Intelligence, Surveillance, and Reconnaissance - Spawar

METHODS
SSC San Diego has developed an automated oil spill
sensing technology to provide early notification of
the presence of a petroleum spill on water. The
fluorescence-based sensor operates from just below
the water’s surface and is continuously measuring
for an increased concentration of hydrocarbons or a
surface sheen, which is indicative of an oil spill.
When a spill is detected, the data are immediately
transmitted to another computer base station for
analysis, display, and telephonic alarming.
Ultraviolet (UV) fluorescence provides a sensitive
means of detecting petroleum hydrocarbons in
water. When UV light excites petroleum, the aromatic
constituents like benzene and naphthalene
emit fluorescence at longer wavelengths. The greater
the fluorescence, the higher the concentration of
hydrocarbons present. The sensor is an upwardlooking
multispectral underwater flourometer.
Multiple ports in the buoy permit water and any
potential oil slick to flow unimpeded past the sensor
window. The excitation source is a pulsed xenon flash lamp operating at
10 watts average electrical power. Fluorescence resulting from the presence
of petroleum hydrocarbons is collected back through an optical
window and passed through a series of dichroic filters for separation into
three spectral bands. Since different classes of petroleum products fluoresce
at different characteristic wavelengths, multispectral analysis provides
a means to discriminate between various classes of oils and fuels.
It also allows for discrimination between petroleum and non-petroleum
(e.g., chlorophyll) fluorescence.
Bioluminescence-Water Clarity Sensors
The bioluminescence system consists of a 1-inch-diameter Hamamatsu
photomultiplier tube (PMT) viewing a light-tight darkened 25-mL volume
chamber. Seawater is continuously pulled into the chamber by an electric
pump at a constant rate of 0.25 L/sec. The turbulence associated with seawater
mixing in the chamber stimulates bioluminescent plankton (singlecell
dinoflagellates) to emit light within the darkened chamber in front of
the PMT. At these flow rates, small bioluminescent zooplankton are also
sampled and contribute to the overall bioluminescent signal. A SeaTech
red transmissometer (680 nm) is also mounted on the BioBuoy and provides
water clarity measurements. In coastal environments, water clarity
or percent transmission (%T) is distinctly lower than in the open ocean
where seawater is much clearer and can provide information on the
regions where microscopic plankton and debris are concentrated. In this
system, bioluminescence and %T are programmed to measure these optical
properties every one-half hour. Sequentially, the PMT is powered up
for 4 seconds before the pump is activated for 10 seconds. During the
10-second sampling period, bioluminescence is quantified and averaged.
As the pump is reactivated, %T is measured. The raw data are then sent
via the RF link to a home base computer logging the data via a secure net
address. Data are processed automatically and posted to a real-time http
address. Data are logged into a time series graph and posted to a data file
for offloading.
Buoy-Mounted Bioluminescence Sensor (BioBuoy) 143
FIGURE 1. A diver’s swimming motion several feet below the water’s
surface stimulates hundreds of thousands of cells of the bioluminescent
dinoflagellate Pyrodinium bahamense to emit a visible bluegreen
light in a bioluminescent bay in Vieques, Puerto Rico. (Photo
by Frank Borges LLosa, www.frankly.com.)