PSN-L Email List Message

Subject: interesting infrasound detections?
From: "David Saum" DSaum@............
Date: Mon, 24 Apr 2006 12:50:04 -0400

I am still debugging my infrasound
detector, but I have been picking up
some interesting detections recently:

Here is a 24 hour data plot from this morning
with an interesting data spike at 10:35UT (6:35AM local).

Here is a blow up of the data showing that it is
actually a small spike followed about 3 seconds
later by a larger spike.

And here is a blow up of the two similar detections
at 1:30 and 1:35UT (9:30 and 9:35PM local)

I have been picking up 0-10 similar detections per day,
generally with the first spike smaller than the second,
the spacing is about 3 seconds (all less than 10 seconds)
and occasionally there is a third small spike about 3 seconds
after the large spike.

My infrasound monitor is on my 4th floor deck, with
no spatial averaging.  I am located in the Washington, DC
metro area about 10 miles from Reagan airport and 10
miles from major construction on the Springfield, VA
I95 interchange and the Potomac bridge project.

Anyone have any idea what these signals could
be coming from?

System info:

Exterior of microbarograph with serial cable:
Interior of microbarograph:
PCB removed from box
PCB and high-pass pneumatic filter removed from box:

System Bandpass: 0.01 to 4 Hz.
High-Pass filter: ~100 sec or 0.01 Hz using volume/capillary tube.
Low pass filter: 4 Hz anti-alias, 8 pole Bessel filter (MAX4701)
Differential pressure sensor: silicon, bridge type, 1"wc (DUXL01D)
Pres Resolution: ~0.004 Pa - possibly lower depending offsets
Range: +/- 120 Pa (32768 times pressure resolution)
Amp: instrumentation,1000x,single supply,micropower,RTR out(INA122P)
Power: ~2ma 5VDC, derived from PC serial port, no external power supply
Regulator: 5VDC, low dropout micropower, precision (LP2950-5.0)
Amplifier Reference Voltage: 2.5VDC fixed, precision reference (LT1004-2.5)
Microprocessor: 4mhz, onboard 16 bit ADC and serial I/O (PIC14000)
Firmware: ADC sampling at ~35 SPS, zero drift tracking ~5 min TC.
Enclosure: diecast aluminum box for shielding (Hammond 1590P)
Serial Out: RS232, 9600 baud, 8N1, ASCII records, -32767 to +32767
Wind Spatial Averaging: array of micro-perforated garden tubing
Data Log/Display: freeware PC AMASEIS seismic log/analysis software



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