1.0
0
20
0.8
40
0.6
60
0.4
80
0.2
100
0
120
0
50
100
150
200
0
50
100
150
200
1.0
0
20
0.8
Figure 18. Microphone spectrum
40
for .45 caliber pistol shot: (left) Lin-
0.6
60
ear scaling and (right) logarithmic
0.4
80
scaling. The large spectral depres-
0.2
100
sion at 60 Hz is a result of notch
0
120
filtering during the recording pro-
0
50
100
150
200
0
50
100
150
200
cess. The 180-Hz peak is probably a
1.0
0
20
0.8
40
0.6
60
0.4
80
0.2
100
0
120
0
50
100
150
200
0
50
100
150
200
Frequency (Hz)
Frequency (Hz)
spectra are the broadband nature of the signal and
complex and may be a result of several propaga-
tion factors such as modal effects associated with
the presence of two high-amplitude bins at 45 and
surface wave propagation and acoustic-to-seismic
70 Hz, separated by a deep spectral low around 60
coupling. The majority of the energy in vertical-
Hz (produced from a notch filter). The appearance
geophone spectra is contained in a band between
of the geophone response is considerably more
1.0
0
20
0.8
40
0.6
60
0.4
80
0.2
100
0
120
0
50
100
150
200
0
50
100
150
200
1.0
0
20
0.8
40
0.6
60
Figure 19. Spectra for three center
0.4
80
elements of the geophone subarray
0.2
for a .45 caliber pistol shot.
100
0
120
0
50
100
150
200
0
50
100
150
200
1.0
0
20
0.8
40
0.6
60
0.4
80
0.2
100
0
120
0
50
100
150
200
0
50
100
150
200
Frequency (Hz)
Frequency (Hz)
18
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