Satellite and airborne remote sensing has proven to be a relatively cost-effective
and useful approach for detecting, mapping, and monitoring surface and subsurface
water as compared to conventional hydrological methods. Moderate resolution
satellites, such as Landsat TM and SPOT, and high-resolution satellites, such as
IKONOS and QuickBird, have been used to study surface water bodies and
determine their extent in arid and semiarid regions. Remotely sensed seasonal
changes of lake water area/extent can be combined with available topographic
data to estimate water volumetric storage changes. Where clouds, trees, and other
vegetation obscure the water surface, SAR is being used, since it can penetrate
clouds and vegetation to detect standing water. Radar altimetry has been applied to
obtain point measurements of water surface elevation in order to determine volumetric water storage.
Soil moisture is an indicator of subsurface water that is found in the unsaturated
zone above the water table. Soil moisture information is required to improve
meteorological and climate predictions and for assessing agricultural conditions,
irrigation management, hydrologic problems, and studies of desertification. Both
active radars and passive microwave systems can sense soil moisture. However, soil
moisture remote sensing still faces many challenges: the spatial resolution over land
needs improvement, accurate soil moisture estimates are limited to regions with
either bare soils or low amounts of vegetation cover, and better corrections for
surface roughness, vegetation cover, soil temperature, and topography must be
devised. Until recently, the moisture in only the top few centimeters of the soil
could be detected. The SMAP satellite mission, planned for the 2015–2020 time
frame, is designed to use advanced modeling and data assimilation to provide
information on deeper root-zone soil moisture.
To identify groundwater potential zones, powerful computer programs are being
developed to merge refined geological knowledge with large samples of data from
ground sensors and space-based remote sensors. The data used include traditional
geologic maps, hydrologic data, satellite images, and gravity and seismic survey
data. Thematic layers in a GIS, including remote sensing data, and multi-criteria
decision-making (MCDM) techniques are being used to delineate groundwater
potential zones. The selected thematic maps can then be integrated by weighted
linear combination methods in a GIS environment to generate the groundwater
potential maps.
Only one satellite mission can directly estimate/measure the quantity of groundwater stored deep beneath the Earth’s surface. The GRACE mission accomplishes
this by measuring the Earth’s gravity field which is influenced by the quantity of
groundwater below the surface.
Freshwater springs can occur on dry land, in wetlands, and along the coast.
Springs may discharge at the land surface or below the water surface. In arid areas,
freshwater springs and irrigated areas induce the growth of a dense vegetation
cover, including trees, shrubs, or grasses. Vegetated areas can be detected by
remote sensors on aircraft and satellites and thus help find locations of freshwater
springs.
Using Remote Sensing to Map and Monitor Water Resources in Arid and Semiarid. . .
53
and useful approach for detecting, mapping, and monitoring surface and subsurface
water as compared to conventional hydrological methods. Moderate resolution
satellites, such as Landsat TM and SPOT, and high-resolution satellites, such as
IKONOS and QuickBird, have been used to study surface water bodies and
determine their extent in arid and semiarid regions. Remotely sensed seasonal
changes of lake water area/extent can be combined with available topographic
data to estimate water volumetric storage changes. Where clouds, trees, and other
vegetation obscure the water surface, SAR is being used, since it can penetrate
clouds and vegetation to detect standing water. Radar altimetry has been applied to
obtain point measurements of water surface elevation in order to determine volumetric water storage.
Soil moisture is an indicator of subsurface water that is found in the unsaturated
zone above the water table. Soil moisture information is required to improve
meteorological and climate predictions and for assessing agricultural conditions,
irrigation management, hydrologic problems, and studies of desertification. Both
active radars and passive microwave systems can sense soil moisture. However, soil
moisture remote sensing still faces many challenges: the spatial resolution over land
needs improvement, accurate soil moisture estimates are limited to regions with
either bare soils or low amounts of vegetation cover, and better corrections for
surface roughness, vegetation cover, soil temperature, and topography must be
devised. Until recently, the moisture in only the top few centimeters of the soil
could be detected. The SMAP satellite mission, planned for the 2015–2020 time
frame, is designed to use advanced modeling and data assimilation to provide
information on deeper root-zone soil moisture.
To identify groundwater potential zones, powerful computer programs are being
developed to merge refined geological knowledge with large samples of data from
ground sensors and space-based remote sensors. The data used include traditional
geologic maps, hydrologic data, satellite images, and gravity and seismic survey
data. Thematic layers in a GIS, including remote sensing data, and multi-criteria
decision-making (MCDM) techniques are being used to delineate groundwater
potential zones. The selected thematic maps can then be integrated by weighted
linear combination methods in a GIS environment to generate the groundwater
potential maps.
Only one satellite mission can directly estimate/measure the quantity of groundwater stored deep beneath the Earth’s surface. The GRACE mission accomplishes
this by measuring the Earth’s gravity field which is influenced by the quantity of
groundwater below the surface.
Freshwater springs can occur on dry land, in wetlands, and along the coast.
Springs may discharge at the land surface or below the water surface. In arid areas,
freshwater springs and irrigated areas induce the growth of a dense vegetation
cover, including trees, shrubs, or grasses. Vegetated areas can be detected by
remote sensors on aircraft and satellites and thus help find locations of freshwater
springs.
Using Remote Sensing to Map and Monitor Water Resources in Arid and Semiarid. . .
53