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Virtual Journal for Biomedical Optics

Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editors: Andrew Dunn and Anthony Durkin
  • Vol. 7, Iss. 8 — Aug. 2, 2012

Long Island Sound Coastal Observatory: assessment of above-water radiometric measurement uncertainties using collocated multi and hyper-spectral systems: reply to comment

Tristan Harmel, Alexander Gilerson, Soe Hlaing, Alan Weidemann, Robert Arnone, and Samir Ahmed  »View Author Affiliations


Applied Optics, Vol. 51, Issue 17, pp. 3893-3899 (2012)
http://dx.doi.org/10.1364/AO.51.003893


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Abstract

Uncertainties associated with the derivation of the exact normalized water-leaving radiance (LWN) from an above-water radiometric system were analyzed in Harmel et al. [Appl. Opt. 50, 5842 (2011)] based on collocated hyperspectral (HyperSAS) and multispectral (SeaPRISM) systems installed on the Long Island Sound Coastal Observational (LISCO) platform. Based on a 1.5 year time series of LISCO data, uncertainty contributors in the derivation of LWN were quantified in units of unbiased relative percentage differences (URPD) by applying the different steps of the respective data processing incrementally. Results showed that discrepancy between LWN data of two systems is significantly reduced when the average total sea radiance data of SeaPRISM is used in lieu of the standard one, which utilizes only the lowest total sea radiance measurements to remove the sky glint perturbations. The Zibordi comment [Appl. Opt. 51, 3888 (2012)] rejects the conclusion that attributes the sky glint removal step as the major uncertainty contributor in the SeaPRISM processing. It then states that the observed discrepancy might be due to an increased probability of sun-glint contamination in HyperSAS measurements because of its wider field of view and longer integration time. It was also underlined that observed dispersion between the atmospheric transmittance data derived from HyperSAS and SeaPRISM measurements can be attributed to probable contamination by stray light perturbation or issues with the noncosine response of the HyperSAS irradiance sensor. Finally, it was suggested to thoroughly investigate those instrumental perturbations. In this reply, impacts of nonperfect cosine response of the irradiance sensor are shown to be relatively low (<2% on average) and therefore can only partially explain the bias in atmospheric transmittance. Additional discrepancies between the HyperSAS and SeaPRISM downwelling irradiance derivation are attributed to the presence of absorbing aerosols. Intercomparisons of the total sea radiance and nonnormalized water-leaving radiance, complementary to those discussed in the LISCO paper, are analyzed, and this analysis shows that discrepancies in normalized water-leaving radiance retrievals arise from data processing and not from instrumental uncertainty. In addition, limitations in the standard data processing to meaningfully derive normalized water-leaving radiance for various appropriate viewing configurations are discussed. It is finally advocated that the issue of sky glint perturbation correction requires further analysis based on radiative transfer computations, including refined modeling of wave slope distributions.

© 2012 Optical Society of America

OCIS Codes
(010.0010) Atmospheric and oceanic optics : Atmospheric and oceanic optics
(010.1320) Atmospheric and oceanic optics : Atmospheric transmittance
(010.4450) Atmospheric and oceanic optics : Oceanic optics
(280.0280) Remote sensing and sensors : Remote sensing and sensors
(110.4234) Imaging systems : Multispectral and hyperspectral imaging

ToC Category:
Atmospheric and Oceanic Optics

History
Original Manuscript: March 6, 2012
Revised Manuscript: April 2, 2012
Manuscript Accepted: April 11, 2012
Published: June 8, 2012

Virtual Issues
Vol. 7, Iss. 8 Virtual Journal for Biomedical Optics

Citation
Tristan Harmel, Alexander Gilerson, Soe Hlaing, Alan Weidemann, Robert Arnone, and Samir Ahmed, "Long Island Sound Coastal Observatory: assessment of above-water radiometric measurement uncertainties using collocated multi and hyper-spectral systems: reply to comment," Appl. Opt. 51, 3893-3899 (2012)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=ao-51-17-3893

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