Data Acquisition and Quality Control

Introduction

Stations from the networks operated by the BSL transmit data continuously to the BSL facilities on the UC Berkeley campus for analysis and archival. In this section, we describe activities and facilities which pertain to the individual networks described in Sections 1, 3, and 4, including procedures for data acquisition and quality control, and sensor testing capabilities and procedures. Some of these activities are continuous from year to year and have been described in prior BSL annual reports. In this section, we describe changes or activities which are specific to 2007-2008.

Figure 3.24: Data flow from the BDSN, NHFN, MPBO, HRSN, and BARD network into the BSL central processing facility.

Data Acquisition Facilities

Before 2005-2006, both the BSL staff monitoring routine data acquisition and the computers and facilities to acquire, process, and archive the data were located in McCone Hall. Since 2006, the computers and telemetry equipment associated with data acquisition reside in the new campus computer facility at 2195 Hearst Avenue. This building was constructed to current ``emergency grade'' seismic codes, and is expected to be operational even after a $M$ 7 earthquake on the nearby Hayward Fault. 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. With the move of many BSL and NCEDC operations servers to the campus computer center, the generator power and air conditioning resources in the BSL server room in 237 McCone better match our needs for the infrastructure remaining in McCone Hall. The BSL generator is maintained by Physical Plant Capital Services and is run without load twice monthly. During the past year, we noted problems with the UPS and replaced defunct batteries. In addition, during a spell of hot weather the cooling system failed, requiring repairs.

Data Acquisition

Central-site data acquisition for data from the BDSN/NHFN/MPBO networks is performed by two computer systems in the 2195 Hearst Avenue data center (Figure 3.24). These acquisition systems also collect data from the Parkfield-Hollister electromagnetic array and the BARD network. A third system is used primarily for data exchange with the USNSN and transmits data to the USNSN from HOPS, CMB, SAO, WDC, HUMO, MOD, MCCM, and YBH. Data acquisition for the HRSN was upgraded during the past year, to use the USGS T1 from Parkfield to Menlo Park. This is described in Section 4. We also collected data from local USArray travelling array stations from the orb-server of the Anza Network Facility at the University of California San Diego until the array moved out of California in the late fall of 2007.

Figure 3.25: 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.

The BSL uses the program comserv developed by Quanterra for central data acquisition. This 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 3.25). The two computers performing data acquisition also serve as REDI processing systems and hold the databases now used by these systems for storing earthquake information. 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 data logger that uses frame relay telemetry is configured to enable data transmission 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 streams 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 has 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 waveforms 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. For several years now, we have been monitoring the seismic stations and telemetry using the program seisnetwatch. This program extracts current informaiton such as time quality, mass positions, and battery voltage and allows it to be displayed. If the parameter departs from the nominal range, the station is marked with yellow or red to indicate a possible problem.

Seismic Noise Analysis

BSL seismic data are routinely monitored for state-of-health. An automated analysis is computed regularly to characterize the seismic noise level recorded by each broadband seismometer.

PSD Noise Analysis

The estimation of the Power Spectral Density (PSD) of the ground motion recorded at a seismic station, as documented in the 2000-2001 BSL annual report (http://seismo.berkeley.edu/annual_report/ar00_01/), 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 bar graph output which compares all the BDSN broadband stations by components. We also use the weekly PSD results to monitor trends in the noise level at each station. 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 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/.

PDF PSD 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 performs 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://www.ncedc.org/ncedc/PDF/. One difficulty with using these plots for review of station quality is that it is necessary to look at data from each component separately. To provide an overview, we have developed summary figures for all components in two spectral bands, 30 - 60 s and 0.125 - 0.25 s.

Sensor Testing Facility

The BSL has an Instrumentation Test Facility in the Byerly Seismographic Vault in order to systematically determine and 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. A GPS rebroadcaster has also been installed, so that all data loggers in the Byerly vault operate on the same time base. Upon acquisition of data at up to 200 samples-per-second (sps) from the instruments under test, PSD analysis, coherence analysis, and additional ad hoc analysis algorithms 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 BSL 2001-2002 Annual Report (available on-line at http://www.seismo.berkeley.edu/). Several projects made use of the sensor testing facility in 2007-2008. Initial tests of the new STS-1 electronics (E300) took place in Byerly Vault (see Section 9). In addition, the new pressure/temperature sensors were installed and data collected for calibration and assessment (see Section 9). Finally, the facility will house initial tests of new STS-1-type sensors being developed jointly by Metrozet and the BSL.

Acknowledgements

Doug Neuhauser, Bob Uhrhammer, Peggy Hellweg, Pete Lombard, Rick McKenzie and Jennifer Taggart 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 section. The STS-1 project is funded by the NSF through the IRIS/GSN program (IRIS Subaward Agreement number 388). This is a collaborative project with Tom VanZandt of Metrozet, LLC (Redondo Beach, CA).

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