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Proceedings Paper

Modern spectral transmissometer
Author(s): Mark J. Borgerson; Robert Bartz; J. Ronald V. Zaneveld; James C. Kitchen
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Paper Abstract

We have evaluated a number of spectral attenuation meter designs based on constraints related to power consumption, spectral bandwidth, sampling time, accuracy and stability . Our fmal instrument design employs a unique optical bridge deve1oped1r Sea Tech with ONR support, a tungsten light source and a holographic grating monochromatorThe instrument design is summarized as follows: White light from a 10-Watt tungsten lamp with a 1mm2 filament is collected by a condensing lens and then spatially filtered by a 1mm diameter pinhole which is placed at the entrance port of a monochromator. The monochromator has a 45°, 1200 lines/mm, holographic grating 37 mm in diameter with a 91 mm focal length. The grating is rotated about its vertical axis with a sine arm driven by a stepping motor, allowing wavelength to be selected from 400 to 800 nm. At the exit port of the monochromator we use a 1mm diameter pinhole which spectrally filters the output light, resulting in a spectral bandwidth of 9. 1 nm. This nearly monochromatic light is then measured by a unique reference detector with a 0.5mm diameter pinhole at its center, allowing light to be transmitted through the center of the detector. The transmitted light has a bandwidth of 4.5 nm. The monochromatic light is then collimated by a 50mm focal length achromatic lens and stopped down to a beam 1 cm in diameter. This light then enters the sample chamber. After passing through the sample the light is received by a 61mm focal length achromatic lens and is focused onto a signal detector with a diameter of 1.25mm. Digitized ratios ofreference detector to signal detector voltages allow transmission to be measured with an accuracy of 0.05% and a resolution of 0.01%. By monitoring temperature we were able to temperature compensate the instrument to within 0.05% transmission from 00 C to 25° C. Based on these results it is now possible to construct a spectral attenuation meter with the required sensitivity and accuracy to measure beam attenuation in water as clean as oligotrophic ocean waters.

Paper Details

Date Published: 1 September 1990
PDF: 13 pages
Proc. SPIE 1302, Ocean Optics X, (1 September 1990); doi: 10.1117/12.21458
Show Author Affiliations
Mark J. Borgerson, Sea Tech, Inc. (United States)
Robert Bartz, Sea Tech, Inc. (United States)
J. Ronald V. Zaneveld, Sea Tech, Inc. (United States)
James C. Kitchen, Sea Tech, Inc. (United States)

Published in SPIE Proceedings Vol. 1302:
Ocean Optics X
Richard W. Spinrad, Editor(s)

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