Today's passive monitoring requirements far exceed those found on even the most advanced active land operations.
So instrumentation designed for traditional surveys is not best suited to this environment.
Signals may be much smaller ruling out 24 bit convertors. Passive surveys may be hundreds of square miles, data flow is relentless and no second chance to record. This means shootblind or cabled equipment is ruled out.
So hardware deployment must be efficient and data retrieval must flexible while not interrupting acquisition.

iSeis has, therefore, developed several unique features for the Sigma recording system:

• Real time/continuous recording over vast areas combined with internal data backup
• 32 bit convertors for unrivalled noise floor and dynamic range for wide range of sensors, incl. 3C
• Can be used on land and on water
• Ultra accurate clock and VHF timing options for when GPS reception is problematic
• Mesh Radio Network can be used over large areas so all channels can be remotely controlled/monitored and power saved
• Sigma "Passive Recording" central system software monitors entire system, makes sure no data is lost
• Support for multiple harvesting techniques
• Sigma supports cabling together of ground units.