Landslide dynamics is considered in the framework of a two-layer system involving water and landslide material. The problem is formulated both in the Cartesian coordinates and in a generalized form relying on curvilinear boundaryfitted coordinates. An essential element of landslide dynamics is the account for nonhydrostatic pressure component defined by the solution of the nonlinear dispersive Boussinesq equation. A numerical implementation for curvilinear coordinates uses the second-order difference splitting scheme with restriction on the grid size only imposed by advection, and includes a module for computing draining in the shallow zone. The results of extensive series of numerical experiments simulating changing physical and energetic characteristics of landslide in function of slope angle are presented together with modeling results for coastal wave dynamics generated by a landslide as well as estimation of the impact of nonhydrostatic effects. The model is verified by comparing its simulation results with the results of laboratory experiments for three events: a tsunami wave at the Japan coast, wave passage over a submarine barrier and a gravity wave generated by a landslide. As a practical model application simulations of the flow generated by the Alaska mega-landslide (1958) are presented.

To improve the quality of simulation of thermohaline structure in the Gulf of Finland a three-dimensional hydrodynamic model is proposed. It is based on the model complex NEMO (Nucleus for European Modelling of the Ocean). Angular steps of the model grid on latitude and longitude are, respectively 0.25 and 0.5' (≈ 0.5 km), that is 4–8 times less than the value of the baroclinic Rossby deformation radius in the Gulf of Finland. Vertical turbulent exchange is described using a turbulent closure scheme of k-ε type. The calculation results are compared with contact measurements of temperature and salinity obtained using CTD probe at 38 stations in the expedition of the Russian State Hydrometeorological University in the eastern Gulf of Finland in the period from 25 to 28 July, 2011 and data CTD probe (15 stations) for the summer period, 2011 from the BED (Baltic Environment Database). Calculated sea surface temperature is also compared with its satellite estimates, having a resolution of 1×1 km and obtained by the Moderate-resolution Imaging Spectroradiometer (MODIS). It is shown that the choice of the appropriate scheme of turbulent closure and implementation of the model on the grid of high-resolution (≈ 0.5 km) led to significant improvement (compared with the calculations on a coarse grid) of the quality of simulation of temperature in the spring-summer period.

The paper is devoted to the experimental and theoretical research of the influence of peculiarities of the form of a submarine vessel (depending on its lengthening and displacement) on the efficiency of breaking ice cover by flexuralgravity waves. The experiments were carried out in a natural fresh-water pond with the following parameters L×B×H = 10×3×1 m using model underwater vessels (a scale of 1:100). The model ice cover of necessary thickness was prepared by natural freezing. The necessary equipment was designed and made for the experiments to be carried out and a measuring complex for registration of deflections of model ice was formed. By towing the model SV its velocity was determined and the profiles of deflections in the ice cover were registered. In the course of experiments the curve caused by flexural-gravity waves was studied, namely the attitude of deflection to the lengths and amplitudes and the possibility of complete destruction of the ice plate. In the theoretical part of the work previously received analytical integral dependence is referred to, to calculate the deflection of the floating plate with rectilinear unsteady motion of a slender and almost axisymmetric body near the water surface. The authenticity of calculations is proved by the comparison of the results with experiments data of ice breaking by flexural-gravity waves. The results show that wave formation in the ice cover and the efficiency of its destruction essentially depend on relative lengthening and displacement of an underwater body as well as on the speed of its motion and the depth of its immersion.

The paper presents an overview of the underwater imaging problem. A history of this problem is given. A universal underwater imaging theory is intended for computing image parameters and the maximal visibility distance of an extended target with inhomogeneous reflectance for various, including laser, underwater imaging systems. We consider the main elements of this theory: image transfer equation, beam spread function and modulation transfer function, the algorithms for computing image parameters of a target of limited size and the maximal visibility distance in water. Parameters of underwater light field, which are necessary for these algorithms, are given as a result of solution of the radiative transfer equation in terms of the water inherent optical properties. We present also a universal model of water inherent optical properties for wavelength close to 550 nm which makes it possible to determine all IOPs required for the underwater imaging theory using only the water attenuation coefficient or even Secchi depth. An algorithm for calculating the signal/noise ratio and the maximal sighting range in water are presented and used for comparison of efficiency of the imaging systems of various types. The main directions of the current investigations on the underwater imaging problem are considered, in particular, imaging through wavy sea surface.

This paper describes a method for detection of marine bioacoustic signals. The method is based on higher-order statistics technique to identify transients in passive array data. A prototype underwater unit with integrated phased circular array has been engineered to test the approach. Results of in-situ measurements obtained using artificial targets are presented. Specifically, implementation of Jarque-Bera test is shown to have resulted in a substantial increase in detection efficiency as against that achieved by traditional signal processing techniques.

The problem of detection in passive sonar is one of the most popular in all underwater acoustics field and it remains the one of the most sparse. Since the early seventies adaptive algorithms received an attention, but due to great difficulties in their implementation in the modern sonar systems, interest has weakened over time. In addition to adaptive algorithms in passive sonar rarely appear quantitative probabilistic characteristics for complex tactical environment, which significantly complicates the solution of the detection problem using them. With the current understanding of the sound propagation dynamics in the water environment, namely the presence of the effects of multipath propagation and scattering, the algorithms working on the short sample for adaptation become the main interest. In this article we derive approximations for the first two moments of the most promising fast projection type algorithms, which is built on a short sample of the antenna array elements. The results of modeling represented as the dependences for different configurations of antenna arrays. A comparison of the results from the output signal to noise ratio on weak signals with a classic non-adaptive algorithm Bartlett was presented. We propose a method to eliminate the loss of weak sources detection by using the spectral decomposition of the matrix involved in the construction of the orthogonal projector.

The two-channel system of noise signal reception with different frequency filters in each channel is considered. With the use of such two-channel system two methods of distance estimation can be realized. The first method of distance estimation can be executed when it is possible to tune parameters of filters of two channels on frequency scale, and hence on distance. The second method of distance estimation can be executed when parameters of filters of two channels are fixed. In the first case the distance to the source is determined at equality of output signal to noise ratios in two channels. In another case — by calculations according to the relationship of output signal to noise ratios. Analytical description of a two-frequency method of determination of distance to noise signal source is received in two variants: when using optimum filters and when using filters with limited frequency band. Calculations for quantitative comparison and estimation of applicability of band-pass filters are carried out. It is shown that twochannel system with band-pass filters has no output characteristics symmetrical with respect to the center of distances determined as average geometrical value of distances of two filters tuning. Efficiency of the method will be different for signal source located closer or further than the center of distances. It is shown that the distance determination method based on tuning filter parameters on frequency cannot be realized in considered two-channel system similarly to how it occurs at the use of optimum filters. Functional dependences received in the research provide possibility of the further development of the two-frequency method of determination of distance to noise signal source with the use of band-pass filters for conditions of real noise.

The numerical study of interferential structure of the low-frequency hydroacoustic fields in shallow sea excited by the concentrated directed sources of signals is made. The study is executed with the assumption that the amplitudephase distributions in the vertical and horizontal plane formed in a wave guide by extended volume real sources can be formed by system of local sources as superposition of a monopole and various image of the focused three dipoles and five quadrupoles concentrated in one point. The calculations are performed for the analysis of hydroacoustic fields in the near- and far-field, for different frequencies and depth of the source and receiver locations. It is found that the structure of the fields at distances of less or more than 1–2 depths of the waveguide is substantially different. It is shown that the intensity decrease of fields generated by a monopole, horizontal dipoles and horizontally oriented quadrupoles goes noticeably slower at the distance increase than the decrease of signals from vertical dipoles or vertically oriented quadrupoles. It is also shown that the signals from the sources or got by a receiver located at shallow depths or bottom area decrease significantly faster than the intensity of the fields in case if the receivers and sources are located close to the equivalent middle of waveguide. It is recommended to measure the characteristics of the fields of low-noise sources by vector-scalar receivers or antennas in the areas of signal interference maxima and in the middle of waveguide. When predicting the given noise values and processing the experimental data it is recommended to take into account the transfer functions of the waveguide, resulting from acoustic calibration of soil models in the study area.

Approach in the hydrosphere ecotoxicological control – microscale biotests with small organisms and volumes of probes is analysed in the review. The approach more economical than bioassay with fish and plants, but problems of biotests replacement on micro biotests and differencies between tests for natural water and drink water or effluents are discussed in review. Tests with objects of different phylogenetic levels and measuring methods of their endpoints, which are analised. Their diversity makes it possible to control different objects of biosphere and many harmful factors of natural water pollution: pesticides, heavy metals, oil, detergents and others. Attention is drawn to identification of harmful pollution and detection their harmful propertyes: acute, chronic toxicity, phyto-, geno-, embriotoxicity. Description of tests are illustrated by schemes, which explains principals for solve task of detection harmful factors in environment. Problems of biotechnology and their influence on assessment of bioassay are briefly discussed.. Given that journal is not only biological, in the review are more demonstrated applications of microbiotests for ecotoxicological control of natural waters. The review covers the literature from the beginning of the 1990s until 2013.

From: University of Helsinki
Department of Physics
Division of Atmospheric Sciences
Press release 16.02.2015