SMART: A Guided Tour - Part 2

Below is an observer's view of a dispersed oil slick at West Cameron Block 1988, Gulf of Mexico. This photo is an example of a case in which, just using visual observation, it is possible to see that application of dispersant to an oil slick has caused successful dispersion: what had been a cohesive slick has broken up into streaks, and oil that has been dispersed into the water column appears as a light-colored plume around the remaining streaks of surface oil.

Visual observation, however, is not always sufficient to determine whether or not dispersants are effective.

An example of an application of dispersant to an oil slick that resulted in successful dispersion.

A NOAA and U.S. Coast Guard team prepares a fluorometer for a dispersant monitoring exercise near Mobile, Alabama.

Tier II: Fluorometry

Tier II monitoring provides real-time data from a dispersant-treated oil slick. When Tier II monitoring is used, a sampling team on a boat uses a fluorometer to continuously monitor for dispersed oil 1 meter under the slick. The team records fluorometer data and conveys them to the Unified Command (UC). Water samples are also taken for later analysis at a laboratory.

What is a Fluorometer?

A fluorometer is an instrument that measures the amount of fluorescent radiation produced by a sample exposed to monochromatic radiation. The fluorometer's measurements can help spill responders determine if the dispersants applied to the oil slick are effective in dispersing the oil. For SMART operations, fluorometers are used as follows:

A Teflon hose is lowered into dispersant-treated water. (A lead weight is attached to the end of the hose to keep it at the designated depth.) Water is pumped through the hose to the fluorometer. In the fluorometer, the water passes through a cell where it is exposed to ultraviolet light from a special light source. Some molecules, such as hydrocarbon molecules in the oil, absorb the energy from this radiation, and then give back this energy by becoming fluorescent and emitting light. The light is detected by a sensitive detector in the fluorometer, is converted into an electrical current, and is transmitted to the instrument's display. The amount of fluorescent light that is produced depends on the amount of fluorescing molecules, so a high reading above background under a dispersant-treated slick indicates that hydrocarbons were dispersed into the water column.

Shown below is an example of a SMART fluorometer reading. The left section of the plot shows flat readings, representing background readings. The rest of the graph shows variable readings, indicating the presence of dispersed oil in the water column.