slope_filter

function of dascore.proc.filter

source

slope_filter(
    patch: Patch ,
    filt: collections.abc.Sequence[float] ,
    dims: tuple[str, str] = (‘distance’, ‘time’),
    directional: bool = False,
    notch: bool = False,
)-> ‘PatchType’

Filter the patch over certain slopes in the 2D Fourier domain.

Most commonly this used as an F-K (frequency wavenumber) filter to attenuate energy with specified apparent velocities.

Parameters

Parameter	Description
patch	The patch to filter.
filt	A length 4 array of the form [va, vb, vc, vd]. If notch is False, the filter selects the apparent velocites between ‘vb’ and ‘vc’ with tapering boundaries from ‘va’ to ‘vb’ and from ‘vc’ to ‘vd’.
dims	The dimensions used to determine slope. The first dim is in the numerator and the second in the denominator. (eg distance, time) represents a velocity since distance/time has units of |L|/|T| (commonly m/s).
directional	If True, the filter should be considered direction. That is to say, the sign of the values in filt indicate the direction (towards or away) with increasing coordinate values. This can be used for up-down/left-right separation, assuming a near-linear fiber layoyt.
notch	If True, the filter represents a notch, meaning the slopes specified by the inner filt parameterse are attenuated rather than those outside of them.

Examples

# Example 1: Compare slope filtered patch to Non-filtered.
import matplotlib.pyplot as plt
import numpy as np
import dascore as dc
from dascore.units import Hz
# Apply taper function and bandpass filter along time axis from 1 to 500 Hz
patch = (
    dc.get_example_patch('example_event_1')
    .set_units(distance='m', time='s')
        .taper(time=0.05)
        .pass_filter(time=(1*Hz, 500*Hz))
)
filt = np.array([2e3,2.2e3,8e3,2e4])
# Apply fk filter
patch_filtered = patch.slope_filter(
    filt=filt,
        directional=False,
    notch=False
)
# Plot results
fig, (ax1, ax2) = plt.subplots(1, 2, figsize=(12, 8))
ax1 = patch.viz.waterfall(ax=ax1, scale=0.5)
_ = ax1.set_title('Raw')
ax2 = patch_filtered.viz.waterfall(ax=ax2, scale=0.5)
_ = ax2.set_title('Filtered')

# Example 2: Notch filter
patch_filtered = patch.slope_filter(filt=filt, notch=True)

# Example 3: specify units
filt = np.array([2e3,2.2e3,8e3,2e4]) * dc.get_unit("m/s")
patch_filtered = patch.slope_filter(filt=filt)