es alter the optical properties of marine waters. Remote sensing, which shows up colour variations of sea water, can therefore be used to draw up a map of this turbidity. This map, put together using images transmitted by the Landsat satellite, was studied alongside quantified data derived from in situ measurements, and against figures gleaned from the numerical model. Estimation of concentrations of suspended matter by remote sensing proved to be reliable, with a low average uncertainty rate of 17.5 %. However, satellite images are accessible only in clear weather without strong wind (i.e. at < 10 m/s wind speed or < 20 knots), which would generate too much foam and make it difficult to determine the optical properties of the waters. Remote sensing is nevertheless a powerful tool, which when coupled with numerical models provides a means of indirectly determining the spatial distribution of the erosion rate over the whole of the southwest lagoon. The data provided thus help to refine and validate the numerical models, the only type capable of rendering three-dimensional information on the dynamics and movement of sedimentary particles with temporal predictions.

Furthermore, the combined use of remote sensing and numerical models opens up new prospects for research. Seeing that it is possible to plot the spatial distribution of the sea-floor erosion rate, future research will attempt to analyse this parameter taking into consideration the origin of the sediment particles that have been put back into suspension. These can be the result of soil erosion (terrigenous origin) and subsequent transport by rivers. In this case, they are more easily put back into suspension in the lagoon. Other sedimentary particles can come from the activities of marine organisms (biogenic origin). These muds of marine origin, more compact, are more difficult to put into suspension. Accurate indications of the sedimentary particles' biogenic or terrigenous nature shoul
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Contact: Hlne Deval
presse@paris.ird.fr
33-01-4803-7519
Institut de Recherche Pour le Dveloppement
5-Apr-2005

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