**1. Introduction to oil spills: Sources, effects, and reaction**

Petroleum products are used across the globe by most industries and for different applications, where the requirement for the presence of petroleum materials on site is often imperative. This need stresses the necessity of moving petroleum substances using maritime ships or underwater pipelines internationally between different continents and countries. To move the oil from its source to the final consumer, up to 15 transfers are involved [1, 2]. Several reasons could cause the occurrence of oil spills: in addition to the intentional petroleum waste spill in seawater, transportation is vulnerable to involuntary oil spills from tanker collisions with rocky shoals, ship accidents, and pipeline ruptures [3]. On a global scale, the European Space Agency (ESA) has stated that the worldwide spillage exceeds 4.5 million tons of oil annually, where

45% of the amount is due to operative discharges from ships [4]. Accordingly, spills in seawater including light oil, gasoline, fuel, crude oil, and bulk oil have adverse longterm repercussions on the maritime environment. They happen on a global scale, influence maritime and human life, and have socioeconomic implications on communities [5, 6]. Depending on the ocean state and seawater currents, an oil spill can scatter over a very wide area in the open sea within only a few hours. Once the spill occurs, the oil quickly spreads to form a thick slick that becomes thinner over time when moving away from the source. This thin layer is called a "sheen" and has a rainbow-like appearance [1]. Therefore, oil spills can have varying thicknesses, ranging from less than a micrometer (um) for sheens to millimeters (mm) for thick slicks as documented in the Deep-Water Horizon case field samples [7, 8]. Based on the oil type and its thickness, a slick can evaporate quickly or can persist in the environment for a long time. For example, even though light oils are highly toxic, they evaporate quickly. But heavy oils, which are less toxic, persist in seawater for a much longer time and can get mixed with pebbles and sandy beaches where they remain for years [1]. Worldwide, fuels and crude oils account for 48% and 29% of the total oil spilled into the seawater, respectively, highlighting again how much the impact on the environment could be severe [9].

In the last decades, thousands of tons of oil were spilled worldwide. The quantity of oil spilled from tankers in the 1990s is estimated to be more than 1.13 million tons of oil, while 73% of the total amount occurred in 10 incidents only [10]. For example, during the Gulf War spill that occurred in 1991 on the sea island in Kuwait, around 800,000 tons of heavy crude oil were released from storage and ships [11]. Another huge spill occurred in 1992 in Fergana Valley in Uzbekistan due to an oil well blowout. During this accident, the estimation of the spilled oil is around 300,000 tons [2]. According to the international tanker owners' pollution federation (ITOPF), the estimated amount of oil spilled from tankers in the 2000s is 196,000 tons [10]. In 2010, while 4000 tons of diluted bitumen were spilled in Kalamazoo, Michigan, due to a pipeline rupture, an approximation of 500,000 tons of light crude oil were spilled in the same year in the Gulf of Mexico due to an oil well blowout [11]. Very recently in 2018, an oil spill of 113,000 tons size happened off Shanghai in China [10] in the Sanchi oil tanker collision.

While environmental rules, regulations, and strict operating procedures have been imposed to prevent oil spills, these measures cannot completely eliminate the risk [2]. Therefore, there is a need to set up oil spill contingency plans in countries where the chances of such disasters are high. These plans are usually prepared by the petroleum administration in close cooperation with ministries, governmental and nongovernmental organizations as well as regional and international entities. They aim to protect human life, natural resources, and the economy by preserving the coastal and marine environment from any adverse effects an oil spill might pose. The main objective of such plans is to maintain the alertness and readiness of the involved entities to ensure a timely and effective response to oil spills and to prevent further pollution. In most scenarios, it requires the quick mobilization of aerial surveillance resources and consultation with international remote sensing institutions to provide oil spill modeling data or remote sensing images. Accordingly, to permit a swift and appropriate reaction and limit contamination, a need to establish an effective oil spill monitoring system presents itself in utmost urgency.

The contingency plan deals with various transformation processes including weathering, evaporation, and emulsification that occur when the oil is spilled on water. Also, the plan considers oil movements in seawater given the oil's physical

#### *Recent Advances in Oil-Spill Monitoring Using Drone-Based Radar Remote Sensing DOI: http://dx.doi.org/10.5772/intechopen.106942*

characteristics and how it interacts with ocean waves. To contain the oil and prevent its spread over time, special equipment such as booms is used on-site. Afterward, devices such as skimmers and absorbing material such as sorbents are used to recover oil from the surface. Other alternatives are to use surface-washing and chemical dispersant agents to treat the oil or to have in-situ controlled burning as a cleanup technique [2]. All previous measures are very critical to making the contingency plan very effective. But a necessary factor for their usefulness is the pre-knowledge that is available about the spill. The more information is collected from the spill scene, the better the measures used for containment and cleaning-up operations are. The first and most critical information is the spill location. Other information, including the volume spilled or the type of the oil, is also necessary to define proper measures in the contingency plan. Since this information is not available at an early stage in many spills, surface techniques, as well as remote sensing techniques, are frequently used for the first assessment and evaluation.

Remote sensing is the field that combines science and technology to extract ("sense") information about an object or phenomenon at a distance ("remotely") by instrument-based techniques. A detailed description of the state-of-the-art remote sensing technologies for oil spill surveillance is listed in [1, 12–14]. The sensors used are usually mounted on aircraft or satellite platforms. They target the detection, thickness estimation, classification, or a combination of these functionalities. As an addition to the state-of-the-art systems, the aim of this chapter is to present a new advancement in oil spill monitoring using drone-based radar remote sensing, which complements currently available systems for better oil spill surveillance. Section 2 provides an overview of the oil spill monitoring system and gives the necessary background about the techniques used up to now for monitoring. It describes the pros and cons of the sensors (2.1) and platforms (2.2) used by state-of-the-art techniques to monitor oil spills. Furthermore, it describes the required information (2.3) and the main features (2.4) for good monitoring and an effective contingency plan. In addition, a system-level view of the new drone-based proposed solution is presented (2.5) and compared with recently developed state-of-the-art techniques in terms of their functionalities and the used sensors (2.6). Section 3 elaborates more on the new proposed approach for oil spill monitoring for oil spill detection, estimation, and classification. It describes in detail the system model (3.1), the new probabilistic detection algorithms (3.2), the new statistical thickness estimation algorithms (3.3), and the neural network regression algorithm for the oil type classification (3.4). The feature of onboard processing is elaborated more (3.5), and the system-level complementary solution is described (3.6). Section 4 concludes this chapter by summarizing the importance of the presented approach as a complementary solution to state-of- the-art techniques and highlights new aspects that should be considered in future developments.
