Hi-Star: A spectrophotometer for measuring the absorption and attenuation of natural waters in-situ and in the laboratory.

A new submersible spectrophotometer with 3.3 nm spectral resolution throughout the visible range, 400 - 730 mn, has been developed for the Navy. Within the sample chamber, the Hi-Star incorporates an optical configuration similar to that of the existing WET Labs ac-9 dual path absorption and attenuation meter. The absorption path includes a reflective tube to collect the scattered light throughout the sample volume while the attenuation path uses conventional transmissometer optics. The Hi-Star uses fiber optics to couple a single white light source into the two sample optical paths and a reference path. The absorption and attenuation receivers consist of primary collection optics which couple the light into two spectrometers. A third spectrometer is used to directly measure the light from the reference path. Data collected from the absorption and attenuation paths are subsequently reference normalized to correct for changes in the lamp output over time. The Hi-Star is designed to be used either in a continuous flow mode or with discrete samples in cylindrical cuvettes, thus making it suitable for both laboratory or field applications. We show preliminary data collected with the Hi-Star instrument both in the laboratory and in-situ. Laboratory tests will include determination of basic instrument coefficients and determination of the mean scattering error for the absorption measurement Field results are also presented using the instrument in both bench-top and in-situ profiling operation modes.