The first location was a pipeline pumping station about 10 kilometers north of LIGO. The pipeline itself runs under the X-arm of LIGO. Another location was on Highway 63 where it runs closest to the Y-arm end station, less than 1.5 kilometers away. We additionally stopped at locations south of LIGO where a back road with several houses run close to the Y-arm end station.

(The term "light pollution" was coined by optical astronomers complaining about man-made lights around observatories. You might say that we were monitoring "seismic pollution"--that is, if you wanted to perpetuate abuse of the term "pollution.")

Additionally, they took readings at the Y-arm end station itself. This was my first opportunity to see an end station. We drove down the 4-kilometer service road alongside the arm to reach the station. Within that building too we must exercise clean room procedures: brushing shoes and donning booties. (The end mirror chamber was closed, so more extensive measures like face masks were not needed.)

Another presentation occurred today, and I had not previously listed the topics for some of last week's presentations:

• --Thursday's was by Dr. Warren Anderson, one of the professors from UT-B. He discussed methods of processing the raw data from LIGO to extract a gravitational wave (GW) signal. As an example, one method in essence searches the raw data for a match to the form expected from a particular type of source, such as two black holes spiraling into each other. His presentation included sound clips representing the nature of assorted GW signals. This is an intuitive way of understanding these signals: the information LIGO will provide includes frequency and amplitude, and we are used to having our ears and brain process frequency and amplitude data (sound) for us. (The various means of data processing, you will recall, are an area of focus for the physicists from UT-B. This puts it high on the list of possible topics for my master's thesis.)
• --Friday's by Dr. Joe Kovalik discussed the method by which the RF signal is used to produce the electronic information that allows alignment of the mirrors. He also discussed Fabry-Perot cavities (the term for the arrangement which traps laser light between two mirrors in each arm).
• --Today's presentation explained the nature of shot noise in the interferometer. Because of fundamental uncertainties when we deal with nature on a subatomic level, there are physical limits on how well LIGO can measure distances.

I have learned a little more about LIGO's future schedule. The "mock data challenge" I referenced in the last report is essentially an exercise of the software alone. It will test the various data analysis software packages by running through fictitious data and seeing what comes out. That will happen about September. (Note added 2 Oct: This did take place in early September at MIT in Boston; review of results is continuing. Some participants were flying out of Boston on September 11, but all eventually reached their homes.) This fall is also a target for having LIGO readjusted and closed up again, when another engineering run will be conducted. This is when the laser and everything else is operated to test for problems. Between November and next spring will be the first opportunity for the two LIGO sites to work in conjunction and do some low quality scientific listening (but not sensitive enough that detectable events are expected). Between next spring and 2002 is when planned operational sensitivity should be attained.

Weather has remained sunny. We did actually have a breeze today, though.

Image credits: Wm. Robert Johnston, © 2001 (all).

© 2001 by Wm. Robert Johnston.
Last modified 1 August 2001.
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