Download HydroLight Technical Documentation

Thus the new model uses the chlorophyll-dependence of cp(660) from Loisel and Morel
(1998), Eq. (9), and assumes that cp has the same chlorophyll-dependent wavelength
dependence as the bp model of Morel et al. (2002), Eq. (8). The values of co and n can be
chosen by the user in the HE52 UI. The default values, which apply to near-surface waters,
are co = 0.407 and n = 0.795 (from Loisel and Morel, 1998, Eq. 5).
Figure 8 shows example ap for mid-range UV absorption, bp, and cp spectra for nearsurface waters (co = 0.416 and n = 0.766 in Eq. 10), along with the “classic” bp of Eq. (4)
with bo = 0.3, n = 0.62, and m = 1. The scattering coefficients are not too different at low
chlorophyll values, but the new bp has a different wavelength dependence and is much larger
in magnitude, by up to a factor of three, at high Chl values. Unlike in the classic scattering
model of Eq. (4), the wavelength dependence of bp now depends on Chl and is more
complicated. These differences in scattering will have a significant effect on computed
radiances.
Fig. 8. Beam attenuation cp as determined by from Eq. (10) and near-surface values of co
= 0.407 and n = 0.795 (blue). The red curves are the same ap as the mid-UV absorptions in
Fig. 6. The solid green curve is the new bp = cp - ap; the dashed green curve is the “classic”
bp of Eq. (4).
17