"""
This module contains functions for correcting data for ship motion
"""
import numpy as np
[docs]def correct_wind(
ds,
wspd_name='wind_speed',
wdir_name='wind_direction',
heading_name='yaw',
cog_name='course_over_ground',
sog_name='speed_over_ground',
):
"""
This procedure corrects wind speed and direction for ship motion
based on equations from NOAA tech. memo. PSD-311. A Guide to Making
Climate Quality Meteorological and Flux Measurements at Sea.
https://www.go-ship.org/Manual/fluxhandbook_NOAA-TECH%20PSD-311v3.pdf
Parameters
----------
ds : xarray.Dataset
The ceilometer dataset to correct. The backscatter data should be
in linear space.
wspd_name : string
Wind speed variable name.
wdir_name : string
Wind direction variable name.
heading_name : string
Navigiation heading variable name.
cog_name : string
Course over ground variable name.
sog_name : string
Speed over ground variable name.
Returns
-------
ds : xarray.Dataset
The Xarray dataset containing the corrected values.
References
----------
Bradley, F. and Farall. C. (2007) A Guide to Making Climate Quality Meteorological
and Flux Measurements at Sea. Boulder, CO, NOAA, Earth System Research Laboratory,
Physical Sciences Division, 44pp. & appendices. (NOAA Technical Memorandum OAR PSD-311).
http://hdl.handle.net/11329/386
"""
# Set variables to be used and convert to radians
rels = ds[wspd_name]
reld = np.deg2rad(ds[wdir_name])
head = np.deg2rad(ds[heading_name])
cog = np.deg2rad(ds[cog_name])
sog = ds[sog_name]
# Calculate winds based on method in the document denoted above
relsn = rels * np.cos(head + reld)
relse = rels * np.sin(head + reld)
sogn = sog * np.cos(cog)
soge = sog * np.sin(cog)
un = relsn - sogn
ue = relse - soge
dirt = np.mod(np.rad2deg(np.arctan2(ue, un)) + 360.0, 360)
ut = np.sqrt(un**2.0 + ue**2)
# Create data arrays and add corrected wind direction and speed
# to the initial dataset that was passed in
wdir_da = ds[wdir_name].copy(data=dirt)
wdir_da.attrs['long_name'] = 'Wind direction corrected to ship motion'
ds[wdir_name + '_corrected'] = wdir_da
wspd_da = ds[wspd_name].copy(data=ut)
wspd_da.attrs['long_name'] = 'Wind speed corrected to ship motion'
ds[wspd_name + '_corrected'] = wspd_da
return ds