Optical absorption spectra of 0.2- um filtered sea-water samples originating from diverse oceanic and coastal waters were measured with a long pathlength capillary wave-guide; results were compared with those of three different lab-oratory spectrophotometers. The 0.5-m long 550- um (inside diameter) aqueous waveguide uses only 120 ml of filtered sea-water, making it convenient for use in flow-through cells or when sample volumes are restricted. Source light propagates inside the capillary waveguide by total internal reflection because of the lower refractive index of the waveguide walls with respect to the aqueous core. The absorption coefficient of colored dissolved organic matter (CDOM) at 355 nm and S, the slope of the log linearized CDOM absorption spectra, were determined for all samples. The CDOM absorption spec-tra measured by the capillary waveguide closely matched that measured by spectrophotometers for CDOM concentrations varying over an order of magnitude. The deviations between the absorption spectra obtained with the capillary waveguide and those obtained with the standard spectrophotometers increased with decreasing total absorption and with increase in wavelength, presumably because of the greater baseline offsets observed in the capillary waveguide. The offsets are due to differences in refractive indices between the seawater samples and the freshwater reference. With a suitable reference, the capillary waveguide will be very useful for monitoring surface seawater CDOM absorption semicontinuously.

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This article may be accessed from the publisher's website (additional fees may apply) at: http://www.aslo.org/lo/toc/vol_44/issue_4/1142.pdf We thank Harry Fein of World Precision Instruments, Sarasota, for use of the waveguide spectrometer and Chris Brown for helpful suggestions. E.J.D. was supported by a National Research Council– NOAA Resident Research Associateship. Work at the University of South Florida was supported by NOAA Coastal Ocean Program and NASA Earth Observing System. N.V.B. was supported by the Office of Naval Research contract N00014-95-1020. D.P. acknowledges support from NASA grant NAG5-6579 and NOAA grant NA67EC0362.ISSN:0024-3590 Note: imported from RIT’s Digital Media Library running on DSpace to RIT Scholar Works in February 2014.

Document Type


Department, Program, or Center

Chester F. Carlson Center for Imaging Science (COS)


RIT – Main Campus