Polarized light field under dynamic ocean surfaces: Numerical modeling compared with measurements

You, Yu; Kattawar, George W.; Voss, Kenneth J.; Bhandari, Purushottam; Wei, Jianwei; Lewis, Marlon R.; Zappa, Christopher J.; Schultz, Howard

doi:10.1029/2011jc007278

Cited by 26 publications

(19 citation statements)

References 39 publications

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“…At the same time, it can also be argued that this possible excessive sky-glint perturbation or residual sun-glint contribution might not be properly removed from HyperSAS data in the L T to L T transformation procedure due to the HyperSAS instrument's relatively longer integration time. In conclusion, further analysis of the correction for surface-reflected light are recommended and should be achieved based on full radiative transfer computations, including accurate modeling of the capillary waves dynamic [16,[18][19][20], which play an important role on light reflection when dealing with small field of view and short time integration [21].…”

Section: Commentarymentioning

confidence: 99%

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

et al. 2012

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Uncertainties associated with the derivation of the exact normalized water-leaving radiance (L WN ) 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 L WN 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 L WN 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.

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Section: Commentarymentioning

confidence: 99%

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

et al. 2012

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“…Hence in areas of rapid change (the edge of the Snell's circle), this can lead to more noise/error in the polarization calculation. Furthermore, the edge of the Snell's cone can move along with the motion of the surface waves (see video associated with You et al [2011]). Because of these reasons, we can see two small peaks in the derived DoLP near the Snell's boundary (Figure 5a).…”

Section: Sbc Experimentsmentioning

confidence: 99%

The variation of the polarized downwelling radiance distribution with depth in the coastal and clear ocean

et al. 2011

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[1] The spectral polarized radiance distribution provides the most complete description of the light field that can be measured. However, this is a very difficult parameter to measure, particularly near the surface, because of its large dynamic range, changes in the skylight illumination, and waves at the air-sea interface. To measure the Stokes vector of the downwelling light field, which contains the polarization information, requires the combination of four images acquired simultaneously. To achieve this, we used the downwelling polarized radiance distribution camera system (DPOL) during the Radiance in a Dynamic Ocean (RaDyO) program Santa Barbara Channel and Hawaiian experiments. DPOL consists of four fisheye lenses and a spectral filter changer that allow us to capture the downwelling hemisphere of the polarized radiance distribution at seven wavelengths. Our measurements show that very near the surface, for clear sky conditions, the dominant source of polarization is the refracted sky light. As one progresses in the water column the polarization due to light scattering by the water increases and polarization due to light scattering in the water becomes dominant.Citation: Bhandari, P., K. J. Voss, L. Logan, and M. Twardowski (2011), The variation of the polarized downwelling radiance distribution with depth in the coastal and clear ocean,

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“…One explanation for the deviations is that we partly consider extreme sea events with significant wave heights up to 7 m. However, there are clear differences at high wind speeds (> 10 m s −1 ) that raise the question on the validity of our approach with linear wave theory and the disregard of nonlinearities. Just recently, there have been two studies on polarized underwater light fields by You et al (2011) andXu et al (2011), where three-dimensional wave elevations were derived from highresolution wave slope measurements and from a numerical "high-order spectral method", respectively. Both realizations of the sea surface sound promising and could be applied in future studies.…”

Section: Discussion Of the Applied Methodsmentioning

confidence: 99%

On the influence of wind and waves on underwater irradiance fluctuations

Hieronymi

Macke

2012

Ocean Sci.

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Abstract. The influence of various wind and wave conditions on the variability of downwelling irradiance E d (490 nm) in water is subject of this study. The work is based on a two-dimensional Monte Carlo radiative transfer model with high spatial resolution. The model assumes conditions that are ideal for wave focusing, thus simulation results reveal the upper limit for light fluctuations. Local wind primarily determines the steepness of capillary-gravity waves which in turn dominate the irradiance variability near the surface. Down to 3 m depth, maximum irradiance peaks that exceed the mean irradiance E d by a factor of more than 7 can be observed at low wind speeds up to 5 m s −1 . The strength of irradiance fluctuations can be even amplified under the influence of higher ultra-gravity waves; thereby peaks can exceed 11 E d . Sea states influence the light field much deeper; gravity waves can cause considerable irradiance variability even at 100 m depth. The simulation results show that under realistic conditions 50 % radiative enhancements compared to the mean can still occur at 30 m depth. At greater depths, the underwater light variability depends on the wave steepness of the characteristic wave of a sea state; steeper waves cause stronger light fluctuations.

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Polarized light field under dynamic ocean surfaces: Numerical modeling compared with measurements

Cited by 26 publications

References 39 publications

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

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

The variation of the polarized downwelling radiance distribution with depth in the coastal and clear ocean

On the influence of wind and waves on underwater irradiance fluctuations

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