Sensor density or sensor sensitivity?

Abstract

It is widely recognized that image quality can be improved by acquiring seismic data with long offsets, wide azimuths, low frequencies, and dense source and receiver sampling. To achieve this in an affordable way, we see a trend toward single-sensor recording in high-productivity land seismic surveys. Moving away from field arrays has a material effect on requirements for sensors and channels and for the way their performance is specified and displayed. While increased sampling density can compensate for the lack of sampling and noise reduction achieved by field arrays, there is a trade-off in the resultant sensitivity change of the sensor compared to the array and the preamplifier gain setting. Higher sensitivity geophones should be selected and lower preamplifier gain considered for single-sensor surveys. Two measures are introduced to help in finding a balance between adequate sampling and sensor/recorder channel performance at the acquisition design stage. The amplitude spectral density (ASD) expressed in ground-motion units is proposed as a frequency-dependent alternative for root-mean-square (rms) values to evaluate noise properties of the sensor/recorder channel combination. The operating range diagram (ORD) is adopted to offer a more meaningful dynamic-range measure than the instantaneous dynamic range by honoring the differing mathematical properties of signal and noise. The ORD compares full-scale rms values at a range of frequencies with narrowband noise values centered at the same frequencies.