Brooks L., Kidner M., Zander A., Hansen C., Zhang Y.

The determination of seabed properties and their incorporation in sound propagation models for estimating the effectiveness of sonar and underwater communications is generally required in shallow water regions in the vicinity of commonly used shipping and fishing routes. It has been suggested by others that the extraction of acoustic data from interference patterns observable in ambient noise spectrograms can be used as an effective means of determining seafloor properties in these situations. Within this paper, the problem of obtaining information from a frequency vs. range spectrogram and relating this to the governing modal model is discussed. An existing method for estimating modal group and phase velocities (and hence seabed properties) from spectrogram information, based upon a dual mode analysis, is critically reviewed and the need for a more complete description of the modal model is outlined.