Array processing

Analaysing seismic data with array processing tools.

Get and pre-process seismic data

Read

The package provides a top-level function read (module: data.py) based on the Obspy's read function. It returns a object of class stream with all the useful tools provided by Obspy. It can read almost all file formats (.sac, .mseed, ...).

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')

Pre-processing methods

In addition to the original methods attached to Obspy's stream class, some new methods are defined.

Trim the data without using UTCDateTime in the main code

This method simply allows not to import obspy.UTCDateTime in the main script in order to trim the data with the trim method. Additional kwargs to starttime and endtime are passed to the trim method of obspy.core.stream.Stream class.

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')
stream.cut(starttime='2017-01-01 01:34', endtime='2017-01-01 01:34')

Binarize the traces in the temporal domain

Divides each trace by its envelope. In order not to divide by 0, a regularization kwarg epsilon is define by default to 1e-10.

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')
stream.binarize()

Stationarize in the temporal domain

Divides each trace by their smooth envelopes. The smoothing is calculated with the Savitzky-Golay algorithm. The window kwargs controls the length of smoothing window, and the order controls the order of the method. Defaults are window=11, order=1. As with the binarization methods, a default epsilon is defined to 1e-10.

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')
stream.binarize()

Whiten each trace in the frequency domain

Divides each trace spectrum with its amplitude. if the method kwarg is set to onebit, no smoothing is applied to the amplitude. Otherwise, the amplitude is smoothed with the Savitzky-Golay algorithm, with a window of length smooth and a order 1.

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')
stream.whiten(method='smooth, smooth=11)

Show data

You can use the methods provided by obspy in order to show the data. Also, a show method is defined, currently under tests.

Calculate spectrograms

The spectrograms are calculated with the short-time Fourier transform function provided by Scipy (scipy.stft). This function is computationally efficient. The parameters are segment_duration_sec which defines the duration of the window in seconds onto which the spectra are calculated. The bandwidth kwarg is usedful to cut the spectra within a frequency band (in Hz), and therefore to reduce the memory usage.

Other keyword arguments are passed to the scipy.stft function. Default are:

• Sampling rate fs (obtained from the stream directly)
• Number of dots per segments nperseg (obtained from the stream directly)
• Overlapping between segments noverlap: by default 50%
• Number of frequency points for calculating the Fourier transform nfft (by default next power of two of the segments length)
• Window shape window (by default Hanning)
• Calculate one side of the spectra return_onesided (by default true because signals are real, we do not need both parts because of hermitian symmetry)

The function returns three variables: the spectrograms (shape = [n_traces, n_frequencies, n_times]), the frequncies in Hz, and the times in absolute matplotlib.dates format.

import arrayprocessing as ap

stream = ap.read('/path/to/traces/*.sac')
# some preprocessing

spectrogram, frequencies, times = stream.stft(segment_duration_sec=16, bandwidth=[3, 10])

Show speectrograms

You can show the spectrograms with the spectrogram method. Doc will come soon.

Show speectrograms

You can show the spectrograms with the spectrogram method. Doc will come soon.

correlation.py

antenna.py

synthetic.py

To-do list

• Create a calculate_coherence() method with a kwarg shanon_index or spectral_width
• Enrich the get_eigenvectors() method with datetime selection and frequency range selection
• Create self.z set to 0 when antenna is 2D, otherwise set to th values available in txt or csv file.
• Add a warning message in synthetic.spherical if none of the xyz or llz kwargs is set. Clarify spheri al function.