Optical Absorption of Pure Water in the Blue and Ultraviolet

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This ocean science technology development project builds on previous work developing instrumentation to measure light scattering and absorption in ocean water. These variables are critical in determining the optical properties of the oceans, which has great applicability in making in situ measurements and in remote sensing of oceanic surface waters. Absorption is especially problematic, but newly developed instrumentation for such measurements has obtained reliable data in the spectral range of 380 nm to 700 nm. using isotropic illumination of the sample in an integrating cavity. The goals of this project are: (1) to extend the capabilities of this previous instrumentation and make measurements in the ultraviolet spectral region in the 320 nm to 380-nm range; (2) to investigate the apparent fact that contact of ultra-pure water with glass and quartz leads to increased absorption of the ultra-pure water in the blue to near ultraviolet range; (3) to measure and improve the accuracy of the absorption coefficients in the important UV-C and UV-B spectral regions (specifically 240 nm to 320-nm); (4) to build and test a large spherical integrating cavity to provide higher accuracy in the absorption measurements at the minimum of pure water absorption; and (5) to study, build, and test a long tubular form of the integrating cavity with the objective of an in situ device.