The unique long range of the mapping sonar now allows sea-bottom imagery to be obtained which is comparable to air photography or radar imagery on land. The sonar scans out to a 0.5 mi on each side of a towed fish, making the instrument practical for regional geologic sea-floor mapping. When the sonar is used in conjunction with a vertical-profile sparker, submarine geologic interpretations can be made that are superior to photogeologic interpretations on land. There are 2 modes of operation of the sonar. (1) With proper placement of ship traverses, continuous imagery can be obtained comparable to a stapled air-photo mosaic. (2) The sonar fish can be pulled behind a seismic vessel, producing mile-wide strip-type control. For use in this fashion, the increase in cost per m le is small. There are many geologic and geophysical benefits in this use of the sonar. Practical development of the wide-scan-mapping sonar heralds the beginning of sea-floor mapping comparable to aerial photographic land mapping.

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