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Ludger Küperkoch 2015-04-08 11:29:50 +02:00
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#!/usr/bin/python
# -*- coding: utf-8 -*-
"""
Created Mar 2015
Transcription of the rezipe of Diehl et al. (2009) for consistent phase
picking. For a given inital (the most likely) pick, the corresponding earliest
and latest possible pick is calculated based on noise measurements in front of
the most likely pick and signal wavelength derived from zero crossings.
:author: Ludger Kueperkoch / MAGS2 EP3 working group
"""
import numpy as np
import matplotlib.pyplot as plt
from obspy.core import Stream
import argparse
def earllatepicker(X, nfac, TSNR, Pick1, iplot=None):
'''
Function to derive earliest and latest possible pick after Diehl & Kissling (2009)
as reasonable uncertainties. Latest possible pick is based on noise level,
earliest possible pick is half a signal wavelength in front of most likely
pick given by PragPicker or manually set by analyst. Most likely pick
(initial pick Pick1) must be given.
:param: X, time series (seismogram)
:type: `~obspy.core.stream.Stream`
:param: nfac (noise factor), nfac times noise level to calculate latest possible pick
:type: int
:param: TSNR, length of time windows around pick used to determine SNR [s]
:type: tuple (T_noise, T_gap, T_signal)
:param: Pick1, initial (most likely) onset time, starting point for earllatepicker
:type: float
:param: iplot, if given, results are plotted in figure(iplot)
:type: int
'''
assert isinstance(X, Stream), "%s is not a stream object" % str(X)
LPick = None
EPick = None
PickError = None
print 'earllatepicker: Get earliest and latest possible pick relative to most likely pick ...'
x = X[0].data
t = np.arange(0, X[0].stats.npts / X[0].stats.sampling_rate, X[0].stats.delta)
#some parameters needed:
tnoise = TSNR[0] #noise window length for calculating noise level
tsignal = TSNR[2] #signal window length
tsafety = TSNR[1] #safety gap between signal onset and noise window
#get latest possible pick
#get noise window
inoise = np.where((t <= max([Pick1 - tsafety, 0])) \
& (t >= max([Pick1 - tnoise - tsafety, 0])))
#get signal window
isignal = np.where((t <= min([Pick1 + tsignal + tsafety, len(x)])) \
& (t >= Pick1))
#calculate noise level
nlevel = max(abs(x[inoise])) * nfac
#get time where signal exceeds nlevel
ilup = np.where(x[isignal] > nlevel)
ildown = np.where(x[isignal] < -nlevel)
if len(ilup[0]) <= 1 and len(ildown[0]) <= 1:
print 'earllatepicker: Signal lower than noise level, misspick?'
return
il = min([ilup[0][0], ildown[0][0]])
LPick = t[isignal][il]
#get earliest possible pick
#get next 2 zero crossings after most likely pick
#initial onset is assumed to be the first zero crossing
zc = []
zc.append(Pick1)
i = 0
for j in range(isignal[0][1],isignal[0][len(t[isignal]) - 1]):
i = i+ 1
if x[j-1] <= 0 and x[j] >= 0:
zc.append(t[isignal][i])
elif x[j-1] > 0 and x[j] <= 0:
zc.append(t[isignal][i])
if len(zc) == 3:
break
#calculate maximum period T0 of signal out of zero crossings
T0 = max(np.diff(zc)) #this is half wave length!
#T0/4 is assumed as time difference between most likely and earliest possible pick!
EPick = Pick1 - T0/2
#get symmetric pick error as mean from earliest and latest possible pick
#by weighting latest possible pick two times earliest possible pick
diffti_tl = LPick - Pick1
diffti_te = Pick1 - EPick
PickError = (diffti_te + 2 * diffti_tl) / 3
if iplot is not None:
plt.figure(iplot)
p1, = plt.plot(t, x, 'k')
p2, = plt.plot(t[inoise], x[inoise])
p3, = plt.plot(t[isignal], x[isignal], 'r')
p4, = plt.plot([t[0], t[int(len(t)) - 1]], [nlevel, nlevel], '--k')
p5, = plt.plot(zc, [0, 0, 0], '*g', markersize=14)
plt.legend([p1, p2, p3, p4, p5], ['Data', 'Noise Window', 'Signal Window', 'Noise Level', 'Zero Crossings'], \
loc='best')
plt.plot([t[0], t[int(len(t)) - 1]], [-nlevel, -nlevel], '--k')
plt.plot([Pick1, Pick1], [max(x), -max(x)], 'b', linewidth=2)
plt.plot([LPick, LPick], [max(x)/2, -max(x)/2], '--k')
plt.plot([EPick, EPick], [max(x)/2, -max(x)/2], '--k')
plt.plot([Pick1 + PickError, Pick1 + PickError], [max(x)/2, -max(x)/2], 'r--')
plt.plot([Pick1 - PickError, Pick1 - PickError], [max(x)/2, -max(x)/2], 'r--')
plt.xlabel('Time [s] since %s' % X[0].stats.starttime)
plt.yticks([])
ax = plt.gca()
ax.set_xlim([t[inoise[0][0]] - 2, t[isignal[0][len(isignal) - 1]] + 3])
plt.title('Earliest-/Latest Possible/Most Likely Pick & Symmetric Pick Error, %s' % X[0].stats.station)
plt.show()
raw_input()
plt.close(iplot)
return EPick, LPick, PickError
if __name__ == "__main__":
parser = argparse.ArgumentParser()
parser.add_argument('--X', type=~obspy.core.stream.Stream, help='time series (seismogram) read with obspy module read')
parser.add_argument('--nfac', type=int, help='(noise factor), nfac times noise level to calculate latest possible pick')
parser.add_argument('--TSNR', type=tuple, help='length of time windows around pick used to determine SNR \
[s] (Tnoise, Tgap, Tsignal)')
parser.add_argument('--Pick1', type=float, help='Onset time of most likely pick')
parser.add_argument('--iplot', type=int, help='if set, figure no. iplot occurs')
args = parser.parse_args()
earllatepicker(args.X, args.nfac, args.TSNR, args.Pick1, args.iplot)