Content: General | Data and Methodology | Datasets | Citation


Water Surface Slope from Satellite Altimetry (WSS) is a fundamental parameter in the calculation of river discharge which is one of the Essential Climate Variables (ECVs) defined by the Global Climate Oberserving System (GCOS). In addition, correcting Water Surface Elevation (WSE) observations from satellite altimetry for WSS can significantly improve the accuracy of the resulting water level time series. Depending on river morphology, regulation, bed material, and basin size, the WSS can be highly variable in both space and time.

Data and Methodology

In 2023, DGFI-TUM published a new global dataset ICESat-2 river surface slope (IRIS). It contains reach-scale average and extreme WSS derived from ICESat-2 observations as a supplement to the SWOT Mission River Database (SWORD). Using ICESat-2's unique measurement geometry with six parallel lidar beams, an instantaneous WSS is determined across beam pairs and along individual beams. Within the IRIS dataset, the median of all instantaneous WSS observations is given with the observed minimum and maximum WSS per SWORD reach. Additionally, IRIS contains the number of observations and their standard deviation. All parameters are given separately for the different methods (across and along beams) and as a combined value that has the largest spatial and temporal coverage. The methodology is described in detail in Scherer, 2022.

Example of Water Surface Slopes from ICESat-2
Dataset Input Data SWORD Area
IRISv2.1 ICESat-2 ATL13 v6 (Cycle 1-19)
(October 2018 to April 2023)
Version v16 global Data Access Map
IRISv2 ICESat-2 ATL13 v6 (Cycle 1-19)
(October 2018 to April 2023)
Version v15 global Data Access Map
IRISv1 ICESat-2 ATL13 v5 (Cycle 1-16)
(October 2018 to August 2022)
Version v2 global Data Access Map
IRISv0 ICESat-2 ATL13 v5 (Cycle 1-13)
(October 2018 to October 2021)
Version v1 selected reaches
see Scherer et al., 2022
Data Access


Scherer D., Schwatke C., Dettmering D., Seitz F. .: ICESat-2 Based River Surface Slope and Its Impact on Water Level Time Series From Satellite Altimetry. Water Resources Research, doi: 10.1029/2022WR032842, 2022

Jasinski M., Stoll J., Hancock D., Robbins J., Nattala J., Morison J., Jones B., Ondrusek M., Pavelsky T.M., Parrish C. and the ICESat-2-Science-Team: ATLAS/ICESat-2 L3A Inland Water Surface Height, Version 5. [Dataset], 2021

Altenau E.H., Pavelsky T.M., Durand, M.T., Yang X., Frasson, R.P.d.M., Bendezu, L. : SWOT River Database (SWORD) [Data set] Zenodo doi: 10.5281/zenodo.3898569, 2021