A method for estimating inherent optical properties of New Zealand continental shelf waters from satellite ocean colour measurements

We describe a method to estimate spectral absorption and backscattering coefficients between 412 and 555 nm from measurements of remote sensing reflectance across the visible spectrum. The algorithm described is applicable to ocean colour satellite measurements (e.g., SeaWiFS). In situ measurements of inherent and apparent optical properties were made at 19 coastal stations off the north coast of New Zealand's South Island in December 2001. These measurements were used to parameterise a bio-optical model that estimates remote sensing reflectance from concentrations of water constituents. The model generated a large number (5000) of modelled ocean colour reflectance spectra that represented a greater range of biogeochemical conditions than were measured in the study area. These modelled values spanned a wide range of chlorophyll concentrations (0.1-10 mg m(-3)), total suspended particulate material concentrations (0.1-50 g m(-3)), and dissolved yellow substance absorptions (0.01-3m(-1)). The modelled spectra were then used to test the performance of the algorithm. The median ratio of algorithm values to target values was 0.84 (absorption), and 0.80 (backscatter), and the median absolute errors were 33% (absorption) and 36% (backscatter) across two orders of magnitude. The r(2) values between target and algorithm values of inherent optical properties in log-log space were 0.89 for backscatter, and varied with wavelength for absorption from 0.79 (412 nm), 0.72 (443 nm), 0.63 (490 nm), 0.55 (510 nm), and 0.21 (555 nm).