Tilt monitoring

 

PB016B

Of the many methods at our disposal to measure crustal deformation, tilt (or slow rotation of the surface relative to a plumb bob) is most familiar. Stability of the tilt sensor is important as tilts in the Earth usually accumulate at rates measured in microradians per year.

Quad has developed a tiltmeter for just such measurements. It is an optically-based sensor, so electronic noise is minimized and resolution and cast are improved.

Where is is best used?  Applications include reservoir monitoring, mapping of hydraulic fractures, and earthquake and volcano related research.  This geodetic-grade sensor can operate in deep boreholes at high temperature or on seafloor installations.

Close-up of the internal optical core of the tiltmeter.

Close-up of the internal optical core of the tiltmeter.

How does it work?  The tiltmeter is based on optical interferometric detection of the motion of a pendulum suspended from a monolithic flexure. Two such pendulums are arranged inside a borehole sonde. Optical fibers carry laser light to the sonde and interference fringes back to a surface unit which processes the optical signals into tilt of the sonde.

Sensitivity is at the nanoradian level (Earth’s tilt tides are readily observed) and drift approaching a microradian per year has been achieved in many instances.

How does it compare? – In direct field comparisons against the current volume leader in tilt sensors (using both their both field and reference sensors), Quad’s units achieved 10x the resolution at 1/10th the drift.  Further, our sensors are capable of  handling temperatures up to 250°C.

Contact Quad for results of the competitive benchmarking or more details.

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