Güralp Systems New Generation of “Off-the-shelf” free-fall OBS systems with acoustic telemetry

Libby Passey1

1Güralp Systems Ltd, Midas House, Aldermaston, Reading, RG7 8EA, UK (Lpassey@guralp.com)

Following on from our 30 years of experience in building Ocean Bottom Seismometer (OBS) systems, Güralp is now introducing its newest range of OBS, Aquarius and Aquarius+, a compact free-fall OBS with acoustic telemetry. Current cabled OBS solutions can be both expensive and complicated, whilst typical free-fall OBS generally do not provide users with data until after the system has been recovered; the Aquarius+ provides a solution that bridges the gap between a real-time cabled system and an offline free-fall system – a nearreal-time free-fall system.

The Güralp Aquarius is a free-fall system suitable for deployments at depths of up to 6000m and up to 18 months duration. Utilising proven Güralp sensor technology which can operate at any angle (without the use of gimbals), the Aquarius system is equipped with a digital feedback tri-axial broadband seismometer with a frequency response of 120s to 100Hz.

Upon installation of the OBS, the acoustic communication can allow State of Health parameters and PSDs to be viewed at the surface, ensuring confident commencement of seismic recording before leaving the location. Using the digital feedback system, it is possible to remotely configure the long period corner of the sensor so the operator can adjust the response of the OBS to suit its deployment environment.

The Aquarius+ provides further versatility with its ability to communicate with wave gliders or buoys, which can then telemeter the data to an onshore data centre.  The Aquarius+ can detect seismic events using an STA/LTA trigger and create a table of events that can be downloaded via acoustic link to the wave glider or buoy either automatically, for alert scenarios, or on request. The operator can then select which time windows are of interest and download the waveform data. The quantity of data available is approximately 10-15MB of event data per month, equivalent to at least 10 local events in a month. Operators can start data analysis of seismic events without waiting until the end of deployment and recovery.

In addition to the seismometer, Aquarius comes with an integrated hydrophone and pressure sensor capable of measuring changes in the order of 1 ppm as standard. These can be upgraded to an ultra-low frequency hydrophone and an Absolute Pressure Gauge. With an APG and acoustic telemetry, the Aquarius+ has the hardware necessary to be used in a tsunami warning system.

The Aquarius systems are the most compact and low profile OBS equipped with an acoustic modem on the market, minimising both transportation and installation costs, and reducing the noise generated by current flow on the seabed.