Lineaments Analysis and Mapping From Satellite Images For Southern Iraq

Synergistic d isplay of data recorded b y different remote sensing has p roved extremely valuable for the extraction of geological features such as lineaments . Accordingly , two satellite images were used for lineaments analyses whi ch are considered as indicators for rock fractures . Ima ge re solution merge and di rectional fil tering methods were applied for lineaments e xtraction using GIS techniques .Rose diagram and lineaments density analysis were used for the traced lineaments . The output of these techniques are used to trace new lineaments as a regional lineaments map . a synergistic display of these regional lineaments with geophysical images allows the major lithological and structural boundaries to be mapped . Evaluation of lineaments map and its rose diagram analyses shows that the dominant lineament trend is mainly NW-SE and NE-SW. It is concluded that these lineaments indicate the fault zones within the area. Besides, a considerable conformity has been n oticed between the location and dimension of such lineaments with subsurface anomalies appeared in geophysical images.


Introduction
Lineaments mapping and analysis is one of the routines in mapping large areas using remotelysensed data .Geologic lineaments mapping is very important in solving engineering problems , especially for site selection in construction , seismic and landslide risk assessment , mineral exploration, hot spring detection , hydrology etc [1,2] .
Lineaments are significant lines that reveal the hidden architecture of the landscape that reveal the hidden architecture of the rock basement [2,3] .However O 'Leary et. al. (1976) define lineament as a mappable, simple or composite linear feature of a surface whose parts are aligned in a rectilinear or slightly curvilinear relationship and which differ from the pattern of adjacent features and presumably reflects some sub-surface phenomenon [4] Two different images were used to reduce the missed lineaments in the area.As the area is characterized by its inhomogeneity and its dramatic land cover changes .The used images were : 1-NASA's Landsat GeoCover program mosaic ( 3 bands in visible spectrum portion ) with 14.25 m resolution and acquired in 2000 .2-Landsat 5 TM imagery with 7 bands (only three of these bands were used in this work) and 30m resolution acquired in 1990.
The integration of Landsat 5 TM imagery with high-resolution panchromatic data provides complementary information with respect to the discrimination of major geologic features and allows lineament extraction in detail [5].The higher spatial resolution and spectral differentiation provided by data fusion techniques increase the interpretability of imagery for geology [6].It is very useful for the geologic mapping of structures and lithology [7] .Only three of the seven bands have been used (4, 5 and 7 ) as the resulting image will be applied for visual interpretation only, using PDF created with pdfFactory Pro trial version www.pdffactory.comcomputer display devices in by which only three bands can be displayed each time.

II -Visual Lineament Tracing
In visual method, the lineaments are extracted from satellite image by manual interpretation.The lineaments usually appear as straight lines or " edges " on the satellite images which are , in all cases, contributed by the tonal differences within the surface material [4]   2) for four directions .Each process will generate a GIS layer that can be linked to other layers easily .A single lineament map has been generated from multiple lineament maps to overcome any confusion or complexity as shown in figure ( 3 ).
Most of the lineaments were traced from the first four images obtained from mosaic image .Generally , the lineaments appeared are gathered in two main groups as illustrated in figure ( 4 ), and their locations are : 1. Al-Hammar marsh: Many parallel lineaments were appeared during the periods of acquiring the original images (merge image) when Al-Hammar appeared as natural marsh in 1990 and mosaic image in 2000 when the marsh dried .2. Rumaila: These lineaments appeared due to the big mass of smoke incoming from oil fields .
Finally, an integration was made between topographic maps and lineament map using GIS capabilities to erase lineaments that match exactly roads, oil pipelines and manmade water channels and rivers.

III-Analyses of Surface Lineaments
After lineaments being traced in the processed satellite image , various analyses methods have been employed to analyze these lineaments in order to extract deeper information from surface data .Two approaches were applied for surface lineaments analysis namely rose diagram and lineament density analysis .

Rose Diagram
This technique was used to analyze surface lineaments indicating their lengths and directions.Rose diagram analysis ( Fig. 5 ) showed that surface lineaments are distributed in all directions with predominant directions toward N40º-60ºE and minor directions in N20º-50ºW .Most lineaments are traces of irrigation network and river drainages with normal direction to the main rivers .

Lineaments Density Analysis
This analysis has been carried out using Matlab language with grid intervals 2 km and cell dimension 5km * 5km .Output for the number of lineaments per unit area is given in figure (6).The output of this analysis were converted to raster images representing the number of lineaments per unit area ( n / km 2 ) PDF created with pdfFactory Pro trial version www.pdffactory.com( Fig. 7).Besides, the number of lineaments intersection per unit area (n/km 2 ) and the total length of lineaments per unit area (n/ km 2 ) have been constructed in the same manner ( Figs. 8 to 11 ) .The general trends of these lineaments are directed in NW-SE and NE-SW.To avoid the effect of non-tectonic lineaments, another image representing the average lineament length per km 2 has been constructed ( Fig. 12) reflecting new lineaments which could be of tectonic origin ( faults ).

Regional Lineaments (Expected Subsurface Lineaments )
Three layer image has been combined (Fig. 13) from the above three single band images of lineament density analyses .Other lineaments are appeared in the new image .Also a new rose diagram is given (Fig. 14 ) indicating that the predominant direction of lineaments is N40º-60º W, with maximum length in the direction N40º-50º W and with minor direction is observed in the direction N30º -60º E .

Satellite Image Interpretation Against Geophysical Images
An integration has been made between lineaments obtained from satellite images and anomalies appeared in geophysical images by displaying the GIS layer of lineaments over the geophysical images.A new map / image is obtained which is shown in figure (15 ) .It can be shown that there is a coincidence between the surface structures and their associated gravity and aeromagnetic anomalies with the main axes trending NW-SE or N-S .

Conclusions
From the resulted maps and rose diagrams, one may point out the following points 1-Directionally filtered imagery is excellent for the delineation of major lineaments while synergistic display allows the major boundaries to be mapped even where there is total vegetation cover.2-Generally, there is a great conformity between the direction of lineaments with the main subsurface structures and their associated geophysical anomalies with predominant trending axes in NW-SE indicating that these surface features are reflections for subsurface ones.

SOBEL
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Figure ( 1 )
Figure (1) Flow chart for the procedure applied in the experimental work.

Figure
Figure (3) Example of combining the lineament maps steps.

Figure ( 12 )
Figure (12) Average of the lineaments length per unit area map.

Figure
Figure (13) .Combined map of density analyses with the new lineaments .