Currently the default algorithms used by SeaDAS are the OC4 (SeaWiFS) and
OC3 (MODIS) band-ratio algorithms (O’Reilly et al. 2000; Eq. 7.9 for version 6)
while the Carder et al. (1999) and Maritorena et al. (2002) semi-analytical algorithms as well as the most recent CI algorithm (Hu et al. 2012b) are options within
the software. Based on the Level-2 R rs (k) data one can also implement regional
empirical or semi-analytical algorithms. Finally, the Level-2 Chl data products are
map-projected or binned to produce geo-referenced Chl data products at regional
or global scales. Figure 7.4a–c show examples of map-projected products for the
eastern Gulf of Mexico, while Fig. 7.4d shows an example of the globally mapprojected Chl product (after binning) from SeaWiFS multi-year measurements. All
data products are stored in HDF or NetCDF computer files. Most of these data
products can be obtained from the U.S. NASA Goddard Space Flight Center
(http://oceancolor.gsfc.nasa.gov). Likewise, MERIS data products can be obtained
from the European Space Agency.
7.4 Validation Efforts Using in Situ Measurements
As with algorithm development, in situ Chl must be determined and quality
controlled in order to validate the algorithm performance. Starting in 1997, the
Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic
Studies (SIMBIOS, Fargion et al. 2004) program initiated by NASA has funded
numerous researchers to collect bio-optical data in the global oceans, most of
which have been archived in the SeaWiFS Bio-optical Archive and Storage System (SeaBASS, http://seabass.gsfc.nasa.gov, Hooker et al. 1994) and are available
for both algorithm development and validation. Also available is a subset of
SeaBASS, the NOMAD dataset (Werdell and Bailey 2005), that was specifically
compiled for bio-optical algorithm development, as it contains coincident measurements of Chl, R rs (k), and other data collected simultaneously in the global
oceans. In addition to data available in SeaBASS, researchers working on individual projects have collected regional bio-optical data, which can also be used for
algorithm development and validation.
Most of the Chl data collected from field and laboratory measurements and
available in SeaBASS were determined using fluorometric methods. Other Chl
data have been determined via HPLC (Hooker and Heukelem 2011), most of
which show excellent agreement with fluorometric Chl (Fig. 7.6 of Werdell and
Bailey 2005). However, for low concentrations Chl determined from fluorometric
methods sometimes suffers from contaminations by chlorophyll b and chlorophyll
c (Marrari et al. 2006; Dierssen 2010). Nevertheless, because of its wide availability, fluorometric Chl is often used to validate the satellite observations of Chl.
Chl data products derived from the various ocean color sensors have been
evaluated and validated extensively by the research community. To perform the
evaluation, caution must be taken to address the inherent difference in both time
and space between satellite and in situ measurements. Spatial and temporal
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OC3 (MODIS) band-ratio algorithms (O’Reilly et al. 2000; Eq. 7.9 for version 6)
while the Carder et al. (1999) and Maritorena et al. (2002) semi-analytical algorithms as well as the most recent CI algorithm (Hu et al. 2012b) are options within
the software. Based on the Level-2 R rs (k) data one can also implement regional
empirical or semi-analytical algorithms. Finally, the Level-2 Chl data products are
map-projected or binned to produce geo-referenced Chl data products at regional
or global scales. Figure 7.4a–c show examples of map-projected products for the
eastern Gulf of Mexico, while Fig. 7.4d shows an example of the globally mapprojected Chl product (after binning) from SeaWiFS multi-year measurements. All
data products are stored in HDF or NetCDF computer files. Most of these data
products can be obtained from the U.S. NASA Goddard Space Flight Center
(http://oceancolor.gsfc.nasa.gov). Likewise, MERIS data products can be obtained
from the European Space Agency.
7.4 Validation Efforts Using in Situ Measurements
As with algorithm development, in situ Chl must be determined and quality
controlled in order to validate the algorithm performance. Starting in 1997, the
Sensor Intercomparison and Merger for Biological and Interdisciplinary Oceanic
Studies (SIMBIOS, Fargion et al. 2004) program initiated by NASA has funded
numerous researchers to collect bio-optical data in the global oceans, most of
which have been archived in the SeaWiFS Bio-optical Archive and Storage System (SeaBASS, http://seabass.gsfc.nasa.gov, Hooker et al. 1994) and are available
for both algorithm development and validation. Also available is a subset of
SeaBASS, the NOMAD dataset (Werdell and Bailey 2005), that was specifically
compiled for bio-optical algorithm development, as it contains coincident measurements of Chl, R rs (k), and other data collected simultaneously in the global
oceans. In addition to data available in SeaBASS, researchers working on individual projects have collected regional bio-optical data, which can also be used for
algorithm development and validation.
Most of the Chl data collected from field and laboratory measurements and
available in SeaBASS were determined using fluorometric methods. Other Chl
data have been determined via HPLC (Hooker and Heukelem 2011), most of
which show excellent agreement with fluorometric Chl (Fig. 7.6 of Werdell and
Bailey 2005). However, for low concentrations Chl determined from fluorometric
methods sometimes suffers from contaminations by chlorophyll b and chlorophyll
c (Marrari et al. 2006; Dierssen 2010). Nevertheless, because of its wide availability, fluorometric Chl is often used to validate the satellite observations of Chl.
Chl data products derived from the various ocean color sensors have been
evaluated and validated extensively by the research community. To perform the
evaluation, caution must be taken to address the inherent difference in both time
and space between satellite and in situ measurements. Spatial and temporal
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C. Hu and J. Campbell