Conmy, Del Castillo, Downing, and Chen
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spectral properties of CDOM. Although the changes in ϕ f are typically small, the user
should be aware of these changes and collect calibration samples along the salinity gradient. Sampling along buoyant river plumes is more problematic. A typical flowthrough
water intake in a research vessel is located a few meters below the surface. Therefore,
any instrument connected to the system may not sample the highly colored river plume
waters that are mostly responsible for the water leaving radiance detected by the remote
sensor. Under these conditions, it may be necessary to use a large number of discrete
surface samples collected away from disturbances caused by the research vessel, or to
use an undulating, towed sampling system (i.e., Chen and Gardner, 2004; Gardner et al.,
2005). These instruments allow for very fine scale measurements along the water column
and have the capability of pumping water onboard, so collection of multiple calibration
samples is possible. The use of this instrumentation is a viable option for the validation of
ocean color products in turbid waters.
6.7.2 Active Remote Sensors
LIDAR is a useful use of fluorescence in remote sensing of organic matter in the oceans.
The use of LIDAR for detection of CDOM and chlorophyll fluorescence has been well
demonstrated (Hogue, 2005; Hoge et al. 1981, 1983, 1995, 1998, 2005; Barbini et al.,
2001; Drozdowska, 2007). One excellent examples of the application of LIDAR to CDOM
detection (and other applications) is found in Hoge et al. (1995), who demonstrated that
well-calibrated sensors are very stable and useful in coastal and oceanic waters. LIDAR
is particularly useful in coastal waters because of its high spatial resolution and dynamic
range. For example, the LIDAR system flown by Hoge et al. (1995) has a spatial resolution
of ~130 m – superior to that of any satellite sensor. An additional advantage of airborne
LIDAR is that it can be flown under clouds with obvious advantage over satellite sensors.
The use of airborne LIDAR should be considered as an alternative to satellite imagery to
study highly dynamic coastal regions and when cloud cover limits availability of satellite
imagery. Airborne LIDARS can sample large area of the ocean during a satellite overpass,
making it more productive for satellite validation than traditional sampling from a research
vessel. These capabilities make LIDAR a possible option for validation of future spaceborne high spatial resolution ocean color radiometers.
LIDAR systems can also be deployed from the bow of ocean-going vessels (i.e., Barbini
et al. 2001), and can provide simultaneous measurements of FCDOM (hence a g ) and chlorophyll. Barbini et al. (2001) used a system similar to Hoge et al. (1994) to validate remote
sensing retrievals of Chl from SeaWiFS in the Southern Ocean demonstrating the usefulness of shipboard LIDAR to validate remote sensors. LIDAR, however, has its complications. The instrumentation and mission-planning capabilities are highly specialized and
expensive. Flying a LIDAR system regularly is a luxury that only a well-funded program
can afford. Moreover, LIDAR data, like most field data, are collected for specific campaigns and do not offer the global coverage or temporal resolution available from satellite
sensors.
224
spectral properties of CDOM. Although the changes in ϕ f are typically small, the user
should be aware of these changes and collect calibration samples along the salinity gradient. Sampling along buoyant river plumes is more problematic. A typical flowthrough
water intake in a research vessel is located a few meters below the surface. Therefore,
any instrument connected to the system may not sample the highly colored river plume
waters that are mostly responsible for the water leaving radiance detected by the remote
sensor. Under these conditions, it may be necessary to use a large number of discrete
surface samples collected away from disturbances caused by the research vessel, or to
use an undulating, towed sampling system (i.e., Chen and Gardner, 2004; Gardner et al.,
2005). These instruments allow for very fine scale measurements along the water column
and have the capability of pumping water onboard, so collection of multiple calibration
samples is possible. The use of this instrumentation is a viable option for the validation of
ocean color products in turbid waters.
6.7.2 Active Remote Sensors
LIDAR is a useful use of fluorescence in remote sensing of organic matter in the oceans.
The use of LIDAR for detection of CDOM and chlorophyll fluorescence has been well
demonstrated (Hogue, 2005; Hoge et al. 1981, 1983, 1995, 1998, 2005; Barbini et al.,
2001; Drozdowska, 2007). One excellent examples of the application of LIDAR to CDOM
detection (and other applications) is found in Hoge et al. (1995), who demonstrated that
well-calibrated sensors are very stable and useful in coastal and oceanic waters. LIDAR
is particularly useful in coastal waters because of its high spatial resolution and dynamic
range. For example, the LIDAR system flown by Hoge et al. (1995) has a spatial resolution
of ~130 m – superior to that of any satellite sensor. An additional advantage of airborne
LIDAR is that it can be flown under clouds with obvious advantage over satellite sensors.
The use of airborne LIDAR should be considered as an alternative to satellite imagery to
study highly dynamic coastal regions and when cloud cover limits availability of satellite
imagery. Airborne LIDARS can sample large area of the ocean during a satellite overpass,
making it more productive for satellite validation than traditional sampling from a research
vessel. These capabilities make LIDAR a possible option for validation of future spaceborne high spatial resolution ocean color radiometers.
LIDAR systems can also be deployed from the bow of ocean-going vessels (i.e., Barbini
et al. 2001), and can provide simultaneous measurements of FCDOM (hence a g ) and chlorophyll. Barbini et al. (2001) used a system similar to Hoge et al. (1994) to validate remote
sensing retrievals of Chl from SeaWiFS in the Southern Ocean demonstrating the usefulness of shipboard LIDAR to validate remote sensors. LIDAR, however, has its complications. The instrumentation and mission-planning capabilities are highly specialized and
expensive. Flying a LIDAR system regularly is a luxury that only a well-funded program
can afford. Moreover, LIDAR data, like most field data, are collected for specific campaigns and do not offer the global coverage or temporal resolution available from satellite
sensors.