The Use of Remote Sensing in the Determination of Dispersant Effectiveness

Abstract

An experimental program to test the effectiveness of dispersants in an open-ocean, cold-water environment was conducted off St. John's, Newfoundland in the fall of 1981. The dispersion of Lago Medio oil by Corexit® 9527 was investigated by using surface and subsurface sampling techniques combined with remote sensing which employed infrared (IR), ultraviolet (UV), and visual sensors to define the surface slick and show the position of the sampling vessels within the slick. Infrared photography was used to estimate the area of the thick slick because IR “coolness” (darker gray level) appears to be indicative of thicker oil. The total extent of the slick was determined from the reflectance in the UV region. Both photographic and line-scanning imagery was used in the UV, and a line scanner in the IR. Measurements were taken from a height of 500 to 800 m every 20 min of both a control slick and a slick to which dispersant had been applied from the air. A comparison of the two slicks shows a difference in the dynamics and gives some indication of the nature of the dispersion process. Problems with sampling and determination of hydrocarbons in the water column prevented the comparison of remote sensing results with those from water column chemistry. As a result of these experiments, it is shown that remote sensing can be used to obtain quantitative data on the spreading characteristics of an oil slick and hence changes in interfacial tension that effect dispersion as well as spreading. This technique has the potential to measure the effectiveness of a dispersant without the need for an extensive water sampling program.

The Challenges of Remotely Measuring Oil Slick Thickness

“…The use of sorbents to measure oil by contact on the surface has been suggested and practiced by many [92]. The practice is to apply a sorbent in the field and then take the oil-soaked sorbent home and analyze the amount of oil in it.…”

“…These include: presumption that the sorbent picks up only the oil it overlays and not more; that the sorbent picks up all the oil over which it lays; and that the oil in the sorbent can be accurately quantified. A study of the laboratory use of sorbents to measure slick thickness showed that there were many problems and that the variance of sorbent analysis was about 40% in a good, small laboratory setting [92]. It was estimated that the field variance was as much as 10 times this value, rendering this technique almost entirely useless.…”