Major oil spills in marine environments can have serious biological consequences and economic impacts. The general public, the media, etc. will have great interest in this type of issue, to know the extent of the problem, the volume spilled. To estimate the impact that could possibly occur is fundamental for an efficient response and to describe the incident to the public.
The development of monitoring technologies and remote sensing has made better observation possible, frequently in real time, of the actions for combating oil spills, in many situations being able to determine what measures should be taken in order to minimize the impact of the incident on the environment and society.
A good record by video and by still cameras is still an efficient tool for aiding decision-making. With the development of digital technologies offer the Response Command access to information in real time.
Aerial reconnaissance is an essential element for effective response to oil spills at sea. It is used to evaluate the location and the extent of the contamination of oil and to make predictions, verifying the movement of the oil on the sea. Aerial observation provides information that facilitates the development and control of operations at sea, the timely protection of locations along the threatened shorelines as well as the preparation of resources for the cleanup of the coast.
Observation may be done visually or by means of remote sensing systems.
The rule of thumb for this, is that floating oil will move 100% of the direction and speed of the current and deviate 3% of the wind speed in what ever direction it is blowing.
Note for none seafarers:
A northerly current moves towards the north where as a northerly wind blows to the south.
Knowing this means that the following morning the observation aircraft should be able to find where the oil has moved to during the hours of darkness, this will reduce the time and cost involved in this operation.
Visual observation from the air of floating oil is the simplest method of determining the location of an oil spill. However, obtaining satisfactory results requires detailed preparation before starting to do careful interpretation of the information obtained.
Monitoring of the oil spill may be done by helicopter. This resource makes possible close approximation to the oil slicks, ideal for coastal waters.
Offshore, there is less need for changes in velocity, direction and altitude and the velocity of the aircraft is more advantageous for flight over long distances. However, whatever aircraft is used it has to have good visibility and satisfactory navigational instrumentation.
Approximate predictions of the movement of oil slicks may be made on paper or (nautical charts) with information about the direction and speed of the surface current and the direction and velocity of the wind.
The trajectory of an oil slick may be predicted. Floating oil will move at approximately 3% of the velocity of the wind and at 100% of the surface currents. Close to land, the speed and direction of currents should be taken into account when predicting the movement of the oil as with they tend to be effected by the shape of the shoreline, considering that in the open sea the contribution of other oceanic currents predominate the cyclical nature of movement in relation to the tides.
Computer modeling may delineate the trajectories of oil slicks, but the accuracy of any method depends on the quality of the data used and the confidence in the forecasts of velocity of the wind and its direction. Models made specifically for an area tend to be very good. Where as a model made for the open sea will be of little use close to the shore.
Normally it is necessary to plan a systematic aerial search in order to verify the presence or absence of oil in a given area. A ladder search is frequently the method used and most economic for the oservation of an area. Upon planning a search, one should pay proper attention to visibility, altitude, probable duration of flight and the availability of fuel.
Floating oil has a tendency to be elongated and aligned parallel to the direction of the wind. In order to plan a search of the scale type, it is advisable to know the direction of the wind and of the currents, so as to increase the chances of discovering the oil.
Methods for observations and recording
Precise observation will be done using available nautical charts and maps of the region.
It is also necessary to have basic information, such as the location of the spill, the local coastal characteristics and the type of oil spilled, in order to know the rate of spreading.
During the flight, careful annotation should be made of all of the locations where impact could possibly occur. Coastal characteristics should be recorded in order to prepare an informative flight report.
In particular, the efforts of response are concentrated on the most significant areas of the spill. It is important to record the denser concentrations of oil. The GPS equipment of the aircraft also permits the definition of the location of oil slicks. Photography, especially digital, is also a useful tool for recording information and allows others to see the situation at the location of the accident.
Dedicated remote sensing aircraft frequently have built-in photographic equipment linked to a GPS in order to accurately determine geographic coordinates.
Common errors of evaluation
From an aerial point of view it is very difficult to distinguish between oil and a variety of other phenomena. It is necessary to verify as closely as possible a suspected oil spill. Flying at a low altitude allows for a better identification of an oil slick.
It has been found that high contrast in visible imagery can be achieved by setting the camera at the Brewster angle (53 degrees from vertical) and using a horizontally aligned polarizing filter which passes only that light reflected from the water surface.
An estimate of the quantity of oil seen in the sea is important for orientation, making possible the planning of a strategy of total response. It is critical then that during the flight the observer is able to distinguish between the sheen and the thicker oil slicks.
It is very difficult to have a notion of the density of the oil, principally if the sea is rough. All such estimates should be taken with considerable caution. The table below provides some guidance, but it is difficult to evaluate water-in-oil emulsions of heavy crude oil and fuel oil, which could vary in thickness from millimeters to several centimeters.
These two photos above show the same strech of river from different directions. To see sheens properly you need the sun to reflect of them.
The Theory of Oil Slick Appearances
The visible spectrum ranges from 400 to 750 nm (0.40 – 0.75 µm). Any visible colour is a mixture of wavelengths within the visible spectrum. White is a mixture of all wavelengths; black is absence of all light.
The colour of an oil film depends on the way the light waves of different lengths are reflected off the oil surface, transmitted through the oil (and reflected off the water surface below the oil) and absorbed by the oil. The observed colour is the result of a combination of these factors; it is also dependant on the type of oil spilled.
An important parameter is optical density: the ability to block light. Distillate fuels and lubricant oils consist of the lighter fractions of crude oil and will form very thin layers that are almost transparent. Crude oils vary in their optical density; black oils block all the wavelengths to the same degree but even then there are different ‘kinds of black’, residual fuels can block all light passing through, even in thin layers.
ITOPF - International Tanker Owners Pollution Federation (Estimation of the Quantity spilled of oil) http://www.itopf.org/aerial.html
To determine an approximate quantity, the following formula should be used: L (metres) x W (metres) x Thickness (mm) = Cubic Metres
ITOPF has been superceded by the BONN agreement table below in many countries which is based on scientific measurements.
The lower of the figures is used from a legal point of view as the minimum thickness possible to retain the given colour for fines relating to pollution at sea.
The higher of the figures is used from a response point of view as the maximum thickness possible to retain the given colour allowing for quantities of equipment, manpower and the logistics involved to be put in place for the response.
I still prefer the ITOPF because of its simplicity and the fact that we are estimating the size of the spill from a response point of view. With a spill like Ixtox 1 or Deepwater Horizon where the oil emulsified, the BONN agreement table does not help as orange oil is not metioned.
The Bonn Agreement Oil Appearance Code
Since the colour of the oil itself as well as the optic effects is influenced by meteorological conditions, altitude, angle of observation and colour of the sea water, an appearance cannot be characterised purely in terms of apparent colour and therefore an ‘appearance’ code, using terms independent of specific colour names, has been developed.
The Bonn Agreement Oil Appearance Code has been developed as follows:
· In accordance with scientific literature and previously published scientific papers,
· Its theoretical basis is supported by small scale laboratory experiments,
· It is supported by mesoscale outdoor experiments,
· It is supported by controlled sea trials,
· It is supported by operational experience.
Due to slow changes in the continuum of light, overlaps in the different categories were found. However, for operational reasons, the code has been designed without these overlaps.
Using thickness intervals provides a biased estimation of oil volumes that can be used both for legal procedures and for response.
Again for operational reasons grey and silver have been combined into the generic term ‘sheen’.Five levels of oil appearances are distinguished in code detailed in the following table:
These photos are from the (Main Report The use of colour as a guide to oil thickness by Sintef in 1999).
They show dramatically the difference between the colours with blue skys left and cloudy sky right as well as the difference between different types of crude oil.
These bottom two are not crude oil they are a Fuel oil IF 30 and a Diesel oi. As with Fuel oils there are many different types, colours, viscosities and therefore thickness and so all will have different appearances.
This is why there is a need for experienced observers.
Code 1 Sheen (silvery/grey) 0.04 to 0.30 µm - 40 – 300 Litres per km2
The very thin films of oil reflect the incoming white light slightly more effectively than the surrounding water and will therefore be observed as a silvery or grey sheen. The oil film is too thin for any actual colour to be observed. All oils will appear the same if they are present in these extremely thin layers.
Oiling conditions even thicker films may not be observed.
Above a certain height or angle of view the observed film may disappear.
Code 2 Rainbow 0.30 to 5.0 µm - 300 – 5000 Litres per km2
Rainbow oil appearance represents a range of colours: yellow, pink, purple, green, blue, red, copper and orange; this is caused by constructive and destructive interference between different wavelengths (colours) that make up white light. When white light illuminates a thin film of oil, it is reflected from both the surfaces of the oil and of the water.
Constructive interference occurs when the light that is reflected from the lower (oil / water surface combines with the light that is reflected from the upper (oil / air) surface. If the light waves reinforce each other the colours will be present and brighter.
During destructive interference the light waves cancel each other out and the colour is reduced in the reflected light and appears darker.
Oil films with thicknesses near the wavelength of different coloured light, 0.2 µm – 1.5 µm (blue, 400nm or 0.4 µm, through to red, 700nm or 0.7 µm) exhibit the most distinct rainbow effect. This effect will occur up to a layer thickness of 5.0 µm.
All oils in films of this thickness range will show a similar tendency to produce the ‘rainbow’ effect.
A level layer of oil in the rainbow region will show different colours through the slick because of the change in angle of view. Therefore if rainbow is present, a range of colours will be visible.
Code 3 Metallic 5.0 to 50 µm - 5000 – 50,000 Litres per km2
The oil appearance in this region will depend on oil colour as well as optical density and oil film thickness. Where a range of colours can be observed within a rainbow area, metallic will appear as a quite homogeneous colour that can be blue, brown, purple or another colour. The ‘metallic’ appearance is the common factor and has been identified as a mirror effect, dependent on light and sky conditions. For example blue can be observed in blue-sky.
Code 4 Discontinuous True Oil Colour 50 to 200 µm - 50,000 – 200,000 Litres per km2
Code 4 is intermediate between Code 3 and Code 5, and consists of small areas, or patches, of Code 5, Continuous True Oil Colour in a background of Code 3, Metallic. This is an accurate description of the behaviour of the oil layer – it does not spread as an even thickness layer, but consists of thicker patches in a thinner layer.
Observation of Code 4
Code 4 is intermediate between Code 3 and Code 5; it is a hybrid of Codes 3 and 5. “Discontinuous” refers to the Code being used to describe patches of Code 5 - Continuous True Oil Colour against a background of Code 3 - Metallic. The size of the thicker oil (Code 5 - Continuous True Oil Colour) patches that can be seen will depend on the distance from which they are observed and the visual acuity of the observer.
Observers in boats, looking at the spilled oil from a distance of a metre or so, are able to easily see small patches of Code 5 in a background of Code 3 and should report this appearance as Code 4 - Discontinuous True Oil Colour.
Observers in aircraft, operating at altitudes of 500 ft, 1500 ft or 2500 ft will not be able to see small patches of Code 5 in a background of Code 3, but should be able to see much larger patches of Code 5, perhaps 0.5 to 1 metre across, in a background of Code 3.
From an aircraft, the appearance of a slick containing a large area of Code 4 - Discontinuous True Oil Colour, composed of individually small areas of Code 5 - Continuous True Oil Colour against a background of Code 3 – Metallic, will be a function of the concentration of the Code 5 patches. At low concentrations (5 to 10% of the total area) they will probably be invisible and the area will be observed as Code 3 – Metallic. At some increased concentration (perhaps 40 or 50% of the total area), the appearance of that area of the slick will probably ‘flip’ from being all Code 3 – Metallic to being all Code 5 - Continuous True Oil Colour.’
In addition, to the issue of visual acuity, the human brain needs sufficient time to register and interpret what the eye sees; going lower to solve the height/distance (visual acuity) difficulty will only reduce the time available due to the increase in the relative speed of the aircraft to the object.
Code 5 Continuous True Oil Colour 200 to More than 200 µm - More than 200,000 Litres per km2
For oil thicker than 50 µm the light is being reflected from the oil surface rather than the sea surface. The true colour of the oil will gradually dominate the colour that is observed. Brown oils will appear brown, black oils will appear black.
The true colour of the specific oil is the dominant effect in this category and the area will be generally homogenous (continuous). It is strongly oil type dependent and colours may be more diffuse in overcast conditions.
There is no maximum thickness value for True Colours since it is not possible by visual observation from above to estimate the thickness of oil layers above 200 microns. A spilled oil layer on water that is 0.5 mm thick will look, from the top, exactly the same as an oil layer that is several millimetres thick. The light is reflected from the top surface of the oil; this gives information about the colour and texture of the surface of the oil, but cannot give any direct information about the thickness of the oil layer.
The photo right shows the different colours according to the BONN Agreement codes. It needs to be said that calculating each colour while flying across the oil requires a lot of practice.
This scale below also converts the amouns into inches and gallons per square mile.
Aerial Observation and Recording
A systematic aerial search could be necessary in order to obtain a careful record of the extent and quantity of oil on the water. The aircraft needs to fly over the principal oil slicks so that the peripheral slicks apart from the principal spill may be recorded or disregarded.
It is advisable to use polarized sun glasses to reduce the shine and aid in the detection of oil. All peripheral visibility is essential so that the effects of the sun and the impact of the wind on the ocean waves are minimized.
A good nautical chart or map at a reasonably large scale is essential to mark the contours of the slicks and to make notations about thicknesses, etc.
Changes to Slicks
The oil spreads rapidly and the majority of liquid oils quickly reach an average thickness of 0.1 mm (100 microns). However, large areas may be covered with thinner films of oil.
Glossary of observation terms
How to tell the difference between petroleum spills and natural oil sheens.
Poke the sheen with a stick. If the sheen swirls back together immediately, it's petroleum.
If the sheen breaks apart and does not flow back together, photo right it is from bacteria degrading vegetable matter or other natural source. This is more commonly found with inland spills.
A black or very dark brown-colored layer of oil. Depending on the quantity spilled, oil tends to quickly spread out over the water surface to a thickness of about one millimeter. However, from the air it is impossible to tell how thick a black oil layer is.
A line on the surface of the water that can collect floating objects and oil often caused by the convergence of two bodies of water with different temperatures and/or salinities. Unlike “windrows” and “streamers,” commonly associated with wind, convergence zones are normally associated with the interface between differing water masses, or with the effects of tidal and depth changes that cause currents to converge due to density differences or due to large bathymetric changes. Such zones may be several kilometers in length, and consist of dark or emulsified oil and heavy debris surrounded by sheens. Convergences are very common occurence in the marine environment.
A water-in-oil emulsification. Mousse can range in colour from dark brown to almost red or tan and typically has a “thickened” or “pudding-like” consistency compared to freshly spilled oil. The incorporation of up to 80% water into the oil will cause the apparent volume of a given quantity of oil to increase four times.
There are two types of emulsions:
1. Stable will remain emulsified until either a breaking chemical is used to break the water out of the oil. In this case the chemical will be with the water phase which means the water is contaminated. The emulsion can be heated in some sort of tank in which case the water will just be water.
2. Unstable emulsions usually need a calm area to allow the water to seperate naturally. The photo right shows that the oil emulsified as it came to the surface from the well. The calm area in the boom shows the oil changed colour from orange to black in the boom apex as the water seperated.
There is no way of telling whether the emulsion is stable or not by the colour.
The rule of thumb is, if the crude oil has more than 0.5% asphatene content then there is a good chance the oil will emulsify with agitation from wind and waves.
So we should be prepared for a massive change in viscosity and volume (skimmers / storage space)
An oil configuration or “structure” that reflects a broad range of shapes and dimensions. Numerous “tarballs” could combine to form a “patch”; oil of various colors and consistency could form a patch or single layer 10s of cm to 10s (or even 100s) of meters in diameter; and a large patch of dark or rainbow oil could have patches of emulsion within it. Patches of oily debris, barely able to float with sediment/plants in them.
Isolated realy big patches of roughly circular-shaped oil that range in size from a few feet across to hundreds of yards in diameter become pancakes or tarmats. Sheen may or may not be present.
Oil spilled on the water which absorbs energy and dampens the surface waves making the oil appear smoother or “slicker” than the surrounding water.
This is show in the photo left, notice the waves around the oil are more pronounced than in the oil.
Narrow bands or lines of oil (sheens, dark or emulsified) with clean water on each side. Sometimes referred to as “fingers” or “ribbons.” Streamers may be caused by wind and/or currents, but should not be confused with multiple parallel bands of oil associated with “windrows,” or with “convergence zones or lines” commonly associated with temperature and/or salinity discontinuities.
Discrete, and usually pliable, globules of weathered oil, ranging from mostly oil to highly emulsified with varying amount of debris and/or sediment. Tarballs may vary in size from millimeters to 20-30 centimeters across.
Depending on exactly how “weathered,” or hardened, the outer layer of the tarballs is, sheen may or may not be present.
Tarballs may turn into what we called oil bergs off Mexico photo right.
They got the name because they float very low in the water but may weigh many tonnes. They are actually formed by natural seeps on the sea floor and were ripped up in the shallow water when a hurricane passed though the region.
Weathering or the Fate of oil:
Crude oils and refined petroleum products are mixtures of a large number of components, each with its own chemical and physical properties. Once oil is spilled, it immediately begins to undergo many natural, physical, chemical and biological changes.
These processes are assisted by:
Streaks of oil that line up in the direction of the wind. Windrows or Langmuir streaks, named after the first person to study the phenomenon. Irving Langmuir noticed patterns of floating seaweed when crossing the Atlantic Ocean in 1938.
Intrigued, he conducted experiments in a lake and discovered that wind can cause water to circulate in a pattern that makes material collect in lines on the surface. The lines are roughly parallel to the wind direction, and the windier it is, the further apart the lines. tend to form very early in a spill where the wind is 6 knots or greater. Bands are usually spaced a few meters to 10s of meters apart; however, windrows have been observed with spacings of 100 meters or more.
Methods of Observation
Nowadays, combined resources are used, such as GPSs, photographic equipment, video cameras and sophisticated equipment and the human eye itself in order to observe the location, in order to make a better evaluation of the scene of the accident.
Standard colour photography may be used from the aircraft, as well as from ships and the shore. Normally oil must be thicker than 0.4 microns in order for the photographs to show any results.
Photographs taken with geographic information supplied by GPS makes it possible to better understanding of the behavior of movement of the oil slick, besides making documentation easier.
Photography may be used in order to provide an record of the polluted areas, especially coastlines. An indication of the thickness of the slick may be obtained. Studies show that the best angle for taking photographs is 53 degrees. In order to take photographs of oil slicks a polarized film should be used with the camera in order to reduce the reflection from the surface of the water. Photo ITOPF
The best results are obtained in clear weather. If there are many clouds, the photographs might not have sufficient contrast. The photographer should follow these guidelines:
a. Try to take a photograph as vertically as possible (53 degrees).
b. Use the shortest exposure time (1/250 or faster).
c. Overlap photographs by about 20%.
d. Use high-velocity color film (200 or 400 ASA).
e. Use a polarized filter in order to reduce the brilliance of the surface of the water.
f. Photographs at low tide will yield information about the types of shorelines.
From an aerial point of view it is very difficult to distinguish between oil and a variety of other phenomena. It is necessary to verify as closely as possible a suspected oil spill. Flying at a low altitude allows for a better identification of an oil slick. Looking down at 90° is usually the best way to see black or brown oil.
Errors of interpretation maybe caused by the photos below:
Jelly fish Water density Kelp beds Cloud shadows
Surface currents Red Tide Sea Grass Coal/Mineral deposit
Aerial Sardine bait ball Under the water during the South African sardine run
These systems may show the maximum extent of an oil slick and some information about thickness since thinner oil slicks appear cold and greater thicknesses appear to be hot. The system is used best together with an Ultraviolet scanner and visual images.
It consists of an aerial detection system, including a camera with infrared scanner, recording equipment and telemetry. Some systems may provide in real time a view onboard a ship or from land, if the variation is compatible and the reception equipment available.
The principle of operation depends greatly on small differences of temperature between one area of the sea and another. Good results then are highly dependent on meteorological conditions. Conditions of fog, low clouds and rough seas may yield very poor results. Errors in interpretation are possible such as for example cold water in the ballast of ships during the summer, hot water effluents or irregular cloud formations.
However, with a capable operator and good interpretation, good and accurate results may be obtained and confirmed by other systems. This system could show where the best place is to use skimmers and dispersants.
This system also has problems with algae, coastal areas with upwelling of water masses. Since the price is not very high, this is the tool most used for monitoring.
A sensor detects UV radiation from the sun reflected by the oil and gives an exact estimate of the area of the spill. With information from ultraviolet and infrared scanners, it is possible to obtain an exact estimate of the extent of the oil slick. This equipment results in the best spatial view of the incident, showing even the silver sheens of the oil spills.
The UV system only functions with daylight and, even better, with sunlight. Many errors are committed in areas sheltered from the wind, when the sea loses its roughness, thus increasing the reflection in the presence of biogenetic materials.
Small waves produce a reflection of radar energy, when we have an oil slick. This oil slick reduces the roughness of the ocean’s surface, emitting a signal for the radar, in sheltered locations, where it is receiving fresh water, in waters with ice, fish spawn, kelp forests, induce errors of interpretation. Depending on the altitude, this sensor has the advantage of displaying a linear band of about 30 km, good for detection. Radar is used to understand the velocity of the current for the prediction of the slick.
SAR - Side-looking Aperture Radar A very sophisticated mechanism, although very expensive, which has the best resolution.
SLAR – Side Looking Airborne Radar This radar transmits and receives pulses of energy. The radar receives the return signal that was emitted, deffracted and absorbed by objects on the sea. This system has a low resolution.
The oil calms the capillary waves on the water and yields very slight reflection, so that the slick appears dark on the screen.
The system has a vision of 20 miles on each side of the aircraft, if used at its normal operating altitude of 7,000 feet. The system is used to show the maximum extent of the slick.
It is capable of operating during the day or at night and in most weather conditions, except high winds. It does not assist with the thickness of the oil.
Sar is also used with satelites as in the case of the European Remote Sensing Satelite which passes over the North Sea every 100 minutes, scanning 1000 km2 with a process time of 6 to 8 minutes. If you had a spill today your fine will be in the post.
photo left shows a trial done off Holland, the top photo shows the satelite image and the bottom shows the image from the Dutch Coastguard aircraft.
Various radar system can be found for vessels which means there is competition in the market which means that the equipment will get better. I am not going to say which one I think is the better but they are expensive so investigation into all that are available is necessary.
This passive system measures the natural radiation of energy emitted or reflected by the environment. This device detects different emissions of microwaves. It is useful to determine where the oil is, the equipment also gives an idea of the thickness of the oil slick. This method yields poor results in the field.
It is particularly good for measurement of the comparative thickness of the slick and the area of the surface. Therefore, it results in a good indication of the volume of the oil.
The scanning area is small so it is necessary to fly slowly, at low altitude, in order to obtain the best results.
Much more research and development is required to make this a good response tool in the field.
This detector and measurement device emits energy in the ultraviolet band and receives energy in the visual band. It is used to give an indication of the type of hydrocarbon (heavy, medium or light) and the thickness of the slicks. The equipment results in a digital fingerprint of the hydrocarbon, which could be compared with other known information.
This equipment succeeds in differentiating biological materials originating from the oil, because these materials emit another fluorescent band. This system detects oil on ice, snow and even when it is associated with residues of biogenetic origin such as marine algae. It can also detect oil on the shoreline.
It is capable of operation during the day or at night, except under conditions of fog or rain. The scanning area is small, so it is necessary to fly at low altitudes.
This system is the future but requires more development as the photo left shows in 1956 (IBM 305 RAMAC) 5MB Hard drive and weighed 3 tonnes.
Technology will get us there, sometime in the future it will weigh less the 1 kg.
This equipment requires highly-skilled and trained personnel in order to deal with images of oil slicks. It does not have a rapid turn-around time. It could be very good for documentation after the oil spill.
It may take some time for the satellite to pass over the area of the oil spill, without the presence of clouds, fog. During the Gulf War 91 satellite images were taken of the oil spill but after the well fires started the smoke blocked the view the system does not function well. The system is not good for tracking. The work is easier when the geographical coordinates of affected areas are known.
With technological development, the time needed for interpretation of the images diminishes. Powerful computers process the data more quickly. This type of information is very important to serve as documentation of the post-spill.
It is my opinion that computer programmes should be used to assist with trajectory predictions along with other methods.
I removed the name of the organisation who wrote this disclaimer. To me it says what we all know. The quality of the prediction is only as good as the information used.
(if you put rubbish in you get rubbish out)
disclaimer: The oil spill trajectory predictions, opinions and interpretations contained in predictions are based on observations and data supplied by the client and information sources available to the organisation.
The computer model predictions, interpretations or opinions expressed represent the best judgement of the organisation and its personnel or advisers, assume no responsibility and make no warranty or representations as to the accuracy or reliability of the predictions.
It should be noted that accuracy of predictions may be adversely affected where modelling is carried out in respect of spills in enclosed waters, estuaries, close to shore, or when only low resolution maps are available.
Computer models are usually designed for a certain sea area and cannot be used in other areas. A good example is a programme written for the North Sea there are various.
The database of the programme has the current speeds and directions for the entire year. This information is input at 15 kilometer intervals. There is also a comprehensive database of the crude oils found throughout the North Sea operations.
Basically when using the programme you imput the position of the incident. What type of spill (instant or on going) type, and amount of crude oil. By dragging the arrow on the wind rose you change the direction and the strength.
With this information the programme will calculate the tradjectory and the weathering process of the oil involved.
The programme can also be used to find the point of the spill. Imputing the same information and running the programme backwards it will move the oil to the point of the spill. This can be used in the case of oil arriving in an operators field but the oil is not from that field.
Bearing in mind that the current information is input at 15 km interval the programme will not work correctly within 15km of the shoreline or close to islands because of local currents. For example a terminal or port in this case above right another programme will be needed as in this exercise off the Australian coast.
Left is a NOAA model showing the distribution of the oil from Exxon Valdez during the 2 weeks following the incident.
Trajectory models are used to predict the movement of a spill on a single set of data, be it for a few hours or a few days. Stochastic models, on the other hand, use the statistics of a wide set of wind and current observations to predict the probability that a certain area will be impacted by oil. One Stochastic model is equivalent to tens of thousands of trajectory model runs.
The model consists of a set of algorithms describing the processes of advection, turbulent diffusion, surface spreading, vertical mechanical dispersion, emulsification, and evaporation. Each algorithm is developed separately and is linked to related processes and to environmental and other parameters.
As with the sensitivity maps the brighter the colours the more likely the impact.
A research consortium formed after the Deepwater Horizon oil spill has deployed more than 300 water drifters near the rig’s explosion site to study surface currents in the Gulf of Mexico. Known as the Grand Lagrangian deployment, it is the largest of its kind in history.
By logging the drifters’ locations as they move, scientists have gained insights into the effects sea currents have on the transport of crude oil. The data, collection of which began in July 2012, will help emergency planning and improve forecasts of the pollutant’s movement in future oceanic disasters.
The Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE) won funding for the project from the Gulf of Mexico Research Initiative. The research initiative was founded through an agreement between the Gulf of Mexico Alliance and BP to provide USD500 million in funding for independent scientific research related to the Deepwater Horizon incident over the course of 10 years.
The project began with help from the U.S. Coast Guard, which has routinely used data from drifters in search and rescue missions. The Coast Guard agreed to drop a few drifters into the Gulf in exchange for use of the experiment’s data when it was fully up and running.
To start, four drifters were deployed by air to get a sense of circulation before the mass deployment, followed by 24 around Deepwater Horizon and about 90 each day at different sites. Most of the deployments took place in three days. Data were made available immediately to the U.S. Coast Guard. They used it the whole time for test missions and whenever Hurricane Isaac hit. They saw ours and needed to deploy fewer of their own.
In all, 317 drifters were placed into the Gulf, each one about three feet tall with floats and support screens that keep each GPS unit stable and vertical. A typical research project would only need 10 to 20 drifters.
The GPS transmitters relay the coordinates of each drifter to a satellite, which provides updates to researchers every five minutes. That transmission frequency made it possible for them to find more variations between data points.
A part from the rotation of the Earth causing oscillations and the presence of many rigs, heat in the Gulf also affects the water currents there and is another consideration to take into account. The Florida Straits were a factor, strong currents which only took a few drifters out of the Gulf.
Improving forecast models can be used by the Coast Guard and emergency responders in future disasters.
On average, there is one oil spill per year in the Gulf. Improved forecasting models could help contain them better. The Naval Research Laboratory will likely use the data to strengthen its models.
When a drifter goes offline – in average two a day, fishermen find them and send them back to CARTHE. This organisation is working on a prototype drifter that is biologically degradable and about the size of a sushi box. Ten prototypes were tested in the deployment.
When transmissions end, CARTHE will begin analysing the more than five million data points that have been collected.