Abstract
The BP09 experiment conducted by the Centre for Maritime Research and Experimentation in the Ligurian Sea in March 2009 provided paired vertical profiles of nadir-viewing radiances L(u)(z) and downward irradiances E(d)(z) and inherent optical properties (IOPs, absorption, scattering and backscattering coefficients). An inversion algorithm was implemented to retrieve IOPs from apparent optical properties (AOPs, radiance reflectance R(L), irradiance reflectance R(E) and diffuse attenuation coefficient K(d)) derived from the radiometric measurements. Then another inversion algorithm was developed to infer vertical profiles of water constituent concentrations, including chlorophyll-a concentration, non-algal particle concentration, and colored dissolved organic matter from the retrieved IOPs based on a bio-optical model. The algorithm was tested on a synthetic dataset and found to give reliable results with an accuracy better than 1%. When the algorithm was applied to the BP09 dataset it was found that good retrievals of IOPs could be obtained for sufficiently deep waters, i.e. for L(u)(z) and E(d)(z) measurements conducted to depths of 50 m or more. This requirement needs to be satisfied in order to obtain a good estimation of the backscattering coefficient. For such radiometric measurements a correlation of 0.88, 0.96 and 0.93 was found between retrieved and measured absorption, scattering and backscattering coefficients, respectively. A comparison between water constituent values derived from the measured IOPs and in-situ measured values, yielded a correlation of 0.80, 0.78, and 0.73 for chlorophyll-a concentration, non-algal particle concentration, and absorption coefficient of colored dissolved organic matter at 443 nm, respectively. This comparison indicates that adjustments to the bio-optical model are needed in order to obtain a better match between inferred and measured water constituent values in the Ligurian Sea using the methodology developed in this paper.
Highlights
Simultaneous measurements of the upward and downward irradiances, Eu(z) and Ed(z), or the nadir-viewing radiance Lu(z) combined with Ed(z), where z is the water depth, are among the most common data acquisition products in hydrologic optics
The apparent optical properties (AOPs) data derived from Lu(z) and Ed(z) measurements and paired inherent optical properties (IOPs) data that will be used in this paper are from the BP09 experiment which was conducted in the Ligurian Sea in March
To test the performance of the IOP inversion algorithm, we first generated a synthetic dataset at 488 nm using AccuRT, our radiative transfer model (RTM)
Summary
Simultaneous measurements of the upward and downward irradiances, Eu(z) and Ed(z), or the nadir-viewing radiance Lu(z) combined with Ed(z), where z is the water depth, are among the most common data acquisition products in hydrologic optics. Is obtained from Lu(z) and Ed(z), which are relatively easy to measure compared to the IOPs, a desirable goal is to infer the IOPs from measured profiles of the AOPs, in general, and from the irradiance reflectance RE (z) = Eu(z)/Ed(z) or the radiance reflectance RL(z), in particular. This nonlinear inversion problem is much more challenging than solving the forward problem involving the linear RTE. We describe an algorithm developed to retrieve vertical profiles of water constituents from the retrieved IOP data
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
