shrubs, or grasses. Detecting biomass production is a common approach used to
identify the presence of freshwater springs.
5.1 Detecting Freshwater Plumes
Where groundwater enters a lake or coastal waters, it may display a thermal,
chemical, or vegetation signature that can be sensed remotely. To detect and map
freshwater plumes, remote sensors exploit differences in temperature, salinity,
turbidity, or color from ambient background water [61, 62]. Groundwater discharges in submarine springs have been detected using airborne and satellite TIR
sensors [63, 64]. Thermal anomalies on beaches or in coastal waters are often
associated with freshwater springs.
In the United Arab Emirates, a critical shortage of water is the limiting factor in
municipal, industrial, and agricultural development. Most of the precipitation of up
to 400 mm falls in some of the higher mountainous areas and much of it infiltrates
into the ground. Thomson and Nielsen [65] did a study to determine to what extent
this water was infiltrating into the sea and was therefore lost to human use and
where such losses were occurring. The period of February to March was considered
the best time of the year to conduct an airborne TIR study for locating springs, since
the sea surface temperatures were at a minimum during this time of the year. Two
flights were conducted in the early morning to minimize effects of surface heating
by the sun and to take advantage of low tide conditions [66]. The sea state was
moderate and winds were light during both flights. Coincident with the airborne
data, surface temperatures of several different materials were measured at a number
of locations along the coast, including asphalt roads, sand, etc. Aerial photos at a
scale of 1:60,000 were also analyzed to aid in the identification of possible
groundwater discharge sites. At the time of the airborne data collection, groundwater temperatures were about 13
C higher than the sea surface temperature, and
any groundwater discharges would appear warmer than the surrounding sea water.
Colder discharges would indicate surface runoff from recent storms. Analysis of the
thermal imagery indicated eight possible areas of groundwater discharge which
were pinpointed on a topographic map and each identified with the name of the
nearest village [65]. All groundwater discharges occurred at the shoreline-seawater
interface, and no offshore springs were detected.
Groundwater discharges are usually not uniformly distributed but are strongest
near the shoreline and decrease exponentially away from the shoreline. The spatial
distribution of spring discharges into streams, bays, and lakes has been studied
using TIR and multispectral sensors on aircraft and satellites [9]. Multi-beam sonar
has also been used to characterize submarine freshwater springs down to depths of
tens of meters [67].
Using Remote Sensing to Map and Monitor Water Resources in Arid and Semiarid. . .
45
identify the presence of freshwater springs.
5.1 Detecting Freshwater Plumes
Where groundwater enters a lake or coastal waters, it may display a thermal,
chemical, or vegetation signature that can be sensed remotely. To detect and map
freshwater plumes, remote sensors exploit differences in temperature, salinity,
turbidity, or color from ambient background water [61, 62]. Groundwater discharges in submarine springs have been detected using airborne and satellite TIR
sensors [63, 64]. Thermal anomalies on beaches or in coastal waters are often
associated with freshwater springs.
In the United Arab Emirates, a critical shortage of water is the limiting factor in
municipal, industrial, and agricultural development. Most of the precipitation of up
to 400 mm falls in some of the higher mountainous areas and much of it infiltrates
into the ground. Thomson and Nielsen [65] did a study to determine to what extent
this water was infiltrating into the sea and was therefore lost to human use and
where such losses were occurring. The period of February to March was considered
the best time of the year to conduct an airborne TIR study for locating springs, since
the sea surface temperatures were at a minimum during this time of the year. Two
flights were conducted in the early morning to minimize effects of surface heating
by the sun and to take advantage of low tide conditions [66]. The sea state was
moderate and winds were light during both flights. Coincident with the airborne
data, surface temperatures of several different materials were measured at a number
of locations along the coast, including asphalt roads, sand, etc. Aerial photos at a
scale of 1:60,000 were also analyzed to aid in the identification of possible
groundwater discharge sites. At the time of the airborne data collection, groundwater temperatures were about 13
C higher than the sea surface temperature, and
any groundwater discharges would appear warmer than the surrounding sea water.
Colder discharges would indicate surface runoff from recent storms. Analysis of the
thermal imagery indicated eight possible areas of groundwater discharge which
were pinpointed on a topographic map and each identified with the name of the
nearest village [65]. All groundwater discharges occurred at the shoreline-seawater
interface, and no offshore springs were detected.
Groundwater discharges are usually not uniformly distributed but are strongest
near the shoreline and decrease exponentially away from the shoreline. The spatial
distribution of spring discharges into streams, bays, and lakes has been studied
using TIR and multispectral sensors on aircraft and satellites [9]. Multi-beam sonar
has also been used to characterize submarine freshwater springs down to depths of
tens of meters [67].
Using Remote Sensing to Map and Monitor Water Resources in Arid and Semiarid. . .
45