PSN-L Email List Message

Subject: What is your advice?
From: "rem11560@............
Date: Sun, 11 Jul 2004 16:53:26 GMT

Hi Larry,

    I know that I am a fuss pot, but I would like to submit the following advice to the PSN List. I need your input before I do. I practice what I preach, and I think the files that I now regularly submit are as good or better than most that I see. I am especially annoyed that hardly anyone takes the trouble to calibrate their sensors. Maybe there should be a discussion among list members and a concensus reached on what advice to amateurs would be best to prominently and permanently post on your web site.

    I also don't like overly large over-sampled files. I would think that you would rather not have to archive such files.


Bob McClure
Locust Valley, NY

>Re: What is your advice? 
>Hi Bob,
>I don't have a problem with you sending out your request to the PSN list.


1. Be sure that your STATION COORDINATES are correct. You can use Microsoft Streets and Trips, or online MapQuest for the purpose. Also align horizontal sensors to true North or East, or else give true direction in sensor comments box.

2. LOCK your timing to GPS or WWV or a crystal clock slaved to WWVB.

3. CALIBRATE YOUR SENSOR. You would not have much use for a voltmeter with no scale on it, would you?. For open loop sensors, I have two methods. One uses the raw sensor output of pendulum movement between fixed stops, the other measures the force exerted by the pendulum in response to a known current. I can tell you more if you ask.

4. DO NOT submit files with high sample rates on distant teleseisms. High frequencies are attenuated with distance, and files with excessive sample rate only take up bandwidth and archival storage space. Decimate before submitting. One to five samples per second should handle most teleseisms without loss of waveform detail. Also, do not cover an overly large time span after the L wave onset.

5. DO NOT use any more FILTERING than absolutely necessary. Let some microseisms come through. Leave it to the downloader of files do more filtering if they wish.

6. If possible, adjust your sensor's NATURAL PERIOD to least 16 seconds if you record and report teleseisms. If that is not practical, I have written an application program for WinQuake files which can digitally extend the effective period of your sensor by up to a factor of five. I use it routinely on my sensors which have natural periods of 5, 8, and 14 seconds to extend their response to 24 seconds.

7. Control your sensor DAMPING. The barest amount of overshoot on a displaced pendulum is about right.

8. Use as little AMPLIFIER GAIN as possible to avoid clipping on major events. Most of the files I see on the seismicnet site have been recorded at far more gain than necessary. You may have to make component value changes in your amplifier to accomplish this.

The best thing to hit the Internet in years - NetZero HiSpeed!
Surf the Web up to FIVE TIMES FASTER!
Only $14.95/ month -visit to sign up today!

Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]