Passive fathometry in Australian waters

Cross-correlation function (CCF) between the ocean ambient noise (OAN) fields received at two hydrophones gives estimate of Green´s function (GF) between those two hydrophone positions, which helps in the passive estimation of the bottom profile of the ocean called a passive fathometry. Wind generated ambient noises on the ocean surface mostly contribute to the estimation of passive fathometry. According to the literature this estimation can be improved using broader bandwidth. In the shallow waters near Australia, biological noise is a major component of the broadband OAN field and dominant at low wind speeds because Australian waters are warmer and include a large amount of tropical water which makes them a better place for marine life. In this paper, theoretical analysis of the CCF between OAN fields in the presence of shrimps is presented. The effect of broadband shrimp noise on the passive fathometer is demonstrated using experimental data which shows that in the presence of strong biological activities, only the lower band of the ambient noise is useful in the passive fathometer. Experimental analysis has been performed using both conventional delay and sum (DS) and adaptive minimum variance distortionless response (MVDR) beamforming techniques where the latter technique gives superior estimation.