The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform

Shaoling Shang - One of the best experts on this subject based on the ideXlab platform.

  • Contrast of Visibility in Water and Air
    2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO Europe-EQEC), 2019
    Co-Authors: Shaoling Shang
    Abstract:

    Visibility, a property measured based on human vision, is a common and widely used measurement to represent the quality of air and water. To visibility, theories have been developed in the past century for measurements in both air and water. This includes the century-old Koschmieder model for visibility in air and the Duntley-Preisendorfer model for visibility (Secchi Disk depth) in water, as well as recent model by Lee et al. Here we present a general relationship for the Law of Contrast Reduction based on radiative transfer, which is the key to deduce visibility in both media. And from this general relationship, it suggests the Koschmieder model is applicable only to situations when a common-size object can be viewed 10's of kilometers away, while the Duntley-Preisendorfer model is not applicable for a common size Secchi Disk when viewed in water. We further highlight the difference in "visibility" between "simple detection" and "clear recognition", a key difference of "visibility" in air and water.

  • deriving inherent optical properties from classical water color measurements forel ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is <11% between FZ2ab-derived a and known a, and <28% between FZ2ab-derived bb and known bb. Further, for a data set from field measurements, the difference is < 30% between FZ2ab-derived a and measured a. These results indicate that FZ2ab can bridge the gap between historical measurements and the focus of IOP measurements in modern marine optics, and potentially extend our knowledge on the bio-optical properties of global seas to the past century through the historical measurements of FUI and ZSD.

  • Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is

  • enhance field water color measurements with a Secchi Disk and its implication for fusion of active and passive ocean color remote sensing
    Applied Optics, 2018
    Co-Authors: Shaoling Shang, Keping Du, Xiaolong Li
    Abstract:

    Inversion of the total absorption (a) and backscattering coefficients of bulk water through a fusion of remote sensing reflectance (R-rs) and Secchi Disk depth (Z(SD)) is developed. An application of such a system to a synthesized wide-range dataset shows a reduction of similar to 3 folds in the uncertainties of inverted a(lambda)(in a range of similar to 0.01-6.8 m(-1)) from R-rs (lambda) for the 350-560 nm range. Such a fusion is further proposed to process concurrent active (ocean LiDAR) and passive (ocean-color) measurements, which can lead to nearly "exact" analytical inversion of an R-rs spectrum. With such a fusion, it is found that the uncertainty in the inverted total a in the 350-560 nm range could be reduced to 2% for the synthesized data, which can thus significantly improve the derivation of a coefficients of other varying components. Although the inclusion of Z(SD) places an extra constraint in the inversion of R-rs, no apparent improvement over the quasi-analytical algorithm (QAA) was found when the fusion of Z(SD) and R-rs was applied to a field dataset, which calls for more accurate determination of the absorption coefficients from water samples. (C) 2018 Optical Society of America

  • Secchi Disk observation with spectral selective glasses in blue and green waters
    Optics Express, 2017
    Co-Authors: Shaoling Shang, Keping Du, Kelly Luis
    Abstract:

    Radiative transfer modeling of Secchi Disk observations has historically been based on conjugated signals of eye response and radiance, where water's attenuation in the entire visible band is included in the attenuation when deciding the Secchi Disk depth in water. Aas et al. [Ocean Sci.10(2), 177 (2014)Remote Sens. Environ.169, 139 (2015)] hypothesized that it is actually the attenuation in water's transparent window that matters to the observation of a Secchi Disk in water. To test this hypothesis, observations of Secchi Disks in blue and green waters were conducted via naked eyes, blue-pass glasses, and green-pass glasses. Measurement results indicate that for blue waters, the observed Secchi depths via naked eyes match the depths obtained with blue-pass glasses and much deeper than the depths with green-pass glasses, although the green-pass glasses match the highest response of human eyes. These observations experimentally support the hypothesis that our eye-brain system uses the contrast information in the transparent window to make a judgement decision regarding sighting a Secchi Disk in water.

Alan Weidemann - One of the best experts on this subject based on the ideXlab platform.

  • Secchi Disk depth a new theory and mechanistic model for underwater visibility
    Remote Sensing of Environment, 2015
    Co-Authors: Shaoling Shang, Keping Du, Chuanmin Hu, Alan Weidemann
    Abstract:

    Abstract Secchi Disk depth ( Z SD ) is a measure of water transparency, whose interpretation has wide applications from diver visibility to studies of climate change. This transparency has been explained in the past 60 + years with the underwater visibility theory, the branch of the general visibility theory for visual ranging in water. However, through a thorough review of the physical processes involved in visual ranging in water, we show that this theory may not exactly represent the sighting of a Secchi Disk by a human eye. Further, we update the Law of Contrast Reduction, a key concept in visibility theory, and develop a new theoretical model to interpret Z SD . Unlike the classical model that relies strongly on the beam attenuation coefficient, the new model relies only on the diffuse attenuation coefficient at a wavelength corresponding to the maximum transparency for such interpretations. This model is subsequently validated using a large (N = 338) dataset of independent measurements covering oceanic, coastal, and lake waters, with results showing excellent agreement (~ 18% average absolute difference, R 2  = 0.96) between measured and theoretically predicted Z SD ranging from  30 m without regional tuning of any model parameters. This study provides a more generalized view of visual ranging, and the mechanistic model is expected to significantly improve the current capacity in monitoring water transparency of the global aquatic environments via satellite remote sensing.

  • why does the Secchi Disk disappear an imaging perspective
    Optics Express, 2007
    Co-Authors: Alan Weidemann
    Abstract:

    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.

Shenglei Wang - One of the best experts on this subject based on the ideXlab platform.

  • Secchi Disk Depth Estimation from China’s New Generation of GF-5 Hyperspectral Observations Using a Semi-Analytical Scheme
    Remote Sensing, 2020
    Co-Authors: Chenchao Xiao, Junsheng Li, Fangfang Zhang, Shenglei Wang
    Abstract:

    Water clarity, commonly measured as the Secchi Disk depth ( Z s d ), is an important parameter that depicts water quality in aquatic ecosystems. China’s new generation Advanced HyperSpectral Imager (AHSI) on board the GF-5 satellite has significant potential for applications of more accurate water clarity estimation compared with existing multispectral satellite imagery, considering its high spectral resolution with a 30-m spatial resolution. In this study, we validate the semi-analytical model with various Quasi-Analytical Algorithms (QAA), including Q A A V 5 , Q A A V 6 , Q A A L 09 and Q A A M 14 , for the AHSI images with concurrent in situ measurements in four inland water bodies with a Z s d range of 0.3–4.5 m. The semi-analytical method with Q A A V 5 can yield the most accurate Z s d predictions with approximated atmospheric-corrected remote sensing reflectance. For 84 concurrent sampling sites, the estimated Z s d had a mean absolute error (MAE) of 0.35 m, while the mean relative error (MRE) was 25.3%. Specifically, the MAEs of estimated Z s d were 0.22, 0.46, and 0.24 m for Z s d of 0.3–1, 1–3, and 3–4.5 m, respectively. The corresponding MREs were 33.1%, 29.1% and 6.3%, respectively. Although further validation is still required, especially in terms of highly turbid waters, this study indicates that AHSI is effective for water clarity monitoring.

  • Secchi Disk depth estimation from china s new generation of gf 5 hyperspectral observations using a semi analytical scheme
    Remote Sensing, 2020
    Co-Authors: Chenchao Xiao, Junsheng Li, Fangfang Zhang, Shenglei Wang
    Abstract:

    Water clarity, commonly measured as the Secchi Disk depth ( Z s d ), is an important parameter that depicts water quality in aquatic ecosystems. China’s new generation Advanced HyperSpectral Imager (AHSI) on board the GF-5 satellite has significant potential for applications of more accurate water clarity estimation compared with existing multispectral satellite imagery, considering its high spectral resolution with a 30-m spatial resolution. In this study, we validate the semi-analytical model with various Quasi-Analytical Algorithms (QAA), including Q A A V 5 , Q A A V 6 , Q A A L 09 and Q A A M 14 , for the AHSI images with concurrent in situ measurements in four inland water bodies with a Z s d range of 0.3–4.5 m. The semi-analytical method with Q A A V 5 can yield the most accurate Z s d predictions with approximated atmospheric-corrected remote sensing reflectance. For 84 concurrent sampling sites, the estimated Z s d had a mean absolute error (MAE) of 0.35 m, while the mean relative error (MRE) was 25.3%. Specifically, the MAEs of estimated Z s d were 0.22, 0.46, and 0.24 m for Z s d of 0.3–1, 1–3, and 3–4.5 m, respectively. The corresponding MREs were 33.1%, 29.1% and 6.3%, respectively. Although further validation is still required, especially in terms of highly turbid waters, this study indicates that AHSI is effective for water clarity monitoring.

  • deriving inherent optical properties from classical water color measurements forel ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is <11% between FZ2ab-derived a and known a, and <28% between FZ2ab-derived bb and known bb. Further, for a data set from field measurements, the difference is < 30% between FZ2ab-derived a and measured a. These results indicate that FZ2ab can bridge the gap between historical measurements and the focus of IOP measurements in modern marine optics, and potentially extend our knowledge on the bio-optical properties of global seas to the past century through the historical measurements of FUI and ZSD.

  • Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is

Bing Zhang - One of the best experts on this subject based on the ideXlab platform.

  • deriving inherent optical properties from classical water color measurements forel ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is <11% between FZ2ab-derived a and known a, and <28% between FZ2ab-derived bb and known bb. Further, for a data set from field measurements, the difference is < 30% between FZ2ab-derived a and measured a. These results indicate that FZ2ab can bridge the gap between historical measurements and the focus of IOP measurements in modern marine optics, and potentially extend our knowledge on the bio-optical properties of global seas to the past century through the historical measurements of FUI and ZSD.

  • Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is

Junsheng Li - One of the best experts on this subject based on the ideXlab platform.

  • Secchi Disk Depth Estimation from China’s New Generation of GF-5 Hyperspectral Observations Using a Semi-Analytical Scheme
    Remote Sensing, 2020
    Co-Authors: Chenchao Xiao, Junsheng Li, Fangfang Zhang, Shenglei Wang
    Abstract:

    Water clarity, commonly measured as the Secchi Disk depth ( Z s d ), is an important parameter that depicts water quality in aquatic ecosystems. China’s new generation Advanced HyperSpectral Imager (AHSI) on board the GF-5 satellite has significant potential for applications of more accurate water clarity estimation compared with existing multispectral satellite imagery, considering its high spectral resolution with a 30-m spatial resolution. In this study, we validate the semi-analytical model with various Quasi-Analytical Algorithms (QAA), including Q A A V 5 , Q A A V 6 , Q A A L 09 and Q A A M 14 , for the AHSI images with concurrent in situ measurements in four inland water bodies with a Z s d range of 0.3–4.5 m. The semi-analytical method with Q A A V 5 can yield the most accurate Z s d predictions with approximated atmospheric-corrected remote sensing reflectance. For 84 concurrent sampling sites, the estimated Z s d had a mean absolute error (MAE) of 0.35 m, while the mean relative error (MRE) was 25.3%. Specifically, the MAEs of estimated Z s d were 0.22, 0.46, and 0.24 m for Z s d of 0.3–1, 1–3, and 3–4.5 m, respectively. The corresponding MREs were 33.1%, 29.1% and 6.3%, respectively. Although further validation is still required, especially in terms of highly turbid waters, this study indicates that AHSI is effective for water clarity monitoring.

  • Secchi Disk depth estimation from china s new generation of gf 5 hyperspectral observations using a semi analytical scheme
    Remote Sensing, 2020
    Co-Authors: Chenchao Xiao, Junsheng Li, Fangfang Zhang, Shenglei Wang
    Abstract:

    Water clarity, commonly measured as the Secchi Disk depth ( Z s d ), is an important parameter that depicts water quality in aquatic ecosystems. China’s new generation Advanced HyperSpectral Imager (AHSI) on board the GF-5 satellite has significant potential for applications of more accurate water clarity estimation compared with existing multispectral satellite imagery, considering its high spectral resolution with a 30-m spatial resolution. In this study, we validate the semi-analytical model with various Quasi-Analytical Algorithms (QAA), including Q A A V 5 , Q A A V 6 , Q A A L 09 and Q A A M 14 , for the AHSI images with concurrent in situ measurements in four inland water bodies with a Z s d range of 0.3–4.5 m. The semi-analytical method with Q A A V 5 can yield the most accurate Z s d predictions with approximated atmospheric-corrected remote sensing reflectance. For 84 concurrent sampling sites, the estimated Z s d had a mean absolute error (MAE) of 0.35 m, while the mean relative error (MRE) was 25.3%. Specifically, the MAEs of estimated Z s d were 0.22, 0.46, and 0.24 m for Z s d of 0.3–1, 1–3, and 3–4.5 m, respectively. The corresponding MREs were 33.1%, 29.1% and 6.3%, respectively. Although further validation is still required, especially in terms of highly turbid waters, this study indicates that AHSI is effective for water clarity monitoring.

  • deriving inherent optical properties from classical water color measurements forel ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is <11% between FZ2ab-derived a and known a, and <28% between FZ2ab-derived bb and known bb. Further, for a data set from field measurements, the difference is < 30% between FZ2ab-derived a and measured a. These results indicate that FZ2ab can bridge the gap between historical measurements and the focus of IOP measurements in modern marine optics, and potentially extend our knowledge on the bio-optical properties of global seas to the past century through the historical measurements of FUI and ZSD.

  • Deriving inherent optical properties from classical water color measurements: Forel-Ule index and Secchi Disk depth
    Optics Express, 2019
    Co-Authors: Shenglei Wang, Shaoling Shang, Junsheng Li, Bing Zhang
    Abstract:

    Secchi Disk depth (ZSD) and Forel-Ule index (FUI) are the two oldest and easiest measurements of water optical properties based on visual determination. With an overarching objective to obtain water inherent optical properties (IOPs) using these historical measurements, this study presents a model for associating remote-sensing reflectance (Rrs) with FUI and ZSD. Based upon this, a scheme (FZ2ab) for converting FUI and ZSD to absorption (a) and backscattering coefficients (bb) is developed and evaluated. For a data set from HydroLight simulations, the difference is