Use of Remote Sensing Data to Detect Environmental Degradation in the Oil Rich Region of Southern Nigeria between 2003 and 2015

The oil spill management system aims to achieve a knowledgebased system which can choose the most suitable method of response in shorter time by analyzing the various sensitivity factors of coastal environment, affecting parameters on oil spill movement, environmental concerns in oil spill response, and consequent monitoring and cleanup measurements. The major advantage of this integration is the ability to extract oil spill parameters such as location, linear size and spill areas. Spatial and temporal information, i.e. oil spill distribution at the sea, its frequency and evolution in time allow the scientists to establish the major cause and source of oil spills, and then outline the risk areas. This study has demonstrated the application of GIS and remote sensing as a decision support tool for oil spill management. Its objectives are to perform image classification and accuracy assessment, to perform post classification change detection for oil spill detection and to perform trend of change analysis for oil spill growth trend. Methodology involves planning stage, data requirements, data acquisition, data processing and results presentation. The results indicated that the annual growth rate of water bodies is decreasing at -0.16% from 2003 to 2015, settlements decreased at a rate of -1.16% from 2003 to 2015 while Mangrove and vegetation decreased significantly at the rate of -2.82% and -1.92% respectively from 2003 to 2015, this is by far the most significant decrease in the study area, as oil spill degrades farmland and plantations there by rendering it useless for economical purposes, the results also indicated that degraded environment increased at a rate of 3.39% from 2003 to 2015. It was further recommended amongst others that further studies should be on oil spill management in Gokana L.G.A as this will provide additional information on how to manage the effects of oil spill in Gokana L.G.A. Keywords—Remote Sensing, Geographic Information System, Oil spill, Environmental degradation.


INTRODUCTION
Petroleum products play an important role in modern society, particularly in the transportation, plastics, and fertilizer industries, there are typically ten to fifteen transfers involved in moving oil from the oil field to the final consumer (Jha et al, 2008). Oil spills are serious environmental disasters, often leading to significant, longterm impacts on the environment, ecology and socioeconomic activities of area. Oil spillage refers to the discharge of petroleum onto the surface of inland or coastal waters, comprehensively; it was defined by Adelana et al, (2011) as the release of liquid hydrocarbons (crude and refined oil) and petroleum by-products into the marine, coastal areas and other environments due to human activities. Oil spills can occur during the transportation or storage of the oil, and the spillage can happen in water, ice or on land (Jha et al, 2008). This implies that oil spillage is a form of pollution that has only anthropogenic (nonnatural) cause. In Nigeria, commonly reported causes of oil spillage include pipeline leaks and burst due corrosion and pressure build up, sabotage and oil theft, tankers' accidents, human error due to poor training or laxity, poor and old infrastructures, and failure to meet standards practices and infrastructures. Most of the conflicts, environmental degradation and crisis going on in the Niger Delta region in Nigeria are attributable to poor or total absence of effective environmental management (Okotoni, 2004). The poor environmental management due to business practices in this area has resulted in social, economic and political problems and this have negatively affected the well-being of dwellers in this region. In Rivers state Nigeria, the analogue methods of acquiring information necessary for mitigating oil spills and remediation are slow and inconsistent. There is lack of updated information and situational awareness that will enhance contingency plan in an event of spill. Many issues related to oil spill contingency planning and any emergency management has spatial dimension. There is need for a more efficient method that will speed up response time and save cost. Geographical understanding of the spillage will go a long way in devising ways to manage and control this spillage problem. It will also facilitate responds and therefore mitigate environment and economic damage caused by oil spill.

II.
STUDY AREA The study area, Gokana is a Local Government Area in Rivers State, Nigeria. Its headquarters are in the town of Kpor. It has an area of 126 km² and a population of 228,828 at the 2006 census. The Gokana people have a rich cultural heritage. The main religions are Christianity and African traditional religions; although most of its customs, traditions and festivals have become extinct due to urbanization and rural-urban migration.

III.
METHODOLOGY For a proper and effective optimization, planning is very important. In this phase of the study, a user requirement analysis was done to focus on what information is presently being used, who is using it and how the source is being collected, stored and maintained. There is ideally a map of existing processes which was improved as well as being replicated by the GIS. The necessary information was obtained through interviews, documentations, reviews and workshops. This also involves the data requirement, hardware and software selections and method to be used.

.2 Methods and Techniques
The method incorporated in this study involves image subset, remote sensing image classification techniques as well as spatio-temporal analysis of satellite imagery. Image subset was done on the two multi-temporal sets of images obtained (LandSat7 ETM+, LandSat8 OLI) in order to cut out the study area, after which land cover maps of the study area was produced using the supervised maximum likelihood classification algorithm in ERDAS Imagine used by (Onojeghuo and Onojeghuo, 2013). A post classification change detection technique was also employed to determine the changes that have occurred in the time period between 2003 and 2015 and trend analysis was performed to determine the trend of increase in the time period between 2003 and 2015.

IV.
RESULTS In this section, results of image analysis as obtained from the hard classification procedure of supervised (MLC) classification, change detection and trend analysis are presented. Most of the discussions are supported by maps, tables and illustrative graphs.

Land cover / Land use Distribution of Gokana L.G.A of 2003
In mapping landcover/land use, five different classes were identified to include Settlement, Degraded Environment,

Trend Analysis
The results of the trend analysis from the data presented in figure 4.6 and table 4.6, indicates that the annual growth rate of water bodies is decreasing at -0.16% from 2003 to 2015, this is significant as oil spill affected water bodies are contaminated, thereby rendering it inhabitable and unusable, leading to significant decrease of clean water in the study area. Mangrove and vegetation, is also decreasing significantly at the rate of -2.82% and -1.92% respectively from 2003 to 2015, this is by far the most significant decrease in the study area, as oil spill degrades farmland and plantain there by rendering it useless for economical purposes. Settlements decreased at a rate of -1.16% from 2003 to 2015, oil polluted communities are forced to migrated to other unpolluted areas since oil spill pollutes the water, land and destructs daily activities. With no other way of farming and providing for themselves the inhabitants of these affected communities are forced to abandon their homes for a better environment Degraded environment increased at a rate of 3.39% from 2003 to 2015. This signifies increased oil pollution from oil wells, oil pipelines and pipe vandalism in the study area. The increasing trend of degraded environment in Gokana L.G.A should be monitored and clean up plans should be step up so as not to lose more landuse features in the foreseeable future. The oil spill management system aims to achieve a knowledge-based system which can choose the most suitable method of response in shorter time by analyzing the various sensitivity factors of coastal environment, affecting parameters on oil spill movement, environmental concerns in oil spill response, and consequent monitoring and cleanup measurements. The developed system would be able to provide a reasonable 'any-time' mechanism so that in most cases some reasonable response actions can be put forward.
The system is useful in speeding of response actions especially in the regions which still suffer from the shortage of enough experts for responding the disasters. The major advantage of this integration is the ability to extract oil spill parameters such as location, linear size and spill areas. Spatial and temporal information, i.e. oil spill distribution at the sea, its frequency and evolution in time allow the scientists to establish the major cause and source of oil spills, and then outline the risk areas. Within the GISapproach, the tasks of analysis, modeling and forecasting of natural processes influencing the drift and spreading of oil spills can also be easily solved on the basis of standard GIS modules or linking it with other useful applications. This integration of technologies can qualitatively and quantitatively characterize not only the spatial and temporal distributions of oil spills, but also environmental conditions of the sea basins as a whole.