CHAPTER 1 INTRODUCTION
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CHAPTER – 1
INTRODUCTION
1.1 MOTIVATION AND OVERVIEW
The economy of several countries around the world depends mainly on the
presence of natural minerals, which are associated with hydrothermal alteration zones.
The geological features of Yemen is accomplished by large outcrops of Archean-
Proterozoic metamorphic basement blocks belonging to the Arabian Shield, covered by
rocks of Cambro-Ordovician, Permian, Jurassic, Cretaceous, Tertiary and Quaternary age
(Beydoun, 1964; Beydoun, 1966; Greenwood and Blackley, 1967; Robertson Group,
1992, Mattash, 1994; Menzies et al., 1994; Beydoun et al., 1998; Wanas and Abdel-
Maguid, 2006). That makes it very significant in the field of economic geology.
The study area is composed of an active and dynamic geological setting with
prospects of many different kinds of ore deposits, including shear zones bearing valuable
mineral deposits such as gold, copper, and nickel in Precambrian basement rocks. In the
last ten years the Mineral Resources Exploration Sector, which is represented by the
Geological Survey of Yemen and Mineral Resources Board (GSMRB) drew the attention
of several international and local companies, some of which have already started to work
in this field.
Application of remote sensing and Geographical Information System (GIS) based
on spatial data integration for mapping of hydrothermal alteration zones is still not fully
employed in the activities of the Geological Survey of Yemen. Due to the prevalence of
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roughness of the topography, the application of recent techniques to conduct the
geological survey becomes necessary.
Application of remote sensing and GIS techniques in the field of mapping
hydrothermal alteration zones, which are the sources of valuable minerals is considered
as the first academic study in Yemen. This research work provides a case study to
demonstrate the usefulness of the Enhanced Thematic Mapper Plus (ETM+) and
Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) data for
mapping the hydrothermal alteration zones.
Geological applications of remote sensing and GIS community have attracted
attention since the early stage of their development (Sabins, 1997; Lillesand and Kiefer,
2000; Gupta, 2003; Quattrochi and Luvall, 2004). The earliest use of satellite geological
remote sensing was for the purpose of mineral exploration in the 1970s (Vincent, 1997).
Remote sensing technique has opened up a new era in the mapping of altered and
unaltered litho units. It provides useful information on hydrothermal alteration zones,
which is not otherwise available by other means especially in some areas where the
topography is complicated.
Remote sensing can also identify the hydrothermal alteration zones and rock units
even before conducting geological field survey because their reflectance spectra differ
from those of the unaltered rocks. Hydrothermal alteration zone mapping is one of the
most common applications of remote sensing for mineral exploration, in which the spatial
distribution of hydrothermally altered rocks is a key to locating the main outflow zones of
hydrothermal systems, which may lead to the recognition of mineral deposits (Lowell,
1991; Sabins, 1999).
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The principal aim of reconnaissance mineral exploration is thus to map zones of
hydrothermally altered rocks (Carranza and Hale, 2002). Remote sensing images are
useful for mineral exploration in the following four applications, i) mapping regional
lineaments, ii) mapping local fracture patterns that may control individual ore deposits,
iii) detecting hydro-thermally altered rocks associated with ore deposits, and iv)
providing basic geological data (Sabins, 1997; 1999). Mapping of hydrothermally altered
minerals and understanding the characteristics of hydrothermal alteration zones have
progressively become possible by the use of field and laboratory reflectance
spectroscopy. Geological and hydrothermal alteration zones studies require huge
investment, extended time, and tremendous human labour particularly in areas that are
not easily accessible. In contrast, the low cost and high efficiency of remote sensing in
initial exploration makes it an attractive method (Drury, 2001) because of the focusing
attention on more detailed ground based studies in areas that show more promise.
The application of GIS technique in predicting areas having mineral potential
(altered areas) has provided geologists with a powerful tool to help analyse data much
more efficiently than before (Bonham-Carter et al., 1988; Bonham-Carter, 1994; Rencz et
al., 1994) and also helped in land-use planning and management (Madigan et al., 1988).
Based on preliminary studies carried out by the Administration of Minerals and
Rocks in GSMRB, primary analysis of satellite imagery, and geological map, the study
area has selected. Nabitah belt, which represents a unique site for economic mineral, is
also extends into this area.
To ensure the long term viability of the mineral sector, the government of Yemen
has allotted a portion of the revenues from mineral development, such as taxes and
royalties, towards exploration in frontier areas, new resources and new deposit types. The
government has also collaborated with the private sector to minimize the dislocations of
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community, and facilitate the social and economic adjustments that occur upon the
closure of mining operations. All these facilities have helped to attract many companies
(national and international) to investigate in the mineral sector.
1.2 HYDROTHERMAL ALTERATION
Hydrothermal alteration is defined as the reflection and response of pre-existing
rock-forming minerals that have physical and chemical conditions different from those,
under which were originally formed, especially by the action of hydrothermal fluids
(Beane, 1982; Nehal, 2006). Ore deposits are often produced by fluid flow processes that
alter the mineralogy and chemistry of the country rock. The nature of the altered products
is influenced by 1) the character of the wall rock, 2) the character of the invading fluid,
which defines such factors as Eh, pH, vapor pressure of various volatile species, anion-
cation composition, and degree of hydrolysis, and 3) the temperature and pressure at
which the reactions take place (Guilbert and Park, 1986). This alteration can produce
distinctive assemblages of secondary minerals, which replace the original minerals and
these vary according to the location, and the length of time over which the flow processes
operate (Ferrier and Wadge, 1996; Sabins, 1997; Ferrier et al., 2002; Moghtaderi, et al.,
2007). The alteration minerals commonly occur in the zone of hydrothermal alteration,
processing characteristics relative to the ore body and the style and extent of the
alteration and also reflect the type of mineral deposit (Rajesh, 2004). All alterations are
associated with the ore bodies, but not all ore bodies are accompanied by the alteration,
and the presence of altered rocks is a valuable indicator of possible deposits (Sabins,
1999). Hydrothermally altered zones are the results of change in temperature, pressure,
and chemistry of the hydrothermal solutions. Sources of hydrothermal fluids are not well
understood, however, there are three main possibilities that exist. One source can be the
magmatic rocks themselves, which exsolve water (called “juvenile” water) during the
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final stages of cooling. In metamorphic terrains, a potential source of the fluids is the
dehydration reactions which take place during the metamorphic event. With increasing
temperature under metamorphism, early, low temperature, hydrous minerals recrystallize
into new, higher temperature, anhydrous minerals. The excess water circulates through
the surrounding rocks and may scavenge and transport metals to sites where they can be
precipitated as ore minerals. Near the surface, groundwater is another source of water
(called “meteoric” water). Evidences from some ore deposits suggest that meteoric waters
may mix with juvenile or metamorphic waters during late stages of mineralization.
Hydrothermal alteration zones in the present study area have resulted from the
intrusive tectonic events such as invasion of a variety of syn and post-tectonic pan
African granites, mafic and ultramafic dykes, and movement of Arabian plate away from
the African plate. The various important hydrothermal alteration zones include:
silicification, carbonatization, sericitization, serpentinization, clay mineral, and
oxidiation.
Silicification
These zones are associated with shear zones and are occur as bands and layers
involving high replacement of silica. In most of the cases they are hosted in metarhyolite,
amphibolite schist, carbonate amphibolite biotite schist and graphite schist. These layers
and bands are rich in massive and disseminated sulfide materials (pyrite and
arseonpyrite).
Oxidation
This type of alteration occurred in places where oxygenated groundwater flowed
through the rock and resulted in overall oxidation of the original rock (Arehart and
Hulston, 1998). These zones are wide spread in the entire study area with varying
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thickness and width, and they are highly weathered. They are concentrated in shear zone
and are characterized by massive and compact shape in most places. Quartz with the
boxwork textures is associated with these zones. Most of rock samples collected from this
type of alteration and rich in quartz veins show anomalies of gold. Gossans formed from
weathering such as gossans of western Wadi Sharis does not show any anomaly of gold
but it shows anomalies of Co, Cu and Ni.
Carbonatization
Carbonatization is a general term for the addition of any type of carbonate
mineral. Carbonatised zones are represented in the study area by dolomtic marbles, talc-
serpentinite, carbonate, dolomitic limestone, and carbonate-amphibolite schist. These
zones occur as scattered associated with veins of quartz and gossans in the study area.
Sericiticization
This alteration is typically formed by the decomposition of feldspars and can be
detected by its softness, easily stretchable, greasy feel (when present in abundance), and
its distinctive colours include: white, yellowish, golden brown or greenish. Sericitic
alteration implies low pH (acidic) conditions. Alteration zones consis of sericite and
quartz are called “phyllic” alteration. Phyllic alteration is associated with porphyry
copper deposits and may contain appreciable quantities of fine-grained, disseminated
pyrite, which is directly associated with the alteration event. This type of alteration is
very widely spread in the study area; it also contains high anomalies of gold and other
trace elements.
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Argillitic (Clay Minerals)
Argillitic alteration is characterized by the formation of the clay minerals by
extreme base leaching of alumino-silicates. Different image processing techniques
revealed that this type is widely spread in the study area. It is resulting from leached
feldspars and altered to sericite. The presence of this assemblage suggests low pH
(highly acidic) conditions. In rocks intensely affected by argillic alteration, the clay
minerals completely replace the components of the rock.
Serpentinization
Serpentinization is a descriptive term that denotes many processes involved in
producing serpentine group minerals at the expense of anhydrous or less-hydrous Mg-
rich minerals, such as olivine, orthopyroxene, clinopyroxene, and amphibole (O’Hanley,
1996). This type of alteration is common only when the host rocks are mafic to ultramafic
in composition. The highest anomalies of Co, Cu and Ni are found in this type of
alteration. This type of alteration reflects progressive hydrothermal alteration process
taking place in the study area.
1.3 REMOTE SENSING BACKGROUND
Remote sensing is based on the measurement of Electromagnetic (EM) energy.
EM energy can take several different forms. The most obvious form of EM energy that is
experienced is light. All forms of electromagnetic radiation, including light, behave both
as waves and as particles (Drury, 1987; 2001; AL-Daghastani, 2003). EM energy travels
at the speed of light (3×108 m/sec). It is commonly treated as a wave with both electric
and magnetic fields, which are perpendicular to the propagation direction (Fig. 1.1)
(Hunt, 1980; Harris and Bertolucci, 1989).
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The equation of Planck’s Law, defined the EM energy as a photon:
E=hν = h.c/λ (1:1)
Where, E is the photon energy in joules, h is Planck’s constant (6.6256×10-34 JS)
and ν is frequency (Hz) (Harris and Bertolucci, 1989). The EM spectrum extends from
gamma rays to radio waves and the remote sensing operates in several regions of EM
(Table 1.1) (Fig, 1.2). The visible portion of the spectrum has an extremely narrow range
of wavelengths. It extends from 0.4 to 0.7µ m (blue to red). The Ultraviolet (UV) region
has the shortest wavelengths. Thermal infrared and microwave regions have longer
wavelengths used for remote sensing. The EM energy emitted by the sun is reflected,
absorbed, scattered or transmitted by different materials on the earth’s surface (Elachi,
1987; Jensen, 2005).
This study deals only with the visible, near-infrared, short wave infrared and
thermal regions. The Advanced Space-borne Thermal Emission and Reflection
Radiometer (ASTER) measures reflects radiation in 3 bands between 0.45 and 0.86µ m
[Visible and Near-Infrared (VNIR)], in 6 bands from1.6 to 2.43 µ m [Shortwave Infrared
(SWIR)]; and emitted radiation [Thermal Infra Red (TIR)] in 5 bands in the 8.125 to
11.65µ m. Enhancement Thematic Mapper Plus (ETM+) measures reflected radiation in
6 bands between 0.45 and 2.35µ m (VNIR and SWIR), and emittes radiation in one band
in the 10.40-12.50 µ m range (Table 2.1).
The technical term “remote sensing” was first used in the United States in the
1960s, and encompasses photogrammetry, photo-interpretation, and photo-geology.
Remote sensing technique is the science and art of acquiring information (spectral, spatial
and temporal) about material objects, areas, or phenomenoa, without coming into
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physical contact with the objects, or area, or phenomena under investigation (Campbell,
1996; Buhe et al., 2007). The American Society for Photogrammetry and Remote Sensing
(ASPRS) formally defines remote sensing as “the art, science, and technology of
obtaining reliable information about physical objects and the environment through the
process of recording, measuring, and interpreting imagery and digital representations of
energy patterns derived from non-contact sensor systems” (Colwell, 1997).
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Fig. 1.2 Electromagnetic spectrum
Fig. 1.1 An electromagnetic wave is composed of both electric and magnetic vectors (Jensen, 2005)
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Table 1.1 Electromagnetic spectral regions (Sabins, 1997)
Region Wavelength
Remarks
Gamma ray <0,03 nm Incoming radiation is completely absorbed by the upper atmosphere and not available for remote sensing.
X-ray 0.03 to 3.0
nm Completely absorbed by the atmosphere. Not employed in remote sensing.
Ultraviolet 0.03 to 0.4
µm Incoming wavelengths less than 0.3µm are completely absorbed by ozone in the upper atmosphere.
Photographic UV band
0.3 to 0.4µm
Transmitted through atmosphere. Detectable with film and photo detectors, but atmospheric scattering is severe.
Visible 0.4 to 0.7µm
Imaged with film and photodetectors. Includes reflected energy peak of earth at 0.5µm.
Infrared 0.7 to 100µm
Interaction with matter varies with wavelength. Atmospheric transmission windows are separated by absorption bands.
Reflected IR band
0.7 to 3.0µm
Reflected solar radiation that contains no information about thermal properties of materials. The band from 0.7 to 0.9 µm is detectable with film and is called the photographic IR band.
Thermal IR and
3 to 5 µm, 8 to 14 µm
Principal atmospheric windows in the thermal region. Images at these wavelengths are acquired by optical-mechanical scanners and special vidicon systems but not by film.
Microwave 0.100 cm Longer wavelengths can penetrate clouds, fog, and rain, images may be acquired in the active or passive mode.
Radar 0.1 to 100
cm Active form of microwave remote sensing. Radar images are acquired at various wavelength bands.
Radio >100 cm Longest wavelength portion of electromagnetic spectrum. Some classified radars with very long wavelength operate in this region.
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A more modern definition describes remote sensing as the measurement of EM
energy by aircraft or space-borne-mounted sensor for the interpretation of surface and
subsurface features. Based on the type of energy resources, there are two types of remote
sensing, 1) Active remote sensing, in which sensor provides its own illumination and
measures what comes back from the objectives (Laser and Radar). 2) Passive remote
sensing, which relies on naturally reflected or emitted energy of the imaged surface. Most
of the remote sensing instruments fall into the latter category, obtaining pictures of
visible, near-infrared and thermal infrared energy.
1.4 GEOGRAPHICAL INFORMATION SYSTEM (GIS)
GIS technology was developed in Canada during the later part of 1960s for the
Ministry of Natural Resources of Canada. It is a powerful tool for geological application
because it has the integration of many spatial data sets for visual display and analysis. A
GIS can generate two-or three-dimensional images of an area, showing such natural
features as hills and rivers with man made features such as roads and power lines. De By
et al. (2000) defines GIS as a computerized system that facilitates the phases of data
entry, data analysis and data presentation especially in cases dealing with georeferenced
data. GIS is the software package that can generically be applied to many different
applications. A GIS is designed to accept geographic data from a variety of sources,
including maps, satellite photographs, printed texts and statistics. GIS sensors can scan
some of these data directly: for example, a computer operator may feed a map or
photograph into the scanner, and the computer "reads" the information contained in it.
GIS can be regarded as a set of tools to analyze spatial data - meaning the space
around us, where there is live and function. Specifically, a GIS is an automated system
that can capture, store, retrieve, analyze, and display spatial data from actual surrounding
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for a particular objective (Burrough and McDonnell, 1998). GIS is often described as
integration of data, hardware, and software designed for management, processing,
analysis and visualization of georeferenced data (Neteler and Mitasova, 2007). Remote
sensing played a part in the development of GIS, as a source of technology as well as a
source of data (Paul et al., 2005). GIS is widely used to manage data that have a special
component. A digital GIS offers more viewing flexibility than a simple paper map, and
also has tools to enable data analysis. Remotely sensed data from the earth observation
satellites is particularly well suited for use in GIS since satellite imagery is already in a
digital form. The imagery may be included with minimum processing such as geo-
referencing to form a digital orthomap, or used to create other data layer such as land
cover through analysis of its spectral response patterns.
A key concern in geographical information science is how to process geospatial
data to extract features and visualize spatial patterns. Visualization and other GIS tools
for geological and mineral data can aid the analysis of remote sensing data and the
interpretation of various types of information for mineral exploration (Harris et al., 2001).
Although commercial GIS systems, such as ArcGIS, provide an excellent graphic
user interface for visualizing geospatial data, the complexity of geospatial data and some
specific applications such as visualization of subpixel mineral abundance images,
nevertheless call for new visualization techniques.
1.5 INTEGRATION OF REMOTE SENSING AND GIS FOR
MAPPING THE HYDROTHERMAL ALTERATION ZONES
Mapping of hydrothermal alteration zones is one of the most successful
applications of remote sensing in the mineral exploration (Sabins, 1997; Sun et al., 2001;
Carranza and Hale, 2002; Torres-Vera1 and Prol-Ledesma, 2003; Tommaso and
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Rubinstein, 2007). This is because many of the minerals found in hydrothermal altered
rocks have diagnostic from spectral absorption features caused by presence of OH, and
other hydroxyl bonds like Mg Fe-OH and Al-OH (Hunt, 1977). Multispectral image data
have been successfully used for mapping hydrothermal alteration zones since the launch
of Landsat MSS in 1972. With the launch of landsat ETM+ and ASTER and
hyperspectral imagery the capabilities for mapping hydrothermal alteration zones
significantly increased due to increase in SWIR bands. In the SWIR region most of the
altered mineral features could be diagnostic.
The aggressive physical weathering occurs and hence no soil profile has
developed to enhance the suitability of remote sensing to identify and map the
hydrothermal alteration zones. The study area is an example of the successful application
of remote sensing in mapping of hydrothermal alteration zones. The effect of erosion to
remote sensing of alteration areas can be both positive and negative. The positive effects
of erosion emphasize and highlight the resistant structures, such as quartz veins or
silicified outcrops, exposing the central portions of the hydrothermal alteration process.
The negative effects of erosion are primarily characterized by be removal of geological
evidences.
Remote sensing and GIS have been more widely used as an important tool for
analysis in the areas of mineral exploration. They have become an important tool for
locating mineral deposits, in their own right, when the primary and secondary processes
of mineralization result in the formation of spectral anomalies. Additionally, some factors
can be mitigated with ground support during over flights and field validation to improve
statistical mapping methods. High resolution data are available, which can help in
detecting small objects.
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The introduction of GIS to the geological sciences has provided powerful tools to
help geologists to manage and analyse geological data much more efficiently than ever
before. Several examples exist of GIS applications in the geosciences where multiple data
sets are integrated to provide new information to users. Some of these studies used GIS
for prospecting areas of mineral potential (Bonham-carter et al., 1988; Bonham-carter,
1994; Rencz et al., 1994) and land-use planning and management (Madigan et al., 1988).
GIS offers as a potential tool for accomplishing the archiving, managing, analyzing,
integrating and visualizing of the large volumes of geosciences data collected from a
variety of sources (Harris et al., 2001). Hydrothermal alteration potential is a complex
analytical procedure, which requires simultaneous consideration of spatial evidences such
as geological, geomorphological, geochemical and geophysical. The capability of GIS to
manipulate such classified spatial information through amalgamated layers makes it a
unique tool for delineation of potential locales (Mukhapadhyay et al., 2002).
1.6 LIMITATIONS OF REMOTE SENSING AND GIS
Remote sensing is not a panacea that will provide all the information which we
need. It has several challenges in obtaining precise, remotely sensed measurements from
the surface (Jensen, 2005). Some of the main obstacles are the atmosphere, mixtures and
vegetative cover. Even though some of the factors limiting the efficiency of remotely
sensed data are beyond control, proper planning in the data acquisition process may allow
for their mitigation.
In geological remote sensing, there are special limitations such as the existence of
vegetation cover, which makes the application of remote sensing ineffective. So the issue
of vegetation cover is very important because vegetation tends to obscure the rock, and
soil surfaces (Siegal, 1983). It is also difficult to discriminate between vegetation cover
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and some altered rocks in certain image processing because both are enhanced with the
same brightness - one example in the percent work is the band ratio of 5/7, which is very
sensitive to the vegetation so that altered clay and vegetation cover appeared with the
same brightness. Spectral region between 0.68 to 1.3µ m is more influenced by the
chlorophyll absorption of green plants but dry vegetation cover has minor effect (Ustin et
al., 1999).
Remote sensing involves the high cost of purchasing the images such as
Quickbird and IKONOS. Another limitation is the cost of the equipment used for
processing the image. In areas around the equator, cloud cover is a major problem for
spectral scanners but this can be overcome by using radar, although data from radar
scanners are not collected as frequently as spectral scanners. Ability to penetrate the
ground surface is very limited, which means that it only reflects the spectra of surface
materials.
However, GIS has many beneficial applications just like other technological
systems, there are limitations for its use. For example, data for a specific area may lack
spatial or temporal continuity. Additionally, privacy issues can sometimes limit
distribution of data. GIS data may also be subject to misuse or misinterpretation. GIS
professionals can avoid possible misinterpretation of data by clearly stating the purpose
and limitations of the data set in the metadata file when developing GIS data, and also by
using GIS data from other sources responsibly. Data are expensive; learning process on
GIS software can be long and shows only special relationships but does not provide
absolute solutions.
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1.7 RESEARCH OBJECTIVES
The main objectives of the present research study include:
1. To apply the recent techniques of Remote Sensing and GIS for mapping the
hydrothermal alteration zones in North East of Hajjah, Yemen.
2. To study the utility of spectral reflectance of VNIR and SWIR regions for
mapping of altered zones and calibration of the satellite imagery (ASTER and
ETM+).
3. To delineate the lineaments and their analysis.
1.8 LOCATION OF THE STUDY AREA
Republic of Yemen is located at the south-southwestern edge of Arabian
Peninsula. It extends between 12° and 19° north of the equator and between 42° and 55°
east of Greenwich. Apart from the mainland, it includes more than 100 islands, the
largest of which is Socotra in the Arabian Sea. The total area of the country is
approximately 550,000 km², bordered by Saudi Arabia to the north, Sultanate Oman to
the east, the Arabian Sea and Gulf of Aden to the south, and the Red Sea to the west.
Yemen has a strategic location on Bab El-Mandeb, the strait that links the Red Sea with
the Gulf of Aden, one of world's most active shipping lanes.
The study area is located in the North East of Hajjah city, between 43° 36' 47"
and 43° 40' 24" longitudes and 15° 42' 18" and 15° 50' 09" latitudes, the UTM between
351476.25 and 357860.25 E and from 1736760.00 to 1751268.00 N. Generally the relief
of the area is mountainous with moderate to steep slopes and sharp-ridges (Fig. 1.3).
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1.9 CLIMATE OF YEMEN
The climate of Yemen is diverse and varies from one place to another depending
on the altitudes of the regions. Hot and humid on the coastal, moderate on the mountains,
and hot climate in the desert areas. Yemen has a predominantly semi-arid to arid climate,
with rainy seasons during spring and summer, and with high temperature prevailing
throughout the year in low-altitude zone. The climate in Yemen is affected by the Red
Sea, the Indian Ocean (which includes the Gulf of Aden and the Arabian Sea), and the
Mediterranean Sea. They are the sources of moisture for the passing air masses, and they
have their impact on general atmospheric circulation. Yemen is positively influenced by
its mountainous relief, causing orographic rainfall on the windward side. The annual
rainfall reaches a peak of more than 1000 mm/a in the southern mountain near Ibb and
plunges rapidly at the eastern slopes to less than 50 mm/a (Ramlat As Sabatayn, Ar- Rub-
AL-Khali, and Jawl).
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Fig.1.3 Location and Physiographical map of the study area
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1.10 METHODOLOGY
To achieve the research objectives, studies were undertaken in several stages
which are as follows:
• First stage
This stage includes collating the satellite image data [ETM+, ASTER, and
Quickbird Shuttle Radar Topography Mission (SRTM)] and relevant maps (topographical
and geological). Literature review related to this study was carried out. All data used in
this study were geo-references in the Universal Transverse Mercator (UTM) coordinate
system as the map projection and World Geodetic System (WGS 1984) datum, zone 38
north and to the geographical latitude and longitude. Preliminary analysis of different
data was carried out in order to have an insight into the field work that would be required
prior to actual field study that helped the researcher to conduct the field survey by
pinpointing the potential area.
• Second stage
This stage involves field studies such as lithology, and tectonics and their proper
interpretations. Samples were collected with the coordinates using Global Position
System (GPS) for chemical analysis, petrography and spectral reflectance measurements.
The results such as band ratio, PCA and OIF of primary analysis obtained from satellite
images and field study were compared.
• Third stage
This stage consists of three parts: 1) Chemical analysis, petrographical study and
spectral reflectance measurements. 2) Remote sensing data processing. 3) Integration of
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GIS, remote sensing data and field studies for mapping the hydrothermal alteration zones
of the study area. Finally, this stage included field visits for comparing the above results
with the field investigation results.
• Fourth stage
The data collected have been used to pen down the research by organizing the
related information in the study area, its classification and correlation in an orderly
manner according to the changes that took place and the results of those changes. Finally,
the edited version of the results and recommendations of the research have been
presented.
1.11 OVERVIEW OF THE THESIS
The present research work has been presented in eight chapters: First chapter
introduces the general information about hydrothermal alteration, remote sensing and
GIS techniques and their application in mapping the hydrothermal alteration zones.
Location, physiography of the study area, objectives and literature review are presented.
Methodology adopted is also broadly highlighted.
Second chapter deals with the investigation of the satellite imagery (ASTER,
ETM+, SRTM and Google Earth). It also gives a brief description of the programmes and
instruments which were used.
Third chapter is about the geology of Yemen and the study area, which comprises
of different rock units, classification, structures and stratigraphy. Petrography and
geochemical analysis results are presented.
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Chapter four represents the calibration of both satellite data ASTER and ETM+
using the empirical line method. The laboratory spectral reflectance of selected rocks are
measured, analysed and compared with the USGS and ASTER spectral library.
Application of the OIF for selecting the suitable band colour combination as Red
Green Blue (R-G-B) from multispectral data (ASTER and ETM+) for mapping the
different rock units is presented in chapter five.
In chapter six, the utility of PCA and band ratio techniques for mapping of the
altered, unaltered zones and vegetation cover are presented.
Chapter seven is on creating, analysing and comparing of Digital Elevation
Models (DEMs) from digitizing contour lines and from SRTM data. It also presents the
manual digitizing of the lineaments from the Google Earth, panchromatic band of ETM+
and DEMs, and also automatic extraction of the lineaments from some bands of ETM+
and ASTER data.
In chapter eight, the outcome of this research work are pinpointed, and
summarized. Recommendations for further study are also presented.
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Fig.1.3 Location and Physiographical map of the study area
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