Abstract
A new method, in which a sound speed profile in water is divided into layers at the points of equal sound speed above and below the SOFAR(sound fixing and ranging)axis, is proposed to calculate eigenrays for ocean acoustic tomography under range-independent sound speed profiles.The proposed method yields the following advantages over the conventional shooting method:first, it provides us with an eigenray in an analytical formula, which therefore makes the calculation time much shorter, with less quasi-eigenrays due to split beam rays at layer boundaries.Second, it allows us to easily calculate the number of eigenray cycles and to evaluate the effect caused by the discrepancy in depth between the sound source/receiver and the axis.Moreover, it clarifies how a small change in the structure of a sound speed profile above the axis relates to a structural change in a received pulse group.We can thus say that the proposed method is a promising means for identifying the received pulses.Based on a computer simulation that was performed, the three-pulse structure observed in the experiment was found to depend strongly on the relative arrangement between the source and receiver around the axis.
