Algorithms were developed to determine the free period () and fraction of critical damping () and to determine the highfrequency corner () and fraction of critical damping () parameters by measuring the frequency response of the seismometer to known stimuli. The free period () and fraction of critical damping (), which describe the lowfrequency response, were determined via a grid search for the maximum variance reduction between the observed response and the theoretical time series response to a 401100 second period swept sine wave. The highfrequency corner () and fraction of critical damping (), which describe the highfrequency response, were determined via a grid search for the maximum variance reduction between the observed response and the theoretical phase response to a 0.540 Hz stepped sine wave. Both of these stimuli are generated by the Metrozet E300 electronics as well as output to the STS1 calibration coils, and they can be remotely invoked. Figure 3.29 shows an example of the observed and theoretical time series response to the swept sine wave stimulus, and Figure 3.30 shows an example of the observed and theoretical phase response to the stepped sine wave stimulus.
Figure 3.29:
Plot of the HOPS STS1 vertical seismometer observed time series response (solid line) and the corresponding theoretical time series response (dashed line). The best fitting theoretical response was determined via an adaptive migrating grid search to find the and which maximizes the variance reduction. The best fit was obtained for = 360.08 seconds and = 0.6768 critical.

Figure 3.30:
Plot of the HOPS STS1 vertical seismometer observed phase response (solid line) and the corresponding theoretical phase response (dashed line). The best fitting theoretical response was determined via an adaptive migrating grid search to find the and which maximizes the variance reduction. The best fit was obtained for = 14.998 Hz and = 0.371 critical.

Table 3.17:
Comparison of the sensitivities of the HOPS STS1's with Streckeisen and with Metrozet electronics. The Streckeisen sensitivities were obtained from the factory calibration sheets supplied with each seismometer. The Metrozet sensitivities were calculated using the STS1 Calibration Software Applet supplied by Metrozet.
Comp 
S/N 
Streckeisen BRB 
Streckeisen LP 
Metrozet BRB 
Metrozet LP 
Percent 


V/(m/s) 
V/(m/) 
V/(m/s) 
V/(m/) 
Change 
Z 
109114 
2452 
83.4 
2386 
80.5 
2.7 
N 
29219 
2284 
77.4 
1984 
66.9 
13.1 
E 
29215 
2304 
78.0 
1993 
67.0 
13.5 

Table 3.18:
HOPS STS1 calibration results.
Comp 




C 
Z 
á360.08 
á0.6768 
á15.00 
á0.371 
á0.00939 
N 
á362.93 
á0.6889 
á16.28 
á0.328 
á0.00909 
E 
á388.37 
á0.9920 
á16.29 
á0.343 
á0.00844 

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