Detection of Oil Spillage in the Sea - Research Paper Example

? Detection of Oil Spillage in the Sea Detection of Oil Spillage in the Sea Technological advances have madethe process of monitoring ocean spill possible. The tool used currently, Space-borne synthetic aperture radar is the tool currently used and has several advantages. Its application enhances a large coverage in the sea. Secondly, it is completely independent of the cycles that affect the sea like day and night. Finally, it can be done at all times, regardless of the weather condition. The oil spill detection method used in the paper relied on interpretations done visually from images acquired from Advanced Synthetic Aperture Radar (ASAR). The images were taken during the Prestige oil spill that happened in Spanish coast. Geographical Information System (GIS) database was used in the integration of the images to study the spatial distribution, slick progression and the results compared to field observations. From the results acquired, a relationship is developed between the use of radar imagery and other available options like wind data and in situ interpretations. Integration of these techniques produces efficient ways of monitoring and forecast oil spills in the oceans. Key words Advanced Synthetic Aperture Radar (ASAR), oil spillage, Geographical Information System (GIS), and oil slick. Introduction Oil spillage in the sea or oceans serves as a main source of water pollution and environmental degradation. Most leakages result from ships ferrying oil to various destinations across the world. Storms in the sea cause ship wreckages that lead to oil spillage. Monitoring of such incidences before extensive damage is made is essential. The case study for this project is an oil tanker, Prestige that was damaged in a storm in the coast of Spain. Though it had a capacity of 77000 tons of heavy fuel, after the damage, there was an immediate loss of 5000 tons. Over 190kms of the coast was contaminated with the oil within a period of three days. After a few days, the ship broke and sunk in the Atlantic Ocean. During the incident,3000tons were lost as spillage as other 6000tons as it sunk. Oil spread 270km along the south/south west of the cape of Finisterra. Satellite images have been provided by the European Space Agency daily since the accident occurred. The Envisat space craft and European Remote Sensing (ERS) revealed the leakage, raising an alarm in salvaging process of the sea (Palanzuela, Gonzalez, & Cuadrado 2006). The data retrieved from radar was of great use in oil spillage detection because it covers a wide area. Radar also assists in taking images at all times. This makes it useful in detecting and clean up operations of oil spills. The mode of technology used in the project was Advanced Synthetic Aperture Radar (ASAR). The images retrieved from the radar were very critical in detecting oil spills from the Prestige tanker. The images were integrated by the Geographical Information System (GIS) database that revealed further information about the spillage. The area covered by oil spill, its quantity and spatial distribution in the area within the oil spillage period was traced. Observations made in the field and the condition of wind during the incident could be retrieved. Oil Slick Detection The area affected lies in the north-west coast of Spain on Atlantic Ocean. The coast line covers the Cape of Finisterre to the mouth of Mino River. The marine biodiversity in the area is rich, with a blend of vertical water and column layers. The rich cold water provides nutrients that support pelagic and demersal fisheries. A rich mussel raft culture is also maintained. The fishing industry, mussel culture creates employment to the natives. Beaches, resorts and ecological important areas offer good grounds for national parks. The spillage that occurred became a threat to these areas. ASAR scenes retrieved through wide-swath mode by ScanSAR technique showed that the area affected was greater than 400kms. Several organizations took part in field survey. The data gathered was used in detection and monitoring of oil spills. Helicopters, planes and ships were used in the field survey process. The information gathered was vital in the clean up process implemented. The purpose of the clean up process was to prevent the oil spillage from reaching the coastline. Meteorological station and Quick Scat satellite provided information about wind speed, direction and coverage in the area. The meteorological station near the area was Corrubedo. The data received from the two stations could be used to determine the relationship between the vector of wind and movement of oil slicks. The importance of this data is usually minimized by low spatial resolution. The condition of the sea surface plays a key role in the signal transmission. Since rough surfaces emit a lot of energy to radar sensors, bright signatures are produced. Smooth surfaces produce dark signatures because they reflect radar signals. Bragg backscattering mechanism affects radar strength from the sea surface because of oblique incident angles at which the radar collects signals. Water surface possess capillary and short gravity waves that create high reflectivity, causing Bragg scattering. When capillary and short gravity waves are dampened, dark images are recorded. This is caused by crude oil that form films that vary in thickness on the surface of the sea. Natural phenomena also dampen capillary and short gravity waves. This makes this mode of detection of oil spillage complicated. The speeds of wind at the surface of the sea seen from radar images are essential in the detection of oil spillage. The speed of wind also complicates the whole process. As a result, radar images from oil slick could probably mislead. Visual observations and wind pattern in the field are integrated and used in slick verification to avoid false alarms (Palanzuela, Gonzalez, & Cuadrado, 2006). Analysis of Images Analysis of the images retrieved is done by the operators to detect, and issue facts worthwhile to be used for clean up operations. Seven steps are put to practice. Preprocessing step selects portions of images. The images are converted to 8-bit data. This reduction produces a small file size as well as increase processing speed. Spatial enhancement step improves visual interpretation of oil slicks. The images are located in terms of distance, area measurements and location by the GIS database. Coordinates of the map are indicated in the image data. This step is called Georeferencing. Dark patches are selected because they are suspected to be areas of oil spill. From the data, a histogram is developed. A threshold grey level is established from the mean and standard deviation. Each pixel in the area is classified according to its value. Field observations are used to select areas not affected by oil spill. Filtering of pixels was done. Isolated pixels and individual pixels are separated to avoid difficulties in the image correspondence to oil spills from the tanker. Vector layers are created depending on the possibility of oil spill from radar images. The vectors must be georeferenced because they are derived from images that had been georeferenced. This is the process of digitizing (Palanzuela, Gonzalez, & Cuadrado, 2006). A GIS analysis is done. In this step, the vector layers are integrated in GIS database that provides measurements like area and perimeter. A comparison is done between GIS analysis and visual data to determine the oil slick movement, displacement distances and speeds. The data available in vector format is wind fields derived from Quick Scat satellite data. Field observation data and vector data are studied to establish a relationship with data from the radar. The bases of comparison of data are time, position errors, and oil spill discrimination. Restrictions of oil slick occurs when there is a difficulty in discrimination of real oil slicks and its look-alikes derived from radar images (Palanzuela, Gonzalez, & Cuadrado 2006). Conclusion The use of ASAR and radar images in monitoring and predicting oil spills caused by oil tankers is a success in technology advancement. The methods used in data collection work hand in hand to provide information relevant in establishing leakage areas. The methods used are efficient and simple. Results are easily produced within a short span of time. The results achieved can be used to confirm results of other complicated models. Radar images are essential in determination of direction of wind when other data sources are not available. This can be achieved by the use of the direction of displacement of oil slicks noted in the area. Reference Palanzuela, M. J .T., Gonzalez, V. L. & Cuadrado, S. M. (2006). Use of ASAR images to study the evolution of the Prestige oil spill off the Galician coast. International Journal of Remote Sensing. Vol. 27, No. 10, 1931-1950. Taylor & Francis, UK. Read More