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In an underwater sound channel there are generally three types of turning points,near which three typesof turning-point convergence-zones(TPCZ)are formed.TPCZs of the 3rd type have slightly weaker intensitythan those of the lst and 2nd types which are located at the source and its conjugate depths,but they play animportant part in low-frequency long-range field owing to their wide distribution in space. In this paper,sound fields near turning points of the 3rd type are mainly studied,and expressionscalculating the intensities in the vicinity of the 3rd-type turning points are given.The theory shows that in thecase of low frequency the intensity of the 3rd-type TPCZ is proportional to the cubic root of frequency andinversely proportional to the square of the range.
In an underwater sound channel there are generally three types of turning points, near which three types of turning-point convergence-zones (TPCZ) are formed. TPCZs of the 3rd type have slightly weaker intensitythan those of the lst and 2nd types which are located at the source and its conjugate depths, but they play animportant part in low-frequency long-range field owing to their wide distribution in space. In this paper, sound fields near turning points of the 3rd type are mainly studied, and expressions calculating the intensities in the vicinity of the 3rd-type turning points are given. The theory shows that in thecase of low frequency the intensity of the 3rd-type TPCZ is proportional to the cubic root of frequency and inversely proportional to the square of the range.