Ronald Calhoun

University of Utah, Salt Lake City, Utah, United States

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Publications (35)63.47 Total impact

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    ABSTRACT: The spurt of growth in the wind energy industry has led to the development of many new technologies to study this energy resource and improve the efficiency of wind turbines. One of the key factors in wind farm characterization is the prediction of power output of the wind farm that is a strong function of the turbulence in the wind speed and direction. A new formulation for calculating the expected power from a wind turbine in the presence of wind shear, turbulence, directional shear and direction fluctuations is presented. It is observed that wind shear, directional shear and direction fluctuations reduce the power producing capability, while turbulent intensity increases it. However, there is a complicated superposition of these effects that alters the characteristics of the power estimate that indicates the need for the new formulation. Data from two field experiments is used to estimate the wind power using the new formulation, and results are compared to previous formulations. Comparison of the estimates of available power from the new formulation is not compared to actual power outputs and will be a subject of future work. © 2015 The Authors. Wind Energy published by John Wiley & Sons, Ltd.
    No preview · Article · Sep 2015 · Wind Energy
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    Nihanth Cherukuru · Ronald Calhoun
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    ABSTRACT: Augmented reality (AR) is a technology in which 3-D virtual content is integrated with visual content and presented to the user [1]. In the current study, we explore the potential applications of AR technology in conjunction with Doppler lidar, which enables the user to view the surrounding wind fields collocated in space. As a proof of concept, we used the lidar data from a recent field campaign (METCRAX II) and developed a smartphone application to view the lidar scan in augmented reality. In this pilot study, we give a brief methodology of this feasibility study, present the challenges and promises of using AR technology in conjunction with Doppler wind lidars. 
    Full-text · Conference Paper · Jul 2015
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    ABSTRACT: AbstractThe second Meteor Crater Experiment (METCRAX II) was conducted in October 2013 at Arizona's Meteor Crater. The experiment was designed to investigate nighttime downslope-windstorm-type flows that form regularly above the inner southwest sidewall of the 1.2-km-diameter crater as a southwesterly mesoscale katabatic flow cascades over the crater rim. The objective of METCRAX II is to determine the causes of these strong, intermittent, and turbulent inflows that bring warm-air intrusions into the southwest part of the crater. This article provides an overview of the scientific goals of the experiment, summarizes the measurements, the crater topography and the synoptic meteorology of the study period, and presents initial analysis results.
    No preview · Article · Apr 2015 · Bulletin of the American Meteorological Society
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    ABSTRACT: The second Meteor Crater Experiment (METCRAX II) was designed to study downslope-windstorm-type flows occurring at the Barringer Meteorite Crater in Arizona. Two Doppler wind lidars were deployed to perform a coplanar dual-Doppler lidar analysis to capture the two-dimensional (2-D) vertical structure of these flows in the crater basin. This type of analysis allows the flow to be resolved on a 2-D Cartesian grid constructed in the range height indicator scan overlap region. Previous studies have shown that the dominant error in the coplanar dual-Doppler analysis mentioned above is due to the under sampling of radial velocities. Hence, it is necessary to optimize the setup and choose a scan strategy that minimizes the under sampling of radial velocities and provides a good spatial as well as temporal coverage of these short-lived events. A lidar simulator was developed using a large Eddy simulation wind field to optimize the lidar parameters for METCRAX II field experiment. A retrieval technique based on the weighted least squares technique with weights calculated based on the relative location of the lidar range gate centers to the grid intersection point was developed. The instrument configuration was determined by comparing the simulator retrievals to the background wind field and taking into account the limitations of commercially available lidars.
    No preview · Article · Dec 2014 · Journal of Applied Remote Sensing
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    ABSTRACT: The Second Meteor Crater Experiment (METCRAX II) was designed to study downslope-windstorm-type flows occurring at the Barringer Meteorite Crater in Arizona. Two Doppler wind lidars were deployed to perform a Co-planar Dual Doppler lidar analysis to capture the 2D vertical structure of these flows in the crater basin. This type of analysis allows the flow to be resolved on a 2D Cartesian grid constructed in the RHI scan overlap region. Previous studies have shown that the dominant error in the Co-planar Dual Doppler analysis mentioned above is due to the under sampling of radial velocities. Hence, it is necessary to optimize the setup and choose a scan strategy that minimizes the under sampling of radial velocities and provides a good spatial as well as temporal coverage of these short-lived events, which in turn strongly depend on the lidar parameters and the grid spacing. To optimize the lidar parameters for the METCRAX II field experiment, a lidar simulator was developed using an LES wind field. A wind retrieval technique based on the weighted least squares method with weights calculated based on the relative location of the lidar range gate centers to the grid intersection points was developed. An optimal instrument configuration was devised by comparing the simulator retrievals to the LES-modeled background wind field. Details about the lidar simulator and early results from the field experiment will be presented.
    No preview · Conference Paper · Aug 2014
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    ABSTRACT: The Second Meteor Crater Experiment (METCRAX II) was designed to study downslope-windstorm-type flows (DWF) that occur above the south and west inner sidewalls of the 1.2 km diameter Barringer Meteorite Crater in Arizona. These DWFs occur intermittently within the crater basin on clear, undisturbed nights in connection with a mesoscale drainage flow that approaches the crater from higher terrain to the southwest of the crater. During DWF events a wave descends in the lee of the upwind crater rim, producing strong and turbulent downslope flow above the slope, which rebounds in a hydraulic jump-like flow feature at the base of the slope. Multiple break-ins of these flows occur on suitable nights, and the individual break-ins vary in strength and duration. This presentation will provide an overview of the October 2013 METCRAX II field experiment. This experiment was supported by the National Center for Atmospheric Research's Earth Observing Laboratory and by other organizations, with an extensive complement of field equipment including a radar wind profiler, 2 radio acoustic sounding systems, three scanning Doppler LiDARs, a vertically pointing LiDAR, instrumented 40- and 50-m towers, 3 surface flux stations, 3 SoDARs, a scintillometer, a ceilometer, automatic weather stations, an array of temperature data loggers, multiple pressure sensors, and visual and thermal IR time-lapse cameras. Seven overnight Intensive Observational Periods (IOPs) were selected during the month on the basis of weather forecasts. Three continuously operated tethersondes and 3-hourly radiosondes provided supplementary vertical sounding data during the IOPs. The forecasts were successful in selecting nights when the DWF phenomenon occurred, and analyses of the data are now underway. This presentation will summarize first results, with detailed analyses presented in other related presentations at the conference.
    No preview · Conference Paper · Aug 2014

  • No preview · Conference Paper · Aug 2014
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    ABSTRACT: The second Meteor Crater Experiment (METCRAX-II) was conducted in October 2013 to study downslope-windstorm-type flows that occur on the upwind inner sidewall of the basin of Arizona's Meteor Crater during synoptically quiescent nights under clear sky conditions. The formation of these flows, which lead to warm-air intrusions into the upwind part of the crater basin, is associated with a nocturnal mesoscale drainage flow that develops on the slightly inclined plane surrounding the crater. Three scanning Doppler wind LiDARs were operated during METCRAX-II. Two scanned continuously in a coplanar configuration to measure a vertical cross section through the intruding flows, while a third LiDAR was deployed upwind of the crater basin to measure the characteristics of the evolving drainage flow impinging on the crater topography. We will show initial results of the wind fields retrieved from the three LiDARs, showing (1) the temporal evolution of the drainage flow outside of the crater topography (2) flow splitting of the approach flow around the crater and (3) the development and evolution of the downslope-wind-storm-type intrusions into the crater basin.
    No preview · Conference Paper · Aug 2014

  • No preview · Conference Paper · May 2014
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    ABSTRACT: Pulsed Doppler lidars are powerful tools for long-range, high-resolution measurements of radial wind velocities. With the development of commercial Doppler lidars and the reduction of acquisition costs, dual-Doppler lidar systems will be become increasingly accessible in upcoming years. This study reviews the most common dual-Doppler techniques, describes the setup of a highly synchronized long-range dual-Doppler lidar system, and discusses extensively the different kinds of errors connected with this complex measurement technique. Sources of errors and their interactions are traced through the retrieval algorithm, including errors from single-Doppler lidar and those occurring from a combination of instruments related to various parameters, such as relative beam angles, time and spatial scales of the scan pattern, and atmospheric conditions.
    No preview · Article · Sep 2013 · Journal of Atmospheric and Oceanic Technology
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    ABSTRACT: Wind measurements are fundamental inputs for wind resource assessment and the performance of wind farms. Common approaches for wind energy yield assessment are based on (1) observational data from surface station networks and (2) high-resolution computational fluid dynamic or mesoscale models. In this letter, we investigate the potential of applying a high-resolution nested mesoscale model, Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS), to predict low-level wind characteristics for wind farm domains. The model results are compared to scanning coherent Doppler lidar and tower measurements for a wind energy development. This letter focuses on the magnitude of difference between observations and simulations used for wind energy assessment. The results highlight the challenge for straight-forward application of mesoscale models, even well-established models with a relatively fine resolution on the inner nest (333 m), to produce wind predictions of sufficient fidelity and accuracy appropriate for resource assessment or operational support for individual wind farms. While many of the average wind flow features are captured by the model, their detailed spatial and temporal evolution may be improved through tighter integration with local sensor data.
    No preview · Article · Jan 2013 · Remote Sensing Letters
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    ABSTRACT: Several modifications to the optimal interpolation (OI) technique for light-detection-and-ranging vector retrieval are proposed and shown to result in significant improvement in velocity retrieval accuracy. These modifications include changes to innovation covariance portioning, covariance binning, and analysis increment calculation. A validation of the modified OI technique is presented, comparing the retrievals with the original technique in each case. The modified technique is able to perform retrievals with better accuracy, preserves local information better, and compares well with tower measurements.
    No preview · Article · Nov 2012 · IEEE Geoscience and Remote Sensing Letters
  • Aditya Choukulkar · Ronald Calhoun · Brian Billings · James Doyle
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    ABSTRACT: A study of an interesting meteorological episode over the Owens Valley, California, USA during the Terrain-Induced Rotor EXperiment was conducted using a recently adapted statistical interpolation method to retrieve wind-velocity vectors from Doppler lidar data. This vector retrieval method has been adapted from radar data assimilation techniques. Results show that the method allows better preservation of local variations in the flow field than other techniques. In addition, a high resolution Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS®) run is used to understand the large-scale flow within the valley and compared with lidar retrievals. Observations from 1030 UTC to 1230 UTC (0230 local time to 0430 local time) on March 27, 2006 are presented. Lidar observations show complex and uncharacteristic flows such as sudden bursts of westerly cross-valley wind mixing with the dominant up-valley wind. Model results from COAMPS and other in-situ instrumentation are used to corroborate and complement these observations. The optimal interpolation technique for Doppler lidar data vector retrieval appears well suited for scenarios with complex spatial variations in the flow field.
    No preview · Article · Sep 2012 · Boundary-Layer Meteorology
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    ABSTRACT: In this paper, the effect of several turbulence parameters during various flow conditions in Owens Valley, educed from coherent Doppler lidar data have been studied. Radial velocity structure functions are processed to estimate the turbulent kinetic energy (TKE) dissipation rate, integral length scale and velocity variance, assuming a theoretical model for isotropic wind fields. Corrections for turbulence measurements have been considered to address the complications due to inherent volumetric averaging of radial velocity over each range gate, noise of the lidar data, and the assumptions required to estimate effects of smaller scales of motion on turbulence quantities. Using data from the Terrain-induced Rotor Experiment (T-REX) in April–May 2006, vertical profiles of wind and turbulence parameters have been retrieved. During T-REX, unusual valley flows were detected by the lidar data, for example on 19 and 27 March 2006, daytime down-valley and night time up-valley flows, respectively, were observed. This paper focuses on understanding various turbulence parameters during these flow events. Turbulence estimates during daytime down-valley conditions were observed to be constant for most of the day, while for night time up-valley circumstances the turbulence increased steadily as the day progressed. Good comparison was observed between lidar and tower measurements, which validate the lidar turbulence retrieval assumptions. Comparison between TKE estimates from lidar and the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS) model is also presented. This analysis will be helpful for improving the current turbulence parameterization schemes in COAMPS. Finally, differences and similarities in turbulence measurements between both the flow regimes are discussed. Copyright © 2011 Royal Meteorological Society
    Preview · Article · Aug 2011 · Meteorological Applications
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    ABSTRACT: The Canopy Horizontal Array Turbulence Study (CHATS) experimental study was conducted at a Cilker Orchards's walnut blocks in Dixon, California, before and after leaves emerged, to help improve understanding, simulation capabilities, and modeling of coupled vegetation-atmosphere-land surface interactions. The campaign took place over 12 weeks in the spring of 2007 and was broken into three 4-week phases. Canopy-induced mechanical and thermodynamical vertical variation of turbulence transport characteristics and the linkages between canopy-scale motions and the larger scale planetary boundary layer (PBL) turbulence were measured. The observations focused on measurements characterizing stratification influences on the spatial structure of canopy-induced turbulence, the trace gas source/sink distribution associated with vegetation, and the overall impact of canopy-induced processes on trace gas transport.
    Full-text · Article · May 2011 · Bulletin of the American Meteorological Society
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    ABSTRACT: Accurate estimation of dissipation rate is important in understanding and analyzing turbulent flows found in environment and engineering processes. Many previous studies have focused on measuring the local dissipation rate at a single point or averaged dissipation rate over a suitable area. Since coherent Doppler lidar is capable of providing multi-point measurements covering a large spatial extent, it is well-suited for examining the distribution of dissipation in the atmosphere. In this paper, an approach is presented that is based on retrieving the dissipation rate from coherent Doppler lidar data using large-eddy simulation. Two Coherent Doppler lidars performed range height indicator (RHI) scans of a vertical/cross-barrier plane during the Terrain-induced Rotor Experiment (T-REX). Two-dimensional velocity vectors were retrieved using a least squares method. The velocity vectors retrieved from co-planar RHI scans are used to estimate subgrid scale (SGS) quantities through a known SGS parameterization. For the T-REX datasets analyzed, the dissipation rate was found to increase in the presence of rotors, subrotors, and, as expected, in regions of high wind shear. Owing to the presence of sharper gradients in subrotors, their dissipation rate is generally larger than that of rotors. KeywordsDissipation rate-Doppler lidar-Large-eddy simulations-Rotors-Subgrid scales-Subrotors-T-REX
    Full-text · Article · Jul 2010 · Boundary-Layer Meteorology
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    ABSTRACT: During the field campaign of the Terrain-induced Rotor Experiment (T-REX) in the spring of 2006, Doppler lidar measurements were taken in the complex terrain of the Californian Owens Valley for six weeks. While fast three-dimensional (3D) wind analysis from measured radial wind components is well established for dual weather radars, only the feasibility was shown for dual-Doppler lidars. A computationally inexpensive, variational analysis method developed for multiple-Doppler radar measurements over complex terrain was applied. The general flow pattern of the 19 derived 3D wind fields is slightly smoothed in time and space because of lidar scan duration and analysis algorithm. The comparison of extracted wind profiles to profiles from radiosondes and wind profiler reveals differences of wind speed and direction of less than 1.1 m s−1 and 3°, on average, with standard deviations not exceeding 2.7 m s−1 and 27°, respectively. Standard velocity–azimuth display (VAD) retrieval method provided higher vertical resolution than the dual-Doppler retrieval, but no horizontal structure of the flow field. The authors suggest a simple way to obtain a good first guess for a dual-lidar scan strategy geared toward 3D wind retrieval that minimizes scan duration and maximizes spatial coverage.
    Full-text · Article · Mar 2009 · Journal of Atmospheric and Oceanic Technology
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    Ronald J. Calhoun · H. J. S. Fernando
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    ABSTRACT: The PI's and ASU students/staff deployed their coherent Doppler lidar from May 9, 2007 to June 11, 2007 in support of the Canopy Horizontal Array Turbulence Study (CHATS) The experiment took place in a walnut orchard near Davis, California The overall purpose of the experiment was to investigate the character of within-canopy Sub-Filter-Scale motions The full experiment occurred in two segments: A) from March 18 - April 18, and B) from May 10 - June 10th The time period between the two measurement periods corresponded with the transition of the walnut grove from bare branches to full foliage The ASU lidar group joined the experiment for the second phase The primary motivations of the ASU lidar deployment were:
    Preview · Article · Feb 2008
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    Quanxin Xia · Ching-Long Lin · Ronald Calhoun · Rob K. Newsom
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    ABSTRACT: Two coherent Doppler lidars from the US Army Research Laboratory (ARL) and Arizona State University (ASU) were deployed in the Joint Urban 2003 atmospheric dispersion field experiment (JU2003) held in Oklahoma City. The dual lidar data are used to evaluate the accuracy of the four-dimensional variational data assimilation (4DVAR) method and identify the coherent flow structures in the urban boundary layer. The objectives of the study are three-fold. The first objective is to examine the effect of eddy viscosity models on the quality of retrieved velocity data. The second objective is to determine the fidelity of single-lidar 4DVAR and evaluate the difference between single- and dual-lidar retrievals. The third objective is to correlate the retrieved flow structures with the ground building data. It is found that the approach of treating eddy viscosity as part of control variables yields better results than the approach of prescribing viscosity. The ARL single-lidar 4DVAR is able to retrieve radial velocity fields with an accuracy of 98% in the along-beam direction and 80-90% in the cross-beam direction. For the dual-lidar 4DVAR, the accuracy of retrieved radial velocity in the ARL cross-beam direction improves to 90-94%. By using the dual-lidar retrieved data as a reference, the single-lidar 4DVAR is able to recover fluctuating velocity fields with 70-80% accuracy in the along-beam direction and 60-70% accuracy in the cross-beam direction. Large-scale convective roll structures are found in the vicinity of downtown airpark and parks. Vortical structures are identified near the business district. Strong updrafts and downdrafts are also found above a cluster of restaurants.
    Preview · Article · Jan 2008 · Journal of the Atmospheric Sciences
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    Ching-Long Lin · Quanxin Xia · Ronald Calhoun
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    ABSTRACT: The proper orthogonal decomposition technique is applied to 74 snapshots of 3D wind and temperature fields to study turbulent coherent structures and their interplay in the urban boundary layer over Oklahoma City, Oklahoma. These snapshots of data are extracted from single-lidar data via a four-dimensional variational data assimilation technique. The total velocities and fluctuating temperature are used to construct the data matrix for the decomposition; thus the first eigenmode represents the temporal mean of these data. Roll vortices with a wavelength-height ratio of 3.2 are identified in the first, most energetic eigenmode and are attributed to the inflection-point instability. The second and third spatial eigenmodes also exhibit roll characteristics with different time and length scales, resulting in clockwise-and counterclockwise-rotating roll vortices above the airport and the central business districts. Their positive correlation with temperature fluctuation suggests that those roll structures are driven by thermal as well as wind shear. Their limited horizontal extent seems to coincide with the path of the Oklahoma River. With decreasing rank, coherent structures undergo a transition from roll to polygon patterns. A localized downdraft or updraft located above a cluster of restaurants is captured by the fourth eigenmode. In the capping inversion layer, gravity wave eigenmodes are observed and may be attributed to convection waves. The representation of instantaneous snapshots by high-ranking eigenmodes is then examined by reconstruction of reduced-order fields. It is found that the first four eigenmodes are sufficient to capture the overall characteristics of the 74 snapshots of data.
    Preview · Article · Jan 2008 · Journal of the Atmospheric Sciences

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