Instrumentation and Techniques for Oceanographic Acoustic Surveys by Aircraft Free

Since two‐thirds of the earth's surface is covered with water, surveys of variable oceanographic features such as propagation of sound, temperature variations, bottom scattering, bottom bounce, and ocean currents by use of aircraft would be highly desirable provided suitable instrumentation and techniques could be developed. The simultaneity of data would provide a picture impossible to obtain from ships. This paper describes instrumentation suitable for use by aircraft to obtain the following types of data: ambient noise, marine biological noise, acoustic propagation, bottom reflection, bottom scattering, ocean depth, bathythermograph (B.T.), and velocity gradient. Sonobuoys are used to provide contact with the water. The sound sources are explosive charges which provide a broad band of acoustic energy having a known spectral distribution and level. The frequency distribution of the bottom reflection as a function of time and ocean depth as well as the rate of decrease obtained from aircraft are shown. The vertical temperature gradients can be obtained by means of an acoustical telemetering bathythermograph (B.T.) unit which sinks at constant speed. It is estimated that an aircraft could measure the various acoustic parameters described in intervals of 25 miles along a 1500‐mile flight path in one day. A discussion of data types and data analysis will be given.