Water is perhaps the most vital natural resource of any country. Economic activities, including industry and agriculture, require water. The health of the population is dependent upon an adequate and clean water supply. Problems of water supply, both in terms of quality and quantity, are experienced by many countries but felt especially in the developing world, where population pressure is greatest and the infrastructure is less well developed. Water is the most basic component of any urban, industrial or agricultural development project (Moussa 2007). With the advent of remote sensing and computer technology in the geosciences, geological investigation and interpretation have entered a new era. Remote sensing technology is very efficient for collecting data. Computer technology, such as computerbased geographic information system (GIS), supplies a different method for data storage, integration, analysis, and display. The combination of remote sensing and GIS provides an optimum system for various geological investigations such as groundwater exploration (Chen 2001).

1. *Anwar Abdullah, "Sam M. Abduljalil, " Manal A. Ali, " Hani A. Ali , " Azan A. Ghalib.
* Geology Department, Faculty of Applied Sinces, Taiz University, Taiz, Yemen
" Taiz, Yemen
Band Ratio Enhancement Techniques of The Landsat-7
(ETM) Data For Some Geological Features Mapping In
The Dabab – Yofrs Area SW Of Taiz City, Taiz, Yemen

2. This study attempt on the application of remote sensing such as LANDSAT-7 (ETM) satellite data and digital enhancement
techniques for different types of geological features mapping in the Dabab – Yefros area, south-western part of Taiz city,
Yemen. The study covers an area of ~273.km2. The different digital enhancement processes were used in this work and
applied to enhance the ETM images for geological features mapping such as, new rock units, linear features, drainage
pattern and soil types mapping. These processes were the atmospheric and geometric corrections, the contrast stretch,
and the band ratio techniques. The 840 band ratio images were created and used to produce the colored images of band
ratio from the seven bands of ETM using color combination of the any three band ratio as red (R), green (G) and blue (B)
colors. These images were compared together based on the ability of the images to identify the different rock units,
linear features, drainage pattern and soil types in the area. The result shows that the colored images of 44 -1/5 -1/7, , 7/2
-7/4 -7/1, 7/1 -7/4 -7/3, 5/3 -5/6 -5/1, and 7/2 -7/4 -7/5 were the best images. These images were used to create four
maps by tracing the new rock unit, linear, drainages and type of soil separately.
These maps were compared with same geological features in the previous maps. The result of this comparison shows
that, there is a new rock unit which could be acidic igneous intrusion and there were high numbers of the lineaments and
drainages, as well as, three types of soil were not identified or mapped in the study area by any previous works. This is
because, the previous studies of geological features mapping did not use the new techniques, data, and softwares. For
this reason, all the pervious mapping of different geological features should be renew using the new techniques, data,
and softwares.
ABSTRACT

3. 1- INTRODUCTION
Geological features mapping from satellite data is considered as a very important issue in different disciplines to solve
certain problems in the area. For example, lithology study, landslide risk assessment for mineral exploration , for hot
spring detection and hydrogeological research (Sabins 1996). Since satellite images data are considered to be a better tool
to discriminate the rocks and to produce better information than conventional aerial photographs (Casas et al. 2000).
Remote sensing refers to the activities of recording, observing, and perceiving (sensing) objects or events in far-away
(remote) places. In remote sensing, the sensors are not in direct contact with the objects or events being observed.
Electromagnetic radiation normally is used as the information carrier in remote sensing. The output of a remote sensing
system is usually an image representing the scene being observed. A further step of image analysis and interpretation is
required to extract useful information from the image. In a more restricted sense, remote sensing refers to the science
and technology of acquiring information about the earth’s surface (i.e., land and ocean) (Qihao 2010).
Remote sensing data has a suitable data for studies in many fields such as agriculture, forestry, water resources, land use,
urban sprawl, geology, environment, coastal zone, marine resources, snow and glacier, disaster monitoring and
mitigation, infrastructure development, etc. Remote sensing imagery has many applications in mapping land-use and
cover, agriculture, geology, soils mapping, forestry, city planning, archaeological investigations, military observation, and
geomorphological surveying, among other uses (Moussa 2007).
Landsat Enhanced Thematic Mapper (ETM) with seven spectral bands has been used for regional scales of geological
mapping. Numerous investigators have used Landsat false color composite images to identify geomorphological
expressions and regional structural features (Jensen 2005 ).
Moreover, the geological map of the study area is collected from the Geological Survey of Yemen. This map is very old and
produced from old data such as aerial photos. For these reasons, the important of this study is to test the ability of the
satellite data to map the some different rock units in the study area, where these data are used as a first time as well as a
new data in this area.
.

4. 2- OBJECTIVES
1) To enhance the satellite image of Landsat-7 using band ratio technique for different geological features mapping such
as rock units, linear features, drainage patterns and types of soil in the study area.
2) To compare the result of images obtained from satellite image after color composition of band ratio with the rock
units of the geological, structural and topographical maps (previous works) in terms of the absence and presence of these
features.
3- STUDY AREA
Study area used for the application of the filter
enhancement technique described in this work is
located to the southwestern of Republic of Yemen.
between latitudes 1487152 N to 1503254 N and
longitudes 374456 E and 4391584 E. It is about 273
Km2.
Figure1 Location of the study area.

5. 4- MATERIALS AND METHODS
4-1 satellite images Landsat -7 (ETM)
The main parameters of the Landsat 7 (ETM) data are summarized in Table 3.1. A Landsat-7 ETM scene acquired on 27th
June 2002, with path 166 and row 51 is used in this study.
Table 1 Landsat -7 (ETM) band characteristics.

6. 4-2 Previous Data
The geological map with the different rock units and fault lines of the study area were digitized from pervious works of
geological maps of Yemen at scale 1:250000 produced by Geological Survey of Yemen, these maps are shown in Figures 2
and 3 respectively. Moreover, the drainage pattern map of the study area was digitized from topographical map with
scale 1:50000 produced by Geological Survey of Yemen. Moreover, the soil map of the study area was produced from soil
map with 1: 25000 of geological survey of Yemen. These maps were shown in Figures 4 and 5 respectively.
Figure 2 The geological map of the study area digitized
from previous map
Figure 3 Faults lines mapped from previous geological
map of the study area

7. Figure 4 Drainage pattern mapped from previous
topographical map of the study area
Figure 5 Soil map digitized from previous s
oil map of the study area
4-3 Enchantement Techniques of Landsat-7 (ETM) Images
Detecting and Mapping of different geological features from the remotely sensed data is a complex process and includes
uncertainties related to resolution and spectral characteristics of an image. Some of the uncertainties may be reduced
using various image enhancement techniques which aim at improving the visual interpretability of an image by increasing
the apparent distinction between the features in the scene (Lillesand & Keifer 1999). Hence the atmosphere and
geomatric corrections and contrast technqiues were applied to the Landsat-7 (ETM) images.

8. 4-4 Color Enhancement Processing
Color combinations are image enhancement techniques which provide powerful means to visually interpret a
multispectral image and they can be real or false (i.e. FCC) utilizing individual bands or band ratios. In these respect, band
ratios, band or PC combinations have been explored as a means to distinguish lithology.
The Landsat-7 ETM data was processed with the Ilwis software (V 3.3) developed by ITC, Netherland. The Ilwis software is
provides components for color composition tool bare (R,B,G), and the 2520 different band ratios were combined to
produce the 840 different color images. These colored images were used to identify and recognizing the different
geological features in the study area.
4-5 Visual Interpretation
In the visual interpretation of remotely sensed images, a variety of image characteristics are brought into consideration:
color (or tone in the case of panchromatic images), texture, size, shape, pattern, texture, are used to interpreted the
colored images produce from landsat-7. the 840 different color images of band ratios were compared based on the above
features to find the best colored images for geological features identifications.

9. Figure 6 The best colored images of band ratios to identify
the different geological features. a. Colored image of 1/4-
1/5-1/7 band ratio as R/G/B band combination. b. Colored
image of 5/3-5/6-5/1 band ratio as R/G/B band
combination. c. Colored image of 7/1-7/4-7/3 band ratio as
R/G/B band combination. d. Colored image of 7/2-7/4-7/1
band ratio as R/G/B band combination. f. Colored image of
7-2,7-4,7-5 band ratio as R/G/B band combination

10. 5- RESULTS AND DISCUSSIONS
These colored images were used in this study to identify and map the rock unit , lineaments, drainages, and soils which
were not mapped in the previous maps (previous works).
In the Figure (a) based on the different colors of the rock units in the area, it is clearly to see the different rocks in the
study area which were presences in the geological map of the study area. Moreover, depend on the interpretation
elements, the Colored image of 1/4- 1/5-1/7 band ratio as R/G/B band combination shows there was a new rock body
occurred in central to the east part of the area with brown color. As well this image shows also the cleared drainage
pattern and linear features in the area.
In the Figure (b) based on the different colors of the geological features in the area, it is clearly to see the different rocks
in the study area which were presences in the geological map of the study area. And it shows there was a new rock body
with circular structure occurred in central to the east part of the area with grayish color. As well this image shows also the
cleared drainage pattern, linear features and the distribution of different type of soils in the area.
In the Figure (c) based on the different colors of the geological features in the area, it is clearly to see the different rocks
in the study area which were presences in the geological map of the study area. And it shows very clearly a new rock
body with circular structure occurred in central to the east part of the area with purple color. As well this image shows
also the cleared drainage pattern, linear features and the distribution of different type of soils in the area.
In the Figure (d) based on the different colors of the geological features in the area, it is clearly to see the a new rock
body with circular structure occurred in the central to the east part of the area with rosy color occurred in central to the
east part of the area with purple color. As well this image shows also the cleared linear features and the distribution of
different type of soils in the area.
In the Figure (e) based on the different colors of the geological features in the area, it is clearly to see the a new rock
body with circular structure occurred in the central to the east part of the area with pinkish color occurred in central to
the east part of the area with purple color. As well this image shows also the cleared drainage pattern, linear features and
the distribution of different type of soils in the area.

11. 5-1 Resultant Maps of the Different Geological Features
The best five colored images of band ratioing were used to trace and digitize the new rock body, lineament features,
drainage pattern and soil mapping. The resultant maps were shown in the Figures 7, 8, 9 and 10 respectively.
Figure 7 The new rock unit of acidic igneous intrusion mapped from
the best colored images of band ratio, overlaid by acidic and basic
volcanic rocks
Figure 8 The new linear lines mapped from the best colored images
of the band ratio over the study area

12. Figure 9 The new drainage pattern mapped from
the best colored images of the band ratio over the study area Figure 10 The new type of soils mapped from the best colored
images of band ratio over the study area

13. 5-2 Evaluation of the Different Geological Features Maps
The resultant four geological features maps that were extracted from Landsat 7 (ETM), data using color composition of
band ratioing approaches were compared with the geological features maps digitized from the previous maps of the
study area. This comparison was based on the location and the numbers of lineaments and drainage . A comparison
between the above mentioned maps of the study area. This technique identified the locations of the new rock unit, new
lineaments, new drainages and new types of soils in the study area as shown in the Figure 7, 8, 9, and 10 respectively.
Whereas, these different geological features were not identified or mapped in the previous works about this area.
6- CONCLUSION
Remote Sensing is a powerful tools for geological features study such as rock mapping in the semi arid areas like south
west Taiz, where the geologic features are well exposed. Digitally enhanced Landsat 7 ETM bands with spatial resolution
of 30 m with image enhancement techniques allowed extraction of most of the geological features in the study area. The
atmospheric and geometric corrections followed by contrast stretch and band ratioing followed by color composition of
band ratio enhancement techniques were applied in this study to enhance the ETM images for visual analysis and
interpretation of different types of geological features.
The visual interpretation of the resultant images has been done with the reference of geological, fault, drainage and soil
maps of the previous studies about the area of research. It has been noticed that the new rock unit such as acidic igneous
intrusive overlaid by basic and acidic volcanic rocks in the study area were well identified in the colored images of band
ratio. Moreover, the higher numbers of the new linear and drainages lines were identified and mapped by using this
techniques which were not mentioned in the previous maps. As well, the new soil map of the area was created from
these colored images of the band ratio. This was led to update the existing geological features maps of the area.

14. 7- RECOMMENDATION
The geological survey of Yemen must re-new the existing geological maps using the new source of the data such as
satellite images which minimize the cost and times. The future researchers in this field about the same area should take
the high resolution of the satellite images and use different enhancement techniques for geological feature mapping.
8- REFERENCES