HIGH-RESOLUTION MARINE REFLECTION PROFILING FOR ENGINEERING AND ENVIRONMENTAL PURPOSES .B. DIGITIZING ANALOG SEISMIC SIGNALS

This paper discusses the digitizing of analogue seismic signals. It is assumed that they have been acquired with adequate attention to signa l-to-noise ratio. It is explained how the analogue signals must be amp lified and filtered prior to digitization in order to match the availa ble digital resolution and the intended digitization rate. The causali ty of seismic signals is seen to present some difficulties when specif ying a bandwidth for the high-cut anti-aliasing filter. The direct use of seismic power spectra is demonstrated to be highly subjective in t his regard. An objective method of calculating practical bandwidths fo r causal signals is derived. The method is applied to the signature of a common type of seismic source. The result indicates a sampling rate that seems to be close to the minimum rate required to describe the s ignature. The influence of processing techniques that broaden signal b andwidth is examined and leads to a conclusion that intended processin g procedures can be as important as source bandwidth for determining s ampling rate. Published spectral characteristics and calculated bandwi dths are tabulated with suggested sampling rates for a variety of sour ce types.