The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform

Stuart Bradley - One of the best experts on this subject based on the ideXlab platform.

  • A Sodar for profiling in a spatially inhomogeneous urban environment
    Meteorologische Zeitschrift, 2015
    Co-Authors: Stuart Bradley, Janet F. Barlow, J. Lalley, Christos Halios
    Abstract:

    The urban boundary layer, above the canopy, is still poorly understood. One of the challenges is obtaining data by sampling more than a few meters above the rooftops, given the spatial and temporal inhomogeneities in both horizontal and vertical. Sodars are generally useful tools for ground-based remote sensing of winds and turbulence, but rely on horizontal homogeneity (as do lidars) in building up 3-component wind vectors from sampling three or more spatially separated volumes. The time taken for sound to travel to a typical range of 200 m and back is also a limitation. A Sodar of radically different design is investigated, aimed at addressing these problems. It has a single vertical transmitted sound pulse. Doppler shifted signals are received from a number of volumes around the periphery of the transmitted beam with microphones which each having tight angular sensitivity at zenith angles slightly off-vertical. The spatial spread of sampled volumes is therefore smaller. By having more receiver microphones than a conventional Sodar, the effect of smaller zenith angle is offset. More rapid profiling is also possible with a single vertical transmitted beam, instead of the usual multiple beams. A prototype design is described, together with initial field measurements. It is found that the beam forming using a single dish antenna and the drift of the sound pulse downwind both give rise to reduced performance compared with expectations. It is concluded that, while the new Sodar works in principle, the compromises arising in the design mean that the expected advantages have not been realized

  • scale model evaluation and optimization of Sodar acoustic baffles
    Journal of Atmospheric and Oceanic Technology, 2015
    Co-Authors: Adrien Chabbey, Stuart Bradley, Fernando Porteagel
    Abstract:

    AbstractA 21:1 scaled Sodar, operating at 40 kHz, has been built and tested in the laboratory. Sodars, which use sound scattered by turbulence to profile the lowest few hundred meters of the atmosphere, need good acoustic shielding to diminish annoyance and to reduce unwanted reflections from nearby objects. Design of the acoustic shielding is generally inhibited by the difficulty of testing on full-scale systems and uncertainty as to accuracy of models. In contrast, the scale model approach described allows for “bench testing” of many designs under controlled conditions, and efficient comparison with models. Measured beam patterns from the scale model were compared with those from a numerical model based on the Kirchhoff integral theorem. Satisfactory agreement has allowed using the numerical model to optimize the acoustic shield design, both for the gross acoustic baffle geometry and for the geometry of rim modulations known as thnadners. Optimization was performed in the specific case of a scaled model...

  • Aspects of the Correlation between Sodar and Mast Instrument Winds
    Journal of Atmospheric and Oceanic Technology, 2013
    Co-Authors: Stuart Bradley
    Abstract:

    AbstractOn a uniform terrain site, differences between a Sodar and a mast-mounted cup anemometer will arise because of turbulent fluctuations and wind components being measured in different spaces, and because of the inherent difference between scalar and vector averaging. This paper develops theories for turbulence-related random fluctuations resulting from finite sampling rates and sampling from spatially distributed volumes. Coefficients of determination (R2) are predicted comparable to those obtained in practice. It is shown that more than two-thirds of the reduction in R2 arises from differences in the winds measured by mast instruments and by Sodars, rather than by Sodar errors: both instruments are measuring accurately, but just not in the same place or at the same time. The result is that Sodars being used operationally should be able to measure winds to a root-mean-square accuracy of around 2%.

  • a simple model for correcting Sodar and lidar errors in complex terrain
    Journal of Atmospheric and Oceanic Technology, 2012
    Co-Authors: Stuart Bradley
    Abstract:

    AbstractGround-based sensing of wind profiles by Sodars and lidars is becoming the standard for wind energy and other applications. However, there remain difficulties in complex terrain since the instruments sense wind components in spatially separated volumes, and systematic spatial variations of the wind components can lead to systematic bias in wind estimation. The errors are typically less than 6%, so corrections do not need to be very sophisticated.Analytic potential flow models are developed for the flow over a bell-shaped hill and over an escarpment. These models are then used to find the radial Doppler shift from sampling volumes in typical Sodar and lidar beam geometries, thereby allowing spatial variation bias to be removed. Since the models are straightforward, bias removal is readily achieved, and also lends itself to an understanding of the significant parameters affecting wind errors.The bell model is tested against field data from Sodars and lidars in both moderately complex and in very com...

  • A Bistatic Sodar for Precision Wind Profiling in Complex Terrain
    Journal of Atmospheric and Oceanic Technology, 2012
    Co-Authors: Stuart Bradley, Sabine Von Hünerbein, Torben Mikkelsen
    Abstract:

    AbstractA new ground-based wind profiling technology—a scanned bistatic Sodar—is described. The motivation for this design is to obtain a “mastlike” wind vector profile in a single atmospheric column extending from the ground to heights of more than 200 m. The need for this columnar profiling arises from difficulties experienced by all existing lidars and Sodars in the presence of nonhorizontally uniform wind fields, such as found generically in complex terrain. Other advantages are described, including improved signal strength from turbulent velocity fluctuations, improved data availability in neutral atmospheric temperature profiles, improved rejection of rain echoes, and improved rejection of echoes from fixed (nonatmospheric) objects. Initial brief field tests indicate that the scattered intensity profile agrees with theoretical expectations, and bistatic Sodar winds are consistent with winds from standard mast-mounted instruments.

Vilas Warudkar - One of the best experts on this subject based on the ideXlab platform.

  • Study of different parameters estimation methods of Weibull distribution to determine wind power density using ground based Doppler Sodar instrument
    Elsevier, 2018
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    The effectiveness of nine different numerical methods is examined for calculating the parameters of Weibull distribution at three different heights 80 m, 100 m and 120 m to estimate wind power density. The measurement campaign was conducted at Kayathar, Tamil Nadu, India. The time series wind data were recorded using SecondWind Triton Sodar (Sound Detection and Ranging) instrument. Firstly, the fidelity assessment of Sodar measurement was examined. The aim of this study is to identify the more accurate method for computing wind power density of a selected region. The performance of the selected methods is judged based on goodness of fit test i.e. Root Mean Square Error Test (RMSE), Coefficient of Determination (R2), Mean Absolute Percentage Error (MAPE), and Chi-square Test (X2). Wind power densities are estimated with the help of estimated parameter values. This study proposes an approach to utilize Sodar and also aims to examine the accuracy of Sodar measurement by comparing the results with cup anemometer, in an attempt to establish adequate criteria for an effective utilization of Sodar for wind resource assessment. The results suggest that Sodar may be used as an alternative to meteorological mast. Keywords: Weibull parameters, Wind frequency distribution, Wind speed, Probability distribution function, Statistical analysi

  • study of different parameters estimation methods of weibull distribution to determine wind power density using ground based doppler Sodar instrument
    alexandria engineering journal, 2017
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    Abstract The effectiveness of nine different numerical methods is examined for calculating the parameters of Weibull distribution at three different heights 80 m, 100 m and 120 m to estimate wind power density. The measurement campaign was conducted at Kayathar, Tamil Nadu, India. The time series wind data were recorded using SecondWind Triton Sodar (Sound Detection and Ranging) instrument. Firstly, the fidelity assessment of Sodar measurement was examined. The aim of this study is to identify the more accurate method for computing wind power density of a selected region. The performance of the selected methods is judged based on goodness of fit test i.e. Root Mean Square Error Test (RMSE), Coefficient of Determination (R2), Mean Absolute Percentage Error (MAPE), and Chi-square Test (X2). Wind power densities are estimated with the help of estimated parameter values. This study proposes an approach to utilize Sodar and also aims to examine the accuracy of Sodar measurement by comparing the results with cup anemometer, in an attempt to establish adequate criteria for an effective utilization of Sodar for wind resource assessment. The results suggest that Sodar may be used as an alternative to meteorological mast.

  • Wind characteristics observation using Doppler-Sodar for wind energy applications
    Elsevier, 2017
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    This paper presents an application of Doppler Sodar (Sound Detection and Ranging) system for the assessment of wind characteristics at an onshore site in Tamil Nadu, India. The wind speed is statistically analyzed by means of Weibull distribution function and results were used to compute several characteristics parameters related to wind energy applications and no significant discrepancies were observed. The characteristics of wind shear coefficient were evaluated for different altitudes. The vertical profile of wind speed measured from Sodar system was compared with existing models. Furthermore, the turbulence characteristics were analyzed and compared along with the turbulence intensity. From the economic point of view the Sodar system was found to be cost-effective at higher heights. The results of this study are expected to provide useful information for the deployment of remote sensing instruments for wind energy development in India. Keywords: Sodar, Met mast, Weibull parameter, Wind power density, Turbulence intensit

Thierry Lebel - One of the best experts on this subject based on the ideXlab platform.

  • The diurnal cycle of lower boundary-layer wind in the West African monsoon
    Quarterly Journal of the Royal Meteorological Society, 2010
    Co-Authors: Kassimou Abdou, D.j Parker, B. Brooks, N. Kalthoff, Thierry Lebel
    Abstract:

    Measurements of lower boundary-layer winds collected from four Sonic Detection And Ranging (Sodar) systems during the African Monsoon Multidisciplinary Analysis (AMMA) are presented. The Sodars were located in a mesoscale network in the vicinity of Niamey, Niger, in the period 31 May to 17 August 2006; from this network 41 days of good measurements have been obtained from at least one of the Sodars, while there are several days in which two or more Sodars produced good simultaneous data. The average variation of the winds in the lower boundary layer is here presented, as a function of height and of time of day. The results confirm previous studies of the diurnal cycle of winds, and quantify the variation of this diurnal cycle with height at low altitudes. On many nights, a distinct nocturnal low-level jet was observed, at 200–400 m altitude. In profiles averaged over all of the sample days, the peak wind shear was in the layer below 300 m, with the strongest wind shear from 0000 to 0600 UTC. In particular, the magnitude of low-level wind shear, which is a significant hazard for aviation, is shown to be strongly dependent on time of day. Strong low-level wind shear (more than 4 m s−1 per 100 m), was observed on more than 35% of days in the 0000–0300 UTC period. Copyright © 2009 Royal Meteorological Society

  • The diurnal cycle of lower boundary-layer wind in the West African monsoon
    Quarterly Journal of the Royal Meteorological Society, 2009
    Co-Authors: A. Kassimou, D.j Parker, B. Brooks, N. Kalthoff, Thierry Lebel
    Abstract:

    Measurements of lower boundary-layer winds collected from four Sonic Detection And Ranging (Sodar) systems during the African Monsoon Multidisciplinary Analysis (AMMA) are presented. The Sodars were located in a mesoscale network in the vicinity of Niamey, Niger, in the period 31 May to 17 August 2006; from this network 41 days of good measurements have been obtained from at least one of the Sodars, while there are several days in which two or more Sodars produced good simultaneous data. The average variation of the winds in the lower boundary layer is here presented, as a function of height and of time of day. The results confirm previous studies of the diurnal cycle of winds, and quantify the variation of this diurnal cycle with height at low altitudes. On many nights, a distinct nocturnal low-level jet was observed, at 200–400 m altitude. In profiles averaged over all of the sample days, the peak wind shear was in the layer below 300 m, with the strongest wind shear from 0000 to 0600 UTC. In particular, the magnitude of low-level wind shear, which is a significant hazard for aviation, is shown to be strongly dependent on time of day. Strong low-level wind shear (more than 4 m s−1 per 100 m), was observed on more than 35% of days in the 0000–0300 UTC period.

Prem Kumar Chaurasiya - One of the best experts on this subject based on the ideXlab platform.

  • Study of different parameters estimation methods of Weibull distribution to determine wind power density using ground based Doppler Sodar instrument
    Elsevier, 2018
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    The effectiveness of nine different numerical methods is examined for calculating the parameters of Weibull distribution at three different heights 80 m, 100 m and 120 m to estimate wind power density. The measurement campaign was conducted at Kayathar, Tamil Nadu, India. The time series wind data were recorded using SecondWind Triton Sodar (Sound Detection and Ranging) instrument. Firstly, the fidelity assessment of Sodar measurement was examined. The aim of this study is to identify the more accurate method for computing wind power density of a selected region. The performance of the selected methods is judged based on goodness of fit test i.e. Root Mean Square Error Test (RMSE), Coefficient of Determination (R2), Mean Absolute Percentage Error (MAPE), and Chi-square Test (X2). Wind power densities are estimated with the help of estimated parameter values. This study proposes an approach to utilize Sodar and also aims to examine the accuracy of Sodar measurement by comparing the results with cup anemometer, in an attempt to establish adequate criteria for an effective utilization of Sodar for wind resource assessment. The results suggest that Sodar may be used as an alternative to meteorological mast. Keywords: Weibull parameters, Wind frequency distribution, Wind speed, Probability distribution function, Statistical analysi

  • study of different parameters estimation methods of weibull distribution to determine wind power density using ground based doppler Sodar instrument
    alexandria engineering journal, 2017
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    Abstract The effectiveness of nine different numerical methods is examined for calculating the parameters of Weibull distribution at three different heights 80 m, 100 m and 120 m to estimate wind power density. The measurement campaign was conducted at Kayathar, Tamil Nadu, India. The time series wind data were recorded using SecondWind Triton Sodar (Sound Detection and Ranging) instrument. Firstly, the fidelity assessment of Sodar measurement was examined. The aim of this study is to identify the more accurate method for computing wind power density of a selected region. The performance of the selected methods is judged based on goodness of fit test i.e. Root Mean Square Error Test (RMSE), Coefficient of Determination (R2), Mean Absolute Percentage Error (MAPE), and Chi-square Test (X2). Wind power densities are estimated with the help of estimated parameter values. This study proposes an approach to utilize Sodar and also aims to examine the accuracy of Sodar measurement by comparing the results with cup anemometer, in an attempt to establish adequate criteria for an effective utilization of Sodar for wind resource assessment. The results suggest that Sodar may be used as an alternative to meteorological mast.

  • Wind characteristics observation using Doppler-Sodar for wind energy applications
    Elsevier, 2017
    Co-Authors: Prem Kumar Chaurasiya, Siraj Ahmed, Vilas Warudkar
    Abstract:

    This paper presents an application of Doppler Sodar (Sound Detection and Ranging) system for the assessment of wind characteristics at an onshore site in Tamil Nadu, India. The wind speed is statistically analyzed by means of Weibull distribution function and results were used to compute several characteristics parameters related to wind energy applications and no significant discrepancies were observed. The characteristics of wind shear coefficient were evaluated for different altitudes. The vertical profile of wind speed measured from Sodar system was compared with existing models. Furthermore, the turbulence characteristics were analyzed and compared along with the turbulence intensity. From the economic point of view the Sodar system was found to be cost-effective at higher heights. The results of this study are expected to provide useful information for the deployment of remote sensing instruments for wind energy development in India. Keywords: Sodar, Met mast, Weibull parameter, Wind power density, Turbulence intensit

Sune R. J. Axelsson - One of the best experts on this subject based on the ideXlab platform.

  • random noise radar Sodar with ultrawideband waveforms
    IEEE Transactions on Geoscience and Remote Sensing, 2007
    Co-Authors: Sune R. J. Axelsson
    Abstract:

    Random noise waveforms with ultrawide bandwidth improve the range resolution and reduces the probability of intercept in radar/Sodar. As a result of the nonperiodic waveform, the range ambiguity is removed as well. By transmitting a sine signal that is phase or frequency modulated by random noise, autocorrelation functions with improved side lobe suppression in range can be formed. There are great similarities in the signal-processing algorithms applied in noise radar and Sodar. The much slower propagation velocity of sound compared to light reduces the signal bandwidth but increases the time of measurement, however. In both Sodar and radar, the range resolution is determined by the wavelength band occupied by the transmitted waveform, while the velocity resolution is controlled by the ratio of wavelength and time of measurement. The slower sound velocity also enhances the range/Doppler ambiguity problem in Sodar when periodic waveforms are applied. This ambiguity could be suppressed if nonperiodic waveforms are introduced, such as random noise. In this paper, fundamental similarities and differences on system level between Sodar and radar are first discussed, and signal-processing algorithms applied in random noise radar/Sodar are reviewed. In particular, the noise floor of the ambiguity function and its relationship to spectrum width and time of measurement are analyzed, including improved side lobe suppression using mismatched filtering. The signal-processing algorithms were tested on raw data from Sodar measurements on moving targets, buildings, vegetation, and water surfaces. An adaptive filter algorithm for suppression of the increased noise floor from dominant reflectors was derived and successfully applied to both Sodar and stepped frequency radar data

  • Random Noise Radar/Sodar With Ultrawideband Waveforms
    IEEE Transactions on Geoscience and Remote Sensing, 2007
    Co-Authors: Sune R. J. Axelsson
    Abstract:

    Random noise waveforms with ultrawide bandwidth improve the range resolution and reduces the probability of intercept in radar/Sodar. As a result of the nonperiodic waveform, the range ambiguity is removed as well. By transmitting a sine signal that is phase or frequency modulated by random noise, autocorrelation functions with improved side lobe suppression in range can be formed. There are great similarities in the signal-processing algorithms applied in noise radar and Sodar. The much slower propagation velocity of sound compared to light reduces the signal bandwidth but increases the time of measurement, however. In both Sodar and radar, the range resolution is determined by the wavelength band occupied by the transmitted waveform, while the velocity resolution is controlled by the ratio of wavelength and time of measurement. The slower sound velocity also enhances the range/Doppler ambiguity problem in Sodar when periodic waveforms are applied. This ambiguity could be suppressed if nonperiodic waveforms are introduced, such as random noise. In this paper, fundamental similarities and differences on system level between Sodar and radar are first discussed, and signal-processing algorithms applied in random noise radar/Sodar are reviewed. In particular, the noise floor of the ambiguity function and its relationship to spectrum width and time of measurement are analyzed, including improved side lobe suppression using mismatched filtering. The signal-processing algorithms were tested on raw data from Sodar measurements on moving targets, buildings, vegetation, and water surfaces. An adaptive filter algorithm for suppression of the increased noise floor from dominant reflectors was derived and successfully applied to both Sodar and stepped frequency radar data