DSP CLOCK DIFFERENCE -1 SECS and 0 MSECS messages mark the beginning of timing errors in the RT130 data, due to the SiRF clock’s erroneous time shift. The SiRF goes back and forth between correct and incorrect time over periods of hours or days. The RT130, and hence your data, will follow suit, generally with a lag of 4 hours.

‘POSSIBLE DISCREPANCY’ messages will be produced whenever the SiRF and the RT130 are not in sync. Four consecutive ‘POSSIBLE DISCREPANCY’ messages will reset (JERK) the RT130 time.

If the clock is being power cycled, the clock is locking and the RT130 is phase locking with the SiRF each time it is powered, the 4-hour lag is produced.

The Guralp CMG-3T seismometer is a 3-axis broadband instrument that has a flat response to ground velocity between 120s and 100Hz.  It has been tested to operate down to -55C and only draws 0.3W of power.

EPIC's Polar program has purchased the cold-rated 3Ts (with active logic high) for broadband experiments in Antarctica.  When powered and locked, the reported mass positions will be '0'.  This does not mean that the instrument is dead or unpowered.  Once the 'unlock' command is initiated, first the lock/unlock and then the centering motors should run and finally result in meaningful mass position readouts.

The CMG-3T has a low tilt tolerance and is sensitive to temperature changes, it therefore requires a well established and well thermally isolated vault.

For summer only deployments, either short-period seismometers and geophones or broadband seismometers are typically installed. In the case of short-period sensors or geophones, a “vault” is not required and the instrument is often buried in the snow at a shallow depth and reasonably leveled.  If broadband seismometers are used, a vault needs to be built to hold the instruments. This involves more work as the sensors have to be accurately oriented, leveled and protected from wind noise and thermal changes.  For a detailed description of broadband seismic vaults for polar environments, see the Specialized Polar Equipment section.

The Reftek RT-130 is a 24bit, low power, robust and very portable seismic data recorder.  It is well suited for deployment in harsh climate environment and is easy to program and retrieve data in the field.  It can have 3 or 6 channels and records data on Compact Flash (CF) cards.