MEMS-based 3D accelerometers for land seismic acquisition: Is it time?

Abstract

Recent advances have allowed development of micro electro mechanical system (MEMS) sensors with the sensitivity, low noise, and dynamic range needed in seismic acquisition. This is a possible “breakthrough” because MEMS accelerometers have the potential to provide broader bandwidth, more accurate amplitude, and less sensitivity to planting tilt than the coil-based geophones that have long been used in the industry. Several papers have presented the advantages of three-component acquisition with single digital sensors based on MEMS, and the advent of these sensors has been promoted as the next big advance in land seismic acquisition—much like the shift to 24-bits recording systems 10 years ago. So, this is a good time to ask an obvious question: Has this technology really advanced to the point that it can, or should, be used for general-purpose land seismic acquisition? This paper will attempt to answer that question by addressing the advantages and disadvantages for the general application of single 3C digital sensors. Ground motion can be measured as displacement, velocity, or acceleration. A mass/spring assembly is used for all these measurements. With a soft spring, the mass (the coil in the geophone) does not move and represents the reference for displacement or velocity measurements. With a stiff spring, the mass moves with the case, but with a small residual displacement related to the acceleration. This acceleration can be measured either by the strain on the spring (e.g., low cost, low power, high distortion air bags) or by a feedback force applied to the mass to cancel the displacement (e.g., high performance digital sensors requiring power supply). In this last implementation the sensor based on MEMS is still analog, while the control loop and the output provided by an application specific integrated chip (ASIC) are digital. Such a “digital” sensor is much smaller than the …