compute_wind_direction

Module for computing wind direction from sonic anemometer measurements.

This module provides functions to convert wind measurements from sonic anemometer coordinate systems to meteorological wind direction conventions. It handles different sonic anemometer types (Gill, Campbell, etc.) and accounts for their specific mounting orientations.

See also

UCAR

https

//www.eol.ucar.edu/content/wind-direction-quick-reference (but there seems to be an error, with arguments of arctg2 eronously signed, and the routine is here vectorized for performance improvement)

Author, ------, B., University, Gembloux, Created, -------, 2020

Functions

compute_wind_direction

Convert sonic anemometer wind components to meteorological wind direction.
compute_wind_direction.compute_wind_direction(Usonic, Vsonic, SonicType, SonicNorthAzimuth)[source]

Convert sonic anemometer wind components to meteorological wind direction.

This function converts wind velocity components measured in sonic anemometer coordinates to meteorological wind direction (direction FROM which the wind is blowing). It handles different sonic types and mounting orientations. The function is vectorized for improved performance.

Coordinate Systems

Meteorological (target):

  • Umet: Positive = wind blowing to East

  • Vmet: Positive = wind blowing to North

  • Forms right-handed system with upward Wmet

  • Wind direction: 0° = North, 90° = East (direction wind is FROM)

Sonic (source):

  • Coordinate system varies by manufacturer

  • Vsonic axis angle (Vaz) depends on type:

    • CSAT3: Vaz = array direction - 90°

    • Gill R2: Vaz = N arrow + 240° (U flipped)

    • Gill R3/HS50 AXIS: Vaz = N arrow + 240°

    • Gill R3/HS50 SPAR: Vaz = N arrow + 270°

Coordinate Diagram:

v>0
^
|
|
+----> U>0

Converting between Sonic and Meteorological Coordinates Determine the angle with respect to true north, (0=N,90=E) of the +Vsonic direction. Call this angle Vaz. Looking from above, the sonic coordinate system is therefore rotated Vaz degrees clockwise from meteorological coordinates.

For ATI and Campbell CSAT3 sonics, Vaz is the direction relative to true north, straight into the array from the un-obstructed direction, minus 90 degrees. For Gill R2 sonics, if the sign of V is flipped, then Vaz is the angle of the N arrow + 60. If the sign of U is flipped, then Vaz is the N arrow direction + 240. For Gill R3s in the AXIS configuration, Vaz is the N arrow direction + 240 degrees.

From this Meteorological Coordinates, the direction the wind is blowing FROM is finaly computed :param Usonic: U wind component in sonic coordinates [m/s] :type Usonic: array_like :param Vsonic: V wind component in sonic coordinates [m/s] :type Vsonic: array_like :param SonicType: Sonic anemometer model/configuration:

  • ‘R2’: Gill R2

  • ‘R3Spar’: Gill R3 SPAR configuration

  • ‘R3Axis’: Gill R3 AXIS configuration

  • ‘HS50Spar’: Gill HS50 SPAR configuration

  • ‘HS50Axis’: Gill HS50 AXIS configuration

  • ‘CSAT3’: Campbell CSAT3

type SonicType:

str

param SonicNorthAzimuth:

Azimuth angle of sonic anemometer reference direction relative to true North [degrees] (=0 if pointing to North)

type SonicNorthAzimuth:

float

returns:

Dirmet – Wind direction in meteorological coordinates [degrees] (0-360°, direction wind is coming FROM)

rtype:

ndarray

Notes

The conversion process: 1. Convert U,V components to direction in sonic coordinates 2. Apply sonic-specific rotation (Vaz) 3. Correct for sonic mounting orientation (SonicNorthAzimuth) 4. Convert from ‘wind blowing TO’ to ‘wind blowing FROM’