pyspec example notebook: 1D spectrum

This notebook showcases a basic usage of pyspec for computing 2D spectrum and its associated isotropic spectrum. Other featrures such as bin average in log space and confidence limit estimation are also shown.



In [1]:

    
import numpy as np
import matplotlib.pyplot as plt
%matplotlib inline

import scipy.signal as signal

import seawater as sw

from pyspec import spectrum as spec

load data



In [2]:

    
fni = "data/lg0703_nb150.npz"



In [3]:

    
data = np.load(fni)

Select a gap-free segment



In [4]:

    
fmax = 135
lon,lat = data['lon1'][:fmax],data['lat1'][:fmax]
u, v = data['u1'][0,:fmax],data['v1'][0,:fmax]
urot, vrot = data['u1_rot'][0,:fmax],data['v1_rot'][0,:fmax]



In [5]:

    
d,ang = sw.dist(lat,lon,units='km') 
dist = np.append(0.,np.cumsum(d))



In [49]:

    
uspec = spec.Spectrum(urot[:].copy(),dt=5)
vspec = spec.Spectrum(vrot[:].copy(),dt=5)



In [67]:

    
ksp, Pu_sp = signal.welch(urot[:], fs=1/5., window='hanning', nperseg=urot[:].size, noverlap=False,
                             detrend='constant', scaling='density', axis=-1)
_, Pv_sp = signal.welch(vrot[:], fs=1/5., window='hanning', nperseg=urot[:].size, noverlap=False,
                             detrend='constant', scaling='density', axis=-1)

Plot spectra



In [7]:

    
fig = plt.figure(figsize=(9,7))
ax = fig.add_subplot(111)
ax.loglog(uspec.f,uspec.spec,'m')
ax.loglog(ksp,2*Pu_sp,'m--')
ax.loglog(vspec.f,vspec.spec)
ax.loglog(ksp,2*Pv_sp,'b--')
ax.set_xlabel('Wavenumber [cpkm]')
ax.set_ylabel(r'KE spectral density [m$^2$ s$^{-1}$/cpkm]')



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