Enhance field water-color measurements with a Secchi disk and its implication for fusion of active and passive ocean-color remote sensing

Inversion of the total absorption (a) and backscattering coefficients of bulk water through a fusion of remote sensing reflectance (R_rs) and Secchi disk depth (Z_SD) is developed. An application of such a system to a synthesized wide-range dataset shows a reduction of ∼3 folds in the uncertainties of inverted a(λ) (in a range of ∼0.01–6.8  m^−1) from R_rs(λ) for the 350–560 nm range. Such a fusion is further proposed to process concurrent active (ocean LiDAR) and passive (ocean-color) measurements, which can lead to nearly “exact” analytical inversion of an R_rs spectrum. With such a fusion, it is found that the uncertainty in the inverted total a in the 350–560 nm range could be reduced to ∼2% for the synthesized data, which can thus significantly improve the derivation of a coefficients of other varying components. Although the inclusion of Z_SD places an extra constraint in the inversion of R_rs, no apparent improvement over the quasi-analytical algorithm (QAA) was found when the fusion of Z_SD and R_rs was applied to a field dataset, which calls for more accurate determination of the absorption coefficients from water samples.