J. Robert Fricke
Dept. Ocean Eng., Rm. 5-218, MIT, Cambridge, MA 02139
In the mid '80s the offshore seismic exploration industry needed a standard procedure for describing transient seismic source signatures. The need was motivated by several issues including a need to specify performance criterion to the operations crew, a need to evaluate one source versus another for a particular seismic program, and the need to determine performance for new seismic source designs. Prior to that time, seismic source signatures were usually described in the time domain in terms of peak-to-peak pressure (bar-m) and peak-to-bubble ratio. Spectral characterization, if it existed, was relative to the peak value, which was usually set to 0 dB. These measures do not provide quantitative descriptions of source energy or spectral energy density, hence a quantitative standard was needed and developed. The standard focused on a spectral, rather than a temporal, description of the seismic signature and allowed for a detailed analysis of the total source energy and the distribution of that energy as a function of frequency. This approach opened the way for a consistent and quantifiable description of the source signature. Using this description, the above mentioned needs regarding performance and evaluation could be addressed.