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Scientists have regarded oil spills as a potential threat to the environment. Even a minor oil spill can bring a significant change in the environment. Therefore, the rapid detection of oil spills in the marine environment is essential for protecting our nature from extensive damage. This article discusses novel photonic technologies for the detection and monitoring of oil spills.
Early detection and quantitative characterization of the affected region are crucial for determining an optimized cleaning approach that could reduce adverse environmental impact. J. R. Salgueiro, the lead researcher at the University of Vigo, has also highlighted the benefits of the rapid detection of oil spills. He stated that early detection and quantitative assessments would avoid further mixing of oil into water and measures undertaken for cleaning up the pollutant would be more efficient.
Scientists have revealed that detecting and investigating oil spills on an ice-covered sea region such as the Arctic is much more challenging and harms our environment. Various techniques can be deployed depending on the affected area's mode of analysis and location, such as an iced-covered region or under the sea. Some of the commonly used techniques are remote sensing for an aerial view of spills on the open sea, optical techniques, distal laser ultrasonic techniques, fluorometer, autonomous underwater vehicles, infrared sensors, and radars.
What Causes Oil Spills in the Marine Environment?
It has been reported that from 1970 to 2019, approximately half of major spills have occurred in open seas. Despite a reduction in the overall numbers of oil spills in the later years, the number caused by collisions has possibly risen due to a gradual increase in vessel traffic.
These accidents take place due to various reasons, some of which are mentioned below:
- A ship hitting another vessel while navigating inland water channels, in harbors or ports.
- A ship ran aground or damaged by hitting something underwater.
- During loading and discharging of cargo
- An equipment or hull failure, fire or explosions, or weather-related damage
How Does it Affect the Environment?
When unwanted oil spills occur in the sea, oil floats on the surface in the form of a thin film. The film adheres to birds and marine mammals' fur and feathers, resulting in the elimination of their insulating and water-repelling properties and thereby exposing these creatures to the cold. Moreover, these birds and marine animals are poisoned when swallowing the oil residue.
Environmental damage cannot be assessed by only determining the volume of the oil spills, as other factors such as prevailing weather conditions and how quickly a clean-up operation took place determine the ultimate impact of an oil spill.
Photonic Technologies for the Detection of Oil Spills
Commonly used techniques for detecting oil spills from under the ice involve using a Remote Operated Vehicle (ROV) or an Autonomous Underwater Vehicle (AUV).
Ultrasonic or sonar technologies are used to quantify the volume of oil spilled, and optical techniques are used to characterize the oil.
Researchers have recently developed a new photoacoustics technology for monitoring oil spills. This technique detects and quantifies oil spills under the ice, open water, and oil that gets encapsulated within the ice.
Photoacoustic technology is a physical technique used for environmental, biological, and industrial monitoring and imaging. This technology has gained popularity for its simplistic process, compactness, sensitivity, and accuracy of the sub-parts per billion (ppb) level measurements.
This novel technology is based on a) underwater optical generation and b) underwater ultrasonic detection (conventional system). A pulsed laser beam of nearly transparent or transparent wavelength is produced in water or ice. The wavelength is directed upwards, towards the floating ice. For this study, researchers have used 532 nm wavelength with solid-state Nd: YAG laser with doubled frequency to produce green light. The oil is not transparent at this wavelength.
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An upwardly faced transducer at a certain distance below the ice is utilized as a receiver for detection. When the pulse laser touches water to oil or ice to oil interface, divergent ultrasonic waves are generated, propagating backward and forward. In the absence of the oil, no laser absorption occurs. This is because ultrasonic waves are only produced in the presence of thin oil film. Therefore, this technology provides an on/off signal indicating the presence or absence of oil.
This technology has proved to be much more efficient than the existing conventional oil detection approaches due to its sensitivity. The device is equipped with a scanning unit that can be controlled using an ROV.
Photodiode Detector for Monitoring Oil Spills in Water
Scientists have designed a simple device that comprises a photodiode detector to detect an oil spill in water. This technology can also determine the type of oil present on the surface.
Researchers at the University of Vigo have developed a device that can float on water to track oil spills in distal and smaller areas. When oil absorbs UV light, it emits a unique fluorescence spectrum that can be easily analyzed by comparing the measured fluorescence with information in a database.
The research team also plans to design a solar-powered prototype that could be actively placed offshore in the ocean or a lake for months and could efficiently transfer data to a remote system user via a radio.
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References and Further Readings
Peter Mwai. (2020) Mauritius oil spill: Are major incidents less frequent? [Online] Available at: https://www.bbc.co.uk/news/world-53757747
Bescond, C., et al. (2019) Photoacoustic detection and monitoring of oil spill. AIP Conference Proceedings 2102, 020025; https://doi.org/10.1063/1.5099729
Sampedro, O. & Salgueiro, J. R. (2017) Remote photonic sensor to detect crude and refined oil. Applied Optics. 56, 2150-2156. https://doi.org/10.1364/AO.56.002150