On the Use of Very high Resolution Optical Images to Map River Bathymetry : Upscaling from Aerial to Satellite Smagery
Feurer, D1; Bailly, J.-S2; Le Coarer, Y1; Puech, C1; Viau, A. A3
1Cemagref; 2Engref; 3GAAP
On the way towards estimation of river discharge from space, the description of river bathymetry at the catchment scale is a key issue. In this paper, we show that very high resolution satellite optical imagery has to be considered as an interesting compromise allowing gravel-bed river depth mapping at a fair spatial resolution at the catchment scale.
We initiated the upscaling approach by analysing the potential of aerial images with a few centimetres ground pixels. Two methods have been assessed : radiometric models and through-water photogrammetry. The basis of radiometric models is to take advantage of the logarithmic relationship between water colour and river depth (light absorption). The model is calibrated with a few points and then extrapolated on the whole image. This study showed that a spatial filtering up to a metric resolution gives the best results. Then we used stereo pairs to measure immersed topography by through-water photogrammetry. In this context, an heterogeneous river bottom (showing distinguishable objects) and not a too wavy water surface are required. This work showed that the measure is feasible within these specific conditions with a precision hardly better than the pixel size. Consequently, we used the radiometric information of Quickbird images to map the river morphology and depths with the view to demonstrate the potentiality of operational river cartography from very high resolution satellite images at the watershed scale.