A STUDY OF ACOUSTIC TRAVEL TIME VARIATION ACROSS THE APERTURE OF THE ARTEMIS ARRAY.
Abstract
Continuous measurements of acoustic travel time within the mile deep ARTEMIS array field were made during a 2-1/2 day period in May 1964. The array field occupies approximately one squar mile on the rise associated with Plantagenet Bank off Bermuda. The measurements, which were conducted using sources and receivers located at the approximate corners of the array field, yielded travel times of 1 second and a measurement accuracy of 0.01 millisecond. In addition, environmental data, obtained with the temperature and current sensors in the array field, and sound velocity versus depth measurements made from a surface craft were obtained. The difference between maximum and minimum travel times observed in the 2-1/2 day period was 1.25 milliseconds corresponding to a 180-degree phase shift for a 400 cps signal. The maximum rate of change was 0.3 millisecond in an hour. The travel time variations are due to a combination of changes in sound velocity and changes in path length resulting from mast motion, currents, and refraction. Several different periods can be seen in a time series plot of travel time data. A study of acoustic travel time variations has shown that the magnitude of variation is probably sufficient to cause measurable changes in array gain. Travel time variations within an array must, therefore, be considered in any similar large array. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 01, 1965
- Accession Number
- AD0359202
Entities
People
- Harold J. Doebler
Organizations
- Columbia University