We report on a field comparison of different seismic motion sensors. The CREWES Project at the University of Calgary acquired a 3C-2D seismic line in the Spring Coulee area of Southern Alberta in January 2008. This was a unique opportunity to compare two types of multicomponent sensors with acquisition occurring at the same time and with the same receiver parameters. This 6.52 km 2D acquisition was laid out with a digital MEMS accelerometer: the DSU3-428 and the accompanying Sercel 428XL recording system; as well as an analog 3C geophone: the SM-7 high resolution geophone element placed in a modified PE-6/S nail type case co-developed by Sensor Nederland (A Division of ION Geophysical) and ARAM Systems with the accompanying ARAM Aries MC recording system. There have been limited acquisition comparison tests performed and/or published with MEMS accelerometers and analog geophones in the past; the purpose of this study is to compare data acquired with single-point 3C receivers laid out side-side in a commercial recording environment.
The introduction of digital MEMS 3C accelerometers in the early part of this decade has led to resurgence in both interest and implementation of multi-component acquisition technology. There are currently two types of MEMS sensors available for use in the seismic acquisition industry: Vectorseis® from ION Geophysical (Maxwell et al., 2001) and the DSU3 from Sercel (Farine et al., 2003). Over the past few years there have been several papers presented that have discussed the merits of: MEMS accelerometers versus analog coil geophones both geophysically and operationally, receiver arrays versus single-point receivers, as well as the merits of multicomponent data in general.
Mougenot (2004) presented an analysis of the advantages and disadvantages of the new MEMS accelerometers and the analog coil geophone. The proposed signal preservation advantage of MEMS, that is, better vector fidelity due to accurate calibration, broad-band linear response and low distortion; is offset by the disadvantage in the inherent use of a MEMS 3C sensor as a single-point receiver and the inability to attenuate ambient and shot-related noise. Lansley et al. (2007) state that the increased noise seen with the use of single point 3C receivers must be compensated with increased data density and more sophisticated data processing, suggesting that single station intervals must be one-half of the normal group intervals. Flat acceleration response to low frequencies, low sensor noise at high frequencies, tilt measurement capabilities: all seem to point to an advantage in using digital MEMS accelerometers over traditional geophones. What do the results of side-side field tests in controlled conditions tell us about the performance of the sensors? The first field test of a MEMS 3C digital sensor in direct comparison to an analog 3C geophone presented to the seismic industry was by Maxwell et al. (1999). The accelerometer data was integrated to represent a velocity signal for comparison to the two types of geophones tested. Power spectra taken over time-offset windows dominated by surface waves were compared, showing qualitative similarity between all of the sensors.