Special Polar Equipment

The Geophysical Earth Observatory for Ice-Covered Environments (GEOICE) project was a NSF collaborative Major Research Instrumentation (MRI) program that expanded the EPIC Polar group’s observational capabilities and logistical efficiencies. GEOICE developed a rapidly deployable, dense footprint seismic observatory system for operation in ice-covered areas. The GEOICE project was a collaborative effort between Central Washington University (CWU), Incorporated Research Institutions for Seismology (EarthScope) and the Portable Array Seismic Studies of the Continental Lithosphere (EPIC) Instrument Center at the New Mexico Institute of Mining and Technology.

Power Management Module (PMM):  Enclosure containing the charge controller and power switcher.
Short battery harness:  Connects battery to multiple battery harness or other load cable.
Short 5-pin/3 battery:  Connects primary and rechargeable batteries to PMM.
Battery harness connects 2:  Connects 2 rechargeable batteries together.
Battery harness connects 10:  Connects 10 primary battery packs together.
Battery harness connects 8:  Connects 8 rechargeable batteries together.

 Solar Panel Mount Drawings Angle Mount: 2x 80 Watt Solar Panels 7' x 4' x 6' 6" deployed 7' x 4' x 6" folded for transport 130 lbs complete Rock or snow deployment   Detailed Drawings Angle Mount rev C:  Assembly with BOM Rock Site Station

 

Vault Equipment Drawings Vault Double wall UV resistant polyethylene shell 2" thick indexed phenolic sensor base 3" thick polystyrene insulation Trillium 240 or Guralp T3 seismometers Detailed Drawings 3" Thick Insulation 2" Thick Indexed Phenolic Base Double Wall UV Resistant Polyethylene Shell

Station Enclosure Drawings   Large Enclosure:  Insulated Hardigg AL3434-2807 External dimensions:  37" x 37" x 37" Internal dimensions:  24" x 24" x 21" 2" thick vacuum insulation panel (VIP) sub-enclosure Protective polypropylene barrier between VIPs and electronics Integrated cable harness with external bulkhead connectors Year round operation with rechargeable AGM batteries   Detailed Drawings Hardigg AL3434-2807 Insulated:  Assembly Drawing with BOM

EPIC's strategy for designing cold-hardened seismic systems is driven by the need to maximize heat efficiency and minimize payload while maintaining continuous recording throughout the Polar winter. Our design is for a basic 2W autonomous system. Power is provided by a primary Lithium Thionyl Chloride battery pack and is backed by a secondary, solar charged AGM battery pack. Station enclosures are heavily insulated and rely on instrument generated heat to keep the dataloggers within operating specification. Although insulated, broadband sensors are operated close to ambient temperature.

Seismic Sensor Vaults

The type of seismic sensor vault and the amount of sophistication it requires, is dependent on the type of seismometer.  A geophone does not require a “vault” per se, it can be buried in dirt or snow and be kept reasonably level in the process. A sensitive broadband seismometer requires a quiet, temperature stable and level vault.  In the Antarctic two main styles of vaults are used for broadband seismometers:  the rock vault and the snow vault.

The Rock Vault

In rocky environments where digging is nearly impossible, a weatherproof enclosure with a rigid bottom, typically aluminium, is secured to the ground.  The seismometer is then set inside, oriented properly and leveled.

To reduce noise caused by wind, and to thermally stabilize the vault and protect the instrument from flying debris, a double walled dome is placed on top of the vault and anchored to the ground as well.

Cold Rated Guralp CMG-3T

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.

Quanterra Q330

To record seismic data during the extremely cold Polar nights, the EarthScope EPIC Polar Group relies on the Quanterra Q330 digitizer due to its exceedingly low temperature tolerance.   The Q330 is a 24 bit, 3 or 6 channel digitizer. In addition to its very low temperature tolerance, its very low power consumption makes it ideal for year round experiments in the Antarctic deep field.

 

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.