# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 4 Use of USVs in Environmental Disasters with Contaminants
### Chemical Hazards
#### 4.1.1 Oil Spill Detection and Monitoring  
The detection and localization of pollutant sources, such as oil spills, is an important research topic for the mitigation of the impact of such sources on the environment by allowing an effective control strategy. Studies have shown that the impacts of oil spills can be minimized by the existence of an efficient and effective spill response plan [128], with the initial hours following an oil release as the most crucial for mitigating the extent of impact on the environment [129; 130]. In this task, the aim is to find the location of a region that is the source of the substance of interest (e.g., oil spill) using a single or a group of cooperative unmanned vehicles [42], equipped with cameras or laser fluorosensors for detecting and classifying oil [131]. The latter is preferred over the former, since cameras may suffer from poor contrast and lack of positive discrimination, while laser fluorosensors use the phenomenon of ultraviolet light absorption by aromatic compounds in petroleum oils, which become electronically excited, and thus enable its operation either during the day or night [132]. UUVs and USVs are especially tailored to deal with such issues since they can carry out tasks in a variety of environments without jeopardizing human life [133]. Most works on oil spills detection use either UUVs [107; 134], since they try to find the underwater location of the oil spill, or UAVs [135] since it is easier to estimate the amount of oil on the surface. [PERSON] et al. [105] affirm that in areas where oil spills frequently occur, such as coastal ports and oil drilling platform surroundings, the use of USV is seemingly more convenient when compared to traditional airborne and shipborne laser fluorosensors. Shipborne fluorosensors are not as agile or versatile as USVs, while airborne ones are more suitable for wide area detection. Moreover, unlike USVs, airborne cannot provide the precise information about the position of the slick on a continuous basis [136]. [PERSON] et al. [102; 103] present a compact vehicle called HydroNet USV, which was designed to detect hydrocarbon, heavy metal concentrations (chrome--Cr(VI) and Cr(II), mercury--Hg(II) and cadmium--Cd(II)), and oil slick in real time using custom-made miniaturized onboard sensors. The USV is designed for long-range missions, lodging an onboard water analysis system. It was tested during a field test spanning 12.5 km along the coast of Livorno, Italy. Later, [PERSON] et al. [106] adapt the HydroNet to collect and store or process onboard water samples from up to 50 m down the water column. The system was again tested in field trials in Livorno, but they do not present any chemical analysis of the water, which was left for future work. [PERSON] et al. [104] use a twin-hull catamaran named ASV-Victoria to perform autonomous surveys in regions polluted by crude oil. They focus on developing a controller to enable the robots to follow lines and curves and maintain formation collectively while measuring reminiscent crude oil along their paths. The robustness of control of both USVs was assessed at Grand Isle, Louisiana, where control challenges were reported due to wind and currents. [PERSON] et al. [94] use a Wave Glider equipped with a multiple channel hydrocarbon detection sensor for oil spill monitoring. The developed USV has a Turner Designs C3 optical sensor for measuring crude oil and an AquaTracka deep-ultraviolet fluorometer for measuring Polycyclic Aromatic Hydrocarbons (PAH), to determine the boundaries and origin of the identified surface slicks. [PERSON] et al. [101]