Subsections


Data Acquisition and Quality Control

Introduction

Stations from most networks operated by the BSL transmit data continuously to the BSL facilities on the UC Berkeley campus for analysis and archive. In this chapter, we describe activities and facilities which cross-cut the individual networks described in Chapters 38, 40 and 41, including procedures for data acquisition and quality control, and sensor testing capabilities and procedures. This year the computer and networking facilities used for data acquisition moved from McCone Hall to the University's seismically safe building at 2195 Hearst Ave.

While some of these activities are continuous from year to year, we have identified changes or activities which are specific to 2005-2006.

Figure 44.1: Data flow from the BDSN, NHFN, MPBO, HRSN, and BARD network into the BSL central processing facility.
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Data Acquisition Facilities

Until 2005-2006, both the BSL staff monitoring routine data acquisition, and the computers and facilities to acquire, process, and archive the data were situated in McCone Hall. There the BSL has facilities designed to provide air conditioning, 100-bit switched network, and reliable power with UPS and generator. During this year, the computers and telemetry equipment associated with data collection and archival were moved to the new campus computer facility in 2195 Hearst Avenue.

The Move to 2195 Hearst Avenue

After several years of actively working with the campus, the BSL has finally relocated the infrastructure supporting the critical operations of data acquisition, processing, archiving, and data distribution to a more robust facility than McCone Hall. With assistance from the Office of the Vice Chancellor for Research, the BSL has been granted space in 2195 Hearst, a recently completed building on the Oxford Tract. 2195 Hearst was constructed to current seismic codes, and the hardened campus computer facility within was designed with special attention for post-earthquake operations. The computer center contains state-of-the art seismic bracing, UPS power and air conditioning with generator backup, and extensive security and equipment monitoring.

During 2005-2006, the BSL completed the relocation of equipment to the new facilities in 2195 Hearst. This includes all of its data acquisition and real-time earthquake processing computers, as well as the data archive and distribution computers. Following the computer move, all telemetry equipment (5 T1s lines, dedicated leased phone circuit to our paging service, dialin/dialout modems, as well as various radio and VSAT communication equipment) were also transferred to the new location over the course of several months. The final elements were moved in February, 2006. During the transition, the private network used for seismic data acquisition and earthquake processing was temporarily bridged between McCone Hall and 2195 Hearst using an encrypted tunnel across the campus backbone network.

Power and Air Conditioning in McCone Hall

In the past, mission-critical earthquake monitoring and review processes ran on several computers in McCone Hall. Thus, these computer systems run on circuits with both UPS and generator power. Air conditioning is provided through both "building air" and two additional AC units. Over the years, the BSL has experienced problems with both the McCone generator system and the air conditioning.

With the move of many BSL and NCEDC operations servers to the campus computer center at 2195 Hearst (SRB1), our generator power and air conditioning resources in the BSL server room in 237 McCone have better matched our needs over the past year. The BSL generator and UPS battery system supported servers during one brief power outage this year. The air conditioning systems for room 237 required maintenance and some parts replacement, but no serious problems resulted during these events. The BSL generator is maintained by Physical Plant Capital Services and was run without load twice monthly.

BSL is developing a long range plan with UCB Communications Network Services (CNS), a division of Information Services and Technology, to replace the generator with a larger, 100 kW unit, and to upgrade the UPS battery backup systems. This joint project is designed to provide generator/UPS power for the two CNS-operated network equipment closets serving all of McCone Hall, in addition to providing emergency power to the BSL suite and the BSL engineering lab in room 298 McCone. BSL and CNS will present this plan to the Vice Chancelor Academic Council for approval and assistance with funding for this proposal.

Data Acquisition

Central-site data acquisition for the BDSN/NHFN/MPBO is performed by two computer systems located at the BSL (Figure 44.1). These acquisition systems are also used for the Parkfield-Hollister electromagnetic array and for the BARD network. A third system is used primarily as data exchange system with the USNSN and transmits data to the USNSN from HOPS, CMB, SAO, WDC, HUMO, MOD, MCCM, and YBH. Data acquisition for the HRSN follows a more complicated path, as described in Chapter 41.

Figure 44.2: Dataflow in the REDI processing environment, showing waveform data coming in from the Quanterra data loggers (Q) into comserv. From comserv, data are logged to disk (via datalog), distributed to other computers (mserv), fed into the CDA for REDI processing, and spooled into a trace ring for export.
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Comserv

The BSL uses the comserv program for central data acquisition, which was developed by Quanterra. The comserv program receives data from a remote Quanterra data logger, and redistributes the data to one or more comserv client programs. The comserv clients used by REDI include datalog, which writes the data to disk files for archival purposes, cdafill, which writes the data to the shared memory region for REDI analysis, and other programs such as the seismic alarm process, the DAC480 system, and the feed for the Memento Mori Web page (Figure 44.2).

The two computers that perform data acquisition also serve as REDI processing systems. In order to facilitate REDI processing, each system maintains a shared memory region that contains the most recent 30 minutes of data for each channel used by the REDI analysis system. All REDI analysis routines first attempt to use data in the shared memory region, and will only revert to retrieving data from disk files if the requested data is unavailable in the shared memory region.

Each BDSN datalogger that uses frame relay telemetry is configured to enable data transmittion simultaneously to two different computers over two different frame relay T1 circuits to UCB. However, the BSL normally actively enables and uses only one of these data stream from each station at any given time. The comserv client program cs2m receives data from a comserv and multicasts the data over a private ethernet. The program mcast, a modified version of Quanterra's comserv program, receives the multicast data from cs2m, and provides a comserv-like interface to local comserv clients. This allows each REDI system to have a comserv server for every station, and each of the two systems have a complete copy of all waveform data.

We have extended the multicasting approach to handle data received from other networks such as the NCSN and UNR. These data are received by Earthworm data exchange programs, and are then converted to MiniSEED and multicast in the same manner as the BSL data. We use mserv on both REDI computers to receive the multicast data, and handle it in an identical fashion to the BSL MiniSEED data.

In 2006, the BSL established a real-time data feed of all BSL waveform between the BSL acquisition systems and the NCEDC computers using the open source Freeorb software. This allows the NCEDC to provide near-real-time access to all BSL waveform data through the NCEDC DART (Data Availabile in Real Time) system.

Seismic Noise Analysis

BSL seismic data are routinely monitored for state-of-health. An automated analysis is computed weekly to characterize the seismic noise level recorded by each broadband seismometer. The estimation of the Power Spectral Density (PSD) of the ground motion recorded at a seismic station provides an objective measure of background seismic noise characteristics over a wide range of frequencies. When used routinely, the PSD algorithm also provides an objective measure of seasonal and secular variation in the noise characteristics and aids in the early diagnoses of instrumental problems. A PSD estimation algorithm was developed in the early 1990's at the BSL for characterizing the background seismic noise and as a tool for quality control. As presently implemented, the algorithm sends the results via email to the engineering and some research staff members and generates a bargraph output which compares all the BDSN broadband stations by components. A summary of the results for 2005-2006 is displayed in Figure 38.2. Other PSD plots for the NHFN, HRSN, and MPBO are shown in Figures 40.2, 41.3, respectively.

Four years ago, we expanded our use of the weekly PSD results to monitor trends in the noise level at each station. In addition to the weekly bar graph, additional figures showing the analysis for the current year are produced. These cumulative PSD plots are generated for each station and show the noise level in 5 frequency bands for the broadband channels. These cumulative plots make it easier to spot certain problems, such as failure of a sensor. In addition to the station-based plots, a summary plot for each channel is produced, comparing all stations. These figures are presented as part of a noise analysis of the BDSN on the WWW at http://www.seismo.berkeley.edu/seismo/bdsn/psd/.

The PSD algorithm has been documented in previous annual reports.

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 McNamara and 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 extended the McNamara code to cover a larger frequency range and 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 44.3 shows noise analysis results for a typical week. We review these plots as part of our assessment of station health.

Figure 44.3: Noise analysis results for the week of 07/02/06 at the newest BDSN station MCCM, on the BHZ component. The prominent feature at short periods are produced by waves from the nearby earthquake off-shore of Fort Ross, California, (2006/07/06, 20:43 UTC; $M_{L}$ 3.7). At long periods, the surface waves of a $M_{w}$ 6.6 earthquake in the Aleutian Islands (2006/07/08, 20:40 UTC) dominate the spectrum.
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Sensor Testing Facility

The BSL has set up an instrumentation test facility in the Byerly Seismographic Vault in order to systematically determine and to compare the characteristics of up to eight sensors at a time. The test equipment consists of an eight-channel Quanterra Q4120 high-resolution data logger and a custom interconnect panel that provides isolated power and preamplification, when required, to facilitate the connection and routing of signals from the sensors to the data logger with shielded signal lines. This year a GPS rebroadcaster was installed, so that all data loggers in the Byerly vault will operate on the same time base. Upon acquisition of the 100 samples-per-second (sps) data from the instruments under test, PSD analysis and spectral phase coherency analysis are used to characterize and compare the performance of each sensor. Tilt tests and seismic signals with a sufficient signal level above the background seismic noise are also used to verify the absolute calibration of the sensors. A simple vertical shake table is used to assess the linearity of a seismic sensor.

The sensor testing facility of the BSL is described in detail in the 2001-2002 Annual Report.

STS-1 Electronics Development

In February 2006, we embarked on a project to develop new electronics for the STS-1 very broadband seismometer. This is a collaborative project with Tom VanZandt of Metrozet, LLC (Redondo Beach, CA) and is funded by a grant from NSF through the IRIS/GSN program.

The STS-1 VBB (Wielandt and Streckeisen, 1982; Wielandt and Steim, 1986), widely viewed as the finest VBB sensor in the world, is currently the principal broad-band seismometer used by the Incorporated research Institutions for Seismology (IRIS) Global Seismographic Network (GSN), GEOSCOPE, and several other global or regional seismic networks operated by members of the Federation of Digital Broad-Band Seismograph Networks (FDSN). The installed base (approximately 750 sensor axes) represents a very significant international investment for low frequency seismology. The BDSN includes 10 STS-1's in its network. Unfortunately, many of the STS-1 seismometers, which were manufactured and installed 10-20 years ago, are encountering both operational failures and age-related errors (Ekström and Nettles, 2005). This problem is exacerbated by the fact that sensors are no longer being produced or supported by the original manufacturer, G. Streckeisen AG (Pfungen, Switzerland). The nature and severity of this problem has been discussed widely. For example, a report from a recent broadband seismic sensor workshop (Ingate et al, 2004) highlights the unique value of the installed base of STS-1 sensors, as well as the current lack of replacements with equivalent long period performance. In the absence of focused action by the seismological community, the state-of-health of the existing STS-1 instruments will continue to decline. Numerous efforts, both commercial and government-funded, are underway to develop future replacements (IRIS Workshop, 2004). Regardless of how one views the potential of these new approaches to delivering a manufacturable, STS-1-equivalent product, given the present funding environment, it is clear that they all would mandate outright replacements of the existing STS-1 sensors.

In collaboration with its commercial partner, Metrozet, LLC (Redondo Beach, CA), the BSL is developing and testing new electronic hardware, and methods for mechanical repair, for the STS-1. The intent of this effort is to develop simple and economical long-term solutions to current and anticipated problems with the existing STS-1 sensors. A primary aim is to develop a fully-tested, modern electronics module that will be a drop-in replacement for the original electronics. This will provide users with a legitimate option for replacing old modules that are no longer functioning. This new electronics design will address environmental packaging problems that have led to operational errors and failures in the existing instruments. This effort will also provide the opportunity to implement a set of electronic improvements that will make the installation and operation of the sensors more efficient.

In the first half of 2006, Metrozet developed the first prototype and reverse engineered electronics for the STS-1, while the BSL engineering staff constructed a test-bed at the Byerly Vault (BKS) and developed the capability to simultaneously test 6-8 STS-1 components. Much time was spent locating spare STS-1's and the associated environmental shields and bringing them back to Berkeley.

Acknowledgements

Doug Neuhauser, Bob Uhrhammer, Peggy Hellweg, Pete Lombard, and Rick McKenzie are involved in the data acquisition and quality control of BDSN/NHFN/MBPO data. Development of the sensor test facility and analysis system was a collaborative effort of Bob Uhrhammer, Tom McEvilly, John Friday, and Bill Karavas. IRIS and DTRA provided, in part, funding for and/or incentive to set up and operate the facility and we thank them for their support. Bob Uhrhammer, Peggy Hellweg, Pete Lombard Doug Neuhauser and Barbara Romanowicz contributed to the preparation of this chapter. The STS-1 project is funded by NSF through the IRIS/GSN program.

References

Ekström, G. and M. Nettles, http://www.seismology.harvard.edu/~ekstrom/Projects/WQC.html, 2005.

Ingate, S. et al, Workshop Report from Broadband Seismometer Workshop, Lake Tahoe, CA, http://www.iris.edu/stations/seisWorkshop04/report.htm, 2004.

McNamara, D. and R. Buland, Ambient Noise Levels in the Continental United States Bull. Seism. Soc. Am., 94, 4, 2004.

Scherbaum, Frank. Of Poles and Zeros: Fundamentals in Digital Seismology, Volume 15 of Modern Approaches in Geophysics, G. Nolet, Managing Editor, Kluwer Academic Press, Dordrecht, xi + 257 pp., 1996.

Tapley, W. C. and J. E. Tull, SAC - Seismic Analysis Code: Users Manual, Lawrence Livermore National Laboratory, Revision 4, 388 pp., March 20, 1992.

Wielandt, E. and G. Streckeisen, The leaf spring seismometer: design and performance, Bull. Seis. Soc. Am., 72, 2349-2367, 1982.

Wielandt, E. and Steim, J. M., A digital very broad band seismograph, Annales Geophysicae, 4 B(3), 227-232, 1986.

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