Inter-annual variability of the acoustic propagation in the Yellow Sea identified from a Synoptic Monthly Gridded Database as compared with GDEM

Abstract

This research investigates the inter-annual acoustic variability in the Yellow Sea identified from the Synoptic Monthly Gridded-World Ocean Database (SMG-WOD) as compared with the Navy's Global Digital Environmental Model (GDEM). The SMG-WOD has a horizontal resolution of 1˚, 28 vertical levels from the surface to 3000 m depth and one-month temporal increments allowing individual years of acoustic data to be analyzed, whereas GDEM is a climatological database with a horizontal resolution of 1/4˚ and 78 vertical levels. The Yellow Sea is a semi-enclosed basin located between China and Korea with a mean depth of 40m; acoustics are driven by shallow water dynamics and interaction with the bottom. Seven distinct locations were selected for acoustic comparison based on various depths and bottom types. Composite analysis of the sound speed profiles reveals evident inter-annual variability at all locations, superimposed into a strong seasonal variability. Overall, SMG-WOD produces longer propagation ranges than GDEM in the winter, while ranges in the summer are similar within the two datasets, as modeled in BELLHOP. The most reflective bottom sediment (gravel) produced the longest ranges in both summer and winter, in contrast to other locations, which presented higher attenuation values and produced extremely limited ranges in the summer. Inter-annual variability, as expressed by extended acoustic ranges in SMG-WOD, indicates the need for a dataset with temporal resolution but optimally with higher vertical and horizontal resolution.