36 
490 and 520 Bands. Moving the 500 nm 
band to 490 nm and including a 520 nm band 
was suggested since these bands would permit 
multiband spectral-curvature algorithms and re- 
lated second-derivative algorithms to be applied 
to derive chlorophyll pigment concentrations in 
coastal (Case-2) waters. These types of algo- 
rithms, and, in particular, one using a combination 
of 460, 490, and 520 nm bands, discovered em- 
pirically by Grew (1981), have been shown to be 
relatively insensitive to the effects of nonchloro- 
phyll absorption and scattering. Comparisons of 
the results obtained from applying curvature al- 
gorithms to remotely sensed data with similar re- 
sults obtained from laser-stimulated chlorophyll 
fluorescence data routinely yield correlation co- 
efficients greater than 0.9 (Hoge and Swift 1986). 
Hoge and Swift's analysis also showed that al- 
though the CZCS band set precluded application 
of the Grew relationship, a combination of 443, 
490, and 520 nm bands was equally effective. 
Another reason presented for including a 
520 nm band was that its use would benefit from 
the CZCS heritage and, like the 665 nm band, 
would permit better comparisons to be made be- 
tween CZCS and SeaWiFS observations. This 
could be especially important in waters with high 
pigment concentrations, where the values from 
nearly 8 years of CZCS observation have been 
derived using a 520/550 nm band ratio. Unless 
this heritage is available, it will be extremely diffi- 
cult to assess the validity of any long-term trends 
observed between CZCS and SeaWiFS data if 
their derivations differ. Where this is likely to be 
most troublesome is in detecting changes in com- 
munity structure based on pigment groups, since 
the 520 and 500 nm bands lie near the peak of 
the complex, multicomponent accessory pigment 
absorbance region. Changes in accessory pig- 
ment composition and concentration are common 
when the phytoplankton community's structure 
changes in response to nutrient stress, eutrophi- 
cation, or other environmental changes. The 
proposed change from 550 to 565 nm will also af- 
fect this comparison, but to a lesser degree, since 
these two wavelengths are both near the mini- 
mum of chlorophyll pigment absorption. 
The combination of 443, 490, and 520 nm was 
considered, but was found to be infeasible from 
an instrument-design point of view. This is be- 
cause the dichroic beamsplitters used to reflect 
the shorter wavelengths and to pass the longer 
wavelengths do not have the ability to precisely 
cleave the spectrum. To avoid polarization ef- 
fects near adjoining spectral regions of band 
pairs, there must be a minimum of 20 nm between 
the upper wavelength of one band and the lower 
wavelength of the adjacent band (in this case 
500 nm and 510 nm).° The concensus was that 
the 443, 500, and 565 nm bands of the baseline 
selection would accomplish the same purposes 
as the 443, 490, and 520 nm set. 
565 and 570 nm Bands. Inclusion of a 
band at 570 nm in conjunction with the band at 
565 nm was discussed because of the recent 
work of Hoge and Swift (submitted to Applied Op- 
tics). In this work they obtained extremely strong 
relationships between their laser-stimulated fluo- 
rescence concentration and results obtained 
from using a 566/571 nm band ratio on data from 
Case-2 waters. Correlation coefficients obtained 
using this band ratio exceeded those obtained 
using 443/550 nm and 520/550 nm band ratios 
when applied to data taken in four flight experi- 
ments. The choice of two closely spaced bands 
is attractive in that it lessens the need for highly 
accurate Angstrom exponent extrapolations. It 
also minimizes errors due to strong vertical inho- 
mogeneity, since the penetration depth for the 
two wavelengths is so similar. The narrow separ- 
ation of these bands would be possible in the 
SeaWiFS design, in contrast to the CZCS, OCI, or 
MODIS sensors, since individual detector filters 
are used for the detectors in band pairs. 
However, selection of 570 nm as the location 
of the additional band was rejected in favor of the 
substantial advantages to be gained in the accu- 
racy of atmospheric-correction algorithms 
through inclusion of a band at 865 nm. 
5 Upper wavelength of the 490 nm band = 490 + 10 = 500 
nm. Lower wavelength of the 520 nm band = 520 - 10 nm 
=o 0%nin 
