HR: 1340h
AN: S43B-1318    [Abstracts]
TI: Seismic Sensor Characterization Using Three-Sensor Coherence Analysis
AU: * Hart, D M
EM: dhart@sandia.gov
AF: Sandia National Lab Ground Based Monitoring R & E (Org. 5736), PO Box 5800 MS0404, Albuquerque, NM 87185-0404, United States
AU: Merchant, B J
EM: bjmerch@sandia.gov
AF: Sandia National Lab Ground Based Monitoring R & E (Org. 5736), PO Box 5800 MS0404, Albuquerque, NM 87185-0404, United States
AU: Chael, E P
EM: epchael@sandia.gov
AF: Sandia National Lab Ground Based Monitoring R & E (Org. 5736), PO Box 5800 MS0404, Albuquerque, NM 87185-0404, United States
AB: Sleeman, van Wettum, and Trampert (2006) recently introduced a method for measuring the intrinsic noise spectra of seismic sensors which relies on determining the mutual signal coherence among three similar, collocated instruments. This in contrast to the standard two-channel coherence tests where it is assumed that the incoherent noise can be equally distributed between the two sensors, or lumped to one of them. The three- sensor coherence technique uses the available comparisons among three sensors to uniquely distribute total incoherent noise power among the individual sensors. This technique also allows us to compare the relative phase and amplitude response between the sensors under analysis. Due to the wealth of sensor characteristics obtained from the three sensor coherence we are looking to add this technique to the suite of analysis tools we use for evaluating sensors at Sandia's Facility for Acceptance, Calibration and Testing (FACT) site. In this poster, we briefly describe the method and demonstrate its effectiveness using synthetic signals with known amounts of coherent and incoherent power. Next we apply the procedure to characterize broadband STS2 low-gain seismometers set up in a vault at the USGS's Albuquerque Seismological Laboratory. We also looked at determining self-noise of a Q330HR digitizer with this technique by feeding a single seismometer component (vertical) into three channels of a common digitizer electronics board. These test configurations allowed us to investigate the use of seismic background as the input signal versus a controlled input signal source. This provided insight into linearity versus SNR of the tested sensors and digitizer. Overall the technique appears promising for providing self-noise, and response characteristics.
DE: 7219 Seismic monitoring and test-ban treaty verification
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 7299 General or miscellaneous
SC: Seismology [S]
MN: 2007 Fall Meeting