Features of the behavior of vertically distributed hydroacoustic receiving systems in the presence of drowned flows

Abstract

The features of the behavior of vertically distributed extended receiving systems (VDRSs) are considered as applied to low-frequency ocean tomography. The most widespread form of such systems is a structure that consists of a conductor-and-support cable of several hundred meters, on which receiving modules are mounted, as well as a buoy and an anchor to ensure the spatial position of the system. The results of experiments performed using VDRSs with lengths of 32 and 128 m in a water area of the White Sea are discussed. The influence of drowned flows on such a VDRS leads to a time dependence of its spatial position with respect to the vertical line passing through the anchor system. In addition, vibrations of system’s elements, especially the conductor-and-support cable, are generated, transferred to hydrophones, and lead to the formation of a pseudoacoustic signal, which, under certain conditions, can substantially exceed the background noise level in the water area. These circumstances considerably reduce the efficiency of VDRSs and limit the measurement frequency range from below. Analysis of the experimental data obtained with this type of receiving system in different World Ocean regions at different depths and under different hydrological conditions reveals a certain similarity in the character of pseudoacoustic signals recorded with VDRSs. The similarity of the results of various experiments points to the existence of a common mechanism of vibration generation and pseudosound induction. Determining this mechanism may reveal how to eliminate these undesirable phenomena and extend the VDRS frequency range toward the infrasonic.