Visual Appearance of Oil on the Sea

Merv Fingas

doi:10.3390/jmse9010097

Abstract

The visual appearance of oil spills at sea is often used as an indicator of spilled oil properties, state and slick thickness. These appearances and the oil properties that are associated with them are reviewed in this paper. The appearance of oil spills is an estimator of thickness of thin oil slicks, thinner than a rainbow sheen (<3 µm). Rainbow sheens have a strong physical explanation. Thicker oil slicks (e.g., >3 µm) are not correlated with a given oil appearance. At one time, the appearance of surface discharges from ships was thought to be correlated with discharge rate and vessel speed; however, this approach is now known to be incorrect. Oil on the sea can sometimes form water-in-oil emulsions, dependent on the properties of the oil, and these are often reddish in color. These can be detected visually, providing useful information on the state of the oil. Oil-in-water emulsions can be seen as a coffee-colored cloud below the water surface. Other information gleaned from the oil appearance includes coverage and distribution on the surface.

Highlights

The knowledge of slick thickness has many uses in the oil spill trade, which include determining the size of a leak and optimizing the effectiveness of oil spill countermeasures [1]
The appearance of an oil slick on water is dependent on several processes including reflection from the oil–air interface, the oil–water interface and various processes in the oil layer itself [10,11]
An important important point point thickness ranges needed for oil spill countermeasure considerations

Summary

Introduction

Other uses of visual observations are suggested These include observation of the formation of water-in-oil emulsions [4], indication of oil-in-water emulsions [5], measurement of subsea discharge rates [2] and the simple measurement of the oil geometry on the sea [6]. Visual observations were standardized in various codes to provide users with a standard way of interpreting appearances of oil on the sea [1]. These did not enter the broad scientific literature; rather, they became industry and government practices. Because oil slicks often cover vast areas, the effect of sea conditions on observations is minimized

Basic Considerations

Fundamental Slick Thickness–Color Relationships

Colors

Visibility of Discharges

Determination of Water-in-Oil Emulsification

Conclusions