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Jeanlouis Roujean - One of the best experts on this subject based on the ideXlab platform.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:In this paper, we present an Operational Procedure for the inversion of kernel-driven bi-directional reflectance distribution function (BRDF) model and further albedo retrieval to be applicable to the SEVIRI/MSG reflectance measurements. Our approach aims at bringing solutions to an ill-posed problem that is when the ratio of extreme eigenvalues of the inverse matrix is of several orders of magnitude due to sparse and irregular angular samplings. The geometric Li-Sparse reciprocal and Roujean kernels are considered in the Procedure applied to space-borne Polarization and Directionality of Earth Reflectance (POLDER) sensor data which decomposes as follows: (1) quality control, (2) accumulation of a priori information on model coefficients of directional hemispherical reflectance, and (3) implementation of BRDF model inversion methods based on the biased estimation instead of usual nonbiased least solution due to its large variance. The first two steps are detailed in this paper; the third one appears in a companion paper. The data control Procedure consists both in filtering inputs of reflectance data and output of model coefficients. In the first stage, the analysis criteria rely on Fisher statistics. In the second stage, a Procedure is applied to red and near-infrared POLDER data corresponding to the 16 classes of International Geosphere Biosphere Program (IGBP) land cover classification. Among the retained criteria, some are based on the BRDF shape. They encompass (1) T-statistics, (2) the bowl shape index (BSI), (3) the dome shape index (DSI), (4) the white sky albedo (WSA, bi-hemispherical reflectance), and (5) the black sky albedo variance (BSA, directional–hemispherical reflectance). Statistical results include mean values and covariance matrix for the spectral BRDF model coefficients. This Procedure eliminates about 10% of data measurements, thereby reducing uncertainty in retrieved BRDF model coefficients and WSA.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements ii comparison of several inversion techniques and uncertainty in albedo estimates
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:Abstract This paper develops a concept related to the significant information extracted from the bidirectional reflectance distribution function (BRDF) of the terrestrial targets. The main issues are: the choice of the BRDF model, the solution to the inverse problem, and the accuracy assessment of estimated albedo. The present concept is based on the fact that the exact solution to the inverse problem belongs to a statistically significant region centered on the least squares solution (LSS). Nonetheless, LSS may be useless if the matrix inversion yields an ill-posed problem. It is then recommended to seek an alternative solution, which will yield a similar confidence interval but will be more physically sound. A list of 15 kernels entering in a basic model is examined by means of factor analysis performed in vector space, which is spanned at all known kernels. The application is carried out with synthetic angular data generated for the SEVIRI/MSG observing system. Models are evaluated based on statistical results—minimum of squared sum of residuals (SSR) and maximum of explained variance—after adjustment on reflectance data corresponding to a wide set of land cover types. Since the matrix of the model is almost singular, we identified an optimal subset model consisting of eight kernels, which has higher conditioned index and falls within the 95% confidence interval. It was found that the reflectance predicted by multi-kernel model is consistent with measurements. The idea in opting for a multi-kernel approach comes from the necessity to perform a higher angular resolution for the BRDF retrieval. Inversion experiments confirmed an advantage of the composite model over conventional three-parameter models in accuracy assessment of reflectance and albedo in the case of uniform and restricted angular samplings. Three methods are considered: statistical inversion (provided by the LSS), ridge regression and statistical regularization. The two latter are advised to solve the ill-conditioned inverse problem. Statistical regularization uses a priori statistical information. The inversion numerical experiment with SEVIRI/MSG angular geometry shows that only ridge regression provides a reasonable solution when a composite model is used. In addition, ridge regression and statistical regularization methods provide physically acceptable solutions in terms of BRDF and albedo predictability, even for three-parameter models. It is advised that LSS be implemented only at the middle of the summer season in the Northern Hemisphere. Otherwise, the use of ridge regression and statistical regularization is recommended to retrieve BRDF and albedo at other time periods in extra-tropical latitudes.
Igor Pokrovsky - One of the best experts on this subject based on the ideXlab platform.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:In this paper, we present an Operational Procedure for the inversion of kernel-driven bi-directional reflectance distribution function (BRDF) model and further albedo retrieval to be applicable to the SEVIRI/MSG reflectance measurements. Our approach aims at bringing solutions to an ill-posed problem that is when the ratio of extreme eigenvalues of the inverse matrix is of several orders of magnitude due to sparse and irregular angular samplings. The geometric Li-Sparse reciprocal and Roujean kernels are considered in the Procedure applied to space-borne Polarization and Directionality of Earth Reflectance (POLDER) sensor data which decomposes as follows: (1) quality control, (2) accumulation of a priori information on model coefficients of directional hemispherical reflectance, and (3) implementation of BRDF model inversion methods based on the biased estimation instead of usual nonbiased least solution due to its large variance. The first two steps are detailed in this paper; the third one appears in a companion paper. The data control Procedure consists both in filtering inputs of reflectance data and output of model coefficients. In the first stage, the analysis criteria rely on Fisher statistics. In the second stage, a Procedure is applied to red and near-infrared POLDER data corresponding to the 16 classes of International Geosphere Biosphere Program (IGBP) land cover classification. Among the retained criteria, some are based on the BRDF shape. They encompass (1) T-statistics, (2) the bowl shape index (BSI), (3) the dome shape index (DSI), (4) the white sky albedo (WSA, bi-hemispherical reflectance), and (5) the black sky albedo variance (BSA, directional–hemispherical reflectance). Statistical results include mean values and covariance matrix for the spectral BRDF model coefficients. This Procedure eliminates about 10% of data measurements, thereby reducing uncertainty in retrieved BRDF model coefficients and WSA.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements ii comparison of several inversion techniques and uncertainty in albedo estimates
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:Abstract This paper develops a concept related to the significant information extracted from the bidirectional reflectance distribution function (BRDF) of the terrestrial targets. The main issues are: the choice of the BRDF model, the solution to the inverse problem, and the accuracy assessment of estimated albedo. The present concept is based on the fact that the exact solution to the inverse problem belongs to a statistically significant region centered on the least squares solution (LSS). Nonetheless, LSS may be useless if the matrix inversion yields an ill-posed problem. It is then recommended to seek an alternative solution, which will yield a similar confidence interval but will be more physically sound. A list of 15 kernels entering in a basic model is examined by means of factor analysis performed in vector space, which is spanned at all known kernels. The application is carried out with synthetic angular data generated for the SEVIRI/MSG observing system. Models are evaluated based on statistical results—minimum of squared sum of residuals (SSR) and maximum of explained variance—after adjustment on reflectance data corresponding to a wide set of land cover types. Since the matrix of the model is almost singular, we identified an optimal subset model consisting of eight kernels, which has higher conditioned index and falls within the 95% confidence interval. It was found that the reflectance predicted by multi-kernel model is consistent with measurements. The idea in opting for a multi-kernel approach comes from the necessity to perform a higher angular resolution for the BRDF retrieval. Inversion experiments confirmed an advantage of the composite model over conventional three-parameter models in accuracy assessment of reflectance and albedo in the case of uniform and restricted angular samplings. Three methods are considered: statistical inversion (provided by the LSS), ridge regression and statistical regularization. The two latter are advised to solve the ill-conditioned inverse problem. Statistical regularization uses a priori statistical information. The inversion numerical experiment with SEVIRI/MSG angular geometry shows that only ridge regression provides a reasonable solution when a composite model is used. In addition, ridge regression and statistical regularization methods provide physically acceptable solutions in terms of BRDF and albedo predictability, even for three-parameter models. It is advised that LSS be implemented only at the middle of the summer season in the Northern Hemisphere. Otherwise, the use of ridge regression and statistical regularization is recommended to retrieve BRDF and albedo at other time periods in extra-tropical latitudes.
Oleg S Pokrovsky - One of the best experts on this subject based on the ideXlab platform.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:In this paper, we present an Operational Procedure for the inversion of kernel-driven bi-directional reflectance distribution function (BRDF) model and further albedo retrieval to be applicable to the SEVIRI/MSG reflectance measurements. Our approach aims at bringing solutions to an ill-posed problem that is when the ratio of extreme eigenvalues of the inverse matrix is of several orders of magnitude due to sparse and irregular angular samplings. The geometric Li-Sparse reciprocal and Roujean kernels are considered in the Procedure applied to space-borne Polarization and Directionality of Earth Reflectance (POLDER) sensor data which decomposes as follows: (1) quality control, (2) accumulation of a priori information on model coefficients of directional hemispherical reflectance, and (3) implementation of BRDF model inversion methods based on the biased estimation instead of usual nonbiased least solution due to its large variance. The first two steps are detailed in this paper; the third one appears in a companion paper. The data control Procedure consists both in filtering inputs of reflectance data and output of model coefficients. In the first stage, the analysis criteria rely on Fisher statistics. In the second stage, a Procedure is applied to red and near-infrared POLDER data corresponding to the 16 classes of International Geosphere Biosphere Program (IGBP) land cover classification. Among the retained criteria, some are based on the BRDF shape. They encompass (1) T-statistics, (2) the bowl shape index (BSI), (3) the dome shape index (DSI), (4) the white sky albedo (WSA, bi-hemispherical reflectance), and (5) the black sky albedo variance (BSA, directional–hemispherical reflectance). Statistical results include mean values and covariance matrix for the spectral BRDF model coefficients. This Procedure eliminates about 10% of data measurements, thereby reducing uncertainty in retrieved BRDF model coefficients and WSA.
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development of an Operational Procedure to estimate surface albedo from the seviri msg observing system by using polder brdf measurements ii comparison of several inversion techniques and uncertainty in albedo estimates
2003Co-Authors: Igor Pokrovsky, Oleg S Pokrovsky, Jeanlouis RoujeanAbstract:Abstract This paper develops a concept related to the significant information extracted from the bidirectional reflectance distribution function (BRDF) of the terrestrial targets. The main issues are: the choice of the BRDF model, the solution to the inverse problem, and the accuracy assessment of estimated albedo. The present concept is based on the fact that the exact solution to the inverse problem belongs to a statistically significant region centered on the least squares solution (LSS). Nonetheless, LSS may be useless if the matrix inversion yields an ill-posed problem. It is then recommended to seek an alternative solution, which will yield a similar confidence interval but will be more physically sound. A list of 15 kernels entering in a basic model is examined by means of factor analysis performed in vector space, which is spanned at all known kernels. The application is carried out with synthetic angular data generated for the SEVIRI/MSG observing system. Models are evaluated based on statistical results—minimum of squared sum of residuals (SSR) and maximum of explained variance—after adjustment on reflectance data corresponding to a wide set of land cover types. Since the matrix of the model is almost singular, we identified an optimal subset model consisting of eight kernels, which has higher conditioned index and falls within the 95% confidence interval. It was found that the reflectance predicted by multi-kernel model is consistent with measurements. The idea in opting for a multi-kernel approach comes from the necessity to perform a higher angular resolution for the BRDF retrieval. Inversion experiments confirmed an advantage of the composite model over conventional three-parameter models in accuracy assessment of reflectance and albedo in the case of uniform and restricted angular samplings. Three methods are considered: statistical inversion (provided by the LSS), ridge regression and statistical regularization. The two latter are advised to solve the ill-conditioned inverse problem. Statistical regularization uses a priori statistical information. The inversion numerical experiment with SEVIRI/MSG angular geometry shows that only ridge regression provides a reasonable solution when a composite model is used. In addition, ridge regression and statistical regularization methods provide physically acceptable solutions in terms of BRDF and albedo predictability, even for three-parameter models. It is advised that LSS be implemented only at the middle of the summer season in the Northern Hemisphere. Otherwise, the use of ridge regression and statistical regularization is recommended to retrieve BRDF and albedo at other time periods in extra-tropical latitudes.
H E Mingyi - One of the best experts on this subject based on the ideXlab platform.
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design and application of relay protection remote control system based on smart grid dispatching and control system
2017Co-Authors: Jiangbo Ren, Fan Lei, Liqiang Sun, Fengran Chang, Shujiang Cao, Huaning Zhang, H E MingyiAbstract:With the development of smart grid dispatching and control system, the unattended substation operation mode has been widely used therefore relay protection remote control needs to be enhanced to accomplish the integration of power dispatching and control. This article is based on IEC 60870-5-104 protocol published by IEC, researched online setting area switching, relay plate switching and setting modification which embedded in new generation of smart grid dispatching and control system. By contrast with the traditional methods, this newly designed system focus on preventing incorrect operation, data rationality optimization and standardized Operational Procedure, significantly improved the reliability and accuracy of remote operation. Practices prove that the application of this system tremendously save the cost of daily maintenance, increase the working efficiency; decrease the potential safety risk which is deserved being highly popularized.
Mark R Virkler - One of the best experts on this subject based on the ideXlab platform.
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comparison of planning and Operational analysis Procedures for signalized intersections from the highway capacity manual
1996Co-Authors: Mark R Virkler, Shashi Gannavaram, Anand RamabhadranAbstract:The 1994 update of the Highway Capacity Manual (HCM) includes a planning Procedure to estimate the capacity condition of a signalized intersection (Xcm). The planning method results can also be extended to a planning application of the more data-intensive HCM Operational Procedure to estimate intersection critical flow-to-capacity ratio (Xc) and level of service with only planning-level data. Both the planning Procedure and the planning application of the Operational Procedure involve default adjustment factors and synthesized traffic signal timing (called the "default signal timing"). Data from 166 Missouri intersections were used to determine how well the planning approaches predict Operational analysis results. In general, the default signal timings had shorter cycle lengths than the timing plans used at pretimed signals. The shorter cycle lengths led to slightly higher flow-to-capacity ratios, since a higher proportion of each cycle was devoted to lost time. The default signal timings also had more eq...
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potential accuracy of a planning application for the hcm signalized intersection Operational Procedure
1992Co-Authors: Mark R Virkler, Chihngchir ChenAbstract:The Highway Capacity Manual signalized intersection planning Procedure uses limited data to identify overcapacity situations. However, the planning Procedure lacks an indication for level of service. The signalized intersection Operational Procedure requires a large amount of data but identifies flow to capacity (v/c) ratios, delay, and level of service. A planning application of the Operational Procedure, using the same inputs as the present planning Procedure, has been suggested. The application would require a large number of default values for inputs along with a method to develop a surrogate signal timing plan. The potential accuracy of such a planning application of the Operational Procedure was examined through applications to morning and evening peak-period data from 40 intersections in Missouri. The default values for adjustment factors performed well. Whereas there was still a strong relationship for the v/c and level of service results derived from the default versus the actual adjustment factors. The surrogate signal timing algorithm performed adequately. There was a reasonably consistent relationship for the results generated by the surrogate signal timings compared with the results from the actual signal timings. A planning application of the Operational Procedure would be a valuable asset for planning and design analyses of intersections similar to those studied here. The application should encourage agencies to calibrate typical values for such variables as saturation flow rate, peak-hour factor, percent trucks, and pedestrian volumes. For consistency, the application should use a signal timing algorithm that at least approximates the best level of service to be expected from the intersection. The application's estimates of v/c, delay, and level of service would be valuable additions to the planning and design processes.
