Home – Home – Jornals – Avtometriya 2024 number 6

An algorithm aimed at searching for small-sized (about ten pixels) objects with constant brightness on a non-uniform random background has been developed. The algorithm is based on the procedure for finding the conditional maximum of the product of probabilities for an object and a local background to have certain brightness values. For the background, these probabilities are estimated from a histogram constructed for an image segment. The algorithm is implemented for the case when all the brightness values of an object in the acceptable range are equally probable. The computational experiment is performed on twenty photographs of clouds with a size of 1200 ⨯ 1200 pixels. Ten circles with a radius of two pixels are placed on each photo. Of the two hundred objects set in this way, 169 are detected by the proposed algorithm, while the number of errors of the second kind is 280.

Three-dimensional time-of-flight cameras are increasingly used in robotics to provide information support for motion control tasks. They are also considered promising for solving docking problems with non-cooperating spacecraft. In this case, the magnitude of relative coordinate measurement errors that a time-of-flight camera can provide is very important. Random (noise) errors are analyzed in the present study, and the presence of significant correlations of random errors in measuring the range of time-of-flight cameras for neighboring pixels is revealed. For a particular example, an analytical solution is constructed that shows significant deterioration in the accuracy of distance measurements in the presence of this correlation.

The initial intensity shape effect on the spatial evolution of the averaged Poynting vector and the intensity distribution of laser beams propagating in a turbulent atmosphere has been studied. The cases of focused Gaussian and annular laser beams are considered. Introducing the term of the power-cutoff-radius, i.e., the radius of the circle spot possessing a fraction of the full power, the beam quality is evaluated and discussed. It is shown that, by varying the shape of the annular intensity profile at the source plane, the energy flux density through the spot with less than one half of the full power can be increased as compared to the Gaussian beam of the same power-cutoff-radius.

The influence of simultaneously acting additive and fluctuating multiplicative noise with a high level on the accuracy of measuring the information parameter of the signal is considered and analyzed. Expressions defining conditional probabilities of the correct measurement of the information parameter and a spurious count are obtained. The channel probability densities for an N-channel receiver are determined; a special case of a two-channel receiver is considered. The probability of correctly measuring the parameter at a high level of multiplicative noise is approximately equal to the probability of detecting a signal in the channel where the undistorted part of the signal is present. The value of the threshold voltage of the N-channel receiver has been determined, which allows us to obtain the specified probabilistic characteristics of the measurement. Dependences characterizing the probability of correct measurement on the level of the undistorted part of the signal are obtained for the case of a bell-shaped power distribution of fluctuations in the distorted signal through the channels of the receiving device with different spectrum widths of the noise modulation function and different numbers of channels of the receiving device. It is proved that, in the case of a large number of channels or with a power-law distribution of fluctuations of the noise component of the signal distorted by multiplicative noise symmetrical with respect to the k-th channel, the average value of measurement errors (spurious counts) is zero, i.e., there are no systematic measurement errors.

The article considers an approach to range determine to point targets based on the images from a thermal camera in the mid-infrared band. The paper shows the analysis of the equation of radiation transfer and demonstrates the statistical stability of the target thermal distribution depending on the range and weather conditions. A multidimensional linear regression model is proposed based on the identified object features in order to predict the distance to the object using a trained artificial neural network. The article simulates the obtained approach according to known experimental data, which showed the advantage of the estimated distance (less than Δ_D/D < 0,04)) in comparison with the direct method of the range determining (Δ_D/D > 0,82). The ways forward of research are given and the need to improve the feature space is valid for the increasing of the accuracy.

A constructive method for solving linear-quadratic problems of spatial-temporal control with amplitude limitations of controlling actions in systems with distributed parameters of parabolic type at a given accuracy of uniform approximation of the final state of the object to a required spatial distribution of the controlled quantity is proposed. The proposed approach is based on the previously developed alternance method of constructing parameterisable algorithms of program control. It is demonstrated that the equations of optimal regulators are reduced to linear feedback algorithms on the measured state of the object with pre-determined non-stationary transfer coefficients.

The problem of calibration of a vector magnetometer is considered. Technological errors of its production lead to measurement errors that are unacceptable during device operation. A statistical calibration method is proposed based on iterative minimization of the residual of the measurement result and the exact value of the magnetic field induction obtained through the use of a stationary high-precision meter. Experimental results illustrating the effectiveness of the method are presented.

Currently, when solving the problem of autonomous navigation according to the parameters of the optical flow captured by a video camera during the movement of an object, only the components of the linear and angular velocities of the object are determined. This determination of velocities is only part of the general task of navigation (current positioning of an object and determining its angular orientation) and does not allow it to be solved as a whole. In this regard, the article describes an integration approach that allows combining the capabilities of an inertial navigation system, which provides a solution to the problem of autonomous navigation in general, and an optical flow navigation system, which allows autonomous observation of linear and angular motion parameters with the minimum hardware expenses. When using these systems, the complexity of accounting for interference with different probabilistic nature is a serious problem, and the synthesis of a stochastic model of the proposed integrated inertial optical system is carried out with due allowance for the possibility of further application of methods that take into account the influence of interference in assessing the navigation parameters of an object, i.e., methods of modern stochastic filtering theory. As a result, a modified extended Kalman filter is built to estimate the full vector of object motion parameters based on measurements of the integrated inertial optical navigation system, with the correlation of object and observer noise taken into account. A numerical experiment has been carried out to illustrate the effectiveness of the proposed approach.

An adaptive optics system for correcting laser radiation distortions on a long atmospheric path in real time is presented, which includes an atmospheric turbulence emulation unit and a forward correction contour for errors in laser beam tilt angles caused by the delay of the correcting Tip-Tilt mirror. The forward correction algorithms are tested based on the numerical analysis of measurements performed by the Shack-Hartmann wavefront sensor.

When designing devices in the terahertz range based on resonant tunneling structures with an operating point in the region of negative differential conductivity, serious problems arise in predicting the current-voltage characteristics of such structures. In this study, the problem of predicting the current-voltage characteristics of resonant tunneling diodes in the area of negative differential conductivity for signal conversion devices is solved. A method for calculating the hysteresis on the current-voltage characteristics of resonant tunneling diodes is proposed. The developed model differs from the previously used approaches by using the stationary version of the wave function formalism to describe the hysteresis, while the nonstationary equations of the Wigner function formalism or quantum hydrodynamics were previously used. It is shown that the hysteresis is a consequence of the interelectronic interaction in the quantum channel of the resonant tunneling structure, which can be taken into account using the self-consistent field method. Three types of initial conditions for the system of the Schrödinger-Poisson equations are considered, and it is shown that the appearance of the hysteresis in the current-voltage characteristics of resonant tunneling diodes is achieved by applying special initial conditions in the self-consistency procedure. It is found that the hysteresis manifests itself in the stationary case of a constant voltage, which can be predicted by varying the initial conditions during the self-consistency procedure.

The nonlinear photothermal effect that occurs during local laser ablation of metal oxide films with different thermal conductivity coefficients is investigated. It is shown that the track width decreases monotonously with a change in the thermal conductivity coefficient in the range from 25 to 1 W/(m∙K). It is found that a moderate decrease in the thermal conductivity of the film does not lead to a significant decrease in the track width. The conclusion is made about a combined effect of the thermal conductivity coefficient and the thermal acceleration factor on the minimum track width, which introduces additional nonlinearity into the oxide film heating process.

Currently, GaSe crystals, as a special case of van der Waals materials, are of increased interest to researchers and developers in the field of terahertz optoelectronics and integrated photonics. From the engineering point of view, it is important to have an accurate knowledge of the nonlinear optical coefficient, in particular, at telecommunication wavelengths. Few papers have been devoted to its studying, and the available data differ significantly. In this regard, an independent estimation of the nonlinear optical coefficient d^eo₂₂ of GaSe_1-xS_x (where x = 0, 0.03, 0.12, 0.16, and 0.22) responsible for interaction of optical radiation frequencies (including telecommunicational) and terahertz ranges is carried out. Based on the totality of data obtained using electro-optical measurements and predictions based on Miller's rule, it is shown that the value of d^eo₂₂ for crystals with various doping does not exceed 20 pm/V for near-infrared wavelengths. The resulting value is up to two times smaller than that reported by other authors.