PDF Noise Analysis

In addition to the PSD analysis developed by Bob Uhrhammer, the BSL has implemented the Ambient Noise Probability Density Function (PDF) analysis system developed by Dan McNamara and Ray Buland (2004). This system does its noise analysis over all the data of a given time period (week or year), including earthquakes, calibration pulses, and cultural noise. This is in contrast to Bob Uhrhammer's PSD analysis which looks at only the quietest portion of data within a day or week. Pete Lombard of the BSL has extended the McNamara code to cover a larger frequency range and to support the many different types of sensors employed by the BSL. Besides the originally supported broadband sensors, our PDF analysis now includes surface and bore-hole accelerometers, strain meters, and electric and magnetic field sensors. These enhancements to the PDF code, plus a number of bug fixes, were provided back to the McNamara team for incorporation in their work. The results of the PDF analysis are presented on the web at http://moho/seismo/PDF/. Figure 9.3 shows the noise analysis results for a typical week.

Figure 9.3: Noise analysis results for the week of 01/30/05 at BDSN station MHC, on the HHZ component. Prominent features in the figure are the Alum Rock earthquake (2005/02/05, 18:43 UTC; $M_{L}$ 4.4; and a prominent noise spike near 30 HZ, probably due to rotating machinery nearby to the station at the Mount Hamilton Observatory.
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