Thread: less smoothing of MUSTANG noise spectra

Started: 2019-09-09 19:50:09
Last activity: 2019-09-09 19:50:09
Topics: MUSTANG Users
Carl Tape
2019-09-09 19:50:09
Dear IRIS MUSTANG:

I wanted to raise a topic that you are probably aware of. (ASL folks
pointed this out to us.) For some applications and interpretations, the
MUSTANG-generated PSDs are overly smoothed. There is a nice test station as
an example: AK.NEA2, which has a 38 m high microwave lattice tower nearby
that had a natural frequency of 2.5 Hz (0.4 s). The sensor is a TA upgrade
(cased borehole into bedrock).

1. The spectral peak is very sharp, as shown in the attached example plot,
which I have flipped for comparison with the other plot (x-axis frequency).
No smoothing is applied to calculate the spectrum. The peak is sharp.

2. From the MUSTANG generated-spectra, you see a mesa-like shape that
arises from the octave smoothing. (You can also see that this "mesa" is
enhanced during windy conditions, which is what you might expect from a
lattice tower.) In this case, the smoothing is detrimental to the
interpretation.

This is part of a recently accepted paper by Kyle Smith and me:
https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JB017695

We discuss the issue of smoothing in the Discussion. It is helpful to be
using a data product, which others can directly compare with. However, in
our case (and in others), there is a strong argument against using the
smoothed MUSTANG spectra, and instead calculating the spectra ourselves,
without the smoothing.

Here at the SCEC meeting I noticed other sharp spectral peaks -- from
sedimentary basins recorded by nodal stations. These, too, would get
smoothed out in MUSTANG.

My question is:* Could MUSTANG deliver a less-smoothed version of the PSDs?*
Or perhaps a couple different versions that could be flagged for download?

Thanks very much for this product!

Carl

P.S. If you have feedback or questions on Kyle's paper, please email him at
kksmith7<at>alaska.edu (and please CC me too!).

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Carl Tape
Associate Professor
Geophysical Institute (office 413D)
University of Alaska Fairbanks
Phone: 907-474-5456
Email: ctape<at>alaska.edu
Web: https://sites.google.com/alaska.edu/carltape
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