We use a multiple regression analysis and a data bank of about 400 reflectance spectra to reconstruct hyperspectral
reflectances between 400 and 900 nm with a 5 nm step using only the values known at the wavelengths of the MERIS
sensor level 2 data. For in situ remote sensing reflectances measured during different oceanographic missions, the
reconstruction is within 2 per cent almost over the entire spectrum. The main difference (to a maximum of 4 per cent)
usually occurs at the inflexion point of the reflectance curve between 580 and 600 nm. Observed in-situ remote sensing
reflectances or reconstructed spectra are inverted using a Water Colour Simulator bio-optical model (WASI) to obtain
the inherent optical properties (IOP) of the water. The values derived by the model are compared with the measurements
when available. To validate the reconstruction, we compare the results of the model inversion using the initial spectrum
or the reconstructed one as input. Preliminary results show that the derived values from the inversion of the reconstructed
spectrum are very close to the values generated from the inversion of the initial spectrum, especially in case 1 waters.
This reconstruction technique is used to generate hyperspectral remote sensing reflectances from reflectance data
calculated by the MERIS sensor. We use the reconstructed spectra as input to be inverted in the WASI model in order to
quantify the substances' concentrations; in particular, the inversion is working well for the suspended particulate matter
concentrations.
During the "Optic-Congo" oceanographic survey which took place in 2005 on board the "Beautemp-Beaupré" SHOM
vessel, different optical measurements of the surface water were acquired using a TRIOS radiance sensor fixed onboard a
mini-catamaran. Hydrological measurements (CTD, fluorescence, attenuation, scattering) and water samples were
simultaneously collected in order to measure SPM, Chlorophyll-a and CDOM concentrations. Four types of surface
water colours (blue, green-yellow, dark and brown) were identified. The main characteristics of these waters were the
very low Chlorophyll-a concentrations for this period of the year (March), and the very high CDOM concentrations
along the Congo coast, and particularly in the turbid plume of the Congo River. The attenuation and scattering
measurements highlighted the predominance of organic matter at the water surface. These observations were documented
using a beam electron microscope and by microanalysis. This data set was used to classify the water bodies along the
Gabon and Congo coasts. We propose here to use the remote sensing reflectance (Rrs) measurements to invert the IOP
(absorption (a) and backscattering (bb)) using the WASI numerical bio-optical model. The model is iterative: the Rrs
WASI simulations are computed given initial values of ocean constituents' concentrations and iteratively adjusted to the
Rrs in-situ measurements. The IOP computations are satisfying when the correlations between simulated and measured
Rrs are optimized. Then, the attenuation coefficients (Kd) are computed from the IOP coefficients. These results are
compared with measurements of Ku carried out during the survey.
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