Seismic and Infrasound Sensor Testing Using Three-Channel Coherence Analysis
Abstract
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. Unlike standard two-channel coherence tests, the available comparisons among three sensors allow the total incoherent noise power to be uniquely distributed among the individual sensors. We are looking to add this technique to the suite of tests we use for evaluating sensors at Sandia National Laboratories' Facility for Acceptance, Calibration, and Testing (FACT) site. In this paper, 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 Albuquerque Seismological Laboratory (ASL) of the United States Geological Survey (USGS). In addition, we have tested some Chaparral 2.5 infrasound sensors, first exposed to ambient atmospheric background and then isolated inside a sealed test chamber for recording a controllable broadband pressure source. We also looked at determining digitizer self-noise 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 two primary aspects of the input signal character, i.e., signal-to-noise ratio (SNR) and background vs. generated signals. They also allow us to investigate the linearity aspects of the sensor and digitizer in the presence of large background signals. Besides permitting the proper allocation of the incoherent noise among the three sensors, the technique also produces more stable sensor noise estimates in high signal-to-noise situations than the two-channel approach, as long as the participating sensors have reasonably similar performance over the analysis band.
Document Details
- Document Type
- Technical Report
- Publication Date
- Sep 01, 2007
- Accession Number
- ADA519294
Entities
People
- Darren Hart
- Eric P. Chael
- John Merchant
Organizations
- Sandia National Laboratories