54
with ex/em maxima at 310 and 360, has long been used as a proxy standard (Atwood
et al. 1987, 1987/1988). Methods available then required retrieval of water samples
and extraction in hexane prior to fluorometric analysis using laboratory instruments.
Today simple, submersible single optical band excitation/emission instruments
equipped with LED photodiode emitters and borosilicate windows allow excitation
down to about 350 nm in the near UV and wide emission bandpass filters (410–
550 nm) irradiating photodiodes that allow monitoring for high concentrations of
crude oils. As more capable UV LED emitters and UV transparent optical windows
become available, more capable instruments should appear.
Remote Sensing of Petroleum Spills
Satellite spill detection is facilitated by the formation of buoyant ocean surface
plumes whose dispersion may be imaged and tracked using optical instruments and
synthetic aperture radar. Both depend on the dampening effect of oil on ocean waves
in opposite fashion. Attenuated wave action reduces wave-induced refraction thus
attenuating the bottom-of-the-swimming-pool effect perceived visually as webs of
diminished or enhanced light. As a result, in areas where waves are dampened by oil
slicks, images from visible light radiometers reflect a lower albedo due to absorption and scattering by seawater and its dissolved and suspended constituents. An
important exception, and indeed a technique exploiting this same effect, is the exacerbation of sunglint, the mirror effect enhanced by the slick oil surface when the sun
reflects directly onto the optical sensor. Radar microwaves on the other hand do not
penetrate the ocean surface and are readily scattered by wave action returning a
fraction of the radiation to the radar detector. Slick ocean surfaces reflect radiation
more coherently away from the source unless the sensor is at direct nadir of the
target slick.
The many variables described above forbid fully automated tracking of oil slicks
by satellite remote sensing. Experienced human operators are still required to usefully interpret combined passive UV/Vis and active radar satellite imagery for spill
detection and tracking.
2.5 Sensors for Biological Compounds and Processes:
Chlorophyll, Accessory Pigments, and Photosynthetic
Activity
Sustained instrumental observation of phytoplankton biomass, productivity, and
community composition informing fisheries managers, health officials, and wildlife
managers is now an integral component of coastal ocean observing systems.
Phytoplankton, microscopic free-living photosynthetic cells and cell colonies suspended in the water column, constitute the bulk of the plant life in the ocean. A
variety of mechanisms are used by phytoplankton to avoid sinking and thus remain
2 Electronic Sensors and Instruments for Coastal Ocean Observing
with ex/em maxima at 310 and 360, has long been used as a proxy standard (Atwood
et al. 1987, 1987/1988). Methods available then required retrieval of water samples
and extraction in hexane prior to fluorometric analysis using laboratory instruments.
Today simple, submersible single optical band excitation/emission instruments
equipped with LED photodiode emitters and borosilicate windows allow excitation
down to about 350 nm in the near UV and wide emission bandpass filters (410–
550 nm) irradiating photodiodes that allow monitoring for high concentrations of
crude oils. As more capable UV LED emitters and UV transparent optical windows
become available, more capable instruments should appear.
Remote Sensing of Petroleum Spills
Satellite spill detection is facilitated by the formation of buoyant ocean surface
plumes whose dispersion may be imaged and tracked using optical instruments and
synthetic aperture radar. Both depend on the dampening effect of oil on ocean waves
in opposite fashion. Attenuated wave action reduces wave-induced refraction thus
attenuating the bottom-of-the-swimming-pool effect perceived visually as webs of
diminished or enhanced light. As a result, in areas where waves are dampened by oil
slicks, images from visible light radiometers reflect a lower albedo due to absorption and scattering by seawater and its dissolved and suspended constituents. An
important exception, and indeed a technique exploiting this same effect, is the exacerbation of sunglint, the mirror effect enhanced by the slick oil surface when the sun
reflects directly onto the optical sensor. Radar microwaves on the other hand do not
penetrate the ocean surface and are readily scattered by wave action returning a
fraction of the radiation to the radar detector. Slick ocean surfaces reflect radiation
more coherently away from the source unless the sensor is at direct nadir of the
target slick.
The many variables described above forbid fully automated tracking of oil slicks
by satellite remote sensing. Experienced human operators are still required to usefully interpret combined passive UV/Vis and active radar satellite imagery for spill
detection and tracking.
2.5 Sensors for Biological Compounds and Processes:
Chlorophyll, Accessory Pigments, and Photosynthetic
Activity
Sustained instrumental observation of phytoplankton biomass, productivity, and
community composition informing fisheries managers, health officials, and wildlife
managers is now an integral component of coastal ocean observing systems.
Phytoplankton, microscopic free-living photosynthetic cells and cell colonies suspended in the water column, constitute the bulk of the plant life in the ocean. A
variety of mechanisms are used by phytoplankton to avoid sinking and thus remain
2 Electronic Sensors and Instruments for Coastal Ocean Observing