Specific Notes:
Regarding surface elevation products:
  1. It is important to consider the location of the satellite ground track AND the section of track used in complex or drought-prone regions where height variability may be location dependent. In such cases check the specific geographical location in the text product header.
  2. The smoothed height variation (lower graphs) products are not available. These can vary according to the smoothing function applied and so are provided as a visualization aid only.
  3. The products are routinely upgraded. End users should note the product version number in the graph legend and table header, and avoid utilizing products of mixed heritage.
10-day Water Level
Water Bodies Date
Monthly Water Level
Water Bodies Date
Project BackgroundTop

This web site provides satellite-based information relating to the current and historical status of the global oceans, lakes & reservoirs, and rivers & wetlands. Here, “status” is primarily centered on variations in surface elevation as provided by a suite of satellite-based radar altimeters. These instruments are onboard various space-agency (NASA/CNES/ESA/ISRO) missions with data set and auxiliary information sourced from NOAA, NASA/GSFC, and RADS? Variations in surface elevation enables changing sea level to be monitored and reveals the seasonal and inter-annual fluctuations in continental waters. The products integrate responses to regional and global climate variations as well as anthropogenic influences. Over land, short- and long-term drought, as well as approaching potential flood conditions, can be highlighted. The data sets span multiple decades and are available in near real time, they thus serve both science and applied science programs. Applications include water resources management, estimating irrigation potential for crop analysis, hazard monitoring, hydro-electric power stability, and regional security.

Satellite Radar AltimetryTop

A satellite radar altimeter is a nadir-pointing instrument continuously recording average surface heights directly below the satellite, as it transverses over the Earth's surface. Operating at Ku or Ka band frequencies, each altimeter emits a series of microwave pulses towards the surface. By noting the two-way time delay between pulse emission and echo reception, the surface height can be deduced. Each returned height value is an average of all surface heights found within the footprint of the altimeter. The diameter of the footprint depends on the surface roughness, but can typically range between 200m (for open pools of water in calm conditions) to a few kilometers (open water with surface waves). Each satellite is placed in a specific repeat orbit, so after a certain number of days the same point (to within 1km), on the Earth's surface is revisited. In this way, time series of surface height changes can be constructed for a particular location along the satellite ground track during the lifetime of the mission. Elevation measurements can be retrieved over ocean surfaces, ice sheets, sea ice, and continental waters such as lakes, reservoirs, river reaches, and wetland regions. Data interpretation techniques are mature, well-validated, and published, and mission continuity is assured to at least to 2030. Ongoing research continually strives to make improvements in both the quality and quantity of available elevation measurements.

There have been a number of altimetric satellite missions to date and follow-on missions can be expected (see Table below).

Instrument Summary
Satellite Operation Repeat Period
Topex/Poseidon 1992-2002 10 days
Jason-1 2002-2008 10 days
Jason-2/OSTM 2008-2016 10 days
Jason-3 2016-current 10 days
Jason-CS/Sentinel-6 Launch 2020 10 days
HY-2A 2011-current 14 days
Seasat 1978 17 days
Geosat 1985-1989 17 days
GFO 2000-2008 17 days
Sentinel-3A 2016-current 27 days
Sentinel-3B 2018-current 27 days
ERS-1 1992-1993, 1995-1996 35 days
ERS-2 1996-2003 35 days
ENVISAT 2002-2010 35 days
SARAL 2013-2016 35 days
ICESat-1 (laser) 2003-2009 90 days
Cryosat-2 2010-current 365 days
ICESat-2 (laser) 2018-current variable
SWOT Launch 2021 variable
Contact UsTop

For general information relating to the satellite products, contact
Dr. Charon Birkett
Tel: 301-614-6464

For technical issue relating to the web site and product access, contact
Dr. Martina Ricko

Funding SourcesTop

The following sources are acknowledged.

  1. Applied Sciences/Water Resources Grant No. NNX17AF89G (Dr. Brad Doorn)
  2. NASA Making Earth Science Data Records (MEaSUREs) (Dr. Lucia Tsaoussi)
  3. NASA Ocean Surface Topography Science Team (OSTST) (Dr. Eric Lindstrom)
  4. The USDA Foreign Agricultural Service (Dr. Curt Reynolds, Mr. Ronald Frantz)

Lake/Reservoir elevation products can also be found at the USDA/FAS CropExplorer and the NASA PO.DAAC portals . Global mean sea level and gridded sea level products can also be found at the NASA PO.DAAC portals.

Data AcknowledgementTop

The project team acknowledges NASA/PODAAC, NASA/GSFC, NOAA, AVISO, ESA, and the TU-Delft/NOAA-NESDID/STAR “RADS” database, for the provision of altimetric datasets and associated physical parameters. The team also gratefully acknowledges Google Earth.


Many elements of this program reside in the research domain. The project management, support staff, and associated science investigators accept no responsibility for the accuracy and application of the surface elevation products