Science and technological developments: article

Geohydroacoustic noise monitoring of the under-ice water areas of the northern seas
A. Sobisevich1
D. Presnov1
R. Zhostkov1
L. Sobisevich1
A. Shurup1,2
D. Likhodeev1
V. Agafonov3
1 Schmidt Institute of Physics of the Earth of the Russian Academy of Sciences, Moscow, Russia
2 Lomonosov Moscow State University, Moscow, Russia
3 Moscow Institute of Physics and Technology, Moscow region, Dolgoprudny, Russia
Journal: Science and technological developments
Tome: 96
Number: 3
Year: 2017
Pages: 3-18
UDK: 550.34.05
DOI: 10.21455/std2017.3-1
Keywords: monitoring of layered media, under-ice waters areas, seabed, geohydroacoustic fields, passive monitoring, mathematical modeling, dispersion of surface waves, information-measuring modules, geohydroacoustic antenna systems, full-scale experiments
Аnnotation: The results of theoretical and experimental studies of the structure of wave geohydroacoustic fields formed in the northern seas covered with continuous ice are presented. A simplified mathematical model is constructed that takes into account experimental data showing that the water layer with the ice cover exerts the greatest influence on the generation process of various types of geohydroacoustic waves in the lithosphere-hydrosphere-ice cover system. The structure of the seabed affects mainly the characteristics of propagating waves, and not the generation of new modes. The results of mathematical modeling became the basis for the development of new localization technologies for inhomogeneities, applicable in ice-covered water areas. The main distinguishing feature of the newly developed technology for monitoring the environment in ice-covered sea conditions is the possibility of measuring the parameters of noise signals without the use of active sources of geohydroacoustic radiation. The most promising for use in the conditions of the northern seas are methods based on measuring the characteristics of surface waves, in particular methods of microseismic sounding and noise tomography. The combination of these methods combines the achievements of passive geophysics in recent years and takes into account the features of hydroacoustics. To obtain information about the wave propagation medium, both the amplitude and phase characteristics of the wave field are used. To reveal in the records the waves of one type or another, methods of spatio-temporal processing of the signal with an appropriate choice of the frequency range are used. A new generation of seismo-hydroacoustic freezing information-measuring modules (buoys) created by the authors, equipped with vector and molecular-electronic primary converters, is described. The information-measuring modules are intended for use in the distributed ice-class antenna systems, the use of which will allow conducting year-round monitoring of the northern seas covered with solid ice sheet. Investigations into the functioning of the ice freezing information and measuring systems and the theoretical results obtained were checked during fieldwork in February 2017. At each measuring station, the receiving system consisted of three reference devices providing measurements at the bottom, in the water column and on the ice surface. The mockups of the tested geohydroacoustic buoys were frozen at points separated by a distance of one kilometer. As emitters, we used falling mass of 32 kg. The use of a controlled perturbation during ice experiments made it possible to obtain qualitative spectrograms of geohydroacoustic perturbations in layered structures and to analyze dispersion curves. In the study of the fundamental bottom mode, a underwater blast at a depth of 10 m was used as the source of the signal. Seismic-hydroacoustic freezing information-measuring modules successfully withstood the ice tests in full-scale conditions at low temperatures, demonstrating the stability of the acquired seismo-hydroacoustic information. The experimental data obtained are in a good agreement with the theoretical estimates made within the framework of the model of layered geological environment. The set of the performed studies showed that the natural noise of the sea contains useful information that reflects the internal structure of the seabed and the water layer and allowed developing instrumental and methodological foundations for the noise technology of localization of inhomogeneities in the aquatic environment and layered bottom structures of the northern seas by passive monitoring of microseismic noise.