From this week, researchers worldwide can follow the flow ofrivers and height of lakes across the African continent from thecomfort of their desks. A new web-based demonstration launched tocoincide with this week's TIGER Workshop makes Envisat-derivedaltimetry data for African inland water freely available in near-realtime.
Envisat's Radar Altimeter-2 (RA-2) sensor fires around1800 radar pulses a second down to the surface of the Earth, thenmeasures very precisely how long it takes for those pulses to bounceback. This travel time can be used to calculate the height of theEarth's oceans, ice masses, land surfaces, and also – thanks to asophisticated algorithm developed by the UK's De Montfort University(DMU) in Leicester under ESA contract – previously elusive results forrivers and lakes on land.
The effort to develop the River andLake product was led by Professor Philippa Berry of DMU's Earth andPlanetary Remote Sensing Laboratory: "Monitoring of water resources isvital over Africa, to enable best use of this precious commodity. Untilnow reliable information has been difficult to access because of thehigh cost in equipment, manpower and communications, and because it isdifficult to obtain these precious hydrological data from manycountries.
"However heights of inland water can now be measureddirectly from space using radar altimeters, currently carried onseveral satellites and originally designed to measure ocean height.This is a very exciting development which has the potential totransform the management of drought crises and water-related conflictaround the world.
"Whilst data from a few selected large lakeshas been available previously, the combination of DMU's sophisticatedprocessing scheme and the unique design of the Envisat altimeter havefor the first time allowed near-real time measurements to be made overlakes and major rivers across Africa.
"The new system identifiedthat part of each surface echo originating from inland water, enablingmeasurement of much smaller targets than has previously been possible.This, combined with the altimeter's capability to return good data evenin rough terrain, means that we can provide much more accurate andup-to-date water level information than has ever been possible before."
Thedemonstration website is being launched at this week's ESA TIGERWorkshop at ESRIN, the European Centre for Earth Observation inFrascati in Rome. Starting 3 October, this four-day event involves morethan 200 African organisations from 31 countries, and aims to applyEarth Observation technologies in support of integrated water resourcemanagement.
"The information will be released using a web-baseddelivery service hosted at ESRIN," Berry added. "It will be availablewithin three days of being measured by Envisat. The system may even bepushed further to deliver water levels in less than six hours, usingnear-real time data from the precise orbit determination system aboardthe satellite known as DORIS (Doppler Orbitography and RadiopositioningIntegrated by Satellite), in order to better satisfy the actual needsof users."
Following the TIGER Workshop the River and Lakedemonstration system – which will start off by featuring products forCanada as well as Africa – will switch to other regions of the Earth ona periodic basis, beginning with Latin America.
Supportedas part of the Agency's Earth Observation Data User Element (DUE), theRiver and Lake project is aimed at developing, demonstrating andassessing an information service based on inland water altimetry.
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