13 Water Quality
299
(Fingas et aI. 1996). Stringer et al. (1992) used Landsat TM data to monitor the
Exxon Valdez oil spillage (see Colour Plate B.D). Visible techniques are used
because of cost and availability of aircraft to make critical measurements when and
where needed.
Oils can be detected by measuring thermal energy in the 8 to 14 Ilm region of the
spectrum. Thick oils have higher temperatures with temperatures decreasing as the
thickness of the oil decreases. The minimum thickness that affects temperatures is
between 10 to 70 microns (Fingas et al. 1996). Spatial resolution of the sensor
becomes important for oil spills distributed in patches and wind rows (Hover 1994).
Measurement of relative thickness of oillayers is important for determining the type
of equipment that will be used for cleanups. Infrared (thermal) remote sensing is
probably the most important tool currently used for planning oil spill cleanups.
Thin layers of oil displays high ultraviolet radiation patterns (O'Neil et al. 1983)
thus making ultraviolet radiation data useful to monitor patterns of oils on water
surfaces. While measurements of ultraviolet radiation are very sensitive to oil in the
environment, they are not often used operationally due to the many interferences
encountered from ultraviolet radiation of natural products which make interpretations
difficult (Fingas et al. 1996).
Fluorosensors are useful for detecting the presence of oil in aquatic systems. While
other substances (i.e., chlorophyll) fluoresce, oils fluoresce with unique spectra that
allow them to be detected easily (Hengstermann and Reuter 1990). Oils from different
sources have unique fluorescent signatures that allow them to be differentiated and
identified (Hengstermann and Reuter 1990). Fluorosensors have a useful role in oil
measurement, monitoring, and especially for identifying possible sources of the oil.
Radar can detect oils on sea surfaces because oil reduces the "sea clutter" of normal
radar images of the sea surface. Many naturally occurring substances can also reduce
"sea clutter" (Frysinger et al. 1992) making interpretation of radar images difficult.
Even with these limitations, radar is widely used for oil spill detection and monitoring
because of its ability to collect data under all weather conditions, day or night, and
over large areas rapidly.
Oil is a much stronger emitter of microwave energy than water so that images of oil
spill areas appear much brighter on a microwave image of water (Ulaby et al. 1986).
A passive microwave sensor can detect these differences and thus patterns of oil spills
can be detected although spatial resolution is usually poor. As with radar, microwave
sensors have the ability to collect data under all weather conditions, day or night, and
over large areas rapidly.
13.5 Future Directions
Limitations in spectral and spatial resolution of current sensors on satellites currently
restrict the wide use of satellite data for monitoring water quality. New satellites
(SEA WIFS, MOS, OCTS, QuickBird, Resource2l, Orb View, etc.) and sensors
(hyperspectral, high spatial resolution) already launched or planned to be launched
over the next decade (Corbley 1996) should provide both the improved spectral and
spatial resolution needed to monitor water quality parameters in surface waters in
299
(Fingas et aI. 1996). Stringer et al. (1992) used Landsat TM data to monitor the
Exxon Valdez oil spillage (see Colour Plate B.D). Visible techniques are used
because of cost and availability of aircraft to make critical measurements when and
where needed.
Oils can be detected by measuring thermal energy in the 8 to 14 Ilm region of the
spectrum. Thick oils have higher temperatures with temperatures decreasing as the
thickness of the oil decreases. The minimum thickness that affects temperatures is
between 10 to 70 microns (Fingas et al. 1996). Spatial resolution of the sensor
becomes important for oil spills distributed in patches and wind rows (Hover 1994).
Measurement of relative thickness of oillayers is important for determining the type
of equipment that will be used for cleanups. Infrared (thermal) remote sensing is
probably the most important tool currently used for planning oil spill cleanups.
Thin layers of oil displays high ultraviolet radiation patterns (O'Neil et al. 1983)
thus making ultraviolet radiation data useful to monitor patterns of oils on water
surfaces. While measurements of ultraviolet radiation are very sensitive to oil in the
environment, they are not often used operationally due to the many interferences
encountered from ultraviolet radiation of natural products which make interpretations
difficult (Fingas et al. 1996).
Fluorosensors are useful for detecting the presence of oil in aquatic systems. While
other substances (i.e., chlorophyll) fluoresce, oils fluoresce with unique spectra that
allow them to be detected easily (Hengstermann and Reuter 1990). Oils from different
sources have unique fluorescent signatures that allow them to be differentiated and
identified (Hengstermann and Reuter 1990). Fluorosensors have a useful role in oil
measurement, monitoring, and especially for identifying possible sources of the oil.
Radar can detect oils on sea surfaces because oil reduces the "sea clutter" of normal
radar images of the sea surface. Many naturally occurring substances can also reduce
"sea clutter" (Frysinger et al. 1992) making interpretation of radar images difficult.
Even with these limitations, radar is widely used for oil spill detection and monitoring
because of its ability to collect data under all weather conditions, day or night, and
over large areas rapidly.
Oil is a much stronger emitter of microwave energy than water so that images of oil
spill areas appear much brighter on a microwave image of water (Ulaby et al. 1986).
A passive microwave sensor can detect these differences and thus patterns of oil spills
can be detected although spatial resolution is usually poor. As with radar, microwave
sensors have the ability to collect data under all weather conditions, day or night, and
over large areas rapidly.
13.5 Future Directions
Limitations in spectral and spatial resolution of current sensors on satellites currently
restrict the wide use of satellite data for monitoring water quality. New satellites
(SEA WIFS, MOS, OCTS, QuickBird, Resource2l, Orb View, etc.) and sensors
(hyperspectral, high spatial resolution) already launched or planned to be launched
over the next decade (Corbley 1996) should provide both the improved spectral and
spatial resolution needed to monitor water quality parameters in surface waters in