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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 15, Iss. 6 — Mar. 19, 2007
  • pp: 2791–2802

Why does the Secchi disk disappear? An imaging perspective

Weilin Hou, Zhongping Lee, and Alan D. Weidemann  »View Author Affiliations

Optics Express, Vol. 15, Issue 6, pp. 2791-2802 (2007)

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The widely-used Secchi disk method is re-examined from the modulation transfer aspect. Namely, by assuming a volume scattering function and applying small angle scattering approximation, we show that the Secchi depth and horizontal visibility can be determined using the water modulation transfer function and the corresponding spatial frequencies associated with the disk. A basic equation of Secchi disk is reached that is comparable to the radiative transfer approach, in that the Secchi depth is inversely proportional to the attenuation coefficient (c). With typical values for parameters applied, we demonstrate that the modulation transfer technique produces a horizontal visibility range of about 4.8/c, which is inline with previous studies. The improvement lies in the fact that the current approach correctly addresses the response of all spatial frequencies according to the modeled optical transfer function of the water. In terms of Secchi disk theory, the current approach helps to understand the effect of disk size as well as the role of scattering on the Secchi disk depth. The approach presented provides an understanding of Secchi disk disappearance by showing that as the disk is moved away from the observer, the spatial frequencies corresponding to the disk size increase, while the modulation transfer dampens contrast at an increased rate.

© 2007 Optical Society of America

OCIS Codes
(010.4450) Atmospheric and oceanic optics : Oceanic optics
(110.4850) Imaging systems : Optical transfer functions
(330.6130) Vision, color, and visual optics : Spatial resolution

ToC Category:
Atmospheric and Oceanic Optics

Original Manuscript: January 2, 2007
Revised Manuscript: February 21, 2007
Manuscript Accepted: February 28, 2007
Published: March 19, 2007

Virtual Issues
Vol. 2, Iss. 4 Virtual Journal for Biomedical Optics

Weilin Hou, Zhongping Lee, and Alan D. Weidemann, "Why does the Secchi disk disappear? An imaging perspective," Opt. Express 15, 2791-2802 (2007)

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