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River monitoring

For certain major rivers and wetlands, hydrological information can often be difficult to obtain due to a region's inaccessibility, the sparse distribution of gauge stations, or the slow dissemination of data. Satellite radar altimeters can potentially monitor height variations of inland waters. These heterogeneous surfaces require special processings.

The Amazon, the largest river system in the world, is well unknown because its inaccessibility, especially in its upstream. If the river is not everywhere as wide as its mouth, flooded areas by reflecting radar altimeter correctly, are sufficient to allow a satellite altimetry monitoring.

River levels, temporary or permanent flooded areas (linked to the occurence of diseases like malaria in developing countries) can be observed and integrated into hydrological models.

On left, satellite image from Google Earth with Solimoes, Negro and Amazon rivers. On right, Amazon level in this area. There are important annual amplitudes of the river and a less accuracy in altimetry measurements during low water where the width of the river is not enough to "hang" the altimeter. Credits Cash Project.

Fifteen years of measurements

The succession of altimetry missions since the early 90s allows a continuous monitoring of rivers. Thus, fifteen years of measurements are accumulated with Topex/Poseidon and Envisat in areas where tracks of the satellites overlap or are not too remote.

River level anomalies over the Orinoco river from Topex/Poseidon (in red and green, from 1993 to 2002) and Envisat (in blue, from 2002 to 2008). Error bars correspond to the standard deviation of the measurement at a given date. Other examples are available for the following rivers: Orinoco, Congo, Indus, Niger, and Nil. Credits Legos / Hydroweb.

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