**3. Characteristics of spilled oil and its impacts**

In this section, characteristics of spilled oil on coastal region and its impacts are discussed in detail. The spilled oil can spread over sea water, on sea shore, land area, and glaciers. It is highly dangerous as wind, waves, and currents could scatter large oil spill over a wide area within a short period of time [12]. The spilled oil quickly spreads to form a thin layer on the water surface, which is called as oil slick. As time progresses, the oil slick becomes thinner, forming a layer called as a "sheen," which has a rainbow-like appearance with a multiple color. The light weigh oil is highly toxic but it gets evaporated quickly, whereas heavy weigh oil is less toxic but persists in the environment for a longer time. The heavy weigh oil can get mixed with pebbles and sandy beaches where they may remain for many years [13].

It is required to measure the spread of spilled oil over the sea surface called "slick measurement." It is achieved through the wavelength of backscattering of capillary waves that are generated only on the very dark region of sea surface. The measurement of slick regions also depends upon the polarization of RADARs and its incidence angle, nature of spilled oil, and metrological ocean conditions [14].

The coastal region monitoring depends on the capability of radar satellite sensors to be used to detect the oil spill on the sea surface. The multi-temporal imaging technology is used to obtain data captured by sensors as it is very important to model the oil spill. Satellite remote sensing sensors can provide the following information for oil spill contingency planning of large area location and oil spill spread, thickness of the oil spill quantity estimation, the classification of the oil spills from the environmental activities and finally assist the information that provides a cleanup valuable operation [15].

The oil spill in water may severely affect the marine environment and causes damage to plankton and other aquatic organisms. The livelihood of many coastal people is severely impacted by oil spill, particularly those who are depending upon fishing and tourism as their livelihood [16].

The movement of oil on land surface depends on various factors such as oil type, soil type, and moisture content of the soil. Oil spilled on agricultural land can impact on soil fertility and pollute ground water resources as well. Oil companies and shipping operators are responsible for controlling spilled oil and cleaning polluted areas. In the event of oil spill, information about the size and extent of it is very critical and it is required to assist the government and industry in oil spill contingency planning to describe the guidelines for estimating oil thickness using visual appearance as shown in **Table 1** [17]. It also explains the appearance of oil varies from silvery-sheen to dark brown with its approximate thickness in micrometer.