Source code for opendrift.readers.reader_current_from_track

# This file is part of OpenDrift.
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# OpenDrift is free software: you can redistribute it and/or modify
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# the Free Software Foundation, version 2
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# GNU General Public License for more details.
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# along with OpenDrift.  If not, see <https://www.gnu.org/licenses/>.
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# Copyright 2019, Ole Baadshaug, MET Norway & Ron Saper, Carleton University Canada.
#
# Caveat: This copyright will not interfere with the open nature of OpenDrift and OpenBerg

import numpy as np
from datetime import timedelta, datetime
import pyproj

from opendrift.readers.basereader import BaseReader, ContinuousReader

[docs]class Reader(BaseReader, ContinuousReader): variables = ['x_sea_water_velocity', 'y_sea_water_velocity'] def __init__ (self, obslon, obslat, obstime, obsfile=None, wind_east=0, wind_north=0, windreader=None, wind_factor=0.018, name=None): """ Reader which statistically extrapolate current forcing. It uses the residual track obtained by subtracting the wind forcing component from the past observed motion of a particle. """ if name is not None: self.name = name else: self.name = 'reader_current_from_observation' # Cover whole earth, no validity radius yet self.proj4 = '+proj=latlong' self.xmin = -180 self.xmax = 180 self.ymin = -90 self.ymax = 90 self.z = np.ma.array([0.], mask=[False],fill_value=1e+20) self.start_time = obstime[1]+timedelta(hours=1) self.end_time = self.start_time+timedelta(days=10) self.times = np.arange(self.start_time, self.end_time, timedelta(hours=1)).astype(datetime) self.time_step = self.times[-1] - self.times[-2] time_delta_seconds = (obstime[1]-obstime[0]).total_seconds() if windreader is not None: x0,y0 = windreader.lonlat2xy(obslon[0], obslat[0]) x1,y1 = windreader.lonlat2xy(obslon[1], obslat[1]) #NB! Use wind speeds at observed positions wind0 = windreader.get_variables_interpolated_xy(['x_wind', 'y_wind'], x=x0, y=y0, z = self.z, time=obstime[0])[0] wind1 = windreader.get_variables_interpolated_xy(['x_wind', 'y_wind'], x=x1, y=y1, z = self.z, time=obstime[1])[0] meanwind_x = (wind0['x_wind'][0]+ wind1['x_wind'][0])/2 meanwind_y = (wind0['y_wind'][0]+ wind1['y_wind'][0])/2 else: meanwind_x = wind_east meanwind_y = wind_north # wind_east/north should be given in m/s g = pyproj.Geod(ellps='WGS84') self.azimuth, backazimuth, self.dist = \ g.inv(obslon[0], obslat[0], obslon[1], obslat[1], radians=False) self.speed = self.dist/(time_delta_seconds) #Calculate the average speed in x/y-direction of the residual self.x_sea_water_velocity = np.atleast_1d(self.speed*np.sin(np.radians(self.azimuth)) - meanwind_x*wind_factor) self.y_sea_water_velocity = np.atleast_1d(self.speed*np.cos(np.radians(self.azimuth)) - meanwind_y*wind_factor) super(Reader, self).__init__()
[docs] def get_variables(self, requested_variables, time=None, x=None, y=None, z=None): requested_variables, time, x, y, z, outside = self.check_arguments(requested_variables, time, x, y, z) nearestTime, dummy1, dummy2, indxTime, dummy3, dummy4 = \ self.nearest_time(time) variables = {} variables['x_sea_water_velocity'] = self.x_sea_water_velocity*np.ones(len(x)) variables['y_sea_water_velocity'] = self.y_sea_water_velocity*np.ones(len(y)) return variables