The Global Reservoir and Lake Monitor (G-REALM) is a NASA/USDA funded operational program that delivers water level products for the world’s largest lakes and reservoirs. It utilizes both NASA and European Space Agency satellite data sets to monitor the seasonal and inter-annual fluctuations in the water levels. The technique being used is satellite radar altimetry, and with emphasis on the TOPEX/Poseidon and Jason series mission, the time period of observation spans 25 years from 1992 to the present day. The advantage of the satellite monitoring is that it can provide water level observations in regions where traditional gauge data is not accessible. The USDA Foreign Agricultural Service (FAS) utilize the archive products to assess longer-term hydrological drought in the region. The near real time products are used to assess shorter-term agricultural drought conditions. FAS regional analysts exploit the products to determine irrigation potential with respect to crop conditions and crop production.
The G-REALM objectives include the delivery of water level products, at 10 or 35 day resolution, in an operational framework, generally 7-10 days after satellite overpass, and to append archive water level observations where feasible. G-REALM also strives to monitor all water bodies, particularly those in arid or semi-arid regions where water and food resources are of concern with respect to regional security, anthropogenic influences, and climate change.
The G-REALM system keeps pace with the latest satellite data set developments to maintain product accuracy and delivery requirements. The products have recently been upgraded and additional lake/reservoirs added to the system. Currently ~230 water bodies are being monitored across all continents.
Geographic Focus
G-REALM has a global outlook, with particular focus on the low to mid latitude regions where water resources are a high priority with respect to agriculture.
Principal Investigator
Dr. Charon Birkett, ESSIC/University of Maryland at College Park
Mr. Robert Tetrault, USDA/FAS, Washington DC
Project Team
Dr. Martina Ricko, Mr. Brian Beckley, Dr. Simon Holmes, and Mr. Xu Yang, SGT Inc. Greenbelt, Maryland.
Miss Katherine O’Brien, Student Intern, University of Maryland at College Park
Collaborators & Stakeholders
Mr. Robert Tetrault and Dr. Curt Reynolds, USDA/FAS, Washington DC.
Collaborators: Prof. Jeppe Kolding, University of Bergen, Norway, and Dr. Paul Van Zweiten University of Wageningen, the Netherlands.
Technical Overview
The application of satellite radar altimetry began with naval and science requirements for the accurate measurement of the sea surface. Exploration of the data sets proved their value for the monitoring of surface variations with respect to ice sheets, sea ice, and continental waters. Today the technology is mature and well validated, with space agencies ensuring both continuity of missions and delivery of operational data sets. Application to the monitoring of lakes, reservoirs, river channels, and wetland regions has been well proven, with research continuing to improve on surface height accuracy, and on temporal and spatial resolution.
Additional Information
The following example is taken from G-REALM on November 2nd, 2016 and show current drought conditions affecting Lake Malawi. Each product depicts a semi-filtered (top) and filtered (bottom) result with 10-day resolution. Results are derived from the NASA/CNES TOPEX/Poseidon (blue), Jason-1 (red), and Jason-2 (purple) missions. The Three Gorges reservoir result will be extended back in time where feasible, and all G-REALM products will continue in the operations domain via data from the new Jason-3 satellite. Jason-3 measurements will ensure continuity and deliver observations in a near real time framework.
Related Research Areas