[data-issues] wrong calibration values in WID2 line of autodrm emails? [SEC=UNCLASSIFIED]

[Marthijn.DeKool at ga.gov.au]

Hi,

Our group occasionally uses the autodrm (email) data request system (when there appear to be problems with the web-based service).

I recently noticed that the emails in GSE format can contain the wrong calibration value. An example for the station AU-PSA00 channel BHZ.

BEGIN IMS1.0
MSG_TYPE DATA
MSG_ID 201211272145330004 USA_DMC
REF_ID 4699-AU-PSA00--Manual
DATA_TYPE WAVEFORM IMS1.0:CM6
TIME_STAMP 2012/11/27 21:45:33
WID2 2012/11/27 07:09:59.994 PSA00 BHZ 00   CM6    48001   40.000000   4.74e-02  20.000 UNKWN   -1.0  0.0

Note the values 4.72e-02 for the system sensitivity and 20.000 for the calibration reference period.
According to the format specification these have the following meaning:

70-79 e10.2  system sensitivity (nm/count) at the calibration reference period, the ground motion in nanometers per digital count at calibration period (calper)
81-87 f7.3     calibration reference period; the period in seconds at which the system sensitivity is valid; calper should be near the flat part of the response curve (in most cases, 1 second

When I go to the channel web page on the IRIS site the sensitivity gain is quoted as 3.358e9 cnts/(m/s) or 3.358 cnts/(nm/s).
The same value is returned by a station metadata query to the web service.

Converting the velocity response to displacement response: |Rd| = omega_ref*|Rv| = 2*pi*0.05*3.358 = 1.055 cnts/nm

So the sensitivity at 20 seconds is 1/Rd = 0.948 nm/count rather than 0.0474 in the WID2 line in the GSE message.

Looking at the noise level at the station it is also clear that something like 0.948 is the correct value.

I note that the value in the WID2 line would be correct for a reference period of 1 second.

Could someone at IRIS please look into this?

Thanks, Marthijn de Kool


Marthijn de Kool
Geophysicist | Nuclear Monitoring  |  Earth Monitoring and Hazards
Minerals and Natural Hazards Division  |  GEOSCIENCE AUSTRALIA
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Phone:  +61 2 6249 9656    Fax:  +61 2 6249 9999
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