Once the altimetry and watermasks datasets selected, the computation of the river geometry is computed using the dedicated workflow presented in Figure 1 in the case of ICESat-2 data for the Z and ExtractEO watermasks to estimate W. The main concept behind this methodology is to merge wse and widths timeseries, by first interpolating in time on common timestamps and then fit a powerlaw W=aZb to filter noise in both the widths and wse observations. Finally priors for the two remaining unknowns for the hydraulic model, namely the bathymetry (or equivalently the unobserved flow area A0 in part 1 – Figure 1) and the friction coefficient are estimated using usual methods (inversion of the Manning equation, geomorphological laws, etc.). 

Figure 1 : Example workflow of the method. 

Figure 2 : Example of a cross-section geometry in the (t,z) plane estimated using our method. (Left) timeseries of Z and W with Z interpolated on the W timestamps, (right) (Z,W) observations in red dots and fitted powerlaw a(Z-Z0)b in dashed blue line. 

The final mesh (geometry) of the model obtained using SWORD v17b and a fusion of ICESat-2 + Sentinel 3 altimetric data with widths computed from ExtractEO watermasks is illustrated on Figure 3. This mesh consists in 11 segments with a total of 5229 cross-sections. 

Figure 3 : mesh of the 1D hydraulic model for the Garonne (La Réole) basin, which contains 11 river segments and a total of 5229 Cross-sections. 

To go further, another application example has been published in Water Resources Research) (see Larnier et al, 2025) with full analysis of the assimilation of a fusion of in-situ and EO data to improve the estimation of discharges along the Maroni River network using a coupled hydrological-hydraulic model. 

References 

Larnier, K., Garambois, P.-A., Emery, C., Pujol, L., Monnier, J., Gal, L., et al. (2025). Estimating channel parameters and discharge at river network scale using hydrological-hydraulic models, SWOT and multi-satellite data. Water Resources Research, 61, e2024WR038455. https://doi.org/10.1029/2024WR038455