The observation of the different color representations within an oil spill and the approximate estimate of the severity of a discharge or pollution at sea by distinguishing the thicker layers and thinner layers of oil (in principle the areas where pollution can be combated and the areas where it can be combated). Code 4. “Color with discontinuous oil” for thicker oil layers 50-200 m thick. For oil films more than 50 m thick, the light is reflected by the oil and not by the surface of the underlying sea, allowing to see the true oil color of the spilled oil. Only gradually does the true oil color become the dominant color, with brown and black oil appearing black. However, code 4 is a transition code because thinner layers alternate with thicker layers due to the action of the waves. This code is also often described as “the real oil color on a metallic background.” From the air, a visual observer will then continue to divide the polluted area into percentage-estimated areas where some oil air is observable. BAOAC studies have shown that a mineral oil can exhibit 5 different oil phenomena, depending on the relative thickness of an oil layer. The “color” of an oil film depends on how light rays that come in from different wavelengths are reflected from the surface of the oil, crossed by oil, by the surface of the water under the oil and/or absorbed by the oil. The observed oil colour is the result of a combination of these factors.
For thicker oil layers, the colour also depends in part on the type of oil spilled. Minimum and maximum volumes derive from part of the minimum thickness of the layer in which a coloration is visible and from the maximum thickness of the layer in which the coloration moves to an “upper” code. The volume of oil is then calculated from a simple mathematical formula, in which the code-polluted surface is multiplied by the percentage of that code, present in a slick, and by the minimum and maximum thicknesses.