Microscale Quantification of the Absorption by Dissolved and Particulate Material in Coastal Waters with an ac-9 Public Deposited

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  • Measuring coastal and oceanic absorption coefficients of dissolved and particulate matter in the visible domain usually requires a methodology for amplifying the natural signal because conventional spectrophotometers lack the necessary sensitivity. The WET Labs ac-9 is a recently developed in situ absorption and attenuation meter with a precision better than ±0.001 m⁻¹ in the raw signal, which is sufficient to make these measurements in pristine samples. Whereas the superior sensitivity of the ac-9 has been well documented, the accuracy of in situ measurements for bio-optical applications has not been rigorously evaluated. Obtaining accurate results with an ac-9 requires careful attention to calibration procedures because baselines drift as a result of the changing optical properties of several ac-9 components. To correct in situ measurements for instrument drift, a pressurized flow procedure was developed for calibrating an ac-9 with optically clean water. In situ, micro- (cm) to fine- (m) scale vertical profiles of spectral total absorption, a[subscript]t(λ), and spectral absorption of dissolved materials, a[subscript]g(λ), were then measured concurrently using multiple meters, corrected for drift, temperature, salinity, and scattering errors and subsequently compared. Particulate absorption, a[subscript]p(λ), was obtained from a[subscript]t(λ) − a[subscript]g(λ). CTD microstructure was simultaneously recorded. Vertical profiles of a[subscript]g(λ), a[subscript]t(λ), and a[subscript]p(λ) were replicated with different meters within ±0.005 m⁻¹, and spectral relationships compared well with laboratory measurements and hydrographic structure
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  • Twardowski, Michael S., James M. Sullivan, Percy L. Donaghay, J. Ronald V. Zaneveld, 1999: Microscale Quantification of the Absorption by Dissolved and Particulate Material in Coastal Waters with an ac-9. Journal of Atmospheric and Oceanic Technology, 16, 691–707.
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  • description.provenance : Made available in DSpace on 2012-02-20T23:46:42Z (GMT). No. of bitstreams: 1 ZaneveldJRonaldV.CEOAS.MicroscaleQuantificationAbsorption.pdf: 319059 bytes, checksum: ebbe103d6b9d6664d41d30e796c3f064 (MD5) Previous issue date: 1999-06
  • description.provenance : Submitted by Deborah Campbell (deborah.campbell@oregonstate.edu) on 2012-02-20T23:46:42Z No. of bitstreams: 1 ZaneveldJRonaldV.CEOAS.MicroscaleQuantificationAbsorption.pdf: 319059 bytes, checksum: ebbe103d6b9d6664d41d30e796c3f064 (MD5)

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