Preliminary Measurements of Pressure Response to Low Frequency Signals in Shallow Water

摘要

The purpose of the study was to determine the magnitude of changes in sound pressure level (SPL) produced by interference patterns (phase effects) in shallow water. For an empirical procedure, relative SPLs were measured in response to sinusoidal signals of 18 frequencies at one-third octave increments for 100 to 5000 Hz. In a total water depth of 32 meters, the projector was set at depths of 1, 16, or 30 meters and the hydrophone at depths of 3, 16, or 31 meters. Measurements were taken of six horizontal ranges (1,16,31,100,320, and 525 meters). Relative SPLs were computed according to a formula derived by P. A. Barakos. Formula parameters were based on measurements associated with the empirical procedure. Both sets of data were compared; minimal agreement was found. The frequency regions where constructive or obstructive interference occurred were different for each method. In addition, the magnitude of interference effects was less for the measured than the computed method in most cases. However, the study does indicate that, under certain conditions, SPL may vary up to 40 dB as a function of frequency. (Author)