The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
A.j. Dolman - One of the best experts on this subject based on the ideXlab platform.
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sonic anemometer co sine response and flux Measurement i the potential for co sine error to affect sonic anemometer based flux Measurements
Agricultural and Forest Meteorology, 2003Co-Authors: John H. C. Gash, A.j. DolmanAbstract:The potential for sonic anemometer (co)sine errors to affect eddy flux Measurements is investigated. Similarity theory is used to show that the standard deviation of the instantaneous angle between the wind vector and the horizontal (the angle of attack), depends on surface Roughness, Measurement height and atmospheric stability. Three days of data from a peat bog and a pine forest are used to test this dependency. The normalised flux-angle distributions are derived for these two sites and it is shown that for the peat bog the sonic anemometer operates outside its manufacturer’s specified angle-acceptance envelope for 20% of the daytime fluxes; for the forest some 50% of the daytime fluxes were measured under these conditions. The highest values of flux-angle were observed at the peat bog site during two 30 min periods when CO2, respired the previous night, was flushed out during the dawn breakdown of the nocturnal boundary layer. The implications for the design of eddy flux measuring systems is discussed.
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sonic anemometer co sine response and flux Measurement i the potential for co sine error to affect sonic anemometer based flux Measurements agriculture and forest meteorology 119 2003
Agricultural and Forest Meteorology, 2003Co-Authors: John H. C. Gash, A.j. DolmanAbstract:The potential for sonic anemometer (co)sine errors to affect eddy flux Measurements is investigated. Similarity theory is used to show that the standard deviation of the instantaneous angle between the wind vector and the horizontal (the angle of attack), depends on surface Roughness, Measurement height and atmospheric stability. Three days of data from a peat bog and a pine forest are used to test this dependency. The normalised flux-angle distributions are derived for these two sites and it is shown that for the peat bog the sonic anemometer operates outside its manufacturer's specified angle-acceptance envelope for 20% of the daytime fluxes; for the forest some 50% of the daytime fluxes were measured under these conditions. The highest values of flux-angle were observed at the peat bog site during two 30 min periods when CO
Tim K Lee - One of the best experts on this subject based on the ideXlab platform.
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surface Roughness Measurement by speckle contrast under the illumination of light with arbitrary spectral profile
Optics and Lasers in Engineering, 2010Co-Authors: Lioudmila Tchvialeva, Igo Markhvida, Haisha Zeng, David I Mclea, Harvey Lui, Tim K LeeAbstract:Abstract Quantification of surface Roughness greater than a micron is desirable for many industrial and biomedical applications. Polychromatic speckle contrast has been shown theoretically to be able to detect such Roughness range using an appropriate light source with a Gaussian spectral shape. In this paper, we extend the theory to arbitrary spectral profile by formulating speckle contrast as a function of spectral profile, surface Roughness, and the geometry of speckle formation. Under a far-field set-up, the formulation can be simplified and a calibration curve for contrast and Roughness can be calculated. We demonstrated the technique using a blue diode laser with a set of 20 metal surface Roughness standards in the range 1–73 μm, and found that the method worked well with both Gaussian and non-Gaussian surfaces.
John H. C. Gash - One of the best experts on this subject based on the ideXlab platform.
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sonic anemometer co sine response and flux Measurement i the potential for co sine error to affect sonic anemometer based flux Measurements
Agricultural and Forest Meteorology, 2003Co-Authors: John H. C. Gash, A.j. DolmanAbstract:The potential for sonic anemometer (co)sine errors to affect eddy flux Measurements is investigated. Similarity theory is used to show that the standard deviation of the instantaneous angle between the wind vector and the horizontal (the angle of attack), depends on surface Roughness, Measurement height and atmospheric stability. Three days of data from a peat bog and a pine forest are used to test this dependency. The normalised flux-angle distributions are derived for these two sites and it is shown that for the peat bog the sonic anemometer operates outside its manufacturer’s specified angle-acceptance envelope for 20% of the daytime fluxes; for the forest some 50% of the daytime fluxes were measured under these conditions. The highest values of flux-angle were observed at the peat bog site during two 30 min periods when CO2, respired the previous night, was flushed out during the dawn breakdown of the nocturnal boundary layer. The implications for the design of eddy flux measuring systems is discussed.
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sonic anemometer co sine response and flux Measurement i the potential for co sine error to affect sonic anemometer based flux Measurements agriculture and forest meteorology 119 2003
Agricultural and Forest Meteorology, 2003Co-Authors: John H. C. Gash, A.j. DolmanAbstract:The potential for sonic anemometer (co)sine errors to affect eddy flux Measurements is investigated. Similarity theory is used to show that the standard deviation of the instantaneous angle between the wind vector and the horizontal (the angle of attack), depends on surface Roughness, Measurement height and atmospheric stability. Three days of data from a peat bog and a pine forest are used to test this dependency. The normalised flux-angle distributions are derived for these two sites and it is shown that for the peat bog the sonic anemometer operates outside its manufacturer's specified angle-acceptance envelope for 20% of the daytime fluxes; for the forest some 50% of the daytime fluxes were measured under these conditions. The highest values of flux-angle were observed at the peat bog site during two 30 min periods when CO
Andreas Klik - One of the best experts on this subject based on the ideXlab platform.
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soil surface Roughness Measurement methods applicability and surface representation
Catena, 2005Co-Authors: Werne Jeste, Andreas KlikAbstract:Abstract In a laboratory rainfall simulator study soil surface Roughness was measured using contact (roller chain, pin meter) and noncontact devices (laser scanner, photogrammetry). Soil surfaces with two initial Roughness conditions (aggregates As for the contact methods, resolution (cm range) and precision (mm range) is limited which constrains their application to calculation of simple surface parameters. Resolution and precision in the sub millimeter range could be obtained with the laser scanner, while for the photogrammetric method the Measurement uncertainty was approximately 1–2 mm. Measurement time was highest (90 min) for the pin meter technique, though data were ready to use for analyses. Laser scanner Measurements took 34 min. Several steps of data post-processing required 30 more minutes. Data acquisition was fastest for photogrammetry (5 min), but expert knowledge as well as special hard- and software were necessary for time-consuming photo analyses, taking about 120 min. The chain and pin meter were compared using a profile index. Profile lengths matched well for smooth surfaces; on rough surfaces, the chain meter gave shorter profile lines. Between profile index from chain Measurements and the random Roughness derived from pin meter data a polynomial regression could be found. Parameters of distributions of elevations as well as inclinations and depressions were used to compare the laser scanner and the photogrammetric technique. Generally the laser scanner was able to reproduce small aggregates as well as voids in between them, while DEM from stereophotos was smoothed between major aggregates. This led to skewed distributions of elevations and inclinations, as well as to a lower surface area (up to 39%), and a lower depression volume (up to 68%). Shapes of depressions were significantly different as well. The used photogrammetric technique is supposed to be successful in producing adequate DEMs for already smoothed surfaces, e.g. after rainfall events. The study revealed different fields of application and limitations of the compared devices. Using a non-adequate technique for certain situations will definitely have implications on further analyses concerning connectivity of runoff pathways, surface protection from raindrop impact or runoff detachment and sediment transport.
Harvey Lui - One of the best experts on this subject based on the ideXlab platform.
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surface Roughness Measurement by speckle contrast under the illumination of light with arbitrary spectral profile
Optics and Lasers in Engineering, 2010Co-Authors: Lioudmila Tchvialeva, Igo Markhvida, Haisha Zeng, David I Mclea, Harvey Lui, Tim K LeeAbstract:Abstract Quantification of surface Roughness greater than a micron is desirable for many industrial and biomedical applications. Polychromatic speckle contrast has been shown theoretically to be able to detect such Roughness range using an appropriate light source with a Gaussian spectral shape. In this paper, we extend the theory to arbitrary spectral profile by formulating speckle contrast as a function of spectral profile, surface Roughness, and the geometry of speckle formation. Under a far-field set-up, the formulation can be simplified and a calibration curve for contrast and Roughness can be calculated. We demonstrated the technique using a blue diode laser with a set of 20 metal surface Roughness standards in the range 1–73 μm, and found that the method worked well with both Gaussian and non-Gaussian surfaces.
