Document Type

Article

Publication Title

Applied Optics

Rights and Access Note

This Item is protected by copyright and/or related rights. You are free to use this item in any way that is permitted by copyright and related rights legislation that applies to your use. Rights assessment remains the responsibility of the researcher. In addition, no permission is required from the rights-holder(s) for non-commercial uses.

Publication Date

8-1-2020

First Page

6765

Last Page

6773

Issue Number

22

Volume Number

59

Abstract/ Summary

Electromagnetic theory predicts spectral dependencies in extinction efficiency near a narrow absorption band for a particle with an index of refraction close to that of the medium in which it is immersed. These absorption band effects are anticipated in oceanographic beam-attenuation (beam-c) spectra, primarily due to the narrow red peak in absorption produced by the phytoplankton photopigment, chlorophyll a (Chl a). Here we present a method to obtain Chl a absorption and size information by analyzing an eigendecomposition of hyperspectral beam-c residuals measured in marine surface waters by an automatic underway system. We find that three principal modes capture more than 99% of the variance in beam-c residuals at wavelengths near the Chl a red absorption peak. The spectral shapes of the eigenvectors resemble extinction efficiency residuals attributed to the absorption band effects. Projection of the eigenvectors onto the beam-c residuals produces a time series of amplitude functions with absolute values that are strongly correlated to concurrent Chl a absorption line height (aLH) measurements (r values of 0.59 to 0.83) and hence provide a method to estimate Chl a absorption. Multiple linear regression of aLH on the amplitude functions enables an independent estimate of aLH, with RMSE of 3.19 · 10−3 m−1 (3.3%) or log10-RMSE of 18.6%, and a raw-scale R2 value of 0.90 based on the Tara Oceans Expedition data. Relationships between the amplitude functions and the beam-c exponential slopes are in agreement with theory relating beam-c to the particle size distribution. Compared to multispectral analysis of beam-c slope, hyperspectral analysis of absorption band effects is anticipated to be relatively insensitive to the addition of nonpigmented particles and to monodispersion.

Citation/Publisher Attribution

Houskeeper, H. F., D. Draper, R. M. Kudela, and E. Boss. 2020. Chlorophyll absorption and phytoplankton size information inferred from hyperspectral particulate beam attenuation, Appl. Opt. 59, 6765-6773, https://doi.org/10.1364/AO.396832

Publisher Statement

©2020 Optical Society of America

DOI

10.1364/AO.396832

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publisher's version of the published document

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In Copyright - Educational Use Permitted.