In situ underwater microwave oil spill and oil slick thickness sensor

Abstract

Nearly 30 percent of oil drilled globally is done offshore. Oil spillage offshore have far-reaching consequences on the environment, aquatic lives, and livelihoods as it was evident in the numerous accidents such as the Deepwater Horizon and Bonga oil spillages. Apart from detecting oil spillages, the determination of the oil slick thickness is very important. This is to enable the estimation of the volume and spread of oil discharged in oceans, seas and lakes. This information could guide the oil spill countermeasures and provide the basis for legal actions against the defaulting parties. The viability of the use of radar in the detection of oil spill has already been established by airborne and space borne synthetic aperture radar (SAR). Notwithstanding, the high latency associated with SARs and its susceptibility of false positive and false negative detection of oil slick makes it vulnerable. It has also not been very successful in the determination of oil slick thickness. In situ methods such as the capacitive, conductive and optical based approaches have been used to detect as well as determine oil slick thickness. Some of these contact-based approaches are susceptible to corrosion, fouling and require several calibrations. Radio frequency (RF) signals in seawater suffer from attenuation and dispersion due to the high conductivity of the medium. Antennas, ideally matched to free space, suffer impedance mismatches when immersed in seawater. In this thesis, we proposed the novel approach of using microwave techniques to detect oil spillage and determine oil slick thickness based on a contact-based in situ approach. The work began by undertaking an investigation into the properties of the North Sea water which was used as the primary transmission medium for the study. Subsequently, the research developed an ultrawideband antenna that radiated underwater, which was encapsulated in polydimethylsiloxane (PDMS). The antenna-sensor with a Faraday cage was used to develop a novel microwave oil spill sensor. A communication backbone was designed for the sensor using long range (LoRa) 868 MHz frequency based on a bespoke braid antenna buffered by oil impregnated papers to ameliorate against the influence of the seawater surface. Using a four layered RF switch controller and an antenna array consisting of four antenna-sensors, a novel microwave oil slick thickness sensor was developed. The antenna-sensors were arranged in a cuboid fashion with antenna-sensor 3 and antenna-sensor 4 capable of detecting oil slick thickness at 23 mm and 46 mm using their transmission coefficient (S43) of -10 dB and -19 dB compared to that of the pure seawater respectively. For the 69 mm and 92 mm thickness, the transmission coefficient (S21) of antenna-sensor 1 and antenna-sensor 2 was used to determine these thicknesses with values of -13.5 dB and -24.14 dB with respect to that of pure seawater.