Part I. A continuous configuration hydrophone array for broadband continuous seismic profiling : Part II. A comparison between the responses of a continuous line array and a discrete linear array

Abstract

The signal-to-noise ratio of towed receivers employed in seismic reflection profiling is significantly improved by using a hydrophone array whose broadband directional response approaches that of a theoretically continuous sensor. Within a broad pass band all secondary lobes of an array of continuous configuration are less sensitive than the main lobe. This design improves upon the directivity and thus the signal-to -noise ratio realized in broadband work by those linear arrays in common use whose transducers are spaced widely compared to the wavelength and duration of transients of acoustical noise projected along the array from all angles of reception. Sensitivity equal to that of the main lobe is developed by the secondary lobes of these commonly used arrays at various frequencies and angles to the array. The 30 -meter arrays of 200 equally-sensitive transducers described here have a broadband response approaching that of a continuous configuration. In order to obtain uniform sensitivity along the array all transducers are calibrated and chosen to be equal in sensitivity within ±0. 4 dB. Long term stability in sensitivity is attained by the use of small, rugged, cylindrical ceramic transducers. The ratio of seismic signal-to-noise from all sources in a 20 to 1000 Hz passband is about+ 6dB while deep-ocean profiling with a 90 k joule sparker at 8 kts in a moderate sea state. The average seismic signal received 1 second after the onset of the bottom reflections during a 0. 5 second period is compared with the average noise received in the same passband for a similar period just prior to the bottom reflections.