Ministry of Transport, Public Works and Water Management Directorate-General for Water Management North Sea Bonn Agreement Oil Appearance Code Assessing oil volumes at sea A tool in daylight operations

Illegal discharge?

Response required?

Purpose of assessing oil volumes Violation of MARPOL Response required? What/How

Violation of MARPOL Netherlands research Visibility limits, 1997 oil in the wake of a ship is visible from 50 ppm onwards

Response required The thicker parts, in a slick, are most important to identify and quantify for an efficient response.

Procedure to estimate volume Detection: SLAR:length and width UV:length and width IR:relative differences in layer thickness

Observation: Area covered with oil %, % of each color according Bonn Agreement Code Grey, 0.02 m 3 /km 2 Silvery, 01 m 3 /km 2 Rainbow, 03 m 3 /km 2 Blue, 1 m 3 /km 2 Blue/Brown, 5 m 3 /km 2 Brown, m 3 /km 2 Black, >100 m 3 /km 2

The results is obtained Multiply length and width and % area covered, then the total area covered with oil is identified. Then take each % of observed color and quantity is “known”

Do you know the color of oil?

Reasons to revise the BA-CC * Only one figure, * False accuracy, * Lack of scientific prove and * In practice observers tend to adjust without justification.

SINTEF study – research Initiated by Norwegian Pollution Control Authority and financially supported by Bonn Agreement Parties, SINTEF: - carried out a literature review, - executed laboratory tests followed by - small scale field trials and Relation appearance and layer thickness -- Volume Reported to Bonn Agreement working group.

The breaking of light Reflection of light on water, Reflection of light on an oil film on the water surface and Reflection of light on an oil layer and absorption in the oil layer. Wave-lengths intensified.

Very thin oil films reflect light slightly better than water, and can therefore be observed as silvery or grey.

Interference causing the rainbow effect. Light reflecting from the oil surface and light reflecting from the water surface is combined. Light waves will cancel each other out (left) or reinforce each other (right). Depending on angle of view and layer thickness, the distinctive colors will be diffuse or very bright. Oil films with thicknesses near the wavelength of different colored light (blue, 400nm or 0,4 µm, through red, 700 nm or 0,7 µm) exhibit the most powerful rainbow effects. This effect will occur up to layers of 5 µm. Bad light conditions may cause the colors to appear duller.

Intermediate layers, the appearance, a combination of light, reflected off the oil and the water surface below the oil, will become less dependent on the light passing through the oil. Thick layers. All the light penetrating the oil is absorbed and no light is reflecting from the water surface. Therefore the appearance is true oil color.

Influence of waves Causing a variation in layer thickness: Wave top à thin layer, causing a discontinuity in the appearance Wave-trough à thicker layer, causing an intensification of the appearance

The Bonn Agreement Oil Appearance Code (BA-OAC) Based on theory, laboratory experiments, supported by small scale field trials: - a lower and upper limit - no colors - scientifically underpinned

BA-OAC The Code identifies following appearances: 1 sheen, m³/km 2 2 rainbow, m³/km 2 3 metallic, m³/km 2 4 discontinuous true color, m³/km 2 5 continuous true color, >200 m³/km 2

Advantages For enforcement purposes the lower limit is applied For decisions on response authorities will consider the upper limit as well

Disadvantages daylight use only, inaccuracy in procedure remain, human interpretation, area estimation not applicable in heavy oils (Erika) and emulsions.

State of the art technique no sensors to accurately provide length and width no sensor to accurately discriminate layer thickness no software to improve estimation of oil volumes by sensor data.

(near) Future work Validation of Appearance Code Study possibilities to estimate volumes by sensor data (day and night use) Sensor development / improvement

In a sea full of oil, You can lose sight of it all And the darkness inside you Can make you feel so small But a BA observer can see your true colors Shining through He sees your true colors And that's why he loves you So, oil slick don't be afraid to let them show Your true colors True colors are beautiful, Like a Rainbow