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). 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. Code 3. `Metallic` for 5-50 m thick oil layers: typical of this appearance is matte metallic shine. The color of this metallic shine is largely determined by the color of the underlying water, because the oil layer is not thick enough to block the light reflected from the surface of the water, and partly also by the « color » of the sky (. B for example blue sky or grey clouds) generated by the reflection of light. 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. The minimum volume estimate is generally used in criminal matters (to give the quantities specified as a minimum), while the maximum volume estimate is generally used in cases of accidental marine pollution (the worst typical cases in crisis management).
In particular, codes 4 and 5 (along with real oil paintings) contain considerable amounts of oil on a small area and are therefore, in most cases, considered slicks that can be fought at sea. The other codes for thinner oil layers, which often cover the largest areas of an oil spill, contain too little oil to be a reasonable prospect, even if dispersants are used. 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. » An approximate estimate of the magnitude of an oil spill. To some extent, this is possible from a ship, but the margin of error will be high, especially in the case of larger slicks that cannot be considered entirely from a ship.
Several steps must be taken to estimate the volume of oil based on the BAOAC method used in the air. The surface of the polluted water can be estimated from the air, either by visual evaluation or by using sensors on a specially equipped surveillance aircraft. These are two steps: when an emergency occurs at sea, a vessel is often the first to arrive at the scene of the incident.