322
A.M.J. Meijerink
14.6 Conclusions and future perspectives
The day-to-day, practical application of remote sensing in groundwater studies, so
far, relies on qualitative approaches whereby hydrogeological experience is
required. Image interpretation of stereo aerial photography, multispectral images
and active microwave images have proven their worth for the compilation and
updating of hydrogeologic maps and mapping of the relative recharge. With the
strides in computer technology, merging of airborne and ground geophysical data,
to obtain subsurface information, has become affordable. This, with satellite data
for surface information, can lead to improved groundwater modelling results. The
modelling approach itself can be adjusted to make better use of remote sensing.
Lubczynski (1997) argues that for the variable hard rock conditions, it will be
difficult, if not impossible, to avail of spatially reliable transmissivity values of the
weathered and the upper fractured zone. Therefore, the spatial recharge patterns,
using remote sensing data could be used as independent input and calibration of
the model can be done for transmissivity. Generally it is done the other way round.
It is expected that the more physically based methods for determining and
monitoring recharge based on actual evapotranspiration and soil moisture status,
will become a welcome complementary addition. The methods for the calculation
of the evapotranspiration using thermal bands and vegetation indices of weather
satellite data, such as NOAA A VHRR have progressed much recently, e.g.
Bastiaanssen (1998) and Chap. 8 of this book.
At regional scale, passive microwave satellite images have been used with
reasonable success for the determination of the surface soil moisture at regional
scale in southern Africa (Owe et a1.l992). This data can be used in conjunction
with soil moisture flux modelling for the estimation of the recharge.
Active microwave images contain, theoretically, information on the soil
moisture, but effects of the status of the vegetation cover on the backscatter has to
be eliminated with a-priori knowledge. This complicates the practical use as yet.
More information is provided in Chap. 9.
The last decade has seen rapid advances in coupling of hydrogeological data
bases to geographic information systems, digital data integration techniques and
hydrogeologic models. Therefore, remotely sensed information can now be
embedded in computational methods. It is to be hoped that this leads to the
development and field testing of robust methods to determine recharge and
groundwater outflow, two important aspects of groundwater.
References
L.Aller, T. Benett, J.H. Lehr, R.J. Petty & G.Hackett, 1987: Standardized System for Evaluating
Ground Water Pollution Potential using Hydrologic Settings. U.S Environm. Protection
Agency, EPN600/2-87/035
Anon, 1990: Use of Remote Sensing for Hydrogeological Studies in Humid Tropical Areas. A
Pilot Study in West Java, Indonesia IW ACO/TNO/ITC. Min. Public Works, Indonesia, 183 pp.
W.G.M. Bastiaanssen, 1998: Remote sensing in water resources management: The state of the art.
IWMI, Colombo, Sri Lanka 118 pp.
A.M.J. Meijerink
14.6 Conclusions and future perspectives
The day-to-day, practical application of remote sensing in groundwater studies, so
far, relies on qualitative approaches whereby hydrogeological experience is
required. Image interpretation of stereo aerial photography, multispectral images
and active microwave images have proven their worth for the compilation and
updating of hydrogeologic maps and mapping of the relative recharge. With the
strides in computer technology, merging of airborne and ground geophysical data,
to obtain subsurface information, has become affordable. This, with satellite data
for surface information, can lead to improved groundwater modelling results. The
modelling approach itself can be adjusted to make better use of remote sensing.
Lubczynski (1997) argues that for the variable hard rock conditions, it will be
difficult, if not impossible, to avail of spatially reliable transmissivity values of the
weathered and the upper fractured zone. Therefore, the spatial recharge patterns,
using remote sensing data could be used as independent input and calibration of
the model can be done for transmissivity. Generally it is done the other way round.
It is expected that the more physically based methods for determining and
monitoring recharge based on actual evapotranspiration and soil moisture status,
will become a welcome complementary addition. The methods for the calculation
of the evapotranspiration using thermal bands and vegetation indices of weather
satellite data, such as NOAA A VHRR have progressed much recently, e.g.
Bastiaanssen (1998) and Chap. 8 of this book.
At regional scale, passive microwave satellite images have been used with
reasonable success for the determination of the surface soil moisture at regional
scale in southern Africa (Owe et a1.l992). This data can be used in conjunction
with soil moisture flux modelling for the estimation of the recharge.
Active microwave images contain, theoretically, information on the soil
moisture, but effects of the status of the vegetation cover on the backscatter has to
be eliminated with a-priori knowledge. This complicates the practical use as yet.
More information is provided in Chap. 9.
The last decade has seen rapid advances in coupling of hydrogeological data
bases to geographic information systems, digital data integration techniques and
hydrogeologic models. Therefore, remotely sensed information can now be
embedded in computational methods. It is to be hoped that this leads to the
development and field testing of robust methods to determine recharge and
groundwater outflow, two important aspects of groundwater.
References
L.Aller, T. Benett, J.H. Lehr, R.J. Petty & G.Hackett, 1987: Standardized System for Evaluating
Ground Water Pollution Potential using Hydrologic Settings. U.S Environm. Protection
Agency, EPN600/2-87/035
Anon, 1990: Use of Remote Sensing for Hydrogeological Studies in Humid Tropical Areas. A
Pilot Study in West Java, Indonesia IW ACO/TNO/ITC. Min. Public Works, Indonesia, 183 pp.
W.G.M. Bastiaanssen, 1998: Remote sensing in water resources management: The state of the art.
IWMI, Colombo, Sri Lanka 118 pp.