Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
D5741-96 – Standard Test Method Technical Guide
📐 Scope and Terminology
ASTM D5741-96 (Reapproved 2023) covers a method for characterizing surface wind speed, direction, peak one-minute speeds, peak three-second speeds, and standard deviations of fluctuation about the means of speed and direction. This practice may be used with other kinds of sensors if their response characteristics are equivalent or faster and measurement uncertainty is equivalent or better. The characterization provided is acceptable for a wide variety of applications based on consensus from a 1992 workshop.
Key terminology defined in this standard includes aerodynamic roughness length (z0), damped natural wavelength (λd), damping ratio (η), and distance constant (L). Aerodynamic roughness length is the height above surface where extrapolation of wind speed measurements would predict zero wind speed, often estimated from landscape description. Damped natural wavelength and damping ratio are characteristics of wind vane dynamic performance, determined per ASTM D5366. Distance constant is the air flow distance during anemometer response time. For terms not defined herein, refer to ASTM D1356.
| 🟦 Term | 📏 Symbol | 📐 Definition | 🎯 Unit |
|---|---|---|---|
| Aerodynamic Roughness Length | z0 | Height where wind speed extrapolates to zero | m |
| Damped Natural Wavelength | λd | Vane characteristic related to delay distance | m |
| Damping Ratio | η | Ratio of actual to critical damping | dimensionless |
| Distance Constant | L | Air flow distance during anemometer response | m |
⚙️ Sensor Requirements and Performance
This practice is intended for use with wind vane and rotating anemometer. Sensors must have response characteristics equivalent or faster than those specified, with measurement uncertainty equivalent or better. Referenced standards include ASTM D5096 for determining the performance of cup or propeller anemometers and ASTM D5366 for determining dynamic performance of wind vanes. The distance constant and damping ratio are critical performance parameters.
The damped natural wavelength can be estimated from the delay distance and damping ratio using equations in D5366. Proper sensor selection ensures reliable wind characterization for wide applicability.
| 🟦 Standard | 📐 Title | 🔍 Purpose |
|---|---|---|
| D1356 | Terminology Relating to Sampling and Analysis of Atmospheres | Provides atmospheric terminology |
| D5096 | Test Method for Determining the Performance of a Cup Anemometer or Propeller Anemometer | Evaluates anemometer performance |
| D5366 | Test Method for Determining the Dynamic Performance of a Wind Vane | Evaluates wind vane dynamics |
📊 Characterizing Wind Variables
This standard provides characterization of surface wind including mean speed and direction, peak one-minute speeds, peak three-second speeds, and standard deviations of fluctuation about these means. These values are essential for meteorological assessments, air quality dispersion modeling, and wind energy applications.
Peak three-second speeds capture short-duration gusts, while peak one-minute speeds indicate sustained conditions. Standard deviations reflect turbulence intensity and atmospheric stability, critical for understanding boundary layer processes.
© 2026 TNLab — This article is a technical interpretation for reference only. The original standard as published by ASTM International takes precedence.