, imagery and gravimetry measurements. Analysis of quality of the obtained results to regional hydrology has been undertaken over several hydrological basins. Several articles in international journals have been published last years.

LEGOS has been involved in international programs with the goal of merging in-situ lake data (level, bathymetry, runoff, etc …) with satellite altimetry for specific region (Central Asia, Caucasus, South America, Africa). A lake database has been developed, for a list of around 230 closed lakes and reservoirs in the world (computation were made on Topex / Poseidon, Jason1/2, Envisat, ERS2 and GFO data) which is made available on the web (www.legos.obs-mip.fr/soa/hydrologie/hydroweb/).

Application of satellite altimetry for studies of large river systems became a new field of applications over the last 15 years. Methodology of analysis of altimetry data over big rivers and flood plains has been developed. Most of the existing altimeter-based studies on river basins have been so far limited to the comparison of satellite-derived water level with in situ observed levels. The altimetry data over big river basin in south America (Amazon, Rio Negro, Parana), Australia (Diamantina) and Asia (Mekong, India) has been analysed in order to model and determine river discharges based on altimetry-derived time series (using rating curves), and volume variations over river flood plain (using other remote sensing data). To do this, combination of water level from altimetry and radar and optic imagery (for determining variable area extent of inundated plains) has been performed. Water level time series over the main world hydrographics basins (15 basins studied so far) are currently available on the hydroweb web site. Besides, altimetry data can be used for calculating discharge: it has applied to large Arctic rivers – the Ob’ river and several Amazon contributors (Negro, Caqueta) and to determine hydrological parameters such as the depth of the river bed, the river slope and Manning coefficients.

Over the last 10 years field campaigns with GPS receivers has been carried out to calibrate altimetry over continental water. GPS water level measurements were made over the Rio Negro River in Brasil, the lake Issykkul in Central Asia, the Caspian Sea in Caucasus, and few small lakes in Chile. This was done under the frame of international cooperation and will continue in the near future.

The Legos is also strongly involved in the new altimetry missions in Ka Band (Altika) in cooperation with Indian Space Agency, and also interferometry in Ka band (SWOT) in cooperation with NASA, for which LEGOS is PI of the mission.