The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Hans G Lemij - One of the best experts on this subject based on the ideXlab platform.
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rpe normalized rnfl Attenuation Coefficient maps derived from volumetric oct imaging for glaucoma assessment
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Koenraad A Vermeer, J Van Der Schoot, Hans G Lemij, Johannes F De BoerAbstract:PURPOSE. We present spatial retinal nerve fiber layer (RNFL) Attenuation Coefficient maps for healthy and glaucomatous eyes based on optical coherence tomography (OCT) measurements. Quantitative analyses of differences between healthy and glaucomatous eyes were performed. METHODS. Peripapillary volumetric images of 10 healthy and 8 glaucomatous eyes were acquired by a Spectralis OCT system. Per A-line, the Attenuation Coefficient of the RNFL was determined based on a method that uses the retinal pigment epithelium as a reference layer. The Attenuation Coefficient describes the Attenuation of light in tissue due to scattering and absorption. En-face maps were constructed and visually inspected. Differences between healthy and glaucomatous eyes were analyzed (Mann-Whitney U test), both globally (average values) and spatially (concentric and per segment). RESULTS. RNFL Attenuation Coefficient maps of healthy eyes showed relatively high and uniform values. For glaucomatous eyes, the Attenuation Coefficients were much lower and showed local defects. Normal and glaucomatous average RNFL Attenuation Coefficients were highly significantly different (P < 0.0001) and fully separable. The RNFL Attenuation Coefficient decreased with increasing optic nerve head distance for both groups, with highly significant differences for all distances (P < 0.001). The angular dependency showed high superio- and inferiotemporal and low nasal values, with most significant differences superio- and inferiotemporally. CONCLUSIONS. Maps of RNFL Attenuation Coefficients provide a novel way of assessing the health of the RNFL and are relatively insensitive to imaging artifacts affecting signal intensity. The highly significant difference between normal and glaucomatous eyes suggests using RNFL Attenuation Coefficient maps as a new clinical tool for diagnosing and monitoring glaucoma. Copyright 2012 The Association for Research in Vision and Ophthalmology, Inc.
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Josine Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE. To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS. We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: J Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ(att)), determined by the scattering properties of the RNFL, we used a model that normalized the reflectivity of the RNFL by the retinal pigment epithelium. The analysis was performed at four preset locations at 1.3 and 1.7 mm from the center of the optic nerve head (ONH) (i.e., temporally, superiorly, nasally, and inferiorly) and on averages per eye. To assess the structure-function relationship, we correlated the μ(att) to the mean deviation (MD) in standard automated perimetry. RESULTS The μ(att) of the RNFL decreased up to 40% with increasing disease severity, on average as well as in each location around the ONH (Jonckheere-Terpstra test, P < 0.019 in all tests). The μ(att) of the RNFL depended significantly on the location around the ONH in all eyes (Kruskal-Wallis test, P < 0.014) and was lowest nasally from the ONH. The μ(att) correlated significantly with the MD in SAP (R(2) = 0.337). CONCLUSIONS The measurements clearly demonstrated that the μ(att) of the RNFL decreased with increasing disease severity. The RNFL Attenuation Coefficient may serve as a new method to quantify glaucoma in SD-OCT images.
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quantitative rnfl Attenuation Coefficient measurements by rpe normalized oct data
Proceedings of SPIE, 2012Co-Authors: Koenraad A Vermeer, J Van Der Schoot, Hans G Lemij, J De BoerAbstract:We demonstrate significantly different scattering Coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the Attenuation Coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL Attenuation Coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL Attenuation Coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm -1 vs. 4.9mm -1 , P<0.01, Mann-Whitney test).
Johannes F De Boer - One of the best experts on this subject based on the ideXlab platform.
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analysis of Attenuation Coefficient estimation in fourier domain oct of semi infinite media
Biomedical Optics Express, 2020Co-Authors: Babak Ghafaryasl, Koenraad A Vermeer, Johannes F De Boer, Jeroen Kalkman, Tom Callewaert, Lucas J Van VlietAbstract:The Attenuation Coefficient (AC) is an optical property of tissue that can be estimated from optical coherence tomography (OCT) data. In this paper, we aim to estimate the AC accurately by compensating for the shape of the focused beam. For this, we propose a method to estimate the axial PSF model parameters and AC by fitting a model for an OCT signal in a homogenous sample to the recorded OCT signal. In addition, we employ numerical analysis to obtain the theoretical optimal precision of the estimated parameters for different experimental setups. Finally, the method is applied to OCT B-scans obtained from homogeneous samples. The numerical and experimental results show accurate estimations of the AC and the focus location when the focus is located inside the sample.
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rpe normalized rnfl Attenuation Coefficient maps derived from volumetric oct imaging for glaucoma assessment
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Koenraad A Vermeer, J Van Der Schoot, Hans G Lemij, Johannes F De BoerAbstract:PURPOSE. We present spatial retinal nerve fiber layer (RNFL) Attenuation Coefficient maps for healthy and glaucomatous eyes based on optical coherence tomography (OCT) measurements. Quantitative analyses of differences between healthy and glaucomatous eyes were performed. METHODS. Peripapillary volumetric images of 10 healthy and 8 glaucomatous eyes were acquired by a Spectralis OCT system. Per A-line, the Attenuation Coefficient of the RNFL was determined based on a method that uses the retinal pigment epithelium as a reference layer. The Attenuation Coefficient describes the Attenuation of light in tissue due to scattering and absorption. En-face maps were constructed and visually inspected. Differences between healthy and glaucomatous eyes were analyzed (Mann-Whitney U test), both globally (average values) and spatially (concentric and per segment). RESULTS. RNFL Attenuation Coefficient maps of healthy eyes showed relatively high and uniform values. For glaucomatous eyes, the Attenuation Coefficients were much lower and showed local defects. Normal and glaucomatous average RNFL Attenuation Coefficients were highly significantly different (P < 0.0001) and fully separable. The RNFL Attenuation Coefficient decreased with increasing optic nerve head distance for both groups, with highly significant differences for all distances (P < 0.001). The angular dependency showed high superio- and inferiotemporal and low nasal values, with most significant differences superio- and inferiotemporally. CONCLUSIONS. Maps of RNFL Attenuation Coefficients provide a novel way of assessing the health of the RNFL and are relatively insensitive to imaging artifacts affecting signal intensity. The highly significant difference between normal and glaucomatous eyes suggests using RNFL Attenuation Coefficient maps as a new clinical tool for diagnosing and monitoring glaucoma. Copyright 2012 The Association for Research in Vision and Ophthalmology, Inc.
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Josine Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE. To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS. We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: J Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ(att)), determined by the scattering properties of the RNFL, we used a model that normalized the reflectivity of the RNFL by the retinal pigment epithelium. The analysis was performed at four preset locations at 1.3 and 1.7 mm from the center of the optic nerve head (ONH) (i.e., temporally, superiorly, nasally, and inferiorly) and on averages per eye. To assess the structure-function relationship, we correlated the μ(att) to the mean deviation (MD) in standard automated perimetry. RESULTS The μ(att) of the RNFL decreased up to 40% with increasing disease severity, on average as well as in each location around the ONH (Jonckheere-Terpstra test, P < 0.019 in all tests). The μ(att) of the RNFL depended significantly on the location around the ONH in all eyes (Kruskal-Wallis test, P < 0.014) and was lowest nasally from the ONH. The μ(att) correlated significantly with the MD in SAP (R(2) = 0.337). CONCLUSIONS The measurements clearly demonstrated that the μ(att) of the RNFL decreased with increasing disease severity. The RNFL Attenuation Coefficient may serve as a new method to quantify glaucoma in SD-OCT images.
M.e. Casey - One of the best experts on this subject based on the ideXlab platform.
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Simultaneous reconstruction of emission activity and Attenuation Coefficient distribution from TOF data, acquired with external transmission source
Physics in Medicine and Biology, 2013Co-Authors: Vladimir Y. Panin, Mehmet Aykac, M.e. CaseyAbstract:The simultaneous PET data reconstruction of emission activity and Attenuation Coefficient distribution is presented, where the Attenuation image is constrained by exploiting an external transmission source. Data are acquired in time-of-flight (TOF) mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object Attenuation Coefficient values. The algorithm alternates between Attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of Attenuation map values. The reconstruction of experimental data from the Siemens mCT scanner suggests that simultaneous reconstruction improves Attenuation map image quality, as compared to when data are separated. In the presented example, the Attenuation map image noise was reduced and non-uniformity artifacts that occurred due to scatter estimation were suppressed. On the other hand, the use of transmission data stabilizes Attenuation Coefficient distribution reconstruction from TOF emission data alone. The example of improving emission images by refining a CT-based patient Attenuation map is presented, revealing potential benefits of simultaneous CT and PET data reconstruction.
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simultaneous reconstruction of emission activity and Attenuation Coefficient distribution from tof data acquired with rotating external line source
IEEE Nuclear Science Symposium, 2011Co-Authors: Vladimir Y. Panin, Mehmet Aykac, M.e. CaseyAbstract:The simultaneous PET data reconstruction of emission activity and Attenuation Coefficient distribution is under investigation, where the Attenuation image is constrained by exploiting an external transmission source. Data are acquired in TOF mode, allowing in principle for separation of emission and transmission data. Nevertheless, here all data are reconstructed at once, eliminating the need to trace the position of the transmission source in sinogram space. Contamination of emission data by the transmission source and vice versa is naturally modeled. Attenuated emission activity data also provide additional information about object Attenuation Coefficient values. The algorithm alternates between Attenuation and emission activity image updates. We also proposed a method of estimation of spatial scatter distribution from the transmission source by incorporating knowledge about the expected range of Attenuation map values. The reconstruction of experimental data from the mCT scanner suggests that simultaneous reconstruction improves Attenuation map image quality, as compared to when data are separated. On the other hand, the use of transmission data stabilizes Attenuation Coefficient distribution reconstruction from TOF emission data alone.
Koenraad A Vermeer - One of the best experts on this subject based on the ideXlab platform.
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analysis of Attenuation Coefficient estimation in fourier domain oct of semi infinite media
Biomedical Optics Express, 2020Co-Authors: Babak Ghafaryasl, Koenraad A Vermeer, Johannes F De Boer, Jeroen Kalkman, Tom Callewaert, Lucas J Van VlietAbstract:The Attenuation Coefficient (AC) is an optical property of tissue that can be estimated from optical coherence tomography (OCT) data. In this paper, we aim to estimate the AC accurately by compensating for the shape of the focused beam. For this, we propose a method to estimate the axial PSF model parameters and AC by fitting a model for an OCT signal in a homogenous sample to the recorded OCT signal. In addition, we employ numerical analysis to obtain the theoretical optimal precision of the estimated parameters for different experimental setups. Finally, the method is applied to OCT B-scans obtained from homogeneous samples. The numerical and experimental results show accurate estimations of the AC and the focus location when the focus is located inside the sample.
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rpe normalized rnfl Attenuation Coefficient maps derived from volumetric oct imaging for glaucoma assessment
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Koenraad A Vermeer, J Van Der Schoot, Hans G Lemij, Johannes F De BoerAbstract:PURPOSE. We present spatial retinal nerve fiber layer (RNFL) Attenuation Coefficient maps for healthy and glaucomatous eyes based on optical coherence tomography (OCT) measurements. Quantitative analyses of differences between healthy and glaucomatous eyes were performed. METHODS. Peripapillary volumetric images of 10 healthy and 8 glaucomatous eyes were acquired by a Spectralis OCT system. Per A-line, the Attenuation Coefficient of the RNFL was determined based on a method that uses the retinal pigment epithelium as a reference layer. The Attenuation Coefficient describes the Attenuation of light in tissue due to scattering and absorption. En-face maps were constructed and visually inspected. Differences between healthy and glaucomatous eyes were analyzed (Mann-Whitney U test), both globally (average values) and spatially (concentric and per segment). RESULTS. RNFL Attenuation Coefficient maps of healthy eyes showed relatively high and uniform values. For glaucomatous eyes, the Attenuation Coefficients were much lower and showed local defects. Normal and glaucomatous average RNFL Attenuation Coefficients were highly significantly different (P < 0.0001) and fully separable. The RNFL Attenuation Coefficient decreased with increasing optic nerve head distance for both groups, with highly significant differences for all distances (P < 0.001). The angular dependency showed high superio- and inferiotemporal and low nasal values, with most significant differences superio- and inferiotemporally. CONCLUSIONS. Maps of RNFL Attenuation Coefficients provide a novel way of assessing the health of the RNFL and are relatively insensitive to imaging artifacts affecting signal intensity. The highly significant difference between normal and glaucomatous eyes suggests using RNFL Attenuation Coefficient maps as a new clinical tool for diagnosing and monitoring glaucoma. Copyright 2012 The Association for Research in Vision and Ophthalmology, Inc.
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: Josine Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE. To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS. We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ
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the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer in spectral domain optical coherence tomography images
Investigative Ophthalmology & Visual Science, 2012Co-Authors: J Van Der Schoot, Koenraad A Vermeer, Johannes F De Boer, Hans G LemijAbstract:PURPOSE To demonstrate the effect of glaucoma on the optical Attenuation Coefficient of the retinal nerve fiber layer (RNFL) in Spectral Domain Optical Coherence Tomography (SD-OCT) images. METHODS We analyzed images of the peripapillary areas in 10 healthy and 30 glaucomatous eyes (mild, moderate, and advanced glaucoma, 10 eyes each), scanned with the Spectralis OCT (Heidelberg Engineering GmbH, Dossenheim, Germany). To calculate the RNFL Attenuation Coefficient (μ(att)), determined by the scattering properties of the RNFL, we used a model that normalized the reflectivity of the RNFL by the retinal pigment epithelium. The analysis was performed at four preset locations at 1.3 and 1.7 mm from the center of the optic nerve head (ONH) (i.e., temporally, superiorly, nasally, and inferiorly) and on averages per eye. To assess the structure-function relationship, we correlated the μ(att) to the mean deviation (MD) in standard automated perimetry. RESULTS The μ(att) of the RNFL decreased up to 40% with increasing disease severity, on average as well as in each location around the ONH (Jonckheere-Terpstra test, P < 0.019 in all tests). The μ(att) of the RNFL depended significantly on the location around the ONH in all eyes (Kruskal-Wallis test, P < 0.014) and was lowest nasally from the ONH. The μ(att) correlated significantly with the MD in SAP (R(2) = 0.337). CONCLUSIONS The measurements clearly demonstrated that the μ(att) of the RNFL decreased with increasing disease severity. The RNFL Attenuation Coefficient may serve as a new method to quantify glaucoma in SD-OCT images.
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quantitative rnfl Attenuation Coefficient measurements by rpe normalized oct data
Proceedings of SPIE, 2012Co-Authors: Koenraad A Vermeer, J Van Der Schoot, Hans G Lemij, J De BoerAbstract:We demonstrate significantly different scattering Coefficients of the retinal nerve fiber layer (RNFL) between normal and glaucoma subjects. In clinical care, SD-OCT is routinely used to assess the RNFL thickness for glaucoma management. In this way, the full OCT data set is conveniently reduced to an easy to interpret output, matching results from older (non- OCT) instruments. However, OCT provides more data, such as the signal strength itself, which is due to backscattering in the retinal layers. For quantitative analysis, this signal should be normalized to adjust for local differences in the intensity of the beam that reaches the retina. In this paper, we introduce a model that relates the OCT signal to the Attenuation Coefficient of the tissue. The average RNFL signal (within an A-line) was then normalized based on the observed RPE signal, resulting in normalized RNFL Attenuation Coefficient maps. These maps showed local defects matching those found in thickness data. The average (normalized) RNFL Attenuation Coefficient of a fixed band around the optic nerve head was significantly lower in glaucomatous eyes than in normal eyes (3.0mm -1 vs. 4.9mm -1 , P<0.01, Mann-Whitney test).
Mingzhu Wang - One of the best experts on this subject based on the ideXlab platform.
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characteristics of diffuse Attenuation Coefficient of underwater irradiance in the lakes in the middle and lower reaches of yangtze river
Environmental Sciences, 2013Co-Authors: Zhiqiang Shi, Yunlin Zhang, Mingzhu Wang, Xiaohan LiuAbstract:Based on the underwater irradiance profile measurement and water samples collection in September, October 2007 in Lake Donghu, Lake Liangzi and Lake Honghu, and in April in 2010 in Lake Kuileihu, the diffuse Attenuation Coefficient and the dominant Attenuation factors were analyzed. The ranges of diffuse Attenuation Coefficient and total suspended solid (TSS), organic suspended solid (OSS), inorganic suspended solid (ISS), chlorophyll a (Chla), and dissolved organic carbon (DOC) concentration varied less in Lake Donghu and Lake Kuileihu than in Lake liangzi and Lake Honghu. The regression analysis showed that ISS was the dominant affecting factor of transparency in Lake Donghu and Lake Kuileihu, but ISS and OSS jointly controlled the transparency in Lake Liangzi and Lake Honghu. The diffuse Attenuation Coefficient minimum occurred near 580 nm. At around 675 nm, the diffuse Attenuation Coefficient peak was due to phytoplankton absorption, especially at sites with high pigment concentration. The euphotic depth was less than the mean water depth in Lake Donghu, suggesting that the submerged aquatic vegetation (SAV) can not grow in the present underwater light climate. However, the euphotic depth was larger than the mean water depth in other three lakes showing that the underwater light climate can meet the light requirements for the growth of SAV. The regression analysis showed that ISS was the dominant affecting factor of PAR Attenuation in Lake Donghu and Lake Kuileihu, but ISS, OSS and Chla jointly controlled PAR Attenuation in lake Liangzi and lake Honghu. The significant correlation between the beam attenuatin Coefficient at 750 nm and PAR difffuse Attenuation Coefficient showed that the particles scattering significantly contributed to underwater irradiance Attenuation.
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a simple optical model to estimate diffuse Attenuation Coefficient of photosynthetically active radiation in an extremely turbid lake from surface reflectance
Optics Express, 2012Co-Authors: Yunlin Zhang, Mingzhu WangAbstract:Accurate estimation of the diffuse Attenuation Coefficient is critical for our understanding and modelling of key physical, chemical, and biological processes in water bodies. For extremely turbid, shallow, Lake Taihu in China, we synchronously monitored the diffuse Attenuation Coefficient of photosynthetically active radiation (Kd(PAR)) and the remote sensing reflectance at 134 sites. Kd(PAR)) varied greatly among different sites from 1.62 to 14.68 m−1 with a mean value of 5.62 ± 2.99 m−1. A simple optical model from near-infrared remote sensing reflectance of MODIS channels 2 (859 nm) and 15 (748 nm) was calibrated, and validated, to estimate Kd(PAR). With the simple optical model, the root mean square error and mean relative error were 0.95 m−1 and 17.0% respectively at 748 nm, and 0.98 m−1 and 17.6% at 859 nm, based on an independent validation data set. Our results showed a good precision of estimation for Kd(PAR) using the new simple optical model, contrasting with the poor estimations derived from existing empirical and semi-analytical models developed in clear, open ocean waters or slightly turbid coastal waters. Although at 748 nm the model had slightly higher precision than at 859 nm, the spatial resolution at 859 nm was four times that at 748 nm. Therefore, we propose a new model based on the MODIS-derived normalized water-leaving radiances at a wavelength of 859 nm, for accurate retrieval of Kd(PAR) in extremely turbid, shallow lakes with Kd(PAR) larger than 1.5 m−1.
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predicting the light Attenuation Coefficient through secchi disk depth and beam Attenuation Coefficient in a large shallow freshwater lake
Hydrobiologia, 2012Co-Authors: Yunlin Zhang, Mingzhu WangAbstract:The diffuse Attenuation Coefficient of photosynthetically active radiation (PAR) (400–700 nm) (Kd(PAR)) is one of the most important optical properties of water. Our purpose was to create Kd(PAR) prediction models from the Secchi disk depth (SDD) and beam Attenuation Coefficient of particulate and dissolved organic matter (Ct−w(PAR), excluding pure water) in the PAR range. We compare their performance and prediction precision by using the determination Coefficient (r2), relative root mean square error (RRMSE), and mean relative error (MRE). Our dataset comprised 1,067 measurements, including Kd(PAR), SDD, and Ct−w(PAR) taken in shallow, eutrophic, Lake Taihu, China, from 2005 to 2010. The prediction models of Kd(PAR) were based on the linear model with an intercept of zero, using the inverse SDD, and the nonlinear model using SDD. The linear model generated a slope of 1.369, which was not significantly different from 1.7, the index used worldwide, but significantly lower than the value of 2.26. The nonlinear model gave a slightly more reliable prediction of Kd(PAR) with a r2 of 0.804. Compared to the SDD, Ct−w(PAR) was more significantly correlated to Kd(PAR) based on the linear model, with a significantly higher r2 and lower RMSE and RE. Considering the measurement simplicity of Ct−w(PAR) and data acquisition feasibility from high-frequency autonomous buoys and satellites, our results demonstrated that this prediction model reliably estimates Kd(PAR), and could be used to significantly expand optical observations in an environment where the conditions for underwater PAR measurement are limited.
