A NOVEL CONCEPT FOR MEASRUING SEAWATER INHERENT OPTICAL PROPERTIES IN AND OUT OF THE WATER

Water inherent optical properties (IOPs) are optical properties specic to a
medium, and independent of the distribution and intensity of light through that
medium. IOPs are key parameters in a wide range of applications in elds like
water quality assessment (e.g., for drinking water or oyster farming), ecology and
human health (e.g., detection of toxic algal blooms) and oceanography (e.g., characterization
of biogeochemical processes in aquatic environments, underwater visibility
studies, calibration and interpretation of satellite ocean color). In particular, the
absorption coecient (a) is the typical IOP used to obtain the concentration of
chlorophyll-a in the water, a critical parameter in biological oceanography studies,
and water quality research makes ample use of the backscattering coecient (bb) as
a measure of turbidity. In this theoretical study we test the feasibility of a small,
robust in situ instrument capable of obtaining good estimates of both IOPs. The
instrument would emit a laser beam into the water and would retrieve the light
intensity scattered back into a series of concentric detector rings located around
the source. We use numerical modeling of light propagation to create an inversion
algorithm that would translate the signal from such an instrument into values of
a and bb. Our results, based on simulations spanning most of the natural range of
seawater IOP combinations, indicate that an 8 cm - diameter instrument would be
capable of predicting bb within less than 13% relative dierence, and a within less
than 54% (for 90% of the inverted a values, the relative errors fall below 29%). Such
a compact and relatively simple device could have multiple applications for in situ
optical measurements, including a and bb retrievals from instrumentation mounted
on autonomous underwater robots, capable of obtaining three-dimensional proling
of the oceans. Furthermore, the same methodology could be used to develop an outof-
water sensor for much needed long-term in situ measurements of backscattering
and absorption.