Satellite altimetry is an important supplement for water level monitoring. Water level time series are traditionally reconstructed at virtual stations (VS), where the satellite ground track intersects the river. The Surface Water and Ocean Topography (SWOT) mission provides a nearly complete spatial coverage, which allows us to study changes in the surface water profile along river reaches. The temporal resolution is approximately 10 days or better, depending on the latitude. However, if we combine SWOT with the traditional nadir altimetry, we can increase the temporal resolution and extend the water level time series back in time.

Here, the R package “Altimetry River Reach Methods” (ARRM) is presented. The core functionality of ARRM is to reconstruct a water level time series using all available satellite altimetry data over a river reach, unlike the classical VS approach, where only one mission is applied. A Gaussian Markov Random Field is used to reconstruct the reach-based water level. ARRM exploits the river center lines from the SWOT River Database (SWORD), ensuring an easy connection with the SWOT data, e.g., the RiverSP product. Here, the functionality of the R packages is demonstrated via examples from different rivers