Use of simplified coupled mode propagation for the prediction of impulse responses of megameter trans-Arctic propagation paths

Abstract

In the spring of 1994, a long-range propagation experiment was conducted in the Arctic during which large time-bandwidth product signals (M sequences) were transmitted to two receiver sites. These data were processed to extract the pulse response of the propagation channel at the vertical arrays at each site and a horizontal array at one of the sites. These data are being used for an assessment of the utility of Arctic acoustic measurements for global warming signature detection and monitoring. A critical part of this measurement is the identification of the observed paths with specific propagating modes. A method has been developed based on coupled normal modes which allows us to estimate pulse responses quickly. The results agree favorably with the experimental data when historical environment data are used as the model inputs. The modeling methods used, comparisons with the measurements and implications, as well as the impact on sound speed accuracy required, will be discussed.

The Transarctic Acoustic Propagation Experiment and climate monitoring in the Arctic

“…14 shows the beamformed pulse-compressed coherently summed arrival structure for transmission #23, the 255-digit MLS discussed above. A predicted received signal using the range-dependent coupled-mode code of Evans [20] modified by Freese [21] with the GDEM model is also shown. The comparison of the arrival times will be discussed below.…”

“…2) Travel-Time Modeling Results: The next rows in Table I indicate the predicted arrival times based upon the coupled normal mode acoustic propagation code discussed earlier [20], [21] at the reference range of 2637.5 km. (The coupledmode code was needed because of the mode conversion at the Lomonosov Ridge.)…”