You have not heard much from us lately because we have been working hard to make new products like RespGen, an instrument response generator.
We designed RespGen as a tool to allow instrument manufacturers and network operators to easily determine the instrument response of any seismograph. In 1994, Pavlis and Vernon published a paper, “Calibration of Seismometers Using Ground Noise“, claiming that if the instrument response of one of two co-located seismometers is known, we can restore the instrument response of the other. The new RespGen program is a highly refined version of the Pavlis and Vernon method.
Nearly every station in the GSN network has an STS-1 co-located on the same pier as an STS-2, Nanometrics Trillium 240 or another broadband sensor. Take, for example, the GSN station in Kyrgyzstan (http://www.iris.edu/mda/II/AAK). Given a single day’s worth of raw data from AAK.00 (STS-1) and AAK.10 (STS-2), RespGen is able to accurately determine the instrument response of AAK.10 from AAK.00:
The blue line is the instrument response of the STS-2 according to Streckeisen. The green line is the instrument response for the STS-2 as we derived it with RespGen. Now that is a pretty good fit!
Getting the instrument response of an “unknown” sensor from another sensor with a “known” instrument response is now easy.
OSOP owns and operates a world-class broadband seismic station called BRU2. The continuous data are shared publicly with IRIS (http://www.iris.edu/mda/PA/BRU2). In February, 2013 Branden set up 3 Nanometrics Trillium Compacts side-by-side to test some new software he was developing to implement the Sleeman method for determining self-noise levels. Here is what the setup looked like:
The blue line is the instrument response of the Trillium Compact according to Nanometrics. The green line is the instrument response for the Trillium Compact as we derived it with RespGen.
- Determining the instrument response of a new sensor
- Confirming the instrument response you have calculated for a new sensor
- Confirming the nominal instrument response provided by the instrument manufacturer is as advertised in the IRIS Nominal Response Library
- Identifying mechanical failures
- Identifying phase (polarity) and gain problems
- Monitoring the instrument responses of seismic instrumentation in your network or pool of campaign instrumentation
- Something a little more extreme: You just returned from a campaign study in the Aleutians. Your Nanometrics Trillium Compact was thrown from a helicopter, banged around in your backpack for a day, was attacked by bears while you cowered in your tent hoping your deodorant did not attract the cubs, then it sat around covered in a meter of slush for a few months only to then suffer through a weeks-long journey on the barge you hitchhiked back to the mainland on. Now you are back in the lab and you want to make sure things are OK.
Many thanks to Professor Pavlis for his guidance and our friend Adam Ringler at ASL for his readiness to answer our questions and talk instrumentation.