Radar altimetry has been used to obtain point measurements of water surface
elevation in order to determine volumetric water storage [16, 21]. For example,
Cazenave et al. [22] and Kostianoy et al. [23] report using satellite altimetry data to
investigate seasonal, interannual, and space-time variability of the level of water
bodies in arid areas of Turkmenistan, including the Caspian Sea water level. They
were able to monitor the water level (filling) of the Altyn Asyr Lake since its
construction began in July 2009. The synergistic application of combined radar and
optical remote sensing was shown to be particularly effective for the analysis of the
morphometric characteristics and sea (lake) level of these water bodies.
Airborne bathymetric Lidar has also been used to map water surfaces and to
estimate the water volume of lakes by producing elevation models for the water
surface and the lake bottom [24, 25]. Some airborne Lidar systems combine nearinfrared wavelengths for topography and green wavelengths for bathymetry,
allowing water depths to be determined with accuracies of about 10 cm. Bathymetric Lidars can penetrate down to about the equivalent of three Secchi depths and
provide bathymetric data down to 6 m depths in lakes of low turbidity.
4 Detecting Subsurface Waters
Subsurface water consists of soil moisture (unsaturated or vadose zone) and
groundwater aquifer (saturated zone).
4.1 Determining Soil Moisture
Soil moisture is an indicator of subsurface water that is found in the unsaturated
zone above the water table. Soil moisture has an important role in the calculation of
water and energy budgets needed for climate studies. Soil moisture improves
meteorological and climate predictions and is important for assessing agricultural
Table 1 Overview of synthetic aperture radar (SAR) satellites
Satellite
ERS-1 and ERS-2
RADARSAT
Envisat
Sensor
SAR
SAR
ASAR
Launch dates (s)
July 17, 1991
Nov 4, 1995
Mar 1, 2002
Apr 20, 1995
Frequency
5.3 GHz
5.3 GHz
5.3 GHz
Wavelength
5.6 cm
5.6 cm
5.6 cm
Polarization
VV
HH
VV, HH, VH, HV
Incidence angle
20–26
10–59
15–45
Swath width
100 km
50–500 km
100–405 km
Ground resolution
25 Â 25 m
8 Â 100 m
25 Â 25 m
38
V. Klemas and A. Pieterse
elevation in order to determine volumetric water storage [16, 21]. For example,
Cazenave et al. [22] and Kostianoy et al. [23] report using satellite altimetry data to
investigate seasonal, interannual, and space-time variability of the level of water
bodies in arid areas of Turkmenistan, including the Caspian Sea water level. They
were able to monitor the water level (filling) of the Altyn Asyr Lake since its
construction began in July 2009. The synergistic application of combined radar and
optical remote sensing was shown to be particularly effective for the analysis of the
morphometric characteristics and sea (lake) level of these water bodies.
Airborne bathymetric Lidar has also been used to map water surfaces and to
estimate the water volume of lakes by producing elevation models for the water
surface and the lake bottom [24, 25]. Some airborne Lidar systems combine nearinfrared wavelengths for topography and green wavelengths for bathymetry,
allowing water depths to be determined with accuracies of about 10 cm. Bathymetric Lidars can penetrate down to about the equivalent of three Secchi depths and
provide bathymetric data down to 6 m depths in lakes of low turbidity.
4 Detecting Subsurface Waters
Subsurface water consists of soil moisture (unsaturated or vadose zone) and
groundwater aquifer (saturated zone).
4.1 Determining Soil Moisture
Soil moisture is an indicator of subsurface water that is found in the unsaturated
zone above the water table. Soil moisture has an important role in the calculation of
water and energy budgets needed for climate studies. Soil moisture improves
meteorological and climate predictions and is important for assessing agricultural
Table 1 Overview of synthetic aperture radar (SAR) satellites
Satellite
ERS-1 and ERS-2
RADARSAT
Envisat
Sensor
SAR
SAR
ASAR
Launch dates (s)
July 17, 1991
Nov 4, 1995
Mar 1, 2002
Apr 20, 1995
Frequency
5.3 GHz
5.3 GHz
5.3 GHz
Wavelength
5.6 cm
5.6 cm
5.6 cm
Polarization
VV
HH
VV, HH, VH, HV
Incidence angle
20–26
10–59
15–45
Swath width
100 km
50–500 km
100–405 km
Ground resolution
25 Â 25 m
8 Â 100 m
25 Â 25 m
38
V. Klemas and A. Pieterse