PIF Reference:
Procurement of GSN Infrasound Instrumentation
Kent Anderson and Chuck Ammon
15 February 2012
Project Description
Procure 130 infrasound sensors and interface boxes for the GSN.
Project Purpose and Business Benefit
The Earth’s surface isn’t opaque to seismic waves arriving from sources in the solid
Earth or infrasound waves from atmospheric phenomena. It is a diaphragm that can
be deformed by either. More generally, there is interaction between all components
of the Earth – between its solid interior, atmosphere, hydrosphere and cryosphere.
In addition to coupling of mechanical energy from one component part of the Earth
to another there are a broad range of geophysical phenomena that occur at an
interface between components and radiate energy into both. One prime example is
a volcanic eruption that is both a significant seismic source and an intense acoustic
source. In short, the Earth is an integrated system. With the rapid expansion of
recording technology it is perhaps the opportune moment to advance our
understanding of the interconnectedness of our planet by, wherever possible,
deploying hybrid networks of sensors that probe across boundaries of the Earth
A example is the USArray Transportable Array (TA). The TA, originally designed as a
broadband seismic network, is now being upgraded with air pressure sensors to
become the world’s first large-scale seismo-acoustic network. Each station has been,
or soon will be, equipped with two long-period barometers and a high-frequency
infrasound microphone. Although coupling at the free-surface permits atmospheric
events to routinely be recorded above noise on seismometers, these events are
more easily observed using pressure sensors – as newly collected microphone data
at the TA is clearly showing. With seismic and atmospheric pressure data now being
collected at 400 stations spanning an area of 2,000,000 square km we anticipate
seminal research on coupling between the solid Earth and atmosphere, on the
physics of seismo-acoustic sources, on the compliance of the Earth’s crust as
seismometers in the TA document its response to the atmospheric forcing function
sensed by co-located pressure sensors.
The GSN is undergoing a similar upgrade. To date approximately 60 GSN stations
have been equipped with long-period barometers sampled at 1 sps. Many of the
remaining GSN stations are slated for a similar upgrade. The GSN seismo-acoustic
stations complement the International Monitoring System (IMS) infrasound
network. Each station in the IMS network is an array of high-frequency barometers,
sensitive to pressure variations at the upper range of the long-period instruments in
the GSN and at higher frequencies. Although the IMS infrasound network is
unprecedented, it is too sparse for detailed study of infrasound propagation in the
atmosphere. Just as the TA has been upgraded with a suite of low- and highfrequency pressure sensors, we believe higher frequency microphones deployed at
GSN stations would not only complement low-frequency barometers now available
but would add significantly to the high-frequency acoustic coverage of the
atmosphere provided by the IMS infrasound network. This additional coverage
would permit significant advances in a number of areas including interferometric
studies of the upper atmosphere and monitoring and study of hazardous volcanic
eruptions and severe storms.
Project Scale and Duration
Procurement can be made throughout the 5 year cooperative agreement (2013-18) and
installations can occur at maintenance/upgrade trips of opportunity. It is expected that
the procurement can be complete by the end of 2018.
Estimated Project Cost
Sensor and interface box cost is ~$3,000 per station. 130 GSN stations would cost
$390,000. This can be scaled to a subset of the GSN as funds allow.
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