For certain major rivers and wetlands, hydrological information can often be difficult to obtain due to a region’s inaccessibility, the sparse distribution of gauge stations, or the slow dissemination of data. Satellite radar altimeters can potentially monitor height variations of inland waters [Birkett, 1998]. Hydrological products from satellites are unaffected by political and logistical considerations and can provide accurate height measurements not only for lakes but also for large rivers such as the Amazon, which has been a primary target of study over the last ten years.


fig 1. Map of surface topography, derived from ESA Cryosat-2 SARin L2 products over the Solimões river (Brazil). A lot of the SARin measurements are focused on the river network sometimes kilometers away from the satellite’s ground track (Credits Along-Track)


Monitoring now covers at least 15 major rivers in all the world’s continents, and a wealth of others are possible, especially with the high-resolution altimetric range (20 Hz) available, or with altimetric waveform-specific retracking. Recent studies (Berry et al 2012) using individual echoes (‘bursts’) should give access to even more new targets. The assimilation of altimetry data in hydrodynamic models should also lead to advances in knowledge and ultimately even in forecasting hydrological systems.


fig 2. Sample multi-mission time series over the Brahmaputra: red Topex, blue ERS-2, pink Envisat. Circles show all possible targets from ERS-2.
(Credits De Montfort University)



  • Birkett, C.M., Contribution of the TOPEX NASA radar altimeter to the global monitoring of large rivers and wetlands. Water Resour. Res., 34 (5), 1223-1239, 1998.
  • Berry, P.A., Smith, R.G., Salloway, M.K. and Benveniste, J., 2012. Global analysis of EnviSat burst echoes over inland water. IEEE Transactions on Geoscience and Remote Sensing, 50(5), pp.1980-1985.