Relationship between Sound Speed Structure near Ocean Surface and Pulses Propagating in Deep Sound Channel in the Ocean

摘要

We analyzed effects of sound speed structure near ocean surface on pulses propagating in deep sound channel in the ocean, such as in ocean acoustic tomography (OAT), by using the normal mode theory proposed by Stickler. In general, time structure of received pulse train in deep sound channel varies in according to the sound speed structure near the surface. We analyzed propagation of pulses whose center frequency is 200 Hz. The sound source and the receiver are located on the channel axis. The sound speed profile used in the calculation is based on a profile measured by 'SHINKAI 6500.' which is deep submersible vehicle of Japan Marine Science and Technology Center (JAMSTEC), in 1992. From the computer simulation, we found following: (1) Slow pulses, which propagate around the channel axis, are hardly affected by the sound speed change near ocean surface. (2) Fast pulses, which propagate far apart, from the channel axis, are shifted monotonically in time with preserving their time structure. (3) Pulses with intermediate propagation speed, which is received in transition time between the slow pulses and fast pulses, show drastic changes when the sound speed gradient near ocean surface changes from positive to negative.