Abstract
A passive fathometer can be formed by two vertically separated hydrophones. The depth can be estimated from the Green’s function between the hydrophones, which is calculated from the cross-correlation between ocean ambient noise fields received at those two hydrophones. The performance of the fathometer depends on the signal to noise ratio (SNR) and the resolution of the noise cross-correlation function. In a given environment, improved SNR and resolution of the cross-correlation function can be achieved through longer observations, more observation points, or increasing bandwidth. Long time averaging has been demonstrated, but requires that the channel be stationary over the averaging time. Hydrophone arrays are commonly used, but result in increased cost and complexity. Recent work shows that the SNR and resolution of the correlation function can also be improved by the use of the large bandwidth noise fields. This paper shows that the non-surface biological noise generated by marine animals, such as shrimp, is one of the major issues in the performance of such a broadband passive fathometer operating in shallow water. This noise tends to occur at higher frequencies. Frequencies at which significant non-surface biological noise is present cannot be used to improve fathometer performance. Consequently, the upper limit of frequencies that can be used in a passive fathometer is limited by the lower limit of the bandwidth occupied by the biological noise.
Highlights
The cross-correlation of wind generated surface noises between two or more hydrophones gives the estimation of the bottom profile of the ocean [1,2,3,4]
This paper shows that the non-surface biological noise generated by marine animals, such as shrimp, is one of the major issues in the performance of such a broadband passive fathometer operating in shallow water
This paper demonstrates the effect of biological activities on the broadband passive fathometer which states that performance of the passive fathometer is affected with the increase of the bandwidth of Ocean Ambient Noise (OAN)
Summary
The cross-correlation of wind generated surface noises between two or more hydrophones gives the estimation of the bottom profile of the ocean [1,2,3,4]. It is shown that large averaging of the NCF is needed for the better estimation of the GF if the noise is recorded at two hydrophones [8,10,12,13,14,15,16] It is demonstrated experimentally that, the usable bandwidth in the passive fathometer at shallow water is limited by the biological activities present in the ocean. This is because, dominant biological sounds are observed at shallow waters all around the world [18].
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