The analysis and geologic interpretation of Landsat imagery in Nsukka L.G.A

ABSTRACT

This study examined “The analysis and geologic interpretation of Landsat imagery in Nsukka L.G.A” This study is aim at using information from the potential field and satellite sensor images from Nsukka area using Landsat which is a scientific satellite that studies the photographs the earth’s surface by using remote-sensing techniques. Satellite images and aerial photographs are extensively used to extract lineaments for different purposes in this study. The satellite images and results show the vegetation and features of the Nsukka Area. In this study, findings reveal that the NDVI shows spare or low vegetation for Nsukka town and thick vegetation for high VDVI in area like Afa, Ikolo and Eho Alumonia as expected because of the built up in Nsukka town. This was also supported from the Red Green Blue (RGB) map with the Short Wave Infrared (SWIR) as it verified and further explains what was seen in the NDVI map. This research work was carried out using data from Landsat imagery. It is limited to the analysis and geologic interpretation of Landsat imagery data.  It is also limited to the information that can be derived from the potential field and satellite sensor images and recommends that further study should be carried out to cover more areas to be able to have a better understanding of the study.

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Land satellites have provided repetitive, synoptic, and global coverage of high resolution images of most parts of the earth surface for some decades now. The use of satellite imagery for regional mapping of geologic units and structures has long been demonstrated as a vital tool for regional geologic mapping (Opara et al, 2012).

This is as result of its ease of operation, speed, accuracy, low cost and coverage. In addition, advancements lately in satellite and digital technologies have led to remarkable improvement in this technique (Opara et al, 2012).

Lineament density analysis is a way of calculating frequency of the lineaments per unit area. This is also known as lineament-frequency (Greenbaum, 1985). This analysis will produce a map showing concentrations of the lineaments over the area.

Lineaments are defined as mapable linear surface features, which differ distinctly from the patterns of adjacent features and presumably reflect subsurface phenomena (O’Leary et al., 1976). The subsurface effect is valid if the origin of the lineament is controlled by geological structures such as faults and fractures. Other types of lineaments result from morphological effects (stream channels or drainage divides) or human effects (roads, field boundaries) can also exist in the region. A lineament is also a linear feature in a landscape which is an expression of an underlying geological structure such as a fault. Typically a lineament will comprise a fault-aligned valley, a series of fault or fold-aligned hills, a straight coastline or indeed a combination of these features. Fracture zones, shear zones and igneous intrusions such as dykes can also give rise to lineaments.

Landsat is a scientific satellite that studies and photographs the earth’s surface by using remote-sensing techniques. Satellite images and aerial photographs are extensively used to extract lineaments for different purposes. Since satellite images are obtained from varying wavelength intervals of the electromagnetic spectrum, they are considered to be a better tool to discriminate the lineaments and to produce better information than conventional aerial photographs (Casas et al, 2000).

Remote Sensing Techniques have opened a new era in mapping lithology. The Landsat Enhanced Thematic Mapper data are extremely useful. In the past, the geological maps were prepared from conventional ground surveys based on field observations. They are made along traverse lines at regular intervals. While plotting such point information collected along the traverse lines on the topographic base and ultimately preparing final maps by extrapolating the details, certain errors are unavoidable and lead to inaccuracies in maps. Since the development of remote sensing technology, mapping procedures have undergone continuous change.

Remote sensing techniques play an important role in mapping programs (Farina et al., 2005). Mapping of lithology and alteration zones in inaccessible mountain and forest terrain has always posed a challenge. There always existed disputes on the accuracy of lithological boundaries and structural details in these maps. Vast area to be surveyed and its inaccessibility, forbids physical investigation of every outcrop. At this juncture, the potential of Remote Sensing is appreciable. The greatest advantage of Remote Sensing is the synoptic view that it provides. It gives a regional and integrated perspective of inter-relations between various land features. The availability of multi-spectral and high resolution data as well as the advanced capabilities of digital image processing techniques, in generating enhanced and interpretable image has further enlarged the potential of RS in delineating the lithological contacts and geological structure in great details and with better accuracy (Drury, 1998). The existing multi spectral satellite systems are designed to investigate natural resources with special focus on vegetation coverage, lithology and mineral exploration (Crippen and Blom 2001; Yousif and Shedid 1999; Abrams 1984). The wide area coverage of the data in connection with their long-term availability allows analysis of the spatial dynamics within larger areas. Most applications of Remote Sensing in geology involve the delineation of structures, discrimination of different rock and soil types and resource exploration (Kruse and Dietz 1991). Following the launch of Landsat Thematic Mapper (TM) in 1982, geologists gained access to better spatial (30m) and spectral resolution (Abrams 1984), compared to the Multi spectral Scanner (MSS) used, for detailed geological studies (Podwysocki et al. 1983). Many geological studies have employed Thematic Mapper and Enhanced Thematic Mapper plus data to discriminate the various lithologies, lineaments and minerals by usighyperspectral laboratory (Abrams, 1984). In the regions where bed rock is exposed multi-spectral RS is useful for mapping lithology and alteration zones. Subsequent Studies, in South-West USA and elsewhere (Prost 1980; Rowan and Kahle 1982; Podwysocki et al 1983; Abrams 1984) have confirmed that areas of hydrothermal alterations may be distinguishable using the ratio of Thematic Mapper band 5 and 7. Also it is evident that the spectral characteristics of Thematic Mapper bands are suitable for mapping lithology.

1.2 Location and Geology of the Area

Nsukka LGA has an area of 1,810 km² and a population of 309,633 at the 2006 census. The Local Government Headquarters is located in the hilly and green sites which Nsukka is known for close to colonial quarters of the pre-Independence years. The Nsukka area is characterized by the existence of mineral resources and the speculation of the existence of hydrocarbon bearing formations in the area.

Studies on the Nsukka area have led to the identification and recognition of varieties of geologic structures, stratigraphic units and the age of formations found therein. The present study would be targeted at interpreting the structures existing in the Nsukka area using landsat Thematic Mapper (remote sensing) data.This research is aimed at harnessing the advantages inherent in the geological interpretation of the Nsukka area.

Figure. 1: Geological Map of Nsukka Area

1.3 STATEMENT OF THE PROBLEM

The need to diversify hydrocarbon exploration in Nigeria has lead to Intense geological and geophysical investigations being carried out for some time in different areas of the Benue Trough of which Nsukka is one of them. Though no petroleum exploration activities have been carried out for petroleum occurrences, chemical analysis of samples of potential source rocks in the area have been carried out by various organizations and for research purposes (Petters and Ekweozor, 1982).

In order to contribute to our understanding of the geology and petroleum potentials of the Nsukka belts, this study is an honest attempt to provide a geological interpretation of the Nsukka belts using remote sensing and geophysical data.

1.4       AIMS AND OBJECTIVES OF THE STUDY

The aim of this study is carry out a detailed geological interpretation of the landsat data over part of Nsukka.

The objectives of the study include the following:

1. To interpret geological features of the study area and to infer their relation with basin architecture, morphology and dynamics, thereby presenting a better understanding of the geology.
2. To present geological interpretation of Nsukka belt based on remote sensing and geophysical data integration.
3. To generate information on the lithology, tectonics, geomorphology and drainage characteristics of the Nsukka belt.
4. To produce a lineament map of the study area and hence attempt an interpretation of mineralization potential of the study area.
5. To provide a lucid picture of the basement morphology beneath the sedimentary rock cover of the study area.

1.5    JUSTIFICATION OF THE STUDY

The need for more detailed work on Nsukka belt and some adjoining areas cannot be over-emphasized. This need becomes essential with the various minerals identified in the area. Fluid flow along vertically aligned fractures is an important factor controlling the deposition of minerals in sedimentary sections. The working hypothesis is that fluids scavenge metals from the basement rocks and these fluids move regionally up-dip along fractures of opportunity. When the metals-rich fluid reach a reducing environment such as shale or a hydrocarbon charged zone, a variety of iron rich minerals are precipitated. Similarly, groundwater movement and accumulation in rocks is facilitated by the increased secondary porosity and permeability resulting from a network of fractures and faults.

The Nsukka trough is yet to be fully mapped geologically; as such this study is to contribute to the knowledge of the solid mineral potential of the area.

1.6    SCOPE OF STUDY

This research work will be carried out using data from Landsat imagery. It is limited to the analysis and geologic interpretation of Landsat imagery data.  Also, this study is limited to the information that can be derived from the potential field and satellite sensor images.

Pages:  61

Category: Project

Format:  Word & PDF         

Chapters: 1-5                                 

Material contains Table of Content, Abstract and References.