GIS


Oil spills pollution

Sep 2008 | No Comment

 

The purpose of this study was to locate most oil-threatened areas and to document occurrences of oil spills through the production of space oil spills Atlas in the Arabian Gulf, offshore UAE
The influx of oil from tankers and offshore oil operations are amongst the major causes of pollution in the marine environment (U. S. Coast Guard, 1990). Ballast water and other oily water
discharged into the Arabian Gulf ranged between 400,000 and 750,000 tones in 1986. There have already been several
remarkable accidents in the Gulf region involving the loss of large quantities of crude oil from disabled tankers (Table 1, Figure 1). Even a small spill can cause havoc to the ecologically sensitive
environment.
Intentional or accidental oil spills, ballast water discharge, dredging and infilling for coastal development, and uncontrolled sewage and industrial wastewater discharges present real threats to the marine environment in the Arabian Gulf region. Oil discharged from ships imposes a much greater longterm threat to the marine environment than one big accident. Monitoring illegal oil discharges is thus an important component in ensuring compliance with marine protection legislations and general protection of the coastal environments.
This contribution documents the detection by means of satellite imagery, direct hydrocarbon pollution (such as big spills by tanker accidents), discharged oil caused by routine maintenance, and
leaking oil from offshore exploration and development operations. Satellite-borne sensors have varying electromagnetic sensitivities characteristics with different limitations for detecting marine surface
features. Therefore a combination of sensors is required to monitor marine.

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oil pollution effectively. This case study indicates that most oil spills are found along the major shipping routes and in anchorage area, as well as in those areas with intensive large-scale oil production
activities with leakage or tank-washing discharges. The results will show locations of potentially vulnerable areas, and serve as an alarm system for the implementation of effective routine monitoring
operations along the UAE offshore.
The aim of this study is to determine marine and coastal affected areas in the events of oil pollution, through the compilation and editing of the first satellite image Atlas for oil spills in the UAE, in a standard GIS format for the West and East coasts of UAE.

Study areas

The study areas are situated in the Arabian Gulf. -It is a shallow sea with its long axis oriented in NW-SE direction, and its average water depth is about 36m. The Evaporation and wind are the main driving forces for water circulation in the Arabian Gulf. Evaporation is stronger in winter due to high wind speed, than summer when the water surface temperature is higher. The overall circulation in the inner Arabian Gulf is cyclonic, with relatively fresh water entering through the Strait of Hormuz.
The study areas have one of the busiest and most important tanker shipping lanes in the world; one ship passes the strait approximately every 6 minutes, another statistic indicates that more than 40 % of
the world’s total oil transportation passes through the region. About 15.5 million barrels of oil per day is transported through the Strait of Hormuz. Contamination influx is mainly from tankers releasing
ballast, tank cleaning, and leakage from drilling rigs and production platforms, and maritime accidents.
Located at longitude 52oE and 56o45’E, latitudes 24o15’N and 26oN, the study area covers two sub-areas -one offshore of Abu Dhabi and northeast wards to Ras al Khaimah in the Arabian Gulf, and the other offshore Fujairah in the Gulf of Oman (Figure 1).

Methodology

More than 300 satellite images have been examined during this study (Table 2). ERS-1/2, RADARSAT, and ENVISAT Cband SAR data has been used for the great majority of oil spill detection operations. However, other satellite images including optical sensor images have shown good detection capabilities. Therefore, we looked for all available image data archives and selected more than one hundred images derived from different platforms that covered most of the offshore waters of the UAE. We conducted a search of ERS-1 and 2 data archives to compile a list of all images acquired over the study areas. To evaluate their suitability for slick detection, historical wind conditions for corresponding SAR images were obtained. For each acquisition date, surface wind speed histories were reconstructed using historical records.
The method used for image data analysis is based on manual interpretation. We start by defining target areas based on historical records and on personal observation, then we select imageries satisfying minimum wind conditions and covering study areas, we reconstruct surface wind speed histories, geometric image transformation, image contrast/brightness manipulation to optimize slick discrimination, an overlay analysis incorporating oil well location layer to discriminate ships and oil production facilities. Finally we perform manual image interpretation to discriminate various oil slicks and conduct the comparison between different satellite sensors (Berry, 1995). Some field pictures of historical oil contamination in the UAE waters were obtained from NOAA historical oil spills information.

Results and discussion

The manual interpretation results indicate that certain coastal areas of the UAE face frequent oil spills. Striking examples of oil slicks are shown on figure 2, offshore Fujairah (centered at the coordinates 25o30’N/56o25’E). Here considerable spill concentrations have been found within successive JERS- 1 OPS, Landsat-7 ETM+ images and ERS-1/2 SAR browse images. Figure 2 compares images from 29 June 1992, 21 May 1995 and 28 May 2000 for the same area of offshore Fujairah. Oil discharged from both anchored and moving vessels can be observed in each image. Immediately after discharging flush ballast water, the simmering water surface can be seen as bright silver to gray colour patches on the surrounding water. Based on the size of the image pixel, most of the vessels are super tankers whose hull is more than 300 m in length.

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Figure 1: Demonstration Study Areas. Remarkable Oil accidents in the Gulf region

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Table 2: Satellite imagery investigated during the study project

–~~~~~~~~~~~~–
Salem Issa 

The purpose of this study was to locate most oil-threatened areas and to document occurrences of oil spills through the production of space oil spills Atlas in the Arabian Gulf, offshore UAE
Fujairah Port Authority has introduced Fujairah Offshore Anchorage Area (FOAA) since February 1993 to restrict and prohibit anchoring in the area from Bidiya (north of Khor Fakkan) to Dibba. Shipping routes bordering the UAE with relatively frequent incidences of oil spills include the offshore area running parallel to the coast of Abu Dhabi, Dubai, Sharjah and Ajman, where intensive oil production activities exist, and the routes through the Strait of Hormuz. Attention was focused on monitoring natural seepage of oil in the area with coordinates 54º 00′ E/25º 15′ of the offshore of Abu Dhabi. The analysis was carried out using images from, ERS- 2 SAR, and RADARSAT-1 SAR images.
Beside the SAR images, other sensors were tested to detect oil slicks in the study areas. In the thermal infrared band images an oil slicked surface shows a lower brightness temperature than the
surrounding clear water surface (Figure 3). The image data observed at night time is a more reliable method for determining water temperature because it avoids the influence of solar illumination on the difference between seawater and oil slicks.
This study is probably the first time that oil pollution has been monitored and mapped at National level over quite a wide sea area in the UAE, using high spatial resolution satellite images of varying sensor types. Standards followed to produce the atlas follow international standards; well known international examples (Al-khudhairy, 2002; European Commission, 2001) were consulted. Examples of maps appearing in the oil spills Atlas are presented in figures. 

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Figure 2: JERS-1 OPS and Landsat-7 ETM+ showing oil discharged, offshore Fujairah, oil tankers anchorage points in the Gulf of Oman. Images are from 29 June 1992, 21 May 1995 and 28 May 2000

Conclusions

Results of this study demonstrate and confirm that the offshore UAE faces frequent occurrences of oil spills both in the Arabian Gulf and the Gulf of Oman. In particular offshore Fujairah in the Gulf of Oman there are considerable spill concentrations found in the multi-temporal image analysis. The spills are thought to be caused by high oil content ballast water discharged from giant oil tankers. It is worth stressing here that the identification of such areas is an important step for any effective monitoring scheme based on space-borne imagery, which is attainable with the current acquisition conditions.
Shipping routes bordering the UAE with relatively frequent incidences of oil spills include the offshore area running parallel to the coast of Abu Dhabi, Dubai, Sharjah and Ajman, where intensive oil production activities exist, and the routes through the Strait of Hormuz.
The analysis showed numerous small oil slicks caused by natural seeps from the seafloor. Visual overlay analysis revealed a close relationship between spills, oil fields and shipping routes.
The production of the actual oil Atlas is a

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Figure 3: Comparison between Landsat-7 ETM+ visible bands composite and thermal infrared band images.

milestone on the road to achieve an early warning system against oil pollution in the Gulf. Gulf States coastlines host most of its capitals, greatest cities and water desalination plants making them highly vulnerable to any offshore oil accident.

References

Berry, J. L., 1995. Detecting and evaluating oil slicks on the sea surface. Space Congress on Remote Sensing for Oil Exploration and Environment, 23- 24 May, Bremen, Germany, pp. 90-110.
Al-khudhairy, D. H. A, 2002. Marine oil pollution: Technology and methodologies for detection and Early Warning, European Commission, Italy.
European Commission, 2001. A Mediterranean Sea surveillance system using satellite imagery in order to detect and monitor oil slicks, http://ramses.esrin.esa.it
U. S. Coast Guard, 1990. Update of inputs of petroleum hydrocarbons into the oceans due to marine transportation activities.
National Research Council, Nationa Academy press,Washington, D.C

Salem Issa Asst. Professor, Geology Department

United Arab Emirates AL AIN, United Arab Emirates
salem.essa@uaeu.ac.ae
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