Evaluation of the impact of backscatter spectral characteristics on Chi retrievals in coastal waters

摘要

With the increasing recognition of the need for using the NIR bands for chlorophyll retrieval in coastal waters it is necessary to account not only for the spectral modulation of the total elastic backscatter by the chlorophyll absorption spectra, as it is normally done, but to also take into account the spectral signature of the backscatter itself, whether from mineral or organic particulates, including algae, and to assess how these factors effect retrieval algorithms. Based on our recent field measurements in coastal waters, we have undertaken a study to examine the spectral behavior of the backscatter to total scattering ratio as a function of suspended solids and chlorophyll loadings. The total scattering spectra is obtained using the WET Labs AC-S instrument which provides hyperspectral measurements of absorption and attenuation, in conjunction with the bb9 instrument which provides direct measurement of backscatter, as well fluorescence measurement of chlorophyll concentration [Chi], The relevant WET Labs absorption and attenuation data were then used as input into Hydrolight radiative transfer simulations to obtain the backscattering ratio spectral distributions. Preliminary NIR algorithms, which were evolved for high [Chi] coastal waters and which focus on the contribution of spectral changes due to chlorophyll backscattering in the NIR, are presented. It is expected that these algorithms will ultimately prove to be less dependent on regional tuning.