The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
Klaus I. Itten - One of the best experts on this subject based on the ideXlab platform.
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The Improved Dual-view Field Goniometer System FIGOS.
Sensors, 2008Co-Authors: J Schopfer, S Dangel, Mathias Kneubuhler, Klaus I. IttenAbstract:Jurg Schopfer *, Stefan Dangel, Mathias Kneubuhler and Klaus I. Itten University of Zurich, Remote Sensing Laboratories, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mails: dangel@geo.uzh.ch, kneub@geo.uzh.ch, klaus.itten@geo.uzh.ch * Author to whom correspondence should be addressed; E-mail: juerg.schopfer@geo.uzh.ch Received: 3 July 2008; in revised form: 22 August 2008 / Accepted: 24 August 2008 / Published: 28 August 2008 Abstract: In spectrodirectional Remote Sensing (RS) the Earth’s surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with Goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field Goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational Goniometer system was able to fulfill this requirement. This study presents the first dual-view field Goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same Goniometer system. Suggestions for further improving Goniometer systems are given and the need for intercalibration of various Goniometers as well as for standardizing spectrodirectional measurements is expressed.
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The improved dual-view field Goniometer system FIGOS
Sensors, 2008Co-Authors: J Schopfer, S Dangel, Mathias Kneubuhler, Klaus I. IttenAbstract:In spectrodirectional Remote Sensing (RS) the Earth's surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with Goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field Goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational Goniometer system was able to fulfill this requirement. This study presents the first dual-view field Goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same Goniometer system. Suggestions for further improving Goniometer systems are given and the need for intercalibration of various Goniometers as well as for standardizing spectrodirectional measurements is expressed.
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Intercomparison of field and laboratory Goniometer measurements
The International Archives of the Photogrammetry Remote Sensing and Spatial Information Sciences, 2005Co-Authors: J Schopfer, S Dangel, M.m. Verstraete, Michael E. Schaepman, M. Kneubuehler, Klaus I. IttenAbstract:Field and laboratory Goniometers are widely used in the remote sensing community to assess spectrodirectional reflectance properties of selected targets. Even when the same target and Goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions: typically Goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the laboratory. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration. It is also critical for all applications that rely on measurements obtained with both types of instruments. One solution is to retrieve the BRDF of the targets of interest for each experimental setup individually and to compare those, since theoretically they are independent from the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for the conicality and inhomogeneity of illumination in the case of laboratory measurements. We present a BRDF retrieval scheme for typical laboratory Goniometers as well as results of measurements and BRDF retrievals using the field and laboratory Goniometer systems (FIGOS/LAGOS) of the University of Zurich and the same artificial target for both Goniometer setups.
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Toward a direct comparison of field and laboratory Goniometer measurements
IEEE Transactions on Geoscience and Remote Sensing, 2005Co-Authors: S Dangel, J Schopfer, Mathias Kneubuhler, M.m. Verstraete, Michael E. Schaepman, Klaus I. IttenAbstract:Field and laboratory Goniometers are widely used in the remote sensing community to assess spectrodirectional reflection properties of selected targets. Even when the same target and Goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions since actual Goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the lab. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration and for all applications that rely on measurements obtained with both types of instruments. One approach to this problem consists in retrieving the bidirectional reflectance distribution function (BRDF) of the targets of interest for each experimental setup and to compare these, since theoretically they are independent of the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for conicity and inhomogeneity of illumination in the case of laboratory measurements. In this paper, we present a novel BRDF retrieval scheme for typical laboratory Goniometers and compare it with the usual correction method assuming Lambertian behavior. We then discuss the first results of measurements and BRDF retrievals using the field and laboratory Goniometer systems of the Remote Sensing Laboratories of the University of Zurich, which share the exact observation geometry, on the same inert, highly anisotropic target. © 2005 IEEE.
Per Jönsson - One of the best experts on this subject based on the ideXlab platform.
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Comparison of measurement accuracy between two wrist Goniometer systems during pronation and supination
Journal of Electromyography and Kinesiology, 2002Co-Authors: Peter W. Johnson, Per Jönsson, Mats HagbergAbstract:Pronation and supination have been shown to affect wrist Goniometer measurement accuracy. The purpose of this study was to compare differences in measurement accuracy between a commonly used biaxial, single transducer wrist Goniometer (System A) and a biaxial, two-transducer wrist Goniometer (System B) over a wide range of pronation and supination (P/S) positions. Eight subjects moved their wrist between -40 and 40?? of flexion/extension (F/E) and -10 and 20?? of radial/ulnar (R/U) deviation in four different P/S positions: 90?? pronation; 45?? pronation; 0?? neutral and 45?? supination. System A was prone to more R/U crosstalk than System B and the amount of crosstalk was dependent on the P/S position. F/E crosstalk was present with both Goniometer systems and was also shown to be dependent on P/S. When moving from pronation to supination, both systems experienced a similar extension offset error; however R/U offset errors were roughly equal in magnitude but opposite in direction. The calibration position will affect wrist angle measurements and the magnitude and direction of measurement errors. To minimize offset errors, the Goniometer systems should be calibrated in the P/S posture most likely to be encountered during measurement. Differences in Goniometer design and application accounted for the performance differences. ?? 2002 Published by Elsevier Science Ltd.
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comparison of measurement accuracy between two types of wrist Goniometer systems
Applied Ergonomics, 2001Co-Authors: Per Jönsson, Peter JohnsonAbstract:Abstract Studies have shown that wrist Goniometers are prone to measurement errors, particularly due to crosstalk. This study compared two wrist Goniometer systems: a commonly used biaxial, single transducer (System A) and a biaxial, two-transducer (System B). Wrist angles, range of movement and crosstalk results were compared. With the wrist in 90° of pronation, eight subjects were placed in 20 different wrist postures between −40° and 40° of flexion/extension and between −10° and 20° of deviation. Relative to System B, System A had larger measurement errors and was more prone to crosstalk. There may be two sources of crosstalk: (1) intrinsic crosstalk associated with the design, application and twisting of the Goniometer transducer when on the wrist, and (2) extrinsic crosstalk associated with the anatomy and complex movement of the wrist joint. It appears that the majority of the radial/ulnar crosstalk measured with System A was intrinsic crosstalk due to the twisting of the Goniometer transducer.
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Comparison of measurement accuracy between two types of wrist Goniometer systems
Applied Ergonomics, 2001Co-Authors: Per Jönsson, Peter W. JohnsonAbstract:Studies have shown that wrist Goniometers are prone to measurement errors, particularly due to crosstalk. This study compared two wrist Goniometer systems: a commonly used biaxial, single transducer (System A) and a biaxial, two-transducer (System B). Wrist angles, range of movement and crosstalk results were compared. With the wrist in 90° of pronation, eight subjects were placed in 20 different wrist postures between -40° and 40° of flexion/extension and between -10° and 20° of deviation.Relative to System B, System A had larger measurement errors and was more prone to crosstalk. There may be two sources of crosstalk: (1) intrinsic crosstalk associated with the design, application and twisting of the Goniometer transducer when on the wrist, and (2) extrinsic crosstalk associated with the anatomy and complex movement of the wrist joint. It appears that the majority of the radial/ulnar crosstalk measured with System A was intrinsic crosstalk due to the twisting of the Goniometer transducer. Copyright © 2001 Elsevier Science Ltd.
J Schopfer - One of the best experts on this subject based on the ideXlab platform.
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The Improved Dual-view Field Goniometer System FIGOS.
Sensors, 2008Co-Authors: J Schopfer, S Dangel, Mathias Kneubuhler, Klaus I. IttenAbstract:Jurg Schopfer *, Stefan Dangel, Mathias Kneubuhler and Klaus I. Itten University of Zurich, Remote Sensing Laboratories, Winterthurerstrasse 190, 8057 Zurich, Switzerland E-mails: dangel@geo.uzh.ch, kneub@geo.uzh.ch, klaus.itten@geo.uzh.ch * Author to whom correspondence should be addressed; E-mail: juerg.schopfer@geo.uzh.ch Received: 3 July 2008; in revised form: 22 August 2008 / Accepted: 24 August 2008 / Published: 28 August 2008 Abstract: In spectrodirectional Remote Sensing (RS) the Earth’s surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with Goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field Goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational Goniometer system was able to fulfill this requirement. This study presents the first dual-view field Goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same Goniometer system. Suggestions for further improving Goniometer systems are given and the need for intercalibration of various Goniometers as well as for standardizing spectrodirectional measurements is expressed.
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The improved dual-view field Goniometer system FIGOS
Sensors, 2008Co-Authors: J Schopfer, S Dangel, Mathias Kneubuhler, Klaus I. IttenAbstract:In spectrodirectional Remote Sensing (RS) the Earth's surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with Goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field Goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational Goniometer system was able to fulfill this requirement. This study presents the first dual-view field Goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same Goniometer system. Suggestions for further improving Goniometer systems are given and the need for intercalibration of various Goniometers as well as for standardizing spectrodirectional measurements is expressed.
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Intercomparison of field and laboratory Goniometer measurements
The International Archives of the Photogrammetry Remote Sensing and Spatial Information Sciences, 2005Co-Authors: J Schopfer, S Dangel, M.m. Verstraete, Michael E. Schaepman, M. Kneubuehler, Klaus I. IttenAbstract:Field and laboratory Goniometers are widely used in the remote sensing community to assess spectrodirectional reflectance properties of selected targets. Even when the same target and Goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions: typically Goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the laboratory. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration. It is also critical for all applications that rely on measurements obtained with both types of instruments. One solution is to retrieve the BRDF of the targets of interest for each experimental setup individually and to compare those, since theoretically they are independent from the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for the conicality and inhomogeneity of illumination in the case of laboratory measurements. We present a BRDF retrieval scheme for typical laboratory Goniometers as well as results of measurements and BRDF retrievals using the field and laboratory Goniometer systems (FIGOS/LAGOS) of the University of Zurich and the same artificial target for both Goniometer setups.
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Toward a direct comparison of field and laboratory Goniometer measurements
IEEE Transactions on Geoscience and Remote Sensing, 2005Co-Authors: S Dangel, J Schopfer, Mathias Kneubuhler, M.m. Verstraete, Michael E. Schaepman, Klaus I. IttenAbstract:Field and laboratory Goniometers are widely used in the remote sensing community to assess spectrodirectional reflection properties of selected targets. Even when the same target and Goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions since actual Goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the lab. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration and for all applications that rely on measurements obtained with both types of instruments. One approach to this problem consists in retrieving the bidirectional reflectance distribution function (BRDF) of the targets of interest for each experimental setup and to compare these, since theoretically they are independent of the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for conicity and inhomogeneity of illumination in the case of laboratory measurements. In this paper, we present a novel BRDF retrieval scheme for typical laboratory Goniometers and compare it with the usual correction method assuming Lambertian behavior. We then discuss the first results of measurements and BRDF retrievals using the field and laboratory Goniometer systems of the Remote Sensing Laboratories of the University of Zurich, which share the exact observation geometry, on the same inert, highly anisotropic target. © 2005 IEEE.
Peter W. Johnson - One of the best experts on this subject based on the ideXlab platform.
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Comparison of measurement accuracy between two wrist Goniometer systems during pronation and supination
Journal of Electromyography and Kinesiology, 2002Co-Authors: Peter W. Johnson, Per Jönsson, Mats HagbergAbstract:Pronation and supination have been shown to affect wrist Goniometer measurement accuracy. The purpose of this study was to compare differences in measurement accuracy between a commonly used biaxial, single transducer wrist Goniometer (System A) and a biaxial, two-transducer wrist Goniometer (System B) over a wide range of pronation and supination (P/S) positions. Eight subjects moved their wrist between -40 and 40?? of flexion/extension (F/E) and -10 and 20?? of radial/ulnar (R/U) deviation in four different P/S positions: 90?? pronation; 45?? pronation; 0?? neutral and 45?? supination. System A was prone to more R/U crosstalk than System B and the amount of crosstalk was dependent on the P/S position. F/E crosstalk was present with both Goniometer systems and was also shown to be dependent on P/S. When moving from pronation to supination, both systems experienced a similar extension offset error; however R/U offset errors were roughly equal in magnitude but opposite in direction. The calibration position will affect wrist angle measurements and the magnitude and direction of measurement errors. To minimize offset errors, the Goniometer systems should be calibrated in the P/S posture most likely to be encountered during measurement. Differences in Goniometer design and application accounted for the performance differences. ?? 2002 Published by Elsevier Science Ltd.
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Comparison of measurement accuracy between two types of wrist Goniometer systems
Applied Ergonomics, 2001Co-Authors: Per Jönsson, Peter W. JohnsonAbstract:Studies have shown that wrist Goniometers are prone to measurement errors, particularly due to crosstalk. This study compared two wrist Goniometer systems: a commonly used biaxial, single transducer (System A) and a biaxial, two-transducer (System B). Wrist angles, range of movement and crosstalk results were compared. With the wrist in 90° of pronation, eight subjects were placed in 20 different wrist postures between -40° and 40° of flexion/extension and between -10° and 20° of deviation.Relative to System B, System A had larger measurement errors and was more prone to crosstalk. There may be two sources of crosstalk: (1) intrinsic crosstalk associated with the design, application and twisting of the Goniometer transducer when on the wrist, and (2) extrinsic crosstalk associated with the anatomy and complex movement of the wrist joint. It appears that the majority of the radial/ulnar crosstalk measured with System A was intrinsic crosstalk due to the twisting of the Goniometer transducer. Copyright © 2001 Elsevier Science Ltd.
Peter Johnson - One of the best experts on this subject based on the ideXlab platform.
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comparison of measurement accuracy between two types of wrist Goniometer systems
Applied Ergonomics, 2001Co-Authors: Per Jönsson, Peter JohnsonAbstract:Abstract Studies have shown that wrist Goniometers are prone to measurement errors, particularly due to crosstalk. This study compared two wrist Goniometer systems: a commonly used biaxial, single transducer (System A) and a biaxial, two-transducer (System B). Wrist angles, range of movement and crosstalk results were compared. With the wrist in 90° of pronation, eight subjects were placed in 20 different wrist postures between −40° and 40° of flexion/extension and between −10° and 20° of deviation. Relative to System B, System A had larger measurement errors and was more prone to crosstalk. There may be two sources of crosstalk: (1) intrinsic crosstalk associated with the design, application and twisting of the Goniometer transducer when on the wrist, and (2) extrinsic crosstalk associated with the anatomy and complex movement of the wrist joint. It appears that the majority of the radial/ulnar crosstalk measured with System A was intrinsic crosstalk due to the twisting of the Goniometer transducer.
