*4.5. Estimation of Volume Variation Time Series*

For the calculation of a time series of volume variations, bathymetry and water levels are required to get information on water depth of different pixels. For that purpose, water levels from satellite altimetry as well as water levels derived from surface areas and hypsometric curve are used. In the first step, each water level is intersected with the bathymetry to calculate the volume below the water level pixel by pixel. Finally, all pixel volumes of the current water level are accumulated to obtain a volume above the minimum observed surface area. Since the volume below is unknown, only time series of volume variations can be estimated. Additionally, surface area errors are converted into volume errors by using the hypsometric curve and bathymetry. Detailed examples and discussion of bathymetry and the resulting time series of volume variations are shown for selected inland water bodies in Section 5.1.
