• With close to 20 presentations over the next three days, speakers were urged to keep to assigned times, and questioners warned that discussion may be cut short at times. The plentitude of talks is a positive reminder of much ongoing detector characterization activity.
• Points to discuss during the sessions:
• Unfilled Data Monitor Tool (DMT) tasks
• Better integration of DC group into on-site science, including participation in upcoming engineering runs (round-table discussion)
• Infrastructure (hardware & software) for future off-site DC analysis (round-table discussion)

• John began with a summary of data acquisition (DAQ) and DMT performance during the April engineering run (2-km single arm). The IFO was in lock most of the time with 42 locked sections of average length 1667 seconds. Unlocked sections averaged only 37 seconds.
• 174 channels were selected and written to to disk, giving 50 GB of data, all of which is available online at LHO and at CACR.  A timing error in initialization caused 18 frames of data to be lost, and 1.5 hours were lost when the fortress computer hung. It is thought that both problems will not recur in the next run, and monitors have been written to look for them in real-time.
• Although a glitch prevented testing of trigger generation during the run, the test was carried out afterward in a real-time replay mode and was successful. One monitor tested looked for discontinuities in the data stream and saturation, and another recorded power in resonance peaks into trend frames.  The interface to the meta-database (GUILD - P. Shawhan) worked very well, but could be further improved with more flexible trigger analysis for verification.
• A new production version (1.2) of the DMT was released July 14 with extensive changes (see /export/home/dmt/pro/Changes on the sand machine). These included various bug fixes and the following new functionality in the infrastructure
• Reworked trigger generation and a trigger manager
• More API's and utilities for background monitors
• More efficient operation
• Extension of many classes
• In addition, software contributed by LSC members was incorporated (multitaper line tracker - A. Ottewill, operational state conditions - KR (see talk below), time-frequency plots - S. Mohanty & S. Siddiqui)
• A new patch release (1.2.1) is in preparation with fixes to new bugs and additional functionality, including a script for monitoring the data distribution. The patch will also include support for wavelet tools and a line remover (S. Klimenko - see talk below) and another line remover (A. Sintes - see talk below).

• A quick review was given of the data reduction milestones decided upon at the last LSC meeting:
• A data distribution template is in draft form. P. Shawhan's clearing house web page  gives information on accessing and understanding the data from the April engineering run. D. Strom has provided a web page of links to more information on data access and includes a sample program for looking at data using root and the DMT.
• A prototype decimation routine (E. Mauceli) for the D MT has been written and used in a tiltmeter study (see talk below). This code needs further development to allow arbitrary bandwidth and should allow for a wavelet compression option.
• Benchmarks for data reductions have been proposed (S. Klimenko) to quantify information loss based on a chi-square method in the time domain and to quantify CPU efficiency using two existing algorithms (differentiation with gzip and frame library algorithm) to any proposed new algorithm.
• Wavelet compression (lossy and lossless) has been tested on the April engineering data (see Klimenko talk below).
• Linear predictors code is under development (N. Zotov).
• The outline of a straw man reduced data set selection was presented at the last LSC meeting, leading to about 200 kB/s per interferometer. No feedback was received on the strawman, but the channels selected for the engineering run in April amounted to about 680 kB/s with no decimation.
• Reduced data samples will be useful in future engineering runs, and an effort will be mounted to prepare for the next one this fall at Hanford. Discussion ensued on what should be attempted during or after that run. It's not clear that manpower is available to complete the necessary software changes for real-time data reduction. D. Sigg pointed out that even using the decimation-by-two algorithm (FIR filter) already installed in the DMT creates non-trivial synchronization problems for channels decimated by different factors. Ultimately it is planned to make available a reduced data set with which DMT  software developers can test their algorithms to see what if any degradation is caused by the reduction.

Note added by KR: Further discussions are underway to make sure these tests can be carried out soon. Benoit Mours of VIRGO who is on sabbatical at Caltech this year has offered to help out. Technical details in data transfer to tape and decisions on what reduction/compression should be done on LDAS computers must be confronted in the long term. For the next engineering run, some data will be written to fortress (as in April) for recording to tape, and data compression will probably not be attempted in real-time (instead carried out afterward with a dedicated program).

• The data set simulation program using phenomenological parametrization (written in Matlab) is essentially complete. It is available on a Penn State web site and has also been given to the End-To-End modelling group for incorporation. Some of that incorporation is complete.
• Additional functionality in this final version includes violin modes, better thermal noise modelling, hooks for astrophysical sources (prototype for inspirals included), and a streamlined frame reader and writer. Version 4 frames are produced. The parametrization used is the same as in Sam's Bench program.
• On a 5-year-old SGI workstation, the program can generate simulated data at a rate 10 times real-time (with all bells & whistles enabled).
• F. Raab would like the program to be available to IFO operators and urged that someone from Penn State arrange for the required knowledge to be imparted.
• D. Sigg mentioned that incompatibilities might arise in frame files since some of the code running on site might not recognize simulated data. It was pointed out that we should be careful to mark in the frames that they represent simulated not real data! One scheme is to use negative run numbers; another is to use the formal simdata structure supported by the frame library, but here incompatibility with data-reading software is more likely.

• Although the DMT infrastructure is in great shape (see Zweizig talk above), there are several problems that need to be addressed:
• LSC-contributed software is arriving in various states, most not amenable to immediate use by operators or commissioners.
• Other DMT code that is in use at one or both sites is not integrated into the DMT process manager environment.
• Some priority 2 tasks have no volunteers yet.
• Some promised software shows no sign of imminent delivery.
• Most DMT software developers must keep in mind two somewhat conflicting goals: to provide flexible tools for general use and specific monitors useful now to non-C++-conversant operators and commissioners. To date providing tools has received by far the most attention.
• To help developers make code more useful, templates are needed for background monitors. Two categories of such monitors are needed: performance characterization, where summary info is written periodically to trend frame files (along with other info perhaps) and transient analysis where aperiodic triggers are generated for logging, setting EPICS alarms and writing meta-database entries. Both types of monitor should also serve up data on request to the DMT display manager (now under development by D. Sigg & J. Zweizig).
• KR will work with John to make a transient analysis template based on servo instability detection code (see talk below). A volunteer was requested to help develop a useful performance characterization template. Peter Shawhan and Sergey Klimenko expressed interest later in helping out on this.
• DMT software developers should model deliverables after one of these templates (or at least provide the same functionality).
• LHO operator Rick Graff has agreed to work with software developers to test new code and to transmit information to other LHO operators.
• Brief status summaries were given for eighteen priority 1 and 2 DMT tasks - see transparencies.

• KR had raised the issue in the opening plenary session (see transparencies) of the need for increasing participation by non-Lab LSC members in the science at the Hanford and Livingston sites. In short, too many members are too detached from site operations to make effective contributions to detector characterization. For example, contributed DMT software sits unused because it requires writing new programs to use tools or simply because no effort has been made to educate the operators or IFO commissioners (see preceding talk too). In addition, there are upcoming engineering runs at LHO and LLO that will required scientific monitoring shifts to be manned.
• B. Barish prefaced the discussion by restating the Lab's willingness to help groups with travel support while they await word from NSF on travel supplement requests or increased-baseline proposals. He stressed, however, that only trips of at least 2 weeks duration would be considered for LAB support. He has spoken with Joe Dehmer of NSF who says he recognizes the need for such travel support and believes it will not be a problem. Barry also mentioned the Lab policy that Lab scientists are expected to spend an average of one week out of four at one of the sites and are encouraged to pick one site to maximize efficiency. It was suggested that physicists responding to the need for more LSC presence at the sites plan to spend an average of at least one week out of six at a site in order not to qualify as a "tourist".
• S. Whitcomb suggested that the LIGO PAC be told explicitly which LSC groups are making the most useful contributions at the sites, information to be used by the PAC in evaluating NSF proposals. Barry remarked that the PAC has begun to take a more active role in prioritizing such proposals and that the NSF does listen.
• Representatives of several groups stated their plans for stationing physicists on site:
• Penn State I (Sam Finn) - Willing to station a postdoc on site one week out of six. Have requested additional travel funds from NSF to start in August 2001. Would have to request Lab support to start sooner.
• Penn State II (Gabriela Gonzalez) - Planning to send a graduate student to a site for two weeks twice in each semester.
• Oregon (Jim Brau) - Postdoc Robert Schofield is resident at Hanford, along with graduate student Masahiro Ito. Departing postdoc Evan Mauceli has been making regular visits to Hanford, and his replacement will too. Faculty and other students make occasional visits.
• Florida (Bernard Whiting) - Planning to send a member to Hanford for an average of one week out of eight (Sergey Klimenko & Bob Goldberg). (This is in addition to Florida physicists working on input optics commissioning). It was suggested that rather than alternating between Sergey and Bob, that only one person make regular visits in order to be more efficient (or to increase the frequency for both).
• Syracuse (Peter Saulson) - Peter is resident at Livingston this year on sabbatical. Willing to ratchet up the presence of postdoc Steve Penn who now makes occasional visits.
• LSU (Joe Giaime) - Postdoc Ed Daw is resident at Livingston. With frequent visits by Joe and students, at least another half-FTE is on site. It is hoped to station an additional postdoc there half time in the future.
• Michigan (KR) - Research scientist Dick Gustafson is resident at Hanford. Graduate student Dave Chin will be making regular visits of at least two weeks duration roughly three times per semester. KR will increase the frequency of his visits.
• Details of the upcoming engineering run haven't been worked out, but the most likely time for the Hanford 2-km run will be the 2nd or 3rd week of November. A "signup sheet" will be posted on the Web showing the commitments by LSC groups to man scientific monitoring shifts during each upcoming run. LSC groups are urged to "vote with their feet" to demonstrate commitment to making LIGO successful. Members of the ASIS working group are also strongly urged to join in this effort.

• Wavelet compression has been developed and tested on the April engineering data, using both lossless and lossy techniques. It was suggested that Level 1 data (first cut at reduction) may be appropriate for lossless or "quasi-lossless" reduction, while Level 2 and 3 data would require lossy techniques.
• Wavelets allow de-correlation and decomposition transformations that give compact representation of the DATA. Some of the same infrastructure can be used for lossless and lossy compression. A lossless Random Data Compression (RDC) algorithm has been developed that exploits the near Gaussianity of LIGO data. A transformation makes the data more Gaussian and then an encoder optimized for Gaussian noise is applied. The bit mapping for the 16-bit sampled LIGO data words was outlined with diagrams and examples. The RDC gives more compression of white Gaussian noise than the gzip program and does so by a factor of five faster.
• A table of lossless compression ratios achieved with various IFO and environmental channels recorded in the April engineering run was shown with comparisons among gzip, ERI (commerical package) and the RDC for time series data and for various forms of transformed data. RDC consistently outcompressed gzip and usually did better than ERI. For 16 kHz channels, the average RDC compression ratio was about 2.2 and for 2 kHz data was about 1.9.
• In carrying out lossy compression, the technique chosen was frequency-dependent reduction of dynamic range in the wavelet domain. To avoid introducing non-random noise artifacts, the algorithm is based on a simple truncation of an integer ratio.
• Tables and plots were shown of achieved compressions for the GW channel vs the loss as defined by the chi-square figure of merit. A compression rate of 3 can be achieved for an information loss of 0.1%. Comparisons were also shown with the MPEG3 algorithm used for audio compression. Plots of spectra before and after lossy compression show well-preserved spectral shapes even for compression ratios approaching five, except near the Nyquist frequency for 16 kHz channels.

• This study (based on the April engineering run data) was carried out to investigate whether tiltmeters could be used as effective accelerometers in a feed-forward control servo to stabilize test masses against micro-seismic motion at about 0.15 Hz (suggested by R. Schofield). Tiltmeters also seem more stable against noise at lower frequencies. They can be used as accelerometers because an acceleration by g*theta is equivalent to a tilt by theta.
• The main component seen in the one-arm test error signal is tidal drift. For the moment, the drift has been fitted with a polynomial and removed. This still leaves oscillations with a period of about 500 seconds, perhaps due to the temperature cycle of the air handling systems (needs further investigation). The power spectrum of the residual error signal shows a very strong micro-seismic peak.
• The tiltmeter signal also shows long-term drift, thought to be from thermal effects, perhaps differential expansion of the legs (needs further investigation).
• One expects a correlation between the length control signal and the difference in tiltmeter signals at the LVEA and the mid station. To make the comparison, the tiltmeter signals were subjected to a simple bandpass filter in the 0.1 to 1.0 Hz range and a pair of coefficients determined from a chi square fit to the error signal and a sum of terms depending on both (filtered) tiltmeter signals. The coefficients found were -0.42 +- 0.01 and +0.23 +- 0.01  times seconds**2 times g.
• Applying the coefficients allows a reduction in total rms of the error signal by 4% (after tidal correction) and in the 0.1-0.3 Hz range by about 30%. Similar results are found from using twice-differentiated seismometer signals with nearly identical coefficients obtained. The seismometer signals provide a 35% reduction in rms in the 0.1-0.3 Hz range.
• The same technique was also applied at much lower frequencies to see if the 500 Hz oscillations might be real tilts. One can reduce the power at those low frequencies, but it's not clear for this 1-day data sample whether the correlations are accidental or secondary. D. Sigg pointed out that during the April run the microseismic activity was much lower than is typical, suggesting that the tiltmeter correction will typically have a larger effect on total rms.
• Future plans include applying better filters, studying long-term tiltmeter behavior and better tidal effect corrections (working with F. Raab).

• Online tools (Data Viewer, Diagnostic Test Tool, Data Monitor Tool) are in good shape, but we will also want to carry out analysis offline for 1) detailed transient investigation, 2) analysis of large data samples, and 3) comparison of different analysis techniques on same data. This talk addressed data access & viewing, environment for automated analysis, summary data object standards, and viewing / manipulation of summary data objects.
• For offline analysis the Guild program allows display of meta-database information and writing of raw data to disk using the frameAPI. The Xlook program allows viewing of the lightweight data files. But what is lacking is display of raw data, display of trend data, and access by programs.
• Peter proposed making the Data Viewer and DTT available for offline use, to set up a trend server for off-site clients, a data flow manager (intermediary btw programs and LDAS, along with network data server for transplanted online programs) , an index of information services, and a LAL package for parsing lightweight LIGO data.
• For manipulating data summary objects (e.g., power spectra), objects would be stored in lightweight format in individual files with indices for random access. Matlab would be used to display and manipulate the objects.
• An offline environment is needed for automated analysis (repetitive tasks). Candidates considered so far include C/C++, Matlab, Triana, and PSE/SCIRun:
• C/C++ provides flexibility and allows (in principle) linking to LAL and DMT libraries, but signal processing functions must be written from scratch. One possibility is to link to the Matlab math library. In any case, one would want to establish a standard i/o paradigm and standard main programs.
• Matlab has many advantages (maturity and widespread use, many built-in functions, nice graphics, good documentation, extensibility with compiled C/C++ code and access to primitive datatypes & operations). Disadvantages include cost ($1200+ for academic license), slowness for interpreted scripts, and difficulty in parallelizing. Adapting to LIGO needs would require creating tools and example scripts. Simulink might be a good model to follow. One would probably want to link in the LAL and/or DMT libraries.
• Triana (developed by GEO in java) has a nice graphical interface, customized GW analysis signal processing tools, a natural pipeline analysis structure and can be parallelized. Disadvantages include unwieldy primitive operations, a limited graphics module,  and the relative unfamiliarity & slowness of java.
• PSE / SCIRun (developed at University of Utah for biophysics and 3-D problem solving/visualization) is written in C++ with a Tcl/Tk graphical interface. Its advantages include that it's free, multi-threading for multi-processor machines, speed & good memory management, and extensibility in familiar programming languages. Disadvantages include no built-in signal processing, no conventional 2-D visualization and little formal documetnation. Much work would be required to make it usable.
• Peter's recommendation is to focus on C++ for batch processing with link access to the DMT and LAL libraries (and perhaps to Matlab libraries) and to focus on Matlab for scripted interactive analysis and for viewing / manipulation of summary data objects.
• A key point is the need to start building tools and expertise for offline analysis with widespread sharing. Peter offered to set up a clearinghouse web site for offline analysis tools, documentation, and usage notes. He will also make a list of tasks needed to provide the ideal analysis environment. Collaborators are most welcome.

• This talk and the previous one served as introductions to a round-table discussion on off-site detector characterization analysis. Daniel began with sobering numbers on data access rates.
• Reading frames from disk, one can read all channels at 5 times real-time and 1-10 channels at 50-100 times real-time. Reading from tape, one contends with a 2-minute delay, data rates of 10-20 MB/s, giving a maximum of four times real-time (if one is reading a tape with all channels recorded).
• In reading data from archived frames at CACR, a request for 1 week of 1 channel requires 2 days of reading and 2 days for T1 internet transfer. 1 week of 1000 channels requires the same time to read, but 1 year to transfer! This assumes data is stored frame by frame, as produced at the sites.
• If the data is stored instead as striped frames (separate files for separate channels), then the total read/transfer time is proportional to the number of channels requested, and 8-bit 2 kHz channels can be read 16 times faster than 16-bit 16 kHz channels. For example, one week of a slow channel that has been compressed by a factor of two can be read in 1-2 minutes and transferred over the internet in 3 hours. Thus striping helps in both read-time and transfer, but the transfer times are still long.
• Four user models for detector characterization analysis were presented for consideration:
• Model 0:  Work with online data only
• Model 1:  Work with reduced data sets at home institutes and contend with substantial delays
• Model 2:  Work on computers near archive (physically or remotely)
• Model 3:  Work online over the internet
• Model 2 seems the most useful and versatile by far, but it requires access to general-purpose computing with high-bandwidth access to the data archive(s).

• Peter's and Daniel's presentations raised many issues that hadn't received much attention, given the focus to date on online analysis, leading to much discussion that wandered at times.
• Here is an over-simplified and abbreviated summary of salient points;
• The issues raised are important and need to be addressed sooner than we had thought.
• Data will disappear quickly at the sites (fortress can store of order 1 day of full data), and the local LDAS tape archive can store about a week.
• Stuart Anderson stated that LDAS plans to provide several general-purpose workstations near the CACR archive that permit five simultaneous users with data access rates of 10 MB/s. This may well be sufficient for our needs. These computers are separate from the "sandbox" linux machines for LDAS analysis development.
• LDAS will keep three copies of the full data: one at CACR in the original frame-by-frame format with all channels, one at CACR in channel-striped frames, and one at another physical location for safekeeping.
• Matlab has served people well for interactive and even batch offline analysis. There are many tools already developed for GW analysis which could be immediately useful. Peter was strongly encouraged to create his proposed clearinghouse web page for Matlab tools and other offline analysis tools. He was also encouraged to compile a list of tasks needed to create a useful offline analysis environment that could run on the LDAS workstations at  CACR (and perhaps elsewhere), based on C/C++ programs and Matlab.

PEM Audit at LIGO Livingston (Joe Kovalik - LIGO-LLO)

• Several UT Brownsville undergraduates (recruited by Joe Romano) spent the summer at Livingston systematically "auditing" the Physical Environment Monitoring (PEM) channels. The purpose of the audit was to verify channel operation from PEM sensor to data acquisition and to catalog the "typical" behaviors of the channels.
• Verification includes checking the sensor for reasonably correct response to controlled disturbances (for the time being, calibrations provided by sensor manufacturers have been assumed to be correct), checking cabling, correct channel labelling and the response of the associated A/D.
• For every data channel, a record is stored of a sample times series, power spectrum of appropriate bandwidth, a long time series where appropriate, a histogram of time series amplitudes (with and without filtering), and probability density plots for the histograms. In addition, records were made for different periods (night/day, quiet/noisy). Input from the DC group on other quantitites to compile is encouraged.
• Roughly 100 channels of non-IFO data have been catalogued. These have various sampling rates and can be used for vetos or for feed-forward servo control.
• Examples of cataloguing info were shown for tiltmeters and accelerometers. The tiltmeters were first run through a "huddle" test with 4 instruments in the same location to estimate systematic noise and test mounting techniques. One instrument each was then placed in the corner station, end stations and on the surface in a "stay clear zone". The tiltmeter showed very good correlation in the huddle test with some variation in DC offset with instrument and support (styrofoam or granite, styrofoam giving a bit less noise).
• For the accelerometers, sample real-time data viewer output, power spectra, amplitude histogram and derived probability density were shown. R. Weiss urged that the compiled information be placed on the Web.
• Joe remarked that this has been an extremely effective outreach program for UTB students from which both they and LIGO greatly benefited.

 

• A new DMT monitor class has been created that allows detection of a variety of environmental transients and is easily extensible. So far derived classes have been written to look for seismic and magnetic field transients.
• A sample calling sequence and a sample class definition code was shown. For the time being, thresholds and other parameters are hardwired into the class definition. Evan (or his successor at Oregon) was urged to provide run-time configuration files to allow easy tuning of monitors during development.
• The basis of each transient detection is a certain number of channels exceeding a threshold absolute deviation from the nominal mean by some number of sigma. Generated triggers contain the start/stop times for a disturbance, an amplitude figure of merit and current channel statistical measures.
• The statistical measures for each channel used to define baseline conditions are based on the last 10 intervals of 30 seconds where no trigger may occur during that time.
• The seismic monitor was run for six days in late July and detected all three earthquakes reported in the Pacific Northwest's seismic network. Three additional triggers were generated of unknown origin, one of which is suspected to come from some cryogenic tank filling. Time series were shown of computed averages and standard deviations for five seismometer channels over the test run, with large quakes clearly visible.
• One problem found in the algorithm for determining the threshold was seen during a large Russian earthquake in which multiple triggers were generated for the single quake.
• Future improvements include triggered threshold adjustments, sending of trigger info to a web page for display, and band-limiting filters.
• A. Lazzarini suggested Evan contact Rohay of Battelle to share seismic data. LIGO seismometers add significantly to the local seismic network.

• Wavelet tools have been integrated into the next DMT release (see Zweizig talk above) in a package called the Wavelet Analysis Tool (WAT). The wavelet compression algorithms described above use these tools, which include several different "families" of wavelets with associated methods. root macro files are also available for plotting wavelet information.
• The families include Daubechies and Lifting wavelets (which allow direct mapping of integers to integers). Wavelet coefficients can be computed according to an ordinary or binary wavelet tree.
• Examples were shown of wavelet transformations on white Gaussian noise data with a linear chirp superposed. The linear chirp is quite visible in the wavelet time-frequency plot. Examples were also shown for the single-arm control signal in the April engineering run. The wavelet tools provide a means for detection, identification and perhaps removal of a broad range of transients.
• A line filter class has also been written for the DMT that allows finding and removing specified harmonics of a given line. The information is stored in a linked list and a number of convenient methods provided for accessing and applying the information to clean data.
• The Quasi-Monochromatic line removal algorithm developed at Florida is used at the moment, but the class has been designed with other line tracking/removal algorithms in mind and can be extended in a straightforward way. Sergey has offered to work with Adrian Ottewill and Alicia Sintes (see talk below) on integrating their algorithms into the same framework.
• Documentation for the Wavelet Analysis tool can be found at http://www.phys.ufl.edu/LIGO/wavelet/index.html and documetnation on the line removal software at http://www.phys.ufl.edu/~klimenko.
• Future plans include adding families of Gaussian and symmetric Daubechies wavelets and developing wavelet-based transient detection.

• Julien began with a detailed explanation of the algorithm used to detect transients and then gave examples of transients found in the April engineering run data. The software (program called tid) is routinely run at both IFO sites using the DMT  library. Operators have been given a tutorial on its use.
• The technique is based on applying an adaptive threshold to spectrograms. The algorithm is fast, robust against stationary non-Gaussian noise, colored noise and strong transients. The statistics of transient detection can be controlled in a known way by resolution choice.
• Actual detection is based on looking for significant "clusters" of pixels in a time-frequency display where a pixel is turned on if the power in a certain frequency band exceeds an adjustable, frequency-dependent threshold. Application of the algorithm to the April 1-arm control signal shows a false-alarm rate much higher than expected for Gaussian noise for nominal parameters.
• This transient detection has been augmented by searches for coincidences between the GW and PEM channels. A "coincidence gate" allows adjustment of false alarm rates. The gate is based on a metric-like measure of closeness of two clusters where the "coordinates" represent numbers of pixels, mean occurrence time, mean frequency, etc. An example was shown of computing a confidence interval for the GW "foreground" rate from measured GW foreground, GW background and seismic foreground.
• The tid program has been used to detect and identify overhead aircraft which shows a characteristic Doppler shift of a monochromatic source (at ~80 Hz) of approach and recession. An example was shown of a fitted curve to an s-shaped band of T-F pixels due apparently to a plane travelling overhead at 560 km/h at 3750 m altitude. A filter bank runs continuously at Hanford to scan over "airplane parameter space", looking for the characteristic s-curve signature.
• Other examples of recurring transient patterns observed include:
• Narrow-band periodic bursts of duration ~100 seconds every ~15 minutes.
• A ~17 Hz resonance (pendulum roll mode?) driven by occasional impulses with the resonance decaying over ~100 seconds.
• Strings of symmetric bursts.

• Operational state conditions allow specifying a set of conditions before undertaking an analysis or writing frames to disk. A DMT class has been written to allow run-time ascii config file specification of such conditions, including Boolean combinations of conditions. Examples conditions include requiring the mean or rms value in a time interval exceed a threshold or lie in a certain range or requiring certain bits in a control flag to be on or off.
• Example code and config files were shown. The code has been integrated into the latest DMT release and is used by the designer data set writer. The source code, sample program, makefile and documentation can be found in ~dmt/cvs/dmt/src/dmtlib/osc on the Hanford sand or stone machines.
• The operational state conditions have been enhanced recently to allow detection of servo instabilities that include true runaway behavior, gain peaking and excitation of out-of-band resonances, such as internal test mass vibration modes. Examples of new conditions include excess power in a given frequency band, rapid rise in absolute or fractional power in a band, and rapid power magnitude rise in a band.
• A separate ascii config file is used to control the behavior of a monitor that uses the new conditions. Examples of config files used to detect excitation of the "butterfly" test mass resonance were shown. One can choose merely to log detected instabilities or in addition, to generate an EPICS alarm and/or write an entry to the meta-database.
• Although the expanded set of servo conditions is complete, a dedicated stand-alone monitor is still under development with completion expected by September 15.
• Future plans include augmenting the monitor to allow communication with the DMT display manager for responding to operator requests for more information and creating a set of tuned config files for some of the key servos used in the Hanford 2-km interferometer (in collaboration with Dick Gustafson on site). That work is planned for completion by November 15.

• There are a variety of lines to worry about, including electrical mains, violin modes, and pendula. The lines are coherent, sometimes large amplitude and can be highly non-Gaussian. Removing the lines can reduce data volume and improve Gaussianity, allowing better matched filters in searches for astrophysical sources.
• A catalog of methods and types of lines removed was shown. This study was a comparison of three of these methods (multitaper - Ottewill/Allen, quasi-monochromatic - Klimenko, and coherent - Sintes/Schutz) on the 1994 40 Meter data. These three methods are now available in the DMT or LAL package. In the comparison the following criteria have been or will be examined:
• Statistical properties: Improvement in Gaussianity, detection of non-Gaussian components
• Spectral properties: Creation of "glitches" in removal, shape of residual noise in cleaned data
• Signal detection ability: False alarm rate, detection failure, dependence upon SNR threshold
• A comparison was shown of a histogram in FFT coefficients (real part)  for the frequency bin centered on 14.46 Hz before line removal and after line removal using the three techniqus. In each case a Gaussian of the same RMS is shown for comparison. The multitaper technique performs best by far in creating a Gaussian residual of low rms at this frequency.
• A comparison of the techniques on an incoherent "bump" near 600 Hz, however, showed much smaller differences among the techniques tried.
• Spectra were shown in the vicinity of 180 and 300 Hz, along with a superposition of spectra from 60, 180 and 300 Hz (+/-30 Hz window). Many nearby lines are visible. The same superposition was shown using the Klimenko code with default and with more extreme removal parameters, with distortion visible in the extreme case. The Sintes and Ottewill (GRASP) techniques do not clean up the superposed spectrum as well, with apparent artificial sidebands created by the Sintes method.
• Finally, the residual non-Gaussian noise was examined via a histogram of real FFT components at 180 Hz before and after the three line removal techniques. Here the Ottewill and Klimenko methods give similar performance, with a distinctly broader residual for the Sintes method.
• KR wondered how much of the difference in performance of the techniques was due to non-linear effects, giving shoulders and sidebands on the visible lines. Bernard mentioned that future plans include looking at magnetometer data for a cleaner determination of 60 Hz amplitude & phase.

• This presentation was a brief description of the method used for line removal and a description of the LAL C code routines used.
• The algorithm is meant to remove coherent lines that generate harmonics while preserving stochastic detector noise and any nearby unassociated lines. The code can also work on lines & harmonics that change slowly in frequency with time (e.g., the drifting 50 Hz mains seen in Glasgow data). It is recommended to monitor at least five harmonics for best performance.
• The principle is to reconstruct a nearly monochromatic time-domain function m(t) whose effect on the data is to add (coherently) a series of lines and harmonics and then to subtract m(t) from the data. Examples were shown from Glasgow data with wandering harmonics (450 and 750 Hz) of the mains. The mains are cleanly removed while preserving a nearby violin mode at 745 Hz and an artificial 452 Hz line.
• Time-frequency plots before and after  line removal show dramatically the cleaning up of the wandering mains at 750 Hz with preservation of two nearby violin modes.
• The line removal code is part of a package called cohlineremoval which includes routines for finding harmonics, generating a reference interference signal, and removing all harmonics. The code is written to the LAL specificiation of July 2000 and has been tested. (The code was originally written in Matlab.)
• Structures for storing time and frequency series and relevant parameters were shown, along with the calling sequences (and arguments) needed for the finder, reference generator and cleaner routines. The package includes code documentation and a sample frame file for testing the code.

• Nergis began with an overview of recent news from the Livingston and Hanford sites. At Livingston, the PSL has been installed and characterized. The mode cleaner (MC) has been installed and tested. Installation of in-vacuum components and realignment of core optics is ongoing. She emphasized that characterization is being carried out more systematically on the 4-km Livingston IFO than was done on the Hanford 2-km IFO because the 2-km was viewed as a "pathfinder" testbed for identifying the major problems to be solved.
• At Hanford, the single-arm cavity tests were completed in April, including the 24-hour engineering run and a test of the critical common mode servo. A number of improvements, including beam-reducing telescopes and rehanging of optics were done afterward. Frequency noise in the input optics was reduced with various improvements, including reduction of acousto-mechanical coupling on the PSL table. The power recycled Michelson (PRM) cavity can now be operated, and work is ongoing to attempt simultaneous locking of the PRM with one and two arms.
• During the single-arm tests in the spring, the locking servo was cobbled together in analog with feedback to the input test mass alone. Although the original design for this servo has a high bandwidth for full IFO lock acquisition, it was found that lock acquisition was easier at lower gain (bw<100 Hz). Gains could then be raised after acquisition (bw=300 Hz).
• It was necessary (as expected) to notch out axisymmetric test mass resonances at 9.5 and 14.5 kHz. Unexpected was the need to notch out the non-axisymmetric "butterfly" mode at 6.5 kHz. Better beam centering is expected to help reduce excitation of this mode. It was pointed out that the butterfly mode has the virtue of giving an error signal on mis-centering!
• The single-arm operation allowed testing of a preliminary version of the common mode servo, the most complex of the LIGO I longitudinal servos. Feedback actuation is made on test mass positions at low frequency and on both the MC length coil driver and the MC error offset at high frequencies. Plots were shown of the original servo design and of the realization in hardware after problems were encountered in locking. In the new scheme the MC length path does not dominate open loop gain at any frequency in the servo realization. .
• A plot of measured open loop gain (inferred from closed loop gain) was shown with a unity-gain frequency of about 9 kHz. The best achieved was 20 kHz with a phase margin of 80 degrees.
• About 40% of the alignment controls system was tested successfully (wave front sensing scheme), i.e., with 4 mirror orientation angles and two input beam pointing degrees of freedom. The alignment controls are low-bandwidth (few Hz).
• Several properties of the single-arm cavities were measured:
• Resonant reflectivity gave a visibility of 0.02, corresponding to an apparent 70 ppm average loss per mirror. Expected was a visibility of 0.01 for 30 ppm per mirror. Beam clipping cannot be excluded as the explanation.
• The cavity storage time was measured to be 467 usec, corresponding to a finesse of 220 and a sum of input mirror transmission and cavity loss of 0.0281 (design = 0.04).
• The cavity length was measured to be 2009.11 m with RF resonant techniques, in excellent agreement with the survey value of 2009.12 m.
• Mode matching into the arm was found to be 96%.
• The Michelson contrast was found to be 0.32%.
• The status of the core optic suspensions was also discussed. There are four sensors and four actuators to control nominally three degrees of freedom (position, pitch, yaw), with non-negligible cross couplings to vertical, side and roll couplings. Diagonalization of the sensor/actuator matrices required some work (see talk by Penn at last LSC meeting).
• Measurements of decay times in situ give Q values for test mass internal modes of 10⁴-10⁷.
• Scattering of the 1 micron main laser beam into the sensor photodiodes has prevented high beam intensities. A solution using new modulated LED's with demodulated sensor output is to be tried soon, along with better shielding and optical filtering.
• The locked single arm allowed a measured of PSL frequency noise. The acousto-mechanical resonances are still apparent, despite improvements in optical mounting and elimination of parasitic interferometers. There is also a broad background ascribed to carrier resonance in the reference cavity with saturation of RF photodetection. The noise level is significantly above the design value (but which itself is 10 times below what becomes a serious problem).
• The digital servo controls will be commissioned soon, with feedback to end test masses (was unavailable in spring running). Next on the agenda is getting the PRM to lock with one and then both arms.

• The primary functions of the Input Optics (IO) system include conditioning of the PSL output (frequency, intensity, pointing stability), mode matching of delivered beam, optical isolation and generation of RF sidebands for IFO sensing. A schematic diagram of the IO system leading up to beam delivery into the IFO was shown, along with a block diagram of IO interfaces to other LIGO subsystems.
• Overview of IO status for the three IFO's:
• LHO 2K - Operational since Aug 99, major characterization complete, including integration with 2K arm cavities, modifications/realignment carried out in April/May 00.
• LLO 4K - Mode cleaner locked in March 00, characterization/improvement March-June 00 and realignment June-August 00.
• LHO 4K - Installation started July 00.
• A large number of characterization measurements have been carried out. Results were shown for the LHO 2K IO system:
• The MC length has been measured with RF resonant sideband detuning.
• The transmission has been measured to be 98 +- 5 % and the mode matching be 95-98%.
• The pointing stability has a long term drift of about 4 urad/hour and a jitter of 10^-10 rad/sqrt(Hz) for freq > 20 Hz. A power spectrum of horizontal and vertical fluctuations shows strong peaks at known resonances below 20 Hz. Wave front sensing is not (presently) effective above 1 Hz.
• The MC cavity linewidth has been measured both using a ringdown technique and via the optical gain. The HWHM was found to be 3.66 kHz in Sept 99 and 3.55 kHz in Feb 00, giving estimated cavity losses of 148 ppm and 14 ppm, respectively, with a +-50 ppm uncertainty, dominated by the uncertainty in transmission.
• The internal Q's of the three MC mirrors have been measured to be 0.75, 0.36 and 1.29 times 10⁶ for MC1, MC2 and MC3, respectively, with resonant frequencies all near 28.2 kHz. Measurements were carried out by observing ringing after excitation.
• The MC has been used to analyze the PSL noise, as discussed by Mavalvala above.
• Power spectra for the MC length control signal were shown for January and June 2000. The June PSD looks much improved, believed to be primarily due to better levelling of the MC  beam plane.
• The frequency noise of the MC/PSL system has been itself measured with the 2K arms. Power spectral densities (units of Hz/sqrt(hz)) were shown for the 2K arm error signal ("common mode"), along with the control signals fed back to the input test mass, the Mode Cleaner length and the AO path.
• Coming up soon is an attempt to lock the MC at the designed input power after installing new OSEM sensors that include demodulation detection to mitigate effects of scattering of the beam into the photodiodes (see Mavalvala talk above).

• A power spectrum of seismometer data at Hanford shows a broad enhancement at the 1-10 nanometer level over about 1 to 50 Hz, with peaking in the 4-10 Hz range. This talk focussed on determining both the predominant source of that noise and pinning down its propagation path to the LIGO seismometers.
• Investigation in the field established early on that the noise comes primarily from automobile traffic (trucks being worse) on highway 240. Other local roads were eliminated, as was a small weir spill on the Yakima River. It wasn't clear, however, whether the primary source was from the engines, or from the interaction of the tires with the pavement. By running both a car and truck along the highway while taking measurements, it was found that the peak frequency of noise correlated well with that expected from the axle spacing between front and back wheels, consistent with the rough and ungrooved pavement on the highway. Resurfacing the highway would help reduce the noise.
• Pinning down the propagation path took some care. Hypotheses included direct acoustic (through air) coupling to seismometers, acoustic coupling to the ground, or an entirely-ground path of propagation.
• The first hypothesis was tested (and rejected) by suspending a speaker near a seismometer to measure its sensitivity to acoustic noise. Also, insulating the seismometer underground successfully suppressed acoustic noise detected by a microphone, but had no effect on the seismometer.
• The acoustic effect on traffic on ground motion was tested with planes and a helicopter where one could estimate reasonably well the expected amplitude of seismic disturbance (from an 1885 calculation!) and remove the possibility of direct coupling to the ground. Measured displacements were within a factor of three of calculation for the aircraft, but the same calculations applied to a truck on the highway failed to account for measured seismic vibrations by three orders of magnitude. These results suggested that the propagation takes places entirely through the ground.
• To test this, the velocity of sound propagation through the ground was measured vs frequency using portable ground tampers and two seismometers. Then the velocity of the highway 240 disturbances was measured via correlations between the two seismometers. The highway 240 disturbance velocity was measured to be 492 +- 62 m/s, consistent with the tamper measurements for signals peaking below 10 Hz.
• A spatial "Q" value was estimated from the attenuation observed in signals between the end and middle Y stations. In the truck peak range (4.4-6 Hz) the measured value was Q = 68 +- 12. One expects a Q of about 40 for the local soil.
• The effect of these road disturbances on the arm control signals will be looked at in the future.