The intensity coherence function of time for partially saturated acoustic propagation through ocean internal waves

The intensity coherence function of time for partially saturated acoustic p ropagation through internal waves is calculated with a method that is impro ved over previous treatments. Two specific improvements are introduced: the usual expansion in (1/Lambda Phi (2)) is carried out to a higher order, an d then the terms of that expansion are calculated with a new perturbative m ethod. The method is applied to propagation without a sound channel, for bo th phase-screen and continuous-medium cases. The validity of the new pertur bative method is estimated by calculating the next order error terms. Accur acies at the few-percent level are found. The new analytic formulas are als o corroborated with numerical integration. Finally, the method is applied t o a specific ocean-acoustic experiment [Azores Fixed Acoustic Range (AFAR)I . In order to achieve good agreement with experiment it will be necessary t o add an accurate treatment of the sound channel to the present perturbatio n method. (C) 2001 Acoustical Society of America.