TOWARD CLOSURE OF THE INHERENT OPTICAL-PROPERTIES OF NATURAL-WATERS

A fundamental relationship of inherent optical properties (IOP) is tha t the beam attenuation coefficient is the sum of the volume absorption and scattering coefficients (c = a + b). A relative calibration of a set of instruments can be provided using this IOP closure equation. Me asurement of the true beam attenuation coefficient c is not practical as all attenuation instrumentation has some finite acceptance angle in which scattered light is collected. We provide a theoretical framewor k for measuring the attenuation and scattering coefficients in a consi stent manner. Using this framework, we provide a practical version of the IOP closure equation. We apply the practical IOP closure equation to measurements made at Lake Pend Oreille, Idaho, in the spring of 199 2. Results of this IOP closure indicate that the practical closure equ ation is a useful approach. Closure was achieved during some measureme nt sets but not at others. The intermittent lack of closure may be due to the method of determining the scattering coefficient from the gene ral angle scattering meter or that the calibration of at least one of the instruments drifted during the time of the experiment.