A comparison of normal mode, WKBJ, and ray theory predictions with measured pulse arrival patterns at the 300‐km range

Abstract

Precise measurements of the impulse response of the ocean sound channel were made during the 1983 reciprocal acoustic transmission experiment at the 300‐km range with source and receiver near the sound channel axis. The transmitted pulse was centered at 400 Hz and had approximately 10‐ms resolution. Using measured XBT data and the technique of inverse theory, a range‐dependent sound‐speed field had previously been computed such that the measurements were consistent with the prediction of range‐dependent ray theory (Howe et al., 1986). Predictions made for the range‐averaged sound‐speed profile using normal mode theory, the WKBJ approximation, and ray theory were found to be in excellent agreement (though a small discrepancy with the measurements remained, since range dependence was neglected). By allowing for range dependence through the use of adiabatic normal mode theory, this discrepancy was largely removed. We conclude that ray theory or WKBJ theory is an adequate prediction technique at 400 Hz in this geometry. [Work supported by NSF and ONR.]