**1. Introduction**

The coastal region monitoring is very important to protect marine environment from oil spill pollution, which is caused due to oil transportation, storage, tanker accident, or intentional drainage of oil into sea water. Day by day the percentage of pollution-affected coastal or ocean region due to fuel is getting increased and thus, it becomes increasingly important to protect ocean regions and lives of marine regions [1, 2]. The spilled oil of ships or tankers spread over the sea surface forms dark regions and causes marine pollution. It could affect the lives of the coastal regions to greater extent. Thus, a suitable mechanism is required to detect and remove those oil spills from coastal regions at the earliest. The above-said task could be accomplished only through remote sensing technique, which is defined as a coherent technique through which any regions or objects in the earth surface could be located at a far distance and monitored. In remote sensing process, information about earth's object is collected either using space-borne satellite or using airborne aircraft [3]. At the initial stage, space-borne satellites could be used for locating the region but further analysis would be carried out with the help of airborne aircrafts. In order to detect and remove spilled oils on sea surface, space-borne satellites such as ERS, ENVISAT, RADARSAT are predominantly used. In general, there two kinds of RADAR are in use, they are Synthetic Aperture Radar (SAR) and Real Aperture Radar (RAR). The Synthetic Aperture Radar (SAR) uses microwave sensors for data collection in the form of 2-D images [4, 5]. These Synthetic Aperture Radars are mounted on satellites and used for earth observations. The microwave sensors reflect the image visual perception of any earth objects and their attributes. Thus, it could be used for monitoring ocean regions during day and night under all weather conditions for detection of spilled oil. Norwegian water pollution authorities are using space-borne satellites for monitoring oil pollution [6].

In this chapter, extensive study on oil spill detection using both manual and semiautomated approaches is carried and presented. The objective of this study is to determine various approaches currently being used for oil spill detection and its accuracy in ocean monitoring for environmental protection. Though the research has been started in 1994, the automatic detection of oil spill is still in infant stage as it is considered as a very complex task. Since oil spill on sea surface resembles look-alike, it is very difficult to differentiate them automatically from it. In general, look-alikes of oil spill are biological film, grease ice, front eddies, rain cells, internal waves, and upwelling zones [7, 8]. In most of the cases, even the trained operator cannot differentiate oil spill from look-alikes, for example, it has been carried out manually at TSS by assigning attributes such as low, medium, and high value to various oil slicks based on its existence with attributes. Once it is characterized as oil spill, this information could be further analyzed through aircraft surveillance system used by Norwegian Pollution Control Authority (NPCA) [9, 10]. Thus, it is very difficult to design an automatic oil spill detection system.

In Section 2, the problems of oil spills in coastal regions were discussed. In Section 3, characteristics of Spilled oil and its impacts in coastal regions are presented in detail. Section 4 discusses about various sensors and satellites employed for ocean monitoring. Section 5 presents existing methodologies till date and Section 6 presents various classifications approaches using features of Oil Slicks. In Section 7, current operational efforts on oil spill monitoring is discussed elaborately. Section 8 briefs case studies in relevant area. Section 9 concludes the work.
