Short Course on Introduction to Meteorological Instrumentation and Observation Techniques

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Short Course on Introduction to Meteorological
Instrumentation and Observation Techniques

• WIND MEASUREMENTS
• Robert A. Baxter, CCM
• Parsons Engineering Science
• Pasadena, CA

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Session Overview
Goal Understand a general approach to measuring
wind and setting up and calibrating the wind
sensors

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Session Overview
Goal Understand a general approach to measuring
wind and setting up and calibrating the wind
sensors

• References and guidance
• Wind measurement
• Wind speed
• Wind direction

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References and Guidance
Document Year
Quality Assurance Handbook for Air Pollution Measurement Systems Volume IV Meteorological Measurements March, 1995
Meteorological Monitoring Guidance for Regulatory Modeling Applications February, 2000
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Measurement of Wind

• Wind is a vector quantity comprised of direction
  and speed

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Measurement of Wind

• Wind is a vector quantity comprised of direction
  and speed

• Measurement Method
• vector quantity
• Individual scalar quantities

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Measurement of Wind

• Wind is a vector quantity comprised of direction
  and speed

• Measurement Method
• vector quantity
• Individual scalar quantities

Most common approach is to measure the individual
scalar quantities
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Wind Measurement Methods

• Mechanical
• Non-mechanical

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Wind Measurement Methods

• Mechanical
• Cup and vane
• Propeller/vane
• Non-mechanical

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Wind Measurement Methods

• Mechanical
• Cup and vane
• Propeller/vane
• Non-mechanical
• Sonic
• Hot wire

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Wind Measurement Methods

• Mechanical
• Cup and vane
• Propeller/vane
• Non-mechanical
• Sonic
• Hot wire

• Focus on mechanical methods

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Measurement Characteristics

• Siting and exposure

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Measurement Characteristics

• Siting and exposure
• Transfer function

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Measurement Characteristics

• Siting and exposure
• Transfer function
• Starting threshold

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Measurement Characteristics

• Siting and exposure
• Transfer function
• Starting threshold
• Calibration and alignment methods

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Measurement Characteristics

• Siting and exposure
• Transfer function
• Starting threshold
• Calibration and alignment methods
• Other characteristics
• Distance constant
• Damping ratio
• Delay distance

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Siting and Exposure

• Siting
• For use in air quality modeling applications,
  meteorological data should be representative of
  conditions affecting the transport and dispersion
  of pollutants in the area of interest as
  determined by the locations of the sources and
  receptors being modeled

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Siting and Exposure

• Siting
• For use in air quality modeling applications,
  meteorological data should be representative of
  conditions affecting the transport and dispersion
  of pollutants in the area of interest as
  determined by the locations of the sources and
  receptors being modeled

• Representativeness
• Simple Terrain
• Complex Terrain
• Coastal Locations
• Urban Locations

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Siting and ExposureSimple Terrain
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Siting and ExposureSimple Terrain
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Siting and ExposureUrban Locations
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Siting and ExposureUrban Locations
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Siting and ExposureUrban Locations
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Siting and ExposureUrban Locations
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Measurement CharacteristicsWind Speed Transfer
Functions

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Measurement CharacteristicsWind Speed Transfer
Functions

• Describes the relationship between the rate of
  rotation and the wind speed

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Measurement CharacteristicsWind Speed Transfer
Functions

• Describes the relationship between the rate of
  rotation and the wind speed
• Determined through wind tunnel testing

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Measurement CharacteristicsWind Speed Transfer
Functions

• Describes the relationship between the rate of
  rotation and the wind speed
• Determined through wind tunnel testing
• Linear relationship above the starting threshold
  of the sensor

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Measurement CharacteristicsWind Speed Transfer
Functions

• Describes the relationship between the rate of
  rotation and the wind speed
• Determined through wind tunnel testing
• Linear relationship above the starting threshold
  of the sensor
• Near threshold response
• Cup anemometer
• Propeller anemometer

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Measurement CharacteristicsWind Speed Transfer
Functions

• What do the transfer functions look like?

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Measurement CharacteristicsStarting Threshold

• The wind speed at which an anemometer or vane
  first starts to perform within its specifications

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Measurement CharacteristicsStarting Threshold

• The wind speed at which an anemometer or vane
  first starts to perform within its specifications
• Applies to both wind speed and wind direction

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Measurement CharacteristicsStarting Threshold

• The wind speed at which an anemometer or vane
  first starts to perform within its specifications
• Applies to both wind speed and wind direction
• Wind tunnels are the only way to measure the
  starting threshold

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Measurement CharacteristicsStarting Threshold

• The wind speed at which an anemometer or vane
  first starts to perform within its specifications
• Applies to both wind speed and wind direction
• Wind tunnels are the only way to measure the
  starting threshold
• The starting threshold can be estimated by
  measuring the starting torque of the sensor

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Measurement CharacteristicsStarting Threshold
Calculation

• T K u2
• Where
• T is the torque( g-cm2/sec2)
• u2 is the square of the wind speed (m/s)
• K is the constant for the aerodynamic shape
  (g)
• u (T/K)

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Calibration and Operation Wind Speed

• Calibration in a wind tunnel

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Calibration and Operation Wind Speed

• Calibration in a wind tunnel
• Application of the transfer function
• Cup anemometer
• Propeller anemometer

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Calibration and Operation Wind Direction

• Vane alignment
• Sensor response and linearity

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Wind DirectionVane Alignment

• Finding true north
• Magnetic north and declination correction
• Solar methods and the Baxter Method
• Alignment using GPS

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Using the Step-by-Step Solar Method for Alignment

1. Measure the relative pointing direction
2. Measure the suns relative azimuth angle
3. Calculate the suns actual azimuth angle
4. Calculate the local deviation
5. Calculate the cross are true alignment
6. Align the wind direction sensor

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GPS Method for Alignment

• Walk off the alignment direction

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Wind DirectionVane Linearity

• Rotation through full range
• Alternative methods to protractor
• Reverse rotation

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Review of Wind Measurement

• References and guidance
• Siting and exposure
• Measurement characteristics
• Starting threshold
• Transfer function
• Calibration methods

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Sun Angle
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