## 2 Experiment  
Figure 1 shows a map scheme of the experiment. A low-frequency hydroacoustic radiator operating at frequency of 22 Hz [16] was submerged from the \"Akademik Oparin\" research vessel to the depth of 18 m. The radiator is a part of radiating hydroacoustic system consisting of a radiator with an electromagnetic transducer, a frame for suspending the radiator, a cable-hose with a control manometer, a power source, an electric pump, a control hydrophone, and two calibration accelerometers. The radiating hydroacoustic system is designed to generate harmonic and phase-shift keyed hydroacoustic signals in the frequency band of about 1 Hz in the range of 19-26 Hz. The amplitude of the volumetric oscillatory displacements of the radiator reaches 0.0123 m\({}^{3}\). At the frequency of 20 Hz in the limitless water area, this corresponds to a radiated acoustic power of 1000 W. The exterior view of the radiating hydroacoustic system is shown in Figure 2. During operation at each station, the low-frequency hydroacoustic radiator created pressure of about 7 kPa, which was registered by the control hydrophone.  
The seismoacoustic signal was recorded by the 52.5-meter laser strainmeter located on Shultz Cape. The laser strainmeter is installed at N42\({}^{\circ}\)35.5817\({}^{\prime}\), E131\({}^{\circ}\)09.9667\({}^{\prime}\) on Shultz Cape underground, at a depth of 3-5 m from the ground surface, in specially built underground hydro-thermally insulated rooms that ensure satisfactory temperature stability; see Figure 3. Operation of the laser strainmeter is described in [17]. The part of the 52.5-m laser strainmeter structure closest to the water (corner reflector) is located at the distance of 120 m from the water edge and at 67 m above sea level. The working arm of the 52.5-m laser strainmeter is oriented at the angle of 18\({}^{\circ}\) relative to the north-south line. All information from the laser strainmeter's registration system is sent via cable lines to the laboratory building, where it is entered into a specially created database. The obtained experimental datasets are then subjected to preliminary and final processing, depending on the set tasks. The interferometry methods used in the laser strainmeter allow measuring changes in the intensity of the interference pattern with high accuracy. Theoretically, using interference methods, it is possible to measure the displacement between the strainmeter plates with an accuracy of \(10^{-6}\times\frac{\lambda_{l}}{2}\), where \(\lambda_{l}\) is the wavelength of the used frequency-stabilized laser. In our case, the accuracy of measuring the displacement between the plates is 0.01 nm.  
Figure 1: Map scheme of the experiment. LS—laser strainmeter, S1–S4—radiation stations.  
Figure 2: Low-frequency hydroacoustic radiator of electromagnetic type on board the vessel before submerging.  
Also during the experiment, in each radiation station, hydrological parameters of the environment such as the temperature, salinity, density, and sound velocity were measured. The purpose of these measurements was to identify sound channels and inhomogeneities of the medium, affecting the sound propagation.  
The obtained experimental datasets at the end of the experiment after preliminary processing were placed in the experimental database for further processing and interpretation of the results.