What is the best broad band in the world?

The market for broad band seismometers is full of good options. Who makes the best?

Many of us ask ourselves this same question when we are getting ready to purchase new equipment. But I think that a better question would be:

What is the most consistent broad band in the world? That is to say, when you compare many broad bands from the same manufacturer, which manufacturer produces the most consistent product?

To answer this, we consult the 2010 paper published by Adam Ringler and Bob Hutt of ASL (see What’s Inside ASL, read the paper here) where the self-noise models for the following broad band sensors are compared:

  • Geotech KS-1/2000/54000 (#different sensors used in test = 1, 1 & 2 respectively)
  • Guralp CMG-3T/3TB (#different sensors used in test = 4)
  • Nanometrics Trillium Compact/ 120P/ 240 (#different sensors used in test = 1, 5 & 4 respectively)
  • Ref Tek 151-120 (#different sensors used in test = 5)
  • Streckeisen STS-1/2 HG (#different sensors used in test = 4 & 8, respectively)

The STS-1 and STS-2 HG had the lowest observed low noise models at long periods:

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Streckeisen makes exceptional sensors. But the STS-1’s were not the most consistent (And this is likely due to their age):

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The newer STS-2’s were more consistent:

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Click to enlarge

The most consistent sensors were the Nanometrics TC, 120P, 240 and Reftek 151-120 whose theoretical, median and low noise models are nearly coincident:

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Click to enlarge

The noise models for these sensors were not only consistent and generally further below the NLNM than the other sensors tested, but also did not have large deviations from their theoretical noise models in the microseism band (~0.1 to 0.6 Hz). Compare the consistent quality of the Trillium 120P and Compact, for instance, with the variable quality of the Guralp sensor:

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Click to enlarge

Notice the average 10 dB difference between the low and median noise models and the large 20 dB difference in the microseism band. This peak is also considerably more pronounced for the Geotech sensors. What this tells me is that when you open the box and take out your brand new Guralp or Geotech sensor it is difficult to know what you are getting. There is less internal consistency when compared to your other broad band options.

It is one thing to make a great quality sensor- something all of these manufacturers are capable of. It is something entirely different to make the next 1000 sensors equally great every time.

— Branden

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