Vol 54, No 6 (2018)

The paper presents the results of theoretical and experimental research into the structure of geohydroacoustic wave fields generated in continuous ice-covered northern seas. A simplified mathematical model is constructed that takes into account experimental data demonstrating that the generation of different types of geohydroacoustic waves in the lithosphere–hydrosphere–ice cover system are primarily influenced by the water layer with the ice cover. The seafloor structure mainly affects the characteristics of propagating waves rather than the generation of new modes. Mathematical modeling results have laid the basis for new technologies to localize inhomogeneities in ice-covered water areas. The main distinguishing feature of this novel technology for monitoring a medium under ice-covered marine conditions is the possibility to measure noise signal parameters without active geohydroacoustic emission sources. Methods that measure the characteristics of surface-type waves are the most promising for use in northern sea conditions, in particular, microseismic sounding and noise tomography. Integration of these methods combines the recent achievements of passive geophysics and takes into account the particularities of underwater acoustics. To obtain information on the wave propagation medium, both the wave field amplitude and phase characteristics are used. To detect particular types of waves in records, spatiotemporal signal processing methods are used with the appropriate choice of frequency range. The authors describe their new-generation seismohydroacoustic information-measuring modules (embedded buoys), which are equipped with vector and molecular-electronic primary transducers. The information-measuring modules are designed for combined use with distributed ice-class arrays capable of monitoring continuous ice-covered northern seas year round. Studies of how ice-embedded information-measuring systems function, as well as verification of the obtained theoretical results, were carried out during field tests in February 2017. At each measurement point, the receiver system consisted of three reference devices that took measurements on the seafloor, in the water column, and on the ice surface. Mockups of the tested geohydroacoustic buoys were embedded at points offset by 1 km. Dropped 32 kg weights were used as the sources. Controlled perturbations in the ice experiments made it possible to obtain qualitative spectrograms of geohydroacoustic perturbations in layered structures and analyze the dispersion curves. When the fundamental bottom modes were studied, the signal source consisted of an underwater charge at a depth of 10 m. The embedded seismohydroaoustic information-measuring modules successfully passed the ice-based tests in field conditions at low temperatures, demonstrating the reliability of the obtained seismohydroacoustic information. The experimental data agree very well with theoretical estimates obtained with the created model of a layered geological medium. These studies demonstrated that natural sea noise contains useful information reflecting the internal structure of the seafloor and the water layer and led to development of the instrumental and methodological foundations of a noise technology for localizing inhomogeneities in the aquatic environment and layered bottom structures of northern seas by means of passive microseismic noise monitoring.

An autonomous three-channel digital recorder developed at the Schmidt Institute of Physics of the Earth, of Russian Academy of Sciences is considered. The recorder was designed to meet the requirements of particularly difficult climatic conditions, minimum energy consumption, and ease of maintenance. Special attention is devoted to the reliability of data storage in case of sudden power loss, for which a new file-free recording format was developed. For each second of data recording, the system assigns a service line consisting of the exact time, the station code, and the station’s coordinates. This prevents loss of data when reading. When power is restored, the recorder automatically switches to the operating mode and continues the interrupted recording. The power supply for the analog part of the recorder is galvanically decoupled from the power supply of the digital part and carefully smoothed by special linear stabilizers and filters. To exclude the penetration of pulsations from the digital to the analog part by the common (grounded) wire, the control interface of the ADC is separated from the microcontroller by digital galvanic isolation circuits. Recorded data is recovered from the instrument by replacing the memory card, which takes just a few seconds. The control functions are also minimized, since the recorder has only two control buttons. The ease of maintenance allows quick installation of a large number of seismic stations with a small number of staff. The most important feature of the recorder is significantly reduced power consumption (less than 0.7 A h per day at a supply voltage of 12 V). This is five to six times lower than that of domestic and foreign counterparts and allows the recorder to operate on a single set of dry manganese–air batteries with a capacity of 150 A h and a weight of 4 kg for more than 6 months. As a component of seismic monitoring systems and in conducting epicentral measurements, these recorders are used in all climate zones of the Northern Hemisphere, from Serbia to Sakhalin and from Yakutia to Bangladesh; they have proved reliable and low-maintenance devices.

The authors discuss their main achievements in developing innovative methodological support for marine gravimetric surveys. They have actively participated in the development of gravimeters and created several generations of gravimetric equipment in cooperation with other organizations. The main characteristics and results of laboratory and marine tests of the mobile Chekan-AM and Shelf gravimetric systems are briefly considered. These systems have operated successfully in harsh Arctic conditions, including the first high-precision marine gravimetric survey in the region of the North Pole. The authors describe the methodological support, results from modern models of Earth’s gravitational field, and integration of data from various gravimetric instruments in the interests of marine gravimetry. The increase in accuracy and resolution of Earth gravitational field models has led to their use beyond solving only fundamental problems. In most areas of the World Ocean, the model field can be used as a reference field when performing a direct marine gravimetric survey. Innovative developments have increased the reliability and accuracy of marine surveys primarily due to the control and correction of systematic errors arising in marine measurements. They make it possible with no loss of measurement reliability to produce surveys at marine test ranges with an error of 0.5 mGal or less, expand the planning capabilities of the survey network, increase the reliability of long-term route surveys, reduce the time of reference measurements, and perform marine gravimetric surveys with only one onboard marine gravimeter and no need for shore-based reference points. An innovative method of accounting for the ocean tide with loading models of the ocean gravitational effect was developed based on the ATLANTIDA3.1_2014 program. Experiments have shown that random errors can thus be reduced by more than 20%. The results of the research have been used to develop ready-made innovative and promising methods for measuring the parameters of Earth’s gravitational field on the surface water area of the World Ocean.

The paper briefly describes the Autonomous Video Information System (AVIS) space experiment conducted as part of the Long-Term Program of Applied Scientific Research and Experiments Planned on the Russian Segment of the International Space Station (ISS RS). The program envisages the development, production, and flight tests of a picosatellite prototype and a sequence of three nanosatellite prototypes with gradually increasing functionality. The main stages include the development of methods and instruments for controlling the separation of the spacecraft, monitoring of their state in an autonomous mode, and experimental testing of the technology of separation, rendezvous, and docking of nanosatellites in orbit. The developed onboard equipment also includes a device for launching pico- and nanosatellites from the ISS RS, manually by an astronaut and by an automatic launcher for nanosatellites from the Progress transport cargo vehicle (TCV), at the command of the ISS or a ground control station. Currently, detailed working design documentation for the spacecraft and the launching device has been created within the experimental program, and work has begun on the production of experimental prototypes.

In order to study the fine structure of temperature fields in the rock strata, precision narrowband temperature sensors have been designed to measure temperature with an accuracy of at least 0.005°C. It is shown that the required sensitivity can be achieved by narrowing the measurement range and application of platinum thermoresistors and 24-bit ADCs for digital signal recording. The developed thermometer uses platinum thermoresistors, which have an almost linear temperature dependence of the change in internal resistance on the external temperature and an excellent long-term stability of their basic characteristics. To reduce the level of self-noise, special technical solutions (low-frequency filtering of both output signals and all supply voltages) are applied. The output differential signals of the thermometer enable its easy connection to a majority of modern digital data acquisition systems. The main methods for calibrating and setting the necessary operating temperature range of sensors are considered. Measurements with the developed sensors in the adit of the Northern Caucasus Geophysical Observatory, Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, in the Baksan gorge will ensure unique data on the structure and dynamics of the thermal field near Elbrus volcano. Continuous monitoring is a particularly important task both for obtaining new fundamental knowledge about the structure of magmatic structures and assessing volcanic hazard from the presence of a fluid magmatic melt in the volcano’s interior. This, in turn, will provide new data on the potential hazard of Elbrus’ volcanic center . This research is especially important today in the light of the developing tourist infrastructure both in the Baksan gorge and in the entire Elbrus region.

The paper presents the first results of full-scale modeling of the state of the foundation of a railway track running through areas with complex natural-climatic and engineering-geological conditions. Our results demonstrate the fundamental possibility of using seismic stations installed along the track foundation to continuously monitor its state. Monitoring parameters that can signal subsoil deterioration have been identified, e.g., flooding, ground thawing, etc. An advantage of the proposed approach over other geophysical methods is the possibility of identifying problem areas at the early stage, as well as real-time monitoring of their state and rapid information transmission to a central communication hub.