Analysis of Wind Speed Measurement Technology and Metrological Assurance Systems

Wind, as the most direct manifestation of atmospheric motion, holds critical significance for precise measurement in fields such as weather forecasting, environmental monitoring, aerospace, and wind power generation.

1. Scientific Definition of Wind Speed and Wind Force

Wind speed refers to the rate of air movement relative to the Earth's surface, with the fundamental unit of measurement being meters per second (m/s). In meteorological applications, unit conversions are often required: 1 m/s = 3.6 km/h. Additionally, conversions to the imperial unit "knot (kn)" are also used (1 m/s ≈ 1.944 kn) to meet the needs of different scenarios.

It is important to clarify that wind speed itself does not have a hierarchical classification; rather, it serves as an objective basis for determining wind force levels. The internationally recognized Beaufort Wind Force Scale defines wind force levels based on empirical wind speed ranges under open and flat terrain conditions at a height of 10 meters above ground level. For example, a Beaufort force of 0 (calm) corresponds to wind speeds ≤0.2 m/s, while a Beaufort force of 12 (hurricane) corresponds to wind speeds ≥32.7 m/s. However, in special scenarios such as high-altitude atmospheres or typhoon centers, where airflow patterns differ, wind speed values must be directly analyzed rather than relying on the Beaufort scale.

Generally, wind speed values are positively correlated with wind force levels. An increase in wind speed signifies enhanced wind energy and potential environmental impacts, such as greater loads on structures or increased dispersion of pollutants.

2. Technical Classification of Wind Speed Measurement Instruments

Modern wind speed measuring instruments can be categorized into mechanical and electronic types based on their working principles. Significant differences exist in their metrological characteristics and applicable scenarios, necessitating selection according to actual needs.

2.1 Mechanical Anemometers

These instruments detect airflow dynamics through mechanical structures. They are simple in design, stable, and suitable for wind speed monitoring in conventional environments.

Propeller Anemometers: Composed of a wind vane and a propeller rotor, the wind vane ensures the rotor plane consistently faces the wind direction, allowing the rotor to fully capture the wind. Their measurement relies on the "linear relationship between rotor speed and wind speed" and is suitable for scenarios requiring simultaneous wind direction measurement, such as wind power generation. Compared to cup anemometers, they respond more sensitively to changes in airflow direction but require regular inspection for blade deformation—even minor bends can cause speed deviations, necessitating correction through metrological calibration.

Cup Anemometers: The core component consists of three hemispherical or parabolic cups mounted at 120° intervals, rotating around a vertical axis under wind force. Their measurement principle is based on the "linear relationship between cup rotation speed and wind speed within a specific range (typically 0.5–60 m/s)." Mechanical rotation speed is converted into electrical signals via photoelectric or magnetoelectric sensors, and the actual wind speed is calculated using a predetermined cup coefficient, determined through metrological calibration.

2.2 Electronic Anemometers

These instruments measure wind speed without mechanical wear by leveraging physical effects such as thermal conduction or acoustic wave propagation. They offer high sensitivity and rapid response, making them suitable for special environments or high-precision requirements.

Hot-Wire Anemometers: Based on the "thermal conduction effect," a fine metal wire is electrically heated to a constant temperature above the ambient level. Airflow passing over the wire dissipates heat, with the heat dissipation rate positively correlated with wind speed. By measuring the current changes required to maintain the wire's constant temperature, wind speed can be inferred. Their advantages include an extremely low starting wind speed and rapid response time, making them suitable for low-wind-speed measurements and turbulence research. However, factors such as air temperature and humidity affect heat dissipation efficiency, requiring correction via temperature compensation algorithms in practical use. Additionally, zero-point calibration every six months is necessary to prevent drift caused by electronic component aging.

Ultrasonic Anemometers: Based on the "vector superposition principle of ultrasonic propagation speed and airflow velocity," these typically feature three pairs of orthogonally installed ultrasonic probes (corresponding to the horizontal x-axis, y-axis, and vertical z-axis). By measuring the time difference (or phase difference) of ultrasonic waves propagating in "downwind" and "upwind" directions, wind speed components for each axis are calculated, and the total wind speed and direction are derived through vector synthesis. Their core advantages include no mechanical moving parts (maintenance-free) and the ability to perform simultaneous three-dimensional wind speed measurements, making them suitable for harsh environments such as plateaus or offshore wind farms.

3. Quality Assurance System for Wind Speed Measurement

To ensure the accuracy and reliability of wind speed measurement data, a comprehensive metrological assurance system covering the entire lifecycle of instruments must be established, encompassing "technical specifications, traceability, and on-site control."

3.1 Technical Specification System

China has developed a complete set of metrological technical regulations for different types of wind speed instruments, specifying calibration/verification methods, indicators, and requirements. Key current regulations include:

JJG 515-2018 "Verification Regulation for Portable Magnetic Wind Direction and Speed Meters": Applicable to portable magnetic wind speed meters commonly used in meteorological and environmental protection fields. This is a mandatory verification regulation (instruments used for trade settlement or environmental monitoring must undergo annual verification per this regulation). It specifies parameters such as the wind speed measurement range (0.5–30 m/s) and maximum permissible error (±(0.3 + 0.03v) m/s, where v is the actual wind speed).

JJF 1194-2023 "Calibration Specification for Vane-Type Digital Anemometers": Applicable to non-mandatory verification vane-type digital anemometers (e.g., instruments for building ventilation testing). It defines calibration items (zero point, linearity, repeatability) and methods, with a typical calibration cycle of one year, adjustable based on usage frequency.

JJF 1934-2020 "Calibration Specification for Ultrasonic Wind Direction and Speed Measuring Instruments": A specialized calibration specification for ultrasonic anemometers, outlining calibration methods for three-dimensional wind speed components. It requires wind speed ranges of 0.1–50 m/s and expanded uncertainties ≤2% (k=2) for each component.

3.2 Traceability System
Wind speed metrology must follow a hierarchical traceability path of "National Standards → Provincial Standards → Working Measuring Instruments" to ensure measurement results align with national benchmarks:

National Standard Level: The "Wind Tunnel-Type National Standard Wind Speed Device" established by the National Institute of Metrology, China, reproduces wind speed values of 0.1–100 m/s with an uncertainty ≤0.3% (k=2). This serves as the highest traceability reference for wind speed measurements nationwide.

Provincial/Municipal Standard Level: "Closed Wind Tunnel Standard Devices" or "Hot-Wire Anemometer Standard Devices" established by provincial metrology institutions achieve value transfer through comparison with national standards. These are used to calibrate working measuring instruments within their jurisdictions, with typical uncertainties ≤0.8% (k=2).

Working Measuring Instrument Level: On-site wind speed instruments must undergo verification or calibration based on their application. Instruments used in mandatory verification fields such as meteorological observation or aviation control must be sent to legal metrology institutions for verification per JJG regulations. Instruments used in non-mandatory fields such as wind power assessment or building ventilation may be calibrated per JJF specifications.

3.3 On-Site Error Control Measures

Even if instruments are verified/calibrated and deemed compliant, on-site installation and environmental conditions can introduce errors, necessitating targeted control measures:

Installation Environment Control:
① Height: Meteorological observation requires sensors to be installed at a height of 10 meters.
② Distance: The horizontal distance between the sensor and obstacles must be ≥2 times the obstacle's height.
③ Direction: Ensure probes face the prevailing wind direction.

Environmental Interference Correction:
① Temperature/Humidity: Hot-wire anemometers must activate temperature compensation functions.
② Precipitation/Dust: Mechanical anemometers must be selected in dust-proof and anti-icing models.
③ Electromagnetic Interference: Ultrasonic anemometers must be kept away from high-voltage lines and radio transmission towers.

4. Application Fields of Wind Speed Metrology

Accurate wind speed measurement and metrological assurance provide critical support for the safe operation and efficiency optimization across multiple fields:

Meteorological Monitoring: Wind speed instruments compliant with JJG 515-2018 are used to obtain near-surface wind speed data, providing foundational inputs for weather forecasting and climate research.

Wind Power Generation: During the preliminary stages of wind power projects, ultrasonic anemometers calibrated per JJF 1934-2020 are used for continuous one-year wind resource monitoring. During operation, real-time wind speed monitoring is required to trigger turbine shutdown protection.

Environmental Engineering: In atmospheric pollutant dispersion simulations, precise wind speed data is needed to calculate pollutant dispersion coefficients, influencing pollution control decisions.

Building Ventilation: Civil buildings use wind speed instruments calibrated per JJF 1194-2023 to measure indoor and outdoor air exchange rates, ensuring per capita fresh air volumes comply with regulations.

Aerospace: Airport runways require real-time wind speed monitoring, with takeoff and landing prohibited for civil aircraft when crosswind speeds exceed 15 m/s. Pre-launch high-altitude wind speed measurements are also critical for spacecraft.

The advancement of wind speed measurement technology and the refinement of metrological systems are central to obtaining reliable meteorological parameters across various fields. From the stability and durability of mechanical instruments to the high-precision responsiveness of electronic devices, and the comprehensive metrological assurance covering "national standards to on-site control," every aspect directly influences the credibility of wind speed data. With the development of sensing and digital technologies, wind speed measurement is evolving toward "intelligence, networking, and miniaturization," poised to play an increasingly critical role in global climate change research, efficient utilization of new energy sources, and extreme weather warnings. The continuous optimization of metrological systems will provide robust technical support for this progress.