PROPAGATION AND INVERSION OF AIRGUN SIGNALS IN SHALLOW WATER OVER A LIMESTONE SEABED Li Fan a , Alec J Duncan b , Alexander Gavrilov b a Institute of Acoustics, Chinese Academy of Science, Beijing, China. b Centre for Marine Science and Technology, Curtin University of Technology, Western Australia. Alec J Duncan, Centre for Marine Science and Technology, Curtin University of Technology, GPO Box U1987, Perth, Western Australia, 6845, Fax +61 8 9266 4799, a.duncan@cmst.curtin.edu.au Abstract: Limestone seabeds with thin or non-existent coverings of unconsolidated sediment are common around the southern Australian continental shelf and often provide strong coupling between the sound wave in the water and the shear wave in the seabed. Sound reflection from such seabeds is very weak except at the p-wave critical angle, which results in the acoustic energy transmitted to long range in the water column being dominated by high- speed Head waves. The characteristics of acoustic propagation in such an environment have considerable practical importance for the propagation of the sound produced by marine seismic surveys and are investigated in this paper, which compares measured signals from a commercial seismic survey with the results of numerical modelling. Techniques for inverting for the geoacoustic parameters of the seabed are also considered. Keywords: Acoustic, propagation, limestone, calcarenite, geoacoustic inversion