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World
Water Day: space tool aids fight for clean drinking water
22 March 2006
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The Amazon River
Basin as observed by ERS-1 Radar Altimeter, including
so-called 'wet'radar echoes from rivers, lakes and swamps.
Radar altimetry data provides researchers with the means to
monitor global river and lake levels.
Credits: ESA
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According to the UN, safe
drinking water remains inaccessible for about 1.1 billion people
in the world. To address this global dilemma, the UN Millennium
Development pledged at the World Summit in Johannesburg in 2002
to reduce by half the proportion of people without access to safe
drinking water by 2015.
Meeting this goal will
demand reliable, current data and information about how much
water is stored in large lakes, rivers and reservoirs around the
world – which radar altimetry can provide.
In the past, hydrological
information could often be difficult to obtain by ground-based
gauge instruments due to the inaccessibility of the region, the
sparse distribution of gauge stations or the slow dissemination
of data due to national policy.
Radar altimetry can avoid these
obstacles because it is located on satellites 800 to 1300
kilometres above the Earth and is able to measure large lakes'
surface water height to two centimetres accuracy and rivers to
ten centimetres by sending 1800 separate radar pulses over bodies
of water per second and recording how long their echoes take to
bounce back. In addition, these data are available in near-real
time.
Today
there are several teams in the world involved in radar altimetry
over inland water, using satellite data from ESA, NASA and the
French Space Agency (CNES). Hydrologists from each of these
research teams met at the ‘15 Years of Progress in Radar
Altimetry’ symposium, organised by ESA and the French Space
Agency (CNES) in Venice Lido, Italy, from 13-18 March 2006, to
discuss the abilities of past and current altimeters for
monitoring the Earth’s changing inland water resources.
Professor Philippa A. Berry of
the UK’s Earth and Planetary Remote Sensing Laboratory
(EAPRS) at De Montfort University said: "This field has
evolved rapidly over the past two decades. Initial work over a
handful of large targets has now expanded to the current
capability to monitor thousands of river and lake heights
worldwide."
Although designed for ocean
studies, hydrologists undertook great efforts for radar altimetry
to include precise river and lake level monitoring. Berry, for
instance, led a River and Lake Level monitoring development
project, under ESA contract, in an effort to track rivers and
lakes to help manage water resources.
As a result, ESA launched a
web-based demonstration in 2005 that allows for radar altimetry
data of African rivers and lakes from its environmental
satellite, Envisat, to be freely available worldwide in near-real
time – within four days of measurements.
Following
the 2002 World Summit, ESA partnered with UNESCO in starting up
the TIGER initiative, which uses satellite data to manage water
resources in Africa. ESA is currently presenting the TIGER
initiative at the World Water Forum in Mexico City. The forum,
being held from 16 to 22 March, has brought government, business,
and non-government organisations together to discuss establishing
a water-secure future and the UN goal of halving the number of
people without drinking water by 2015.
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This image of
African land cover comes from a mosaic of Medium Resolution
Imaging Spectrometer (MERIS) images acquired during the month
of May 2004. Systematic satellite mapping of sub-Saharan
Africa is part of the TIGER project Global Monitoring for
Food Security (GMFS).
Credits: ESA
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The primary objective of
TIGER is to help African countries overcome problems faced in the
collection, analysis and dissemination of water related
geo-information by exploiting the advantages of Earth Observation
technology. More than 200 African water basin authorities,
universities and other organisations have become involved in
TIGER projects across the continent.
Although radar altimetry has
been successful in measuring the height of rivers and lakes,
scientists are looking for ways to improve the instrument in the
future. More than 150 scientists from more than 20 countries have
proposed an Earth Explorer hydrology mission called Water
Elevation Recovery (WatER), which aims to determine how water
storage varies in space and time.
According to Professor Doug
Alsdorf of Ohio State University, conventional profiling
altimetry – which uses a single antenna looking strait down
at Nadir – limits the spatial and temporal sampling of
water surface elevations, making it essential to obtain a
two-dimensional sampling in order to capture the flow dynamics of
highly complex waters.
To this
end, WatER will use an interferometric altimeter, which will
allow it to measure elevations over a 120 kilometre wide swath
and therefore map the world's water bodies repeatedly in less
than a week.
"WatER is designed to meet
high priority targets for all nations and will provide essential
data for the EU Water Framework Directive. WatER will meet the
United Nations’ call for a ‘greater focus on water
related issues,’" CNES’Dr. Nelly Mognard, lead
scientist for the WatER proposal and part of Laboratoire d'Etudes
en Geophysique et Oceanographie Spatiales, said at the symposium
in Venice.
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Credits: AOES
Medialab
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CryoSat-2, the next ESA
radar altimetry mission, expected to launch in 2009, is designed
to measure changing ice fields, but it will also contribute to
monitoring water resources by acquiring samples of data from its
new generation radar altimeter over inland water bodies upon
request from scientists for experimental purposes.
A follow on to CryoSat, ESA
Earth Explorer ice mission, which was lost at launch in 2005 due
to an anomaly in the Russian launcher, CryoSat-2 will fly an
enhanced radar altimeter instrument, called the Synthetic
Aperture Interferometric Radar Altimeter (SIRAL) which will allow
it to improve the resolution of the measurements by increasing
the number of separate radar pulses it sends down to Earth every
second from 1800 to up to 17 800. The experiment will demonstrate
how to benefit from novel technologies to serve emerging science
fields, such as hydrology, from space.
Supported
as part of the Agency's Earth Observation Data User Element
(DUE), the River and Lake project is aimed at developing,
demonstrating and assessing an information service based on
inland water altimetry.
Source
/ Credit: ESA
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