The scattering of light is an inherent property of natural bodies of water. As such, they play a crucial role in the study and characterization of natural water. Every optical measurement done in water must take this property into account. The scattering behavior of natural body is a direct consequence of its constituents, including organic and inorganic matter, suspended and dissolved particulates and an air bubbles. In specific, these constituents have characteristic scattering coefficients.
A new optical instrument has been developed to independently determine the total scattering and backscattering coefficient of natural bodies of water. The measurement is performed by the collecting a sample of the scattered light over a large angular range, such that it introduces a sin θ weight factor onto the detected volume scattering function of the medium. In other words, the instrument proposed consists of a total scatting coefficient (b) meter and a backscattering coefficient (bb) meter. These meters measured the exact value of b and bb, while not making any assumptions of the scatterers.
The measurement principle behind the instrument consists of perfectly calibrated cavity, whose signal output is proportional to the sin of incoming light, scattered light from a light source (532 nm laser). The placement of the meters' aperture is perpendicular to the direction of the laser beam. In other words, at its heart, a highly accurate cosine collector with integrating properties is described.
We present the mathematical description, design and development of each meter, along with calibration methods and results of the prototype test. In short, the backscattering coefficient meter consists of placing a 1.5 mm wide, curved aperture in a 19 mm diameter channel. The instrument's laser beam is centered about the channel and the scattered light enters the bb meter through the aperture, yielding and output signal. This signal can be expressed as a direct function of bb. The bb meter is the first instrument of its kind to make a direct measurement of bb. The total scattering coefficient meter consists of placing a 1 cm wide, curved aperture in a 4 mm diameter channel, also centered about a laser beam. The distance of the light source from the center of the meter's aperture defines the angular resolution of the b measurement
