Persian Gulf
The Persian Gulf, also called the Arabian Gulf by the Arab countries, is a kidney-shaped water body orientated in a northwest to southeast direction. It is approximately 917 km (570 miles) long with its greatest width being 338 km (210 miles). The Shatt-al- Arab, the Gulf's main source of fresh water, flows primarily from Iraq into the northern end of the Gulf. The Tigris and Euphrates, two of the largest river systems in the Middle East, merge together to form the Shatt-al-Arab shortly before it enters the Gulf. At its southeast terminus, the Gulf is linked to the Gulf of Oman and eventually the Arabian Sea and Indian Ocean via the Strait of Hormuz. The Gulf covers 233,100 km2 (90,000 square miles), an area equal in size to New York State and Pennsylvania combined, and contains 8630 km3 (2070 cubic miles) of water. Figure 1, a mosaic of NOAA AVHRR scenes acquired on September 1 and 6, 1990, shows the Persian Gulf and surrounding landforms.
In terms of fresh water intake the Gulf receives an annual average of 34km3 from precipitation and 37km3 from river runoff. The precipitation is concentrated mainly in the winter months, the period of lowest evaporation. When spread out over the Gulf's entire surface area, the fresh water intake accounts for a water layer of nearly .32m (12.6 inches) in depth which represents only a minor portion of the Gulf's total volume. The Gulf's average depth is approximately 36m (118 feet)(Ackleson et al., 1992).
Due to the region's high temperatures, the Gulf loses an estimated 326km3 of water per year to evaporation. The excess of evaporation over fresh water intake creates a circulation where more water (3365km3 per year) flows into the Gulf at its surface than exits (3110km3 per year) it at the lower depths (Ackleson et al., 1992). It also creates a situation where the water in the Gulf is nearly one and a half times more saline than the oceans. The Gulf's counterclockwise current moves the saline water coming through the Strait of Hormuz along the coast of Iran and fresh water and sediment from the Shatt-al-Arab along the very shallow Saudi coastline, providing an ideal habitat for algae which is the primary link in the food chain for the Gulf's principal fisheries. These shallow areas have also been the final resting places for oil from spills. An estimated quarter of a million barrels of oil pollute the Gulf each year and with the Gulf's circulation imbalance it takes more than five years to flush contaminated water through the narrow Strait of Hormuz.
The Study Area
The study area relates to a 512 by 512 pixel image dealing with a
section of the Saudi coastline situated 322km (200 miles) southeast
of Al Kuwayt (Kuwait City) and centered on Dawhat Ad Daffi (Ad
Daffi Bay). Figure 2, a TM Band 4 image taken on March 4, 1991,
identifies the study area and certain geographic features. The bay
is quite shallow with its greatest depths not exceeding 5m (16
feet). The elongated land body near the bottom edge of the image is
Gurmah Island. A portion of what is generally referred to as Abu
Ali Island appears on the east side of the image. Actually, this
land body consists of two islands, Abu Ali and Al Batinah. It is Al
Batinah which appears on the image and not Abu Ali. The city of Al
Jubail is located just south of the study area. The west side of
the image shows the Saudi coast with several inlets. This study
area, especially Ad Daffi Bay and Abu Ali Island, played a key role
in trapping and blocking the oil flow during the Persian Gulf War
so that oil did not move farther south. These land features have
functioned in this manner with previous oil spills coming from the
northern portions of the Gulf. Figure 3, a color composite TM 7,2,1
(RGB) image acquired on February 16, 1991, provides an overview of
the study area and surrounding region.
Ad Daffi Bay and Abu Ali Island experienced the greatest pollution, with the main effect of the spill concentrated in the mangrove areas and shrimp grounds. Large numbers of marine birds, such as cormorants, grebes, and auks, were killed when their plumage was coated with oil. The beaches around the entire bay shoreline were covered with oil and tar balls. Gurmah Island was of particular interest to the groups trying to protect the bay's environments. It has a large stand of rare dwarf black mangroves situated along its southwest edge. Along with these trees grows an asparagus resembling pneumatophore, the roots of which allow the mangroves to respire. Many of these pneumatophores became covered with oil resulting in the eventual death of adjacent trees. Protective booms were placed across the tidal channels but they did not completely control the flow of oil among the trees. The linear features around Gurmah Island, which can be seen in several of the TM bands, are not the protective booms but relate to areas dredged to allow boats passage around the island. The booms were deployed close to the shore and cannot be detected on the imagery. Figure 4 shows the dredged areas as well as the complex water patterns in Ad Daffi Bay related to its currents and bathymetry.
Al Jubail
Immediately south of the study area covered is the city of Al
Jubail (Jubayl). In the early 1970s, Al Jubail, an ancient fishing
and pearling community of some 8,000 people, was selected by the
Saudi government to become a major industrial city which should
reach a population size of 350,000 by the year 2000. Sixteen
primary industries have been or are in the process of being built
in Jubail. These industries include factories producing steel,
gasoline, diesel fuel, petrochemicals, lubricating oil, and
chemical fertilizer. Jubail is basically a new, planned city which
covers a huge area of nearly 365 miles and was designed, with the
aid of remote sensing, by the San Francisco based company called
Bechtel. To handle this industrial development and population
growth, good port facilities and fresh water were needed. Sixteen
berths were constructed to form Jubail's commercial port, and an
industrial port with direct access to the open sea was built at the
end of a six mile long causeway linking the port to the mainland.
Fresh water was obtained by building the world's largest
desalination complex just south of old Jubail. Thus, from an
economic perspective, Saudi Arabia was quite concerned about
protecting Jubail from the oil spill.
Pre-War Conditions
Between 1978 and 1991, prior to the Persian Gulf War, five major
oil spills had occurred in the Gulf, each involving more than a
quarter of a million barrels of crude oil and each being larger
than the 1989 Exxon Valdez spill. See Table 1. The largest of
these spills was associated with a well at Nowruz, Iran that
resulted in 1.9 million barrels of oil being dumped in the northern
section of the Gulf. Also, a considerable amount of industrial
spillage and natural oil seepage occurs in the Gulf each year.
Estimates range from 250,000 to 3 million barrels per year
(DeSouza, 1991;Ackleson et al., 1992). This is the environmental
price which the Gulf must pay to be the world's major oil highway.
Table 1: Major Gulf Oil Spills
| Date | Location | Million Barrels |
| 05/25/1978 | Well 126, Iran | 0.7 |
| 08/20/1981 | Kuwait Petroleum Tank | 0.7 |
| 02/04/1983 | Nowruz, Iran | 1.9 |
| 12/10/1983 | Qatar | 0.3 |
| 08/15/1985 | Khar Island, Iran | 0.5 |
In 1991, several Gulf nations, under the U.N. Intergovernmental Oceanographic Commission, established the Regional Organization for Protection of Marine Environment (ROPME) (Ackleson et al., 1992). ROPME identified a portion of the Persian Gulf as the ROPME Sea Area and sought help from the international scientific community to determine the impact of the 1991 Gulf War oil spill on the marine environment. On February 26, 1992, an international team of scientists started a 100 day survey of the ROPME Sea Area, concentrating its efforts on mapping the shallow marine habitats around Abu Ali Island, a portion of the study area. The team found a massive asphalt surface on the beaches of the island as well as along sections of the Saudi coast north of the island. The asphalt surface ranged over 20m (65 feet) and 0.2m (8 inches) thick. This surface condition pre-dated the 1991 War and indicated the long term effect of the Gulf constantly absorbing oil spills from a variety of sources. Overlaying this asphalt surface was an oily sand layer which resulted from the 1991 Gulf War oil spill. The team also found that this oil spill seemed to have had its greatest effect on the intertidal plant and animal communities in the Ad Daffi Bay. It might be difficult to separate on the imagery old oil spill areas from the 1991 spill.
In spite of the numerous past oil spills, especially during the Iran-Iraq conflict, the natural seeping of oil, and the large number of huge oil tankers, the Gulf has remained an active and unique ecosystem and functions as a significant food source, an important recreation area, a major habitat for endangered species, and a key flyway for migratory birds. How well and how quickly the Gulf will recover from this most recent attack on its ecosystem is not yet known. Comparisons have been made between the 1991 Gulf oil spill and the highly publicized Exxon Valdez spill. However, the Valdez spill was considerably smaller at 240,000 barrels and occurred in a subpolar, rocky-shored, and highly mixed water environment. The Gulf with its tropical temperatures and sandy low shores is a much different water environment than Prince William Sound, Alaska. It is also a much larger water body with a long flow-through rate, about five years, and its water is described as placid and very warm. A more analogous environment with a history of oil spills would be the Gulf of Mexico. An older but more comparable example would be the 1978 IXTOC spill in the Gulf of Mexico, which created a spill of roughly 3.3 to 10.2 million barrels (U.S. Office of Technology Assessment, 1990).
1991 Gulf War
On January 21, 1991, two days after the Coalition forces launched
an air campaign against Iraq for invading Kuwait, Iraqi forces
opened valves at an offshore oil transhipment terminal and
offloaded crude oil from moored tankers, creating a huge oil spill
in the Gulf (Congressional Report, 1992). The spill was first
spotted on January 24th by Saudi Arabia's Meteorological and
Environmental Protection Agency. Baghdad immediately reported that
"American aircraft attacked two Iraqi oil tankers loaded with oil
and the attack led to the outflow of large quantities of oil"
(Reuters, 1991). However, the main source of oil appears to have
been Kuwait's off-shore Sea Island terminal and on January 26, U.S.
Air Force F-111s attempted to stop the oil flow by bombing the
terminal's shoreside pipelines and manifold complex. This bombing
did not terminate completely the flow from the facility and it was
determined that other sources were contributing to the spill. Other
sources included tankers near Mina Al Ahmadi, a damaged refinery
south of Mina Al Ahmadi, the Iraqi Mina Al Bakr terminal, and
tankers anchored north of Kuwait's Bubiyan Island.Initial estimates placed the size of the spill at 10 million barrels, but later and apparently more accurate figures ranged between 4 and 6 million barrels (Congressional Report, 1992). Combined the five previous major spills within the Gulf accounted for 4.1 million barrels, equivalent to the minimum estimated amount released during the Gulf War. Oil continued to be discharged into the Persian Gulf until at least late May, 1991. Practically all of the released oil drifted southwest along the Gulf coast due to the prevailing north winds. However, for the initial two weeks the winds were unseasonably soft and from the southeast which kept the oil from moving to the southwest and provided valuable time to prepare for it. Apparently half of the oil evaporated under the Gulf's warm temperature, and about 1.5 million barrels were recovered by the Saudis. The northerly winds along with persistent coastal sea breezes pushed the remaining .5 to 1.5 million barrels ashore jeopardizing Kuwaiti and Saudi desalination plants, fouling nearly 400 miles of coast line, inundating salt marshes and killing wildlife. The oil might have drifted further south along the Saudi coast if the hook-shaped Abu Ali Island had not blocked the flow and protected the areas south of the island (Ackleson et al., 1992).
Landsat Thematic Mapper (TM) imagery as well as data sets from other satellites were very useful in detecting and monitoring the spilled oil and its flow. The TM mid-infrared bands (Bands 5 and 7) separated the oil's strong reflectance from the low reflectance associated with water. Three weeks after oil was released from the Sea Island Terminal, a February 8 Landsat image showed the oil slick, basically intact, moving down the Saudi coast some 160km (100 miles) south of the terminal. The February 16 Landsat image depicted a slick about 60km (37 miles) long which had travelled 240km (150 miles) south of Kuwait. The image also indicated that the slick was breaking up as it entered Ad Daffi Bay and came into contact with Abu Ali Island. TM images recorded on March 4, 5, and 19 showed that the oil had washed ashore. Ninety different Landsat images were acquired of the Persian Gulf region between January 1 and August 26, 1991, demonstrating the key role played by satellite remote sensing in analyzing environmental problems. Hundreds of other images were available from other non-military satellites and Space Shuttle flights during this period (DeSouza, 1991).
This act of environmental warfare was accompanied by the ignition of Kuwaiti oil wells in February, 1991 when the ground war started. Some 732 wells were damaged with 650 being set aflame, creating enormous smoke plumes, and 82 being opened, causing huge basins of oil. An estimated 3-4 million barrels of oil per day were burned; the United States, as a comparison, imports nearly 5.6 million barrels per day (Congressional Report, 1992). In addition to the apparent environmental damage done by these fires, considerable oil fallout from the smoke plumes affected land and water areas and contributed to the oil spill problem within the Gulf. It was estimated that this black oily rain nearly doubled the amount of oil spilled directly into the Gulf (Ackleson et al., 1992). Deliberate environmental warfare is not new in the annals of war but the world has never experienced a situation at the magnitude of what occurred in the Persian Gulf.
ANALYSIS:
In order to establish an approach to determine the geographic
extent and location of the oil spill, this analysis is based on
understanding and employing the spectral characteristics of the
various bands in the Landsat data sets. Also, simple mathematical
operations are applied rather than using sophisticated statistical
procedures which make it easier for novices to image processing
techniques to understand the exact analytical steps being employed.
All of the following procedures were accomplished using the image
processing software package called PEDAGeOG which is designed for
high school and undergraduate students to use.After loading the seven TM bands into the software package, the next step was to stretch each band to make full use of the absolute data range (0-255), and thereby, create more detailed images. Figure 5 demonstrates the difference between the regular recorded data and the stretched data of an image. Most of the time the dynamic range, that is the range of the recorded values, of a band does not equal the full extent of the absolute data range. The PEDAGeOG software provided the ability to display the statistics and histograms for each band. In this analysis the minimum and maximum values were used to stretch the data. For example, if a band had a minimum and maximum data value of 20 and 155, respectively, these values were converted to 0 and 255 and all of the values in between were stretched accordingly. Rather than automatically using the minimum and maximum values associated with a band, one can establish other values within the dynamic range to be used as the minimum and maximum levels for the stretching procedure, and in the process, center in on a certain portion of the data range to enhance.
