Remote sensing applications

[AGaber]

Remote Sensing in Groundwater Studies

Chapter 2
Remote Sensing in Groundwater Studies
Abstract Groundwater study in an area requires the idea of lithological units,
structural disposition, geomorphic set-up, surface water condition, vegetation, etc.
These can be well understood with the help of remote sensing (RS). It is the study
of satellite images and aerial photographs. Satellite images are basically the electromagnetic
(e-m) record of broad spectrum (ultraviolet, visible, infrared and
microwave regions) by means of instrument such as scanners and cameras located
on mobile platform such as satellite or spacecraft. The e-m radiation may come
from an artificial source in the satellite or from the target itself if the target happens
to be a source of e-m radiation. The radiation travels through the atmosphere being
detected at the satellite recorder. The e-m spectrum in given bands can give
information on the various targets on the earth. Vegetation, in general, appears
green during daytime, because it reflects the green band of visible radiation preferentially,
while absorbing other colour bands of the visible radiation. Before
geophysical investigation, the RS data give the knowledge of the geological
structures. Hence, the geophysicist can focus the survey area from a huge area
which is not potential. The RS data are very accurate, fast and reliable as compared
to the conventional data collection.
Keywords Remote sensing Lithological unit Geomorphic set-up Vegetation
Satellite image Aerial photography Electromagnetic radiation Colour band
Geological structure
2.1 General Considerations
Groundwater study of an area requires knowledge of the nature of lithological units
occurring in the area, their structural disposition, geomorphic set-up, surface water
conditions and the climate of the area. These can be studied through satellite images
and aerial photographs, which provide detailed information about the large part of
the surface of the earth in a very short time. Photograph interpretation studies help
in the indication of groundwater potential through:
© Springer Science+Business Media Singapore 2016
H.P. Patra et al., Groundwater Prospecting and Management,
Springer Hydrogeology, DOI 10.1007/978-981-10-1148-1_2

Although remote sensing (RS) data do not directly detect deeper subsurface
resources, it has been effectively used in groundwater exploration as RS data aid in
drawing inferences on groundwater potentiality of the region indirectly.
The fresh water confined to channels of streams and rivers and stored in ponds,
lakes and reservoirs is normally considered to form the surface water resources.
These sources of surface water are directly detected by satellite RS data as water
absorbs most of the radiation in the infrared region, which helps in the delineation
of even smaller water bodies. Vegetation, which is easily detected through spectral
reflectance, is indicative of the water saturation and moisture of the ground.
RS data provide only superficial and inadequate knowledge on the subsurface
groundwater resources but help indirectly by giving certain ground information that
aid in drawing inferences on groundwater potentiality of the area.
Primarily, the infiltration capacity of the soil determines the groundwater
potentiality. The speed of infiltration is dependent upon mainly on porosity and
permeability of the soil and the velocity of the surface run-off. Infiltration reduces to
a great extent for steeply sloping ground surface as the velocity of surface run-off
increases sharply. Also a vegetative cover gives a higher infiltration capacity
compared to barren lands.
Several factors important in the storage of groundwater are:

Thus, the RS data followed by ground check give an idea of the probable
groundwater potential zones. This should be detailed through surface and subsurface
geophysical methods suitable for groundwater exploration. The scientific
approach consists of three steps:
• RS-based investigations,
• Conventional hydrogeological investigations and
• Ground geophysical investigations.
RS records electromagnetic (e-m) radiation comprising a broad spectrum of
wavelengths. This method, therefore, may be called an applied geophysical method
in a broad sense and an e-m method in particular. The e-m radiation may come from
an artificial source in the satellite or from the target itself if the target happens to be
a source of e-m radiation. The radiation travels through the atmosphere being
detected at the satellite recorder. The e-m spectrum in given bands can give
information on the various targets on the earth.
With the advancement in technology, man is changing the face of the earth at a
rapid phase. In order to channelize the development in proper direction with due
consideration to environmental preservation, a planner needs to have an overall
picture of the status of the region and its resources. Conventional methods of data
collection are extremely time-consuming and are normally out of phase with the
present-day conditions. In such circumstances, earth resource monitoring by space
platforms is the only answer. The generation of accurate and reliable information at
a cost-effective and short turnaround time coupled with a wide range of earth
resource monitoring, prediction of crop yield, estimation of soil moisture conditions,
in forestry applications such as wildlife habitat assessment and timber volume
estimation.
2.1 General Considerations 9
In geological sciences, it is used in the study of morphology of the earth, and in
lithological and structural mapping. Besides this, the technology is also used in
locating sites suitable for major reservoirs and in targeting groundwater.
2.2 Remote Sensing
RS is the non-contact recording of information about the earth surface, from the
ultraviolet, visible, infrared and microwave regions of the e-m spectrum, by means
of instruments such as scanners and cameras, located on mobile platforms such as
aircraft or spacecraft followed by the analysis of acquired information by means of
photograph interpretation techniques, image interpretation and image processing
(Sabins 1987).
The contact between the remote sensor and the target is through e-m energy
(visible, thermal, infrared radiation), force fields (gravity, magnetic) or acoustic
waves (sonar). Remote sensors measure the relative variation of these forms of
energy that is either emanating from the body or being reflected from it for
recognition and detailed studies.
For most of the atmospheric and earth surface observations, e-m energy is
considered to be the supreme medium for two reasons. Primarily, this is the only
form of energy that has the ability to propagate through free space and also a
medium. Further, its property to interact with the media and the target in a variety of
ways ensures the sensor to capture the subtle variations that exist in the nature of the
earth features.
2.3 Remote Sensing Technique
Every part of the earth reflects the incident light depending on its optical characteristics.
The information which characterizes objects is called “signatures”.
Different objects of the earth surface return different amounts of reflected/emitted
energy in different wavelengths of the e-m spectrum (Fig. 2.1a) depending on the
atmospheric windows (Fig. 2.1b), and this reflectance/emittance from each object
depends on the wavelength of the radiation, the molecular structure of the object
and its surface conditions. Vegetation, in general, appears green during daytime,
because it reflects the green band of visible radiation preferentially, while absorbing
other colour bands of the visible radiation.
Detection and measurement of these spectral signatures enable identification of
surface objects both from airborne and spaceborne platforms. But often, similar
spectral response from different surface objects creates spectral confusion leading to
misinterpretation and misclassification. This can be avoided by systematic ground
data verification. However, spectral variation in reflectance or emittance from
objects is not the only characteristic of e-m radiation that helps in establishing their
10 2 Remote Sensing in Groundwater Studies
signatures. Signatures, in fact, comprise of any set of observable characteristics
which directly or indirectly lead to the identification of an object and its condition.
The characteristics are spatial information, temporal (for example, seasonal) variation
and polarization effect. The shape, size, texture, pattern, association, for
example, are associated with special information.
Earth resource satellites collect information about earth’s surface and transmit to
the ground receiving stations. After carrying out initial corrections, two types of
data products are generated for resource study. These are: (i) visual imagery hard
copy and (ii) computer compatible tapes (CCTs). These data are processed and
interpreted for the identification and classification of different objects of the earth.
Each satellite system is composed of a scanner with sensors. The sensors are
made up of detectors. The scanner is the entire data acquisition system, such as the
Landsat Thematic Mapper scanner or the SPOT panchromatic scanner (Lillesand
and Kiefer 1987).
In a satellite system, the total width of the area on the ground covered by the
scanner called the “swath width”, or width of the total field of view (FOV). FOV
Fig. 2.1 Spectral characteristics of energy sources, atmospheric effects and sensing system (after
Lillesand and Kiefer 1987). a Energy sources. b Atmospheric transmittance. c Common remote
sensing system
2.3 Remote Sensing Technique 11
differs from IFOV (instantaneous field of view); in that, the IFOV is a measure of
the FOV of each detector. The FOV is a measure of the FOV of all the detectors
combined together.
A sensor of a satellite is a device that gathers energy, converts it to a signal and
presents it in a form suitable for obtaining information about the environment.
A detector is the device in a sensor system that records e-m radiation. For example,
in sensor system on the Landsat Thematic Mapper scanner there are 16 detectors for
each wavelength band.
The common RS systems given in Fig. 2.1c have several characteristics:
(i) They have circular orbits that go from north to south and south to north;
(ii) They have Sun-synchronous orbits, meaning that they rotate around the
Earth at the same rate as the Earth rotates on its axis, so data are always
collected at the same local time of day over the same region;
(iii) They record e-m radiation in one or more bands; and
(iv) Their scanner produces nadir (the area on the ground directly beneath the
scanner detectors) views.
2.4 Satellite Image
RS image is available in the form of hard copy paper prints visual imagery, in
different scales, which are generated from the digital data collected by the sensors.
In satellite, the sensor measures radiations reflected/emitted from the earth’s surface.
The altitude of the satellite and the size of the detector element define the
spatial resolution or pixel (picture element) size. The value at each pixel on a
satellite image represents the total amount of radiation reaching the sensor from the
ground. Two-dimensional array of pixel values constitute a digital image of the
scene. Each pixel value represents average radiance over a defined smaller area
within a scene. The size of the pixel area affects the representation of the details
within the scene. As the pixel area is reduced, more and more scene detail is
preserved in the digital representation and this governs the spatial resolution.
The continuous radiance of the scene is, therefore, quantized into discrete grey
levels in the digital image. The data are thus routinely recorded in digital form by
space sensors, which are transmitted to the ground stations. These data are reprocessed
by the computer to generate image for interpretation. The data can be
displayed in suitable scales by appropriate computer processing.
2.4.1 Data
There are many data acquisition options available. These options range from
photography to aerial sensors using film, to sophisticated satellite scanners.
12 2 Remote Sensing in Groundwater Studies
A satellite system with detectors which produce digital data may be preferable for
the reasons: (i) the digital data can be easily processed and analysed by a computer,
(ii) the satellite is in orbit around the Earth, so the same area can be covered on a
regular basis for change detection, (iii) once the satellite is launched, the cost of data
acquisition is less than that for the aircraft data, (iv) satellites have stable geometry,
meaning that there is less chance for distortion or skew in the final image. A wide
variety of RS data are acquired from different types of satellites, viz. Landsat,
SPOT, IRS-IB, IRS-1C, IRS-1D, NOAA, LISS-IV Pan merged data through
Cartosat-2 and Resourcesat-2.
Landsat has a 15-m panchromatic sensor and a 30 m enhance. Thematic Mapper
sensor is with 7 bands. SPOT has a 10-m panchromatic sensor and a 20-m multispectral
sensor with 3 bands. IRS-IB has a 36-m multispectral sensor with 4 bands.
LISS-IV sensor on-board satellite has the spatial resolution of 5.8 m as that of IRS
1D PAN, but it has enhanced spectral resolution. LISS-IV sensor consists of three
spectral bands in the green, red and near-infrared regions of the e-m field. It can be
tilted up to ±26° in the across-track direction, thereby providing a revisit period of
5 days and 70 km 70 km stereo pairs. This opens a new field of microlevel
applications. Remotely sensed raw data are not projected onto a plane. Therefore,
rectification is necessary to project the data conforming to a map projection system
before processing.
2.4.2 Resolution
Resolution is a broad term commonly used to describe the number of pixel we can
display on a display device or the area on the ground that a pixel represents in an
image file. Four distinct types of resolutions are associated with RS data discussed
below.
Spectral resolution: Spectral resolution refers to the specific wavelength intervals
in the e-m spectrum that a sensor can record (Simonett 1983). For example,
Band 1 of Landsat Thematic Mapper sensor records energy between 0.45 and
0.53 μm in the visible part of the spectrum.
Spatial resolution: Spatial resolution is a measure of the smallest object that can
be resolved by the sensor, or the area on the ground represented by each pixel
(Simonett 1983). The finer the resolution, the lower, the number. For instance, a
spatial resolution of 36 m is coarser than a spatial resolution of 20 m.
Radiometric resolution: Radiometric resolution refers to the dynamic range, or
the numbers of possible data file values in each band. This is referred to by the
number of bits the recorded energy is divided into. For instance, in 8-bit data, the
values range from 0 to 255 for each pixel, but in 7-bit data, the values for each pixel
range from only 0 to 128.
Temporal resolution: Temporal resolution refers to how often a sensor obtains
imagery of a particular area. For example, the IRS-1B satellite can view the same
2.4 Satellite Image 13
area of the globe once every 22 days. Temporal resolution is an important factor to
be considered when performing change detection studies.
2.5 Image Processing
The image processing is the manipulation of digital image data, including (but not
limited to) rectification, enhancement and classification operations. The purpose of
image processing is to generate thematic maps from satellite images. There is a large
number of image processing softwares available from different vendors, namely
ERDAS, IDRISI for both commercial and educational purposes either on personal or
mainframe computers with array/vector processing capabilities (Fig. 2.2).
2.5.1 Image Interpretation
Image interpretation is a complex process of physical and psychological activities
occurring in a sequence of time. The sequence begins with the detection and
identification of objects and later by their measurements. Images are then considered
in terms of information and final deductions to be confirmed by ground checks
to avoid misclassification.

different grey tones. These grey tones often fail to provide the interpreter a
clear perception of objects, whereas true-colour or false-colour imagery
increases interpretability by providing a subtle tonal contrast between them.
Tonal contrast can be enhanced or reduced optically or by enhancement
techniques on computers.
(ii) Texture: It is defined as a repetition of basic pattern. Texture in the image is
due to tonal repetitions in a group of objects that are often too small to be
discernible. It creates a visual impression of surface roughness or smoothness
of objects and is a useful photo-element in image interpretation.
(iii) Pattern: It refers to the spatial arrangements of surface features which are
characteristics of both natural and man-made objects. Similar features under
similar environmental conditions reflect similar patterns of recurrence. More
often, patterns also reflect association, e.g., intensity of drainage pattern
shows its relation with rock types, soil texture, rainfall, run-off, etc.
(iv) Size: It refers to the spatial dimension of objects on ground. Size of an
object is a function of scale of the image or photograph and is also measurable.
There are different objects with varying sizes and shapes.
(v) Shape: It refers to physical form of an object and is also a function of scale
of the image or photograph. Size and shape are interrelated. In the image,
shape refers to plan or top view of the object as seen by the satellite. Shape
can be irregular, regular and uniform.
(vi) Shadow: These are cast due to Sun’s illumination angle, size and shape of
the object or sensor viewing angle. The shape and profile of shadow help in
identifying different surface objects, e.g. nature of hill slopes, apparent
relief.
(vii) Location: The geographic site and location of the object often provide clues
for identifying objects and understanding their genesis.
(viii) Association: It refers to situation of the object with respect to other
neighbouring and surface features.
2.5.2 Image Enhancement
Improvement in the quality of an image in the context of a particular application is
called image enhancement. Contrast stretching, band combination, data compression,
edge enhancement and filtering, and colour display are some of the
well-established techniques in image enhancement.
Contrast enhancement: In order to accommodate the tonal variations of a variety
of environments spread over the earth, satellite sensors are designed to record a
wide range of radiation intensity within every band width. Due to this, while
scanning a particular scene, signals are recorded only within a small portion of this
wider scale. This imagery when viewed in its raw state will exhibit a low contrast,
often leading to difficulties in feature recognition. Therefore, to increase the
2.5 Image Processing 15
contrast, the recorded digital numbers are rescaled to a new longer scale following
certain statistical criteria (Fig. 2.3). There are different methods of contrast
enhancement, such as linear stretch, histogram equalization, binary stretch, logarithmic
stretch, and Gaussian stretch.
Band combination: Band addition, subtraction and rationing are some of the
common band combinations. Different bands of the same image is subtracted or
rationed to suppress the details common to the two images and enhance details that
are different. Band combination is also performed on geometrically registered
multitemporal scenes to monitor the changes in the environment, such as the effect
of floods, extension of forest fire, urban sprawl and in agriculture.
Principal component analysis (PCA): A major problem frequently encountered
in the analysis of multispectral data is extensive interband correlation. High correlation
indicates high degree of redundancy among the data, i.e., each band data
convey essentially similar information. PCA is a technique designed to remove or
reduce such redundancy in multidimensional data. The PCA compresses the whole
of information contained in the original multiband data into fewer channels or
components with zero correlation and are often more interpretable (Drury 1987).
Fig. 2.3 Principle of contrast stretch enhancement. a Histogram. b No stretch. c Linear stretch.
d Histogram stretch. e Spatial stretch
16 2 Remote Sensing in Groundwater Studies
PCA is the most widely used and popular technique among the digital enhancement
methods (Radhakrishnan et al. 1992).
Edge enhancement and filtering: The edge enhancement is an operation which
helps the analyst in achieving edge-highlighted image (Radhakrishnan et al. 1992).
According to Jensen (1986), the edge enhancement operation delineates the edges
and thereby makes the shapes and details comprising the image more conspicuous
and perhaps easier to analyse. Edge enhancements are the techniques for enhancing
sharp changes in the grey levels, such as lineaments, roads, canals, field boundaries
and contacts of two land use classes. In geology, they are advantageous for
enhancing joints, faults, lineaments and fractures. Edge enhancement is achieved by
a process called “spatial filtering”. Spatial filters emphasize or de-emphasize image
data of various “spatial frequencies”. Spatial frequencies refer to the roughness of
the tonal variations occurring in an image. Image areas of high spatial frequency are
tonally rough. That is, the grey levels in these areas change abruptly over a relatively
small number of pixel (e.g. across roads, linear features). Smooth image areas
are those of low spatial frequency, where grey levels vary only gradually over a
relatively large number of pixel transformation of an image, where the transformation
depends not only on the grey levels of the pixel concerned, but also on the
grey levels of the neighbouring pixels. Spatial filtering is a context-dependent
operation that alters the grey level of pixel according to its relationship with the
grey level of a pixel in the immediate vicinity (Schowengerdt 1983).
Usually, different combinations of low-pass filtering and high-pass filtering are
used in image processing by convolution using convolution windows. The window
is moved over the input image processing by convolution using convolution windows.
The window is moved over the input image from pixel to pixel, performing a
discrete mathematical function transforming the original pixel values to new ones.
The windows or filters may be rectangular or square. Each location in the box filter
is given a certain weight. Many types and sizes of filters can be designed by
changing the window size and varying the weights. The edges may be enhanced
either by directional or non-directional edge enhancement techniques. Various
edge-enhancing operators have been reported to detect linear patterns from images
(Wang and Newkirk 1998; Holyer and Peckinpaugh 1989).
2.5.3 Image Classification and Generation
of Thematic Maps
Multispectral classification is the process of sorting pixels into a finite number of
individual classes, or categories of data, based on their data file values. If a pixel
satisfies a certain set of criteria, the pixel is assigned to the class that corresponds to
the criterion.
The classification process breaks down into two parts—training and classifying.
First, the computer system must be trained to recognize patterns in the data.
2.5 Image Processing 17
Training is the process of defining the criteria by which these patterns are recognized
(Hord 1982). The result of training is a set of signatures, which are statistical
criteria for a set of proposed classes. Training can be performed with either a
supervised or an unsupervised method. Pixels of an image area are then sorted into
classes based on the signatures, by the use of a classification decision rule. The
decision rule is a mathematical algorithm that uses particular statistics such as
maximum likelihood and Bayesian methods to sort the pixels.
Supervised classification: This type of classification is more closely controlled
by the user. In this process, user selects the pixels that represent the pattern with the
help of other sources, such as aerial photographs, ground truth data or maps.
Knowledge of the data, and of the classes desired, is required before classification.
By identifying patterns, user can train the computer system to identify pixel with
similar characteristics. If the classification is accurate, each resulting class represents
an area of interest within the data that corresponds to the pattern user originally
identified.
Unsupervised classification: This type of classification is more computerautomated.
It allows the user to specify some parameters which the computer uses
to uncover statistical pattern that are inherent in the data. These patterns do not
necessarily correspond to directly meaningful characteristics of the scene, such as
contiguous, easily recognized areas of a particular soil type or land use. They are
simple groups of pixels with similar spectral characteristics. In some cases, it may
be more important to identify groups of pixels with similar spectral characteristics
than it is to sort pixel into recognizable categories. Unsupervised classification is
dependent upon the data itself for the definition of classes. The method is usually
used when less is known about the data before classification. It is the responsibility
of the user, after classification, to attach meanings to resulting classes to generate
thematic maps. Unsupervised classification is only useful if the classes can be
appropriately interpreted.
2.5.4 Case Study
The study area is Midnapur District, West Bengal (location map in Fig. 2.4,
reproduced from Nath et al.2000) covers 631 km2. It is a typical soft rock area
having hydrogeological conditions favourable for shallow groundwater reserve. For
the groundwater investigations, thematic maps of surficial geology and drainage
pattern are prepared from IRS-1B LISS-II data. The data have spatial and radiometric
resolutions of 36 m and 7 bits, respectively. In the first step, raw image data
are projected onto a plane using Everest projection method and taken into Universal
Transverse Mercator (UTM) coordinate system for further processing.
Enhancement of the image is accomplished by using PCA on bands 1, 2 and 3
for the generation of geological map of the area. PCA 1, 2 and 3 are assigned the
colours red, green and blue, respectively, for generating a false-colour composite
(FCC) of the image. Three distinct features are identified in the enhanced image
18 2 Remote Sensing in Groundwater Studies
from their tones and textures. From ground check-up, these features are found to be
laterite, older alluvium and newer alluvium. The spectral signature of these features
are used to classify (supervised) the image and generate the thematic map of the
geology of the area, as shown in Fig. 2.4a.
For the preparation of thematic map of drainage pattern of the study area, a
standard FCC (using bands 1, 2 and 3) is generated. The water bodies are identified
by their blue tone and fine texture.
The fresh water that is confined to channels of streams and rivers and accumulated
in ponds and lakes are normally considered as surface water resources. The infiltration
capacity of the earth surface, coupled with evapotranspiration of the region,
controls the volume of water in a channel. Further, the channel size and its gradient
also control the water holding capacity. In order to harvest this resource, barrages or
dams are constructed across the rivers and artificial lakes or reservoirs are formed
from where the water supply is regulated through a network of canals.
Several criteria are taken into consideration while selecting suitable sites for dam
construction. The first and most important factor in dam designing depends on
normal aerial coverage and lower evaporation loss. Further, they are beneficial as
the area of submergence is nominal and also the cost of dam construction works out
to be far cheaper. The nature of the valley bottom material and the catchment area is
another important criteria. Impervious and consolidated basement crystalline rocks
are supposed to be excellent valley bottom material as the loss of water due to
percolation is minimized. Further, catchment area having good vegetative cover and
soils resistant to erosive forces are considered good as the rate of siltation of the
reservoir will be low and also the loss of water due to infiltration will be less.
The ability of recording the earth-related information in narrow wavelength
bands coupled with synoptic coverage makes the satellite data, a potential tool in
the hands of the interpreter in deriving the required information for locating hydel
projects. A careful observation of the satellite imagery helps in determining the
width of the valley, size of the upstream catchment and in evaluating the total area
of submergence and loss of vegetative and forest cover due to submergence, etc.
Further, by coupling the satellite data with other field inputs it is possible to extract
information regarding the nature of valley floor material, lineaments criss-crossing
the area, erodability of the catchment material, area occupied by the artificial
reservoir and finally, in estimating the total area to be irrigated by the hydel project.
2.6.2 Groundwater Exploration
Although remotely sensed data often provide only a superficial and inadequate
knowledge on the subsurface resources, it is time and again used, quite effectively,
in the exploration of groundwater. This is because, the satellite imageries help in
20 2 Remote Sensing in Groundwater Studies
acquiring certain ground information that aid in drawing inferences on groundwater
potential of a region. This section examines the basic requirements of groundwater
accumulation and the hydrogeomorphological features that aid in the exploration
for groundwater resources using satellite RS data.
The water to be stored beneath the surface of the earth as groundwater requires
an intricate balance between many factors. Primarily, the infiltration capacity of the
soil determines the groundwater potential. The speed of infiltration is dependent
upon, mainly, the porosity and permeability of the soil and the velocity of the
surface run-off. If the surface run-off is extremely high due to steeply sloping nature
of the ground then, even if the soil is porous and permeable, the soil infiltration
capacity is reduced to a great extent. Another point to be noted here is the part
played by vegetation. It has been found that the surfaces covered with abundant
vegetative cover have better infiltration capacity than barren lands. The thickness of
the permeable layer is another very important factor that determines the storage of
groundwater.
While making inferences about the groundwater potential of an area using the
satellite data, an interpreter concentrates mainly on the geomorphic units that he can
observe on the imagery. Based on the nature of origin, the geomorphic units can be
grouped into five main classes, namely (i) fluvial, (ii) denudational, (iii) structural,
(iv) aeolian and (v) marine.
2.6.2.1 Geomorphic Units of Fluvial Origin
Alluvial plains, flood plains, alluvial fans, deltaic plains, river cut-offs, bajada, wadi
(dry river bed) are some of the geomorphic features that have come into existence
due to fluvial process. All these features can be mapped easily from the satellite
imagery. All these features occupy the valley portion and are composed of loose
deposits of permeable material like sand or clay. The groundwater prospects range
from excellent to moderately good.
2.6.2.2 Geomorphic Units of Denudational Origin
The surface of the earth is constantly being acted upon by different kinds of exogenetic
forces, such as wind, water and ice. These forces tend to bring about both physical and
chemical weathering of the bed rocks and also transport and deposit the weathered
debris in certain locations on the earth. The complete phenomenon is referred to as
denudational process, and this gives rise to many characteristic landforms.
The earth’s crust is made up of several kinds of material and when the exogenetic
process operates in a region certain resistant rocks are left out without much
damage. These rocks will be appearing as hills of bare rock dotting a plain land.
They are called denudational hills and inselbergs. They can be observed in satellite
imagery as bare rock outcrops and they are normally devoid of any water, as they
are totally made up of compact crystalline rock.
2.6 Applications 21
The gently inclined surfaces that are formed in front of major slopes during the
process of erosion are the pediments. They form the zone of recession due to valley
formation. Sometimes by the process of valley formation and widening, a few
adjoining pediments will merge to give rise to a wider plain—the pediplain.
Usually, they are found to be either poor or at the most moderately good as far as
their groundwater prospects are concerned.
Under humid tropical conditions, the crystalline rocks are subjected to intense
chemical weathering, giving rise to lateritic uplands. Although the laterites are soft,
permeable and porous, their location at the ridge tops prevents them from holding
sufficient water resources, against the gravitation force, to be considered as good
groundwater prospecting zones. On the standard FCC, they appear as bright light
brown spots or lines.
The eroded material that has been deposited in the valleys gives rise to piedmont
and talus cones. Piedmonts are the alluvial fans that are found at the foot of the hills
or mountain chains.
Normally, they are composed of fine silts and clay and are considered to be very
good zones of groundwater accumulation. These are readily visible in standard FCC
as triangular zones of high reflectance at the foot of hills. Talus cones are heaps of
cobble and boulder, found at the foot of hills. They are the result of glacial action,
and due to the absence of finer sediments, they are not suitable for holding any
moisture or groundwater.
2.6.2.3 Geomorphic Units of Structural Origin
Due to the tectonic readjustments that are taking place within the crust of the earth,
many features are formed. The most important features of this category are structural
hills and valleys, fractured plateau, mesa and butte. Mesa and butte are the
resistant rock outcrops of volcanic origin, consolidated in nature and do not qualify
as rich groundwater potential zones. The structural ridges are also considered to be
poor groundwater zones. On the contrary, if these features contain sets of fractures
or faults then they qualify as good sources of groundwater, this is because the
numerous fractures and faults act as conduits for groundwater movement. While
faulting, due to the abrasion of the opposite blocks a zone of breccia is formed and
this zone is considered to be extremely rich in groundwater.
In a standard FCC, the joints and structural hills and valleys can be readily
mapped. The lineaments and faults are also observed on the imagery as faint lines
of straight or curved nature. Sometimes, they are also located by the abrupt tonal
contrast in the imagery. In cases where the lineaments are not readily visible, then
image enhancement techniques like edge enhancement, using high-pass filters, have
yielded good results. In fact it is easy to map the lineaments of fairly large
dimensions from the digitally enhanced satellite imagery rather than by following
the conventional geophysical methods. Once the lineaments are traced from the
satellite imagery, then the conventional methods are adopted to fix their location
with accuracy on the ground.
22 2 Remote Sensing in Groundwater Studies
2.6.2.4 Geomorphic Units of Aeolian Origin
Most of the features that form the desert topography fall into this category. All
except the playa (dry lake) qualify as zones of very low potentiality for groundwater
prospecting.
2.6.2.5 Geomorphic Units of Marine Origin
Coastal plains, salt flats, mud flats, beach/sand bars and lagoons are the features
formed due to marine processes. Most of the features can be mapped easily from the
satellite imageries using their characteristic spectral signatures and spatial associations.
Except a few broad coastal plains, all the other units are rich in saline water
and, therefore, are not of much use, as far as their resource potential is considered.
2.6.3 Monitoring of Freshwater Submarine Springs
Gardino and Tonelli (1983) used RS to detect freshwater submarine springs in the
coastal areas of Italy, Sicily and Sardinia. About seven hundred such springs have
been studied along a coastline of 1500 km.
Isotherm maps were prepared for all the coastal inflows. Ground checks were
carried out to distinguish spring flows from pollution seepage discharges. Isotherm
maps have also been used to compute the likely yield on the basis of thermal
balance between water from the spring and the sea. Aerial thermal surveys have
been found to be quite useful in locating rapidly and cheaply the regional carbonate
aquifers discharging reasonably good amount of water into the sea.
2.6.4 Water Table Depths for Aquifers in Deserts
The possibility of estimating shallow groundwater table depths through remotely
sensed thermal infrared data was studied by Menenti (1983).
In arid zones, both surface and groundwater reservoirs lose water through
evaporation. This aspect of the problem, particularly the evaporation rate, was
analysed cheaply in the Fezzan region of Libya (Menenti 1983). Evaporation loss
through the playas (dry lakes) was estimated by combining ground experiments
with remotely sensed data. An infrared line scraping (IRLS) airborne survey with
adequate agri-meteorological support led to the assessment of shallow water table
depth and evaporation rate in the deserts.
2.6 Applications 23
2.6.5 Lineaments from IRS LiSS H Satellite Data
Prasad and Sivaraj (2000) used IRS LiSS-II satellite data and aerial photographs to
locate structurally controlled weaker zones, i.e., lineaments suitable for groundwater
accumulation in the Nileshwar river basin areas of the state of Kerala (India).
2.6.5.1 Geology of the Area
Nileshwar river flows over a length of 46 km and joins the Laccadive Sea through
Karingotte river. This river drains an area of 190 km2 and is bounded within
latitudes 12° 13′ and 12° 23′N and longitudes 75° 05′ and 75° 17′E. The basin is
covered by hard rocks with only fringes of alluvium along the coast. Basin areas are
characterized by charnockites of Precambrian age, laterites of Pliestocene age and
the alluvium (Prasad and Sivaraj 2000). 
The lineaments obtained from aerial photographs and IRS LISS satellite data are the
surface manifestations of the linear feature like faults joints and fractures. The
nature of two sets lineaments with general trend along NW-SE and NE-SW are
shown in Fig. 2.6.
2.6.5.3 Observation
The wells existing near the lineaments are found to have a perennial shallow
groundwater source. Groundwater potentiality of high order is indicated where
lineament runs along/across the alluvial zones with several lineaments intersecting
each other. However, it has been suggested that further field investigations
involving drilling and yield test be carried out for detailing and confirmation
(Prasad and Sivaraj 2000).

The availability of spaceborne data gave an opportunity to several geologists to
apply it in regional-scale mapping of structural features, thereby leading to the
discovery of several hitherto unknown lineaments, faults and folds in areas considered
to be reasonably well mapped. When this information was correlated with
known mineral deposits of the area, a clear relation between the lineaments and the
zone of mineralization and groundwater accumulation could be established. This
experiment convinced the geological community, beyond doubt, the efficiency of
the spaceborne data in providing the information that is so vital in updating the
existing mineralogical maps. After the initial enthusiasm, geologists slowly started
exploring the potential of space derived data in tackling other geological problems.
But, geological mapping with spaceborne data is not as easy as forest or land use
mapping as most of the geological features of interest are not readily visible on the
initial imagery and requires the application of a series of interactive image
enhancement techniques.
2.7.1 Geomorphology
Geomorphology is one of the principal subdisciplines of geology and deals with the
study of the surface configuration of the earth. Here, the landforms are described,
classified and an attempt is made to explain the origin and development of the
present-day landforms and their relationship to tectonics.
Earlier, the geomorphologist had heavily depended on air photographs for
acquiring the information on earth feature, but now with the availability of the
various kinds of satellite imageries such as visible, near-infrared, thermal infrared
and radar imageries at regular intervals the geomorphologist is better equipped for
mapping and monitoring the various changes that are taking place with regard to the
size and shape of the landforms, slope of the terrain, river courses and the drainage
networks. All these data have provided an insight into the geomorphologist in
understanding of the processes that are shaping the earth and also in predicting the
future trend of the changes.
2.7.2 Geological Mapping
Geological mapping comprises of recording information on the extent and distribution
of different rock types and their structural deformation, through satellite
imageries and subsequent ground checks.
26 2 Remote Sensing in Groundwater Studies
2.7.2.1 Lithological Mapping
The diversity in the spectral reflectance properties of the various geological
materials serves as basis for lithological discrimination using satellite data. For
example, most of the acidic or felsic rocks (rocks composed of light minerals) show
reflectance values between 25 and 50 % in the wavelength region of 0.5–1.1 m and
in the same region most of the mafic rocks (rocks composed of heavy minerals)
have reflectance <25 %. However, in practice it is not very easy to discriminate
rock types, due to the soil and vegetation cover. Recently, it has been found that the
thermal infrared imagery is best suited for the discrimination of consolidated rock
outcrops from the surrounding as their radiation emissions are much higher than the
unconsolidated soil. Further, the differences in the spatial domain such as spread of
the outcrop, drainage pattern of the region, drainage density and associated vegetation
also help in inferring the nature of the rock type.
In case of sedimentary terrain, the discontinuities existing between beds of
differing characters can be distinguished, again by their differing spectral signature
such as variation in colour, texture, tone and the nature of vegetation, by mapping
the ridge and furrow system of semi-parallel nature formed due to the differential
erosion of the beds in a sedimentary basin the nature and orientation of the beds can
be deciphered. Drainage patterns, such as trellis, rectangular, parallel, also furnish
information on the attitude of beds and lineaments.
2.7.2.2 Structural Mapping
Structural study involves the mapping of linear features representing major faults or
joints (lineaments), detection of unconformities, mapping of bedding planes and
folds of regional extent. Satellite imageries provide the most useful single tool for
initiating a regional analysis of large-scale tectonism and structural deformation as
they provide synoptic views of large areas at a constant low-azimuth Sun angle,
thereby creating an apparent relief and accentuating minor variation in the
morphology.
Lineaments, by definition, are two-dimensional geomorphological features,
presumably reflecting the subsurface tectonic phenomena, of mappable dimension
possessing rectilinear or lightly curvilinear characteristics. They are considered to
be weak tracts representing, zones of mineral enrichment or groundwater potential
zones. In an imagery, they are recognized by abrupt changes in the tonal contrast
from the adjacent features or as lines of pixel with distinctive tones. However, due
to certain limitations in the sensor resolution they may not be readily recognizable
and in such instances the data have to be further enhanced by applying high-pass
digital filter. As discussed earlier, this technique involves the transformation of the
raw image to display the quantum of changes that are existing between the adjacent
pixels of the imagery rather than their absolute digital values, thereby enhancing the
zones of maximum variation—the lineaments.
2.7 Other Geological Applications 27
2.8 Geographic Information System (GIS)
Geographic information system (GIS) is a tool to efficiently capture, store, update,
manipulate, analyse and display all forms of geographically referenced data. It
stores data about the world as a collection of thematic layers, a pictorial representation
of which is given in Fig. 2.7, to be linked together in spatial domain using
geographic reference system. This simple but extremely powerful and versatile
concept has proven invaluable in solving many real-world problems from tracking
delivery vehicles, to recording details of planning applications and managing natural
resources. The use of GIS in groundwater investigations is growing tremendously.
Nowadays, it is used for groundwater potential (Chi and Lee 1994;
Krishnamurthy et al. 1996) and vulnerability assessment (Rundquist et al. 1991;
Laurent et al. 1998), groundwater modelling (Chieh et al. 1993; Watkins et al.
1996) and management (Hendrix and Buckley 1989). In regional scale, it requires
to handle large volume of georeferenced (spatial) and attribute (aspatial) data.
Using GIS, one can play around with the data and generate themes as required for
specific applications.
GIS is an organized collection of computer hardware, software, geographic data
and personnel designed to turn the geographic data into information to meet the
users’ needs. For example, if the hydrogeological properties of aquifers, their
locations and lateral extent of an area are given as input, GIS can manipulate these
data into information such as the groundwater potential zones, vulnerability to
pollution. GIS is the only system that can produce this type of spatial information
not possible by any other means.
Fig. 2.7 The real-world
geographics represented as a
number of layers or them
28 2 Remote Sensing in Groundwater Studies
2.8.1 Basic Components of GIS
From the structural point of view, GIS is very similar to conventional database
management system (DBMS), except for the fact that the database of GIS is more
sophisticated and has the capability to associate and manipulate enormous volume
of spatially referenced interrelated data (Fig. 2.8).
GIS stores spatial and aspatial data into two different databases. The geocoded
spatial data defines an object that has an orientation and relationship with other
objects in two- or three-dimensional space. It is also known as topological data,
stored in topological database. The data that described the objects are known as
attribute data stored in a relational database. GIS links the two databases by
maintaining one-to-one relationship between records of object location in the
topological database and records of the object attribute in relational database by
using end-user defined common identification index or code.
GIS uses three types of data to represent a map or any georeferenced data,
namely point type, line type and area type or polygon type. It can work with both
vector and raster geographic models. The vector model is generally used for
describing discrete features, while the raster model is used for continuous features.
GIS uses both operational and analysis tools for generating thematic maps. There
are several commercial GIS packages available in the industry, namely Arcinfo,
Integrated Land and Water Information System (ILWIS) and Earth Resource Data
Analysis System (ERDAS) developed by various software vendors.
A GIS approach comprises three distinct phases: (I) data acquisition, (2) data
processing and (3) data analysis. The data acquisition phase includes establishing
control of the data quality, which consists of positional accuracy, and reliability of
observation. There are several ways of digitizing map data for its incorporation in a
GIS. The data can be directly digitized from the map using a digitizing table or it
can be digitized by tracing the outline of required classes on a transparent overlay in
image processing software. The latter approach is common for hydrogeological
mapping. In the present study, image processing software ERDAS is used for the
processing of satellite imagery. The maps are prepared by tracing the outline of the
classes of the enhanced image in GIS software Arcinfo by activating the live-link
facility between ERDAS and Arcinfo. The slope is calculated from the elevation
G I S
Results

contour given in the topographic sheet of Survey of India. The mapping of slope
classes is done by classifying the slope values into different ranges and digitizing
the polygons of each class using digitizing table. The net recharge of the area is
calculated from the water table fluctuation data. The procedure followed to prepare
different thematic maps for the development of a GIS database is shown by the
flowchart of Fig. 2.9.
2.9 Application of GIS in Groundwater
Groundwater exploration in any terrain is largely controlled by the prevalence and
orientation of primary and secondary porosity. The exploration involves delineation
and mapping of different lithological and morphological units and identifying
quantitative parameters of the drainage network, soil characteristics and slope of the
terrain. These parameters play major roles in evaluating hydrogeological parameters,
which in turn enable in understanding the groundwater situation in an area.
Studying all these parameters in an integrated way facilitates effective groundwater
exploration and exploitation. In many developing countries, readily available RS
data may comprise a majority of the existing information over local and regional
scale. Establishing relationships between features identified in RS data, borehole
records, surface geophysical data and other hydrogeological phenomena, is critical
GIS database
Digitization Net recharge
Water table fluctuation data
Slope
Image interpretation
Image Enhancement Photo Interpretation
Satellite imagery Aerial photographs Geology Geomorphology Soil Toposheet
Existing maps
Remote Sensing data
Fig. 2.9 Preparation of thematic maps
30 2 Remote Sensing in Groundwater Studies
in any strategy aimed at maximizing water development efficiencies. These
strategies are developed using a GIS as the unifying element for all collected data.
Many studies have been attempted to integrate groundwater controlling parameters,
such as geology, landform, soil characteristics, topographic features and quantitative
morphometric characteristics. (Ross and Tara 1993; Krishnamurthy et al. 1996;
Laurent et al. 1998). The topological data structure of GIS allows the hydrologist to
increase the degree of spatial units into the distributed models. Spatial modelling
with GIS can be used to extract relevant information, such as slope, watershed
limits, and flow path. We will now deal with specific applications of GIS in the
present context.
2.9.1 Groundwater in a Soft Rock Area Through GIS:
A Case Study
The occurrence and movement of groundwater are controlled mainly by porosity
and permeability of the surface and underlying lithology. The same lithology
forming different geomorphic units will have variable porosity and permeability
thereby causing changes in the potential of groundwater, this is also true for same
geomorphic unit with variable lithology. The surface hydrological features such as
topography, drainage density, water bodies, play important role in groundwater
replenishment. High relief and steep slopes impart higher run-off, while the topographic
depressions help in an increased infiltration. An area of high drainage
density also increases surface run-off compared to a low drainage density area.
Surface water bodies such as river, ponds can act as recharge zones enhancing the
groundwater potential in the vicinity. Hence, identification and quantization of
these features are important in generating groundwater potential model of a particular
area. GIS can be effectively used for this purpose to combine different
hydrogeological themes objectively and analyse those systematically for demarcating
the potential zone. In the present study, an empirical model is developed
within the logical condition of GIS for the qualitative assessment of groundwater
potential in a soft rock area. It is tested in Midnapur District, West Bengal, India.
The results are benchmarked by correlating with the available borehole and
pumping test data.
2.9.1.1 Methodology
The GIS used hydrogeological settings of an area as the basic mapping units. Seven
themes were evaluated, viz. (i) lithology (L), (ii) geomorphology (G), (iii) soil (S),
(iv) net recharge (R), (v) drainage density (D), (vi) slope (E) and (vii) surface water
body (W). Each theme was assigned a value from 1 to 7 ranges on the basis of its
direct control of the groundwater occurrence. Each feature of an individual theme
2.9 Application of GIS in Groundwater 31
was next ranked in the 1–10 scale in the ascending order of hydrogeological significance.
The Groundwater Potential Index (GWPI) for an integrated layer was
calculated using GIS as follows:
GWPI ¼ LwLr þGwGr þSwSr þRwRr þDwDr þEwEr þWwWr ð Þ=Xw ð2:1Þ
where w represents the weight of a theme and r the rank of a feature in the theme.
GWPI is a dimensionless quantity that helps in indexing the probable groundwater
potential zones in an area.
2.9.1.2 Study Area
The test site in Midnapur District, West Bengal, India (87° 10′E, 22° 15′N to 87°
22′ 30′′E, 22° 27′ 30′′N), covering an area of 631 km2 falls under Gangetic West
Bengal region (Fig. 2.4) with an average annual rainfall of 152 cm and temperature
of 31 °C. This forms a typical soft rock area having hydrogeological conditions
favourable for shallow groundwater reserve. This was, therefore, best suited for
testing the proposed GIS integration tool (Shahid et al. 2000).
2.9.1.3 Preparation of Thematic Maps
All the thematic maps were prepared in 1:50,000 scale with a spatial resolution of
0.1 km2 using GIS package Arcinfo. Depending on the relative importance in
groundwater exploration, the themes were assigned specific weights. As used by
Krishnamurthy et al. (1996), geomorphology was assigned the highest weight of 7
while surface water body the least value of 1. Thematic map preparations and
ranking of various features are highlighted below.
Lithology: The lithological map of the area was prepared from the standard
false-colour composite (FCC) of Indian Remote Sensing (IRS-IB) Linear Image
Scanner System (LISS-II) data (Fig. 2.10a). Three types of lithounits were observed
in the satellite sensor image, viz. (i) laterite as light bluish tone with coarse texture,
(ii) older alluvium as dark bluish tone with fine texture and (iii) newer alluvium as
white and red tone with medium texture. Lithounits were ranked on the basis of
their groundwater yield capacity.
Geomorphology: The geomorphological map of the area was prepared from the
hybrid FCC of PCA of Band 1, 2 and 3 as shown in Fig. 2.10b. The following
seven geomorphological units were identified in the area:
(i) older deltaic formation by reddish brown tone and fine texture,
(ii) older filled valley cuts by reddish brown tone and coarse texture in the
lateritic formation,
(iii) younger deltaic formation by bluish tone and medium to coarse texture,
32 2 Remote Sensing in Groundwater Studies
(iv) younger filled valley cuts by bluish tone and medium to coarse texture in
older deltaic formation,
(v) recent deltaic formation by light yellow tone and fine texture,
(vi) hard crust of laterites by reddish brown tone and coarse texture and
(vii) mottled clay of laterites by reddish brown tone and fine to medium texture.
Depending on the hydrogeological significance, the geomorphic features were
ranked.
Soil: The soil map of the area as shown in Fig. 2.10c was prepared using RS
data, aerial photograph and field investigation. The area is covered by five soil
types, viz. (i) sandy loam, (ii) loam, (iii) silty clay, (iv) sandy clayey loam and

Net recharge: The net recharge can be calculated from the annual water table
fluctuation data in an area. A net recharge of 25 cm and above was ranked 10
following DRASTIC ratings of Aller et al. (1987). The present area was found to be
in this class.
Drainage Density: Using standard FCC, drainage map of the area was prepared
for developing the thematic map of the drainage density as presented in Fig. 2.10d.
The features of drainage density were ranked in the 1–10 by Krishnamurthy et al.
(1966).
Slope: The elevation contours in the topographic sheet No. 73(N/7) of Survey of
India helped us in generating the slope thematic map (Fig. 2.10e), each feature of
which was ranked following the DRASTIC ratings.
Surface water body: Surface water body thematic map (Fig. 2.10f) was generated
from standard FCC. Although there is no yardstick as to what extent the
surface water bodies can recharge in the immediate vicinity, we had chosen two
buffer zones with radii 25 and 75 m and ranked them as 6 and 3, respectively, in our
present analysis. Using the above thematic maps, the GIS integration was
performed.
2.9.1.4 Integration and Modelling
The rank of each thematic map was scaled by the weight of that theme. All the
thematic maps were then registered with one another through ground control points
and integrated step by step using the normalized aggregation method in GIS for
Table 2.1 Assigned weightage for the layers
Sl. no. Theme Attribute Rel. weightage
1 Hydrogeomorphology Valley fill 120
BPP-D 90
BPP-M 60
BPP-S/PP 30
2. Overburden thickness >25 m 140
15–25 m 105
05–15 m 70
<5 m 35
3. Lineament NW-SE orientation 20
NE-SW orientation 10
4 Slope 0–1 % 10
1–3 % 5
Abbreviation—BPP-D Buried Pediplain-Deep, BPP-M Buried Pediplain-Medium, BPP-S Buried
Pediplain-Shallow and PP Pediplain
34 2 Remote Sensing in Groundwater Studies
computing GWPI of each feature. The evolved thematic map of groundwater
potential of the area is displayed in Fig. 2.11a.
2.9.1.5 Field Verification
The accuracy of the estimates from the GIS model was determined with the existing
borehole and pumping test data. The locations of boreholes along with the lithosection
and pumping test sites (T1-T6) are shown on the GWPI map given in
Fig. 2.11b. Lithology sections obtained from the boreholes clearly show that
Fig. 2.11 a Thematic map of GWPI model depicting groundwater potential, and b locations of
boreholes and pumping wells in the study area with available lithosection
2.9 Application of GIS in Groundwater 35
approximately 10-m-thick shallow aquifer of coarse sand is present in the area
where GWPI is greater than or equal to 8. Approximately 8-m-thick shallow sandy
aquifer is occupying in the zone where GWPI is in between 6 and 8. A thin fine
sand and morum sand layer can be detected in the zone where GWPI is less than 6.
2.9.1.6 Concluding Remarks
A model is, therefore, developed to assess the groundwater potential of a soft rock
area by integrating seven hydrogeological themes through GIS. The field verification
of this model undoubtedly establishes the efficacy of the GIS integration tool
in demarcating the potential groundwater reserve in soft rock terrain. Hence, this
method can be used routinely in the groundwater exploration in favourable geological
conditions.
2.10 Integration of Multigeodata for Hard Rock Area:
A Case Study
One of the important aims of GIS application is to integrate the information and its
analysis, which will provide useful information about spatial and non-spatial data.
Arcinfo is the most complete desktop GIS. It can edit and analyse the data in order
to make better decisions in faster way. Arcinfo is the de facto standard for GIS. It
has the functionality of ArcEditor and ArcView and adds advanced spatial analysis,
extensive data manipulation and high-end cartography tools. It can create and
manage personal geodatabases, multiuser geodatabases, and feature data sets. Also
it can perform advanced GIS data analysis and modelling.
The multigeodata technique will provide through various spatial data of the same
area in same geographic coordinate using command like “union” an integrated layer
of the described area containing all useful information. “union” method in GIS is a
topological overlay of two polygon coverages which preserves features that fall
within the spatial extent of either input data sets, i.e. all features from both coverages
are retained. The integration of different data layers involves a process called
overlay. At its simplest, this could be a visual operation, but analytical operations
require one or more data layers to be joined physically. The integration of multigeodata
technique has been used in the Govind Sagar dam environs of Lalitpur
District to have an integrated groundwater potential map. Total four themes, i.e.
hydrogeomorphology, lineament, overburden thickness and slope in the area of
Lalitpur District, have been integrated using “union” command. Each theme has
different categories of attributes, and they have been assigned relative weightage as
per their importance. The relative weightages are the assigned values in places of
attributes of a theme in order to higher groundwater potential is having higher
relative weightage values and less potential is having less values. The assigned
36 2 Remote Sensing in Groundwater Studies
relative weightages for different themes are shown in Table 2.1. To cite an example,
the maximum weight assigned for the valley fill (which is more potential) is 120,
whereas the lower weight of value 30 is assigned to BPP-S (which is less potential)
in hydrogeomorphology theme. On the other hand, in overburden thickness layer, a
maximum weight of 140 is assigned for thickness is having >25 m. and a minimum
weight of 35 for thickness is having <5 m.
There have been number of polygons created in the composite map after integration
and the weightage values of each polygon have been summed up. Sum of
the weightages of these polygons have been reclassified into four distinct classes
according to their groundwater potentiality.
2.10.1 Classification
Depending on the attributes of four GIS coverages and the general properties
pertaining to the groundwater criteria, decision rule has been prepared. The probable
groundwater potential zones have been classified from all the polygons in the
composite coverage. Then, the polygons have been reclassified according to the
weightage. Sum weightage 200–290 has been considered for “Class-4”, which is
“excellent” groundwater potential zone, sum weightage 140–200 has been considered
for “Class-3”, which is “good” groundwater potential zone, sum weightage
110–140 has been considered for “Class-2”, which is “moderate” groundwater
potential zone and sum weightage up to 110 has been considered for “Class-1”,
which is “poor” groundwater potential zone. Figure 2.12 shows that the probable
groundwater potential zones constitute four classes. These classes can respond to
certain specified management practices for the purposes of optimization of the
available resources.
The methodology and results clearly show the usage of GIS in exploration of
groundwater. The technique also envisages the usefulness of RS information in
groundwater exploration. The integrated results of more number of coverages can
yield more accurate information about the groundwater in that area. Also the same
technique can add the proper management of land utilization.
2.10.2 Depth to Bed Rock Contour
Although some information can be obtained regarding the availability of groundwater
from geoelectric depth slicing up to a certain depth, the topography of hard
rock below 15 m depth is not obtainable and, hence, there is a need for depth contour
map. It can give at a glance the variation of resistant substratum with depth in
addition to the thickness of weathered and fractured/jointed rock at the subsurface.
In general, the study area shows that depth of overburden increases from north to
south. The thickness of the overburden (Fig. 2.13) varies in between 5 and 25 m in
2.10 Integration of Multigeodata for Hard Rock Area: A Case Study 37
the study area except the SE part, where the overburden exists up to 40 m. This part
of the area is having moderate to good thickness of aquifer, which is the only
indicative of the presence of exploitable groundwater through tube well in the area.
Further, it is evident also from the boreholes drilled on the basis of geophysical
recommendations. The reported well discharges in this part vary from 30 lpm
(litre/minute) to 600 lpm.
Fig. 2.12 Integrated map showing groundwater potential zones Govind Sagar dam environs,
District Lalitpur
38 2 Remote Sensing in Groundwater Studies
2.10.3 Dar Zarrouk Parameters
The product of the two parameters, longitudinal unit conductance (S), the ratio of
thickness and resistivity (unit is mho), and transverse unit resistance (T) (unit is
ohm-m2), are termed as Dar Zarrouk parameters. Sum of such parameters for a
sequence of layers within a particular depth or total depth column of overburden
gives a qualitative picture of the area regarding groundwater potentiality within that
depth column. It is an established fact that a combination of high T and low S shows
Fig. 2.13 Depth to basement contour map of Goving Sagar dam environs District Lalitpur
2.10 Integration of Multigeodata for Hard Rock Area: A Case Study 39
potential aquifer in hard rock area, where the general quality of groundwater is
more or less uniform (Mallet 1947; Chandra and Athavale 1977). Variation of S
reflects the basement topography if the overburden resistivity is not varying rapidly.
In order to identify the potential aquifer at the Govind Sagar dam environs, the
contours for T and S were drawn from geoelectrical data with the help of Arcinfo
Tin GIS. From the careful examination of the T and S contour maps (Figs. 2.14 and
2.15), it has been observed that the area enclosed by T contours >400 and
<2000 Xm2 and the same area enclosed by S contours >0.20 and <1.3 mho hold

Vadose zone characteristics give the idea of rock formation within the zone of
aeration. From the water table contour map (preferably premonsoon), the thickness
of overburden above the zone of saturation can be determined and, hence, the
transverse resistance of vadose zone (TV) can be calculated. This particular
parameter (TV) can give the quantitative and qualitative picture of the area
regarding relative groundwater recharge. 
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References 45
http://www.springer.com/978-981-10-1147-4

[3dbu]

N

Quote

 

Dude, but each chapter are 29.84 $... perhaps someone can buy it,  regards 

Edited October 1, 2018 by 3dbu

[vapgis]

Details geological-geophysical aspects of groundwater treatment
Discusses regulatory legislations regarding groundwater utilization
Serves as a reference material for scientists in geology, geophysics and environmental studies

Spoiler

Groundwater Prospecting and Management-Springer Singapore (2016).pdf (9.8 MB)

https://mega.nz/#!qAMiwATI  Pass: !0Mr5WeAtumVmWdGl09mHqAUrXSenrNfyOva6WK4bhOU

 

[contiki]

Thank you for sharing!

[dexgeo]

Thank you for sharing