Дослідження якісних показників поляризаційної селекції об’єктів на фоні пасивних завад в поляризаційно-доплерівській радіолокаційній системі

The optimal algorithm of polarization-Doppler selection of targets against the background of passive interference is considered. The polarimetric properties of scattered electromagnetic radiation of objects. The functionally-determined mathematical model of the useful signal, structure and correlation characteristics of the internal radiation of the receiver is determined. The algorithm of optimal processing, synthesized within the method of maximum likelihood, is considered for two limit cases. Algorithmic actions in the processing of passive interference and methods of their compensation are considered and investigated. Based on the obtained results, the expression for the algorithm of compensation of interferences reflected from the earth's surface is written. The obtained algorithm equalizes the variance of the input signals and compensates the residual variance with the help of weight coefficients. On the basis of the developed algorithm the scheme of the structurally simplified optimum compensator of passive disturbances is formed. Feature processing of useful signals in the compensation scheme is investigated. To ensure the adaptability of the generated algorithm, the coefficient of the variance ratio is based on the results coming from the variance meter. It is proposed to introduce quality indicators of polarization object selection on the background of the underlying surface, which combines indicators of efficiency of passive interference compensation and indicators of efficiency of useful signal-processing against the background of internal noise of receivers. The corresponding dependence of the indicators on the correlation coefficients of passive interference of different polarizations, as well as on the coefficients that separately characterize the level of difference in signal intensities and interference in the reception channels. The information value of each indicator of the efficiency of polarization signal selection from the ratio of the input variances, the correlation coefficient of passive interference and the ratio of the input signals is investigated.The obtained results are proposed to be used to improve the quality of polarization selection of objects in ground-based and aerospace-based radar systems.

Оптимізація поляризаційно-доплерівської селекції малорозмірних об’єктів на тлі підстильної поверхні

Using the method of maximum likelihood, the optimal algorithm of polarization-Doppler selection of objects on the background of the underlying surface, hydrometeors, urban buildings from aerospace carriers of radio electronic equipment has been synthesized. To solve the problem polarimetric properties of the scattered electromagnetic radiation of natural environments and anthropogenic objects were analyzed.The functional-deterministic mathematical model of the useful signalis determined. When solving the optimization problem, the method of maximum likelihood functionality and likelihood functionality for correlated processes were used, which contains the inverse matrix of inverse correlation functions of the observation equation. The obtained signal processing algorithm includes operations of spectral resection of passive interference. Polarization compensation of passive interference is performed by a combination of interchannel subtraction of the reflected signals of different polarizations. The quasi-optimal features of the synthesized algorithm, which has an obvious physical value and is optimal in the absence of internal noise, are considered. Based on the obtained results, a block diagram of the polarization-Doppler noise compensator and selection of useful signals against the background of noise reflections from the earth's surface has been developed. The study of the physical characteristics of the elements of the polarization covariance matrix of interferences at a high level of correlation of reflections of passive interferences of different polarizations is conducted.Based on the obtained results, it is proposed to introduce indicators of efficiency of passive interference compensation and selection of useful signals. The results of the analysis of the obtained indicators depending on the coefficient of the ratio of variances of passive interference indicate the need to use the polarization differences between signals and interference for selecting objects against the background of the underlying surface. The results obtained can be used to create ground-based and aerospace-based radar systems for detecting moving objects and objects with pronounced polarization features.

Modeling RL Electrical Circuit by Multifactor Uncertain Differential Equation

The symmetry principle of circuit system shows that we can equate a complex structure in the circuit network to a simple circuit. Hence, this paper only considers a simple series RL circuit and first presents an uncertain RL circuit model based on multifactor uncertain differential equation by considering the external noise and internal noise in an actual electrical circuit system. Then, the solution of uncertain RL circuit equation and the inverse uncertainty distribution of solution are derived. Some applications of solution for uncertain RL circuit equation are also investigated. Finally, the method of moments is used to estimate the unknown parameters in uncertain RL circuit equation.

A Novel Method for the Enhancement of Composite Materials’ Terahertz Image Using Unsharp Masking and Guided Filtering Technology

When terahertz imaging technology is used for the nondestructive testing of composite materials, the signal is often affected by the experimental environment and internal noise of the system, as well as the absorption and scattering effect of the tested materials. The obtained image has degradation phenomena such as low contrast, poor resolution of small targets and blurred details. In order to improve the image quality, this paper proposes a novel method for the enhancement of composite materials’ terahertz image by using unsharp masking and guided filtering technology. The method includes the processing steps of hard threshold shrinkage denoising based on discrete wavelet transform, amplitude imaging, unsharp masking, guided filtering, contrast stretching, and pseudo-color mapping. In this paper, these steps are reasonably combined and optimized to obtain the final resulting image. To verify the effectiveness of the proposed method, a 150–220 GHz high frequency terahertz frequency modulated radar imaging system was used to image three commonly used sandwich structure composites, and the enhancement processing were carried out. The resulting images with significantly enhanced contrast, detail resolution and edge information were obtained, and the prefabricated defects were all detected; Five objective evaluation indexes including standard deviation, mean gradient, information entropy, energy gradient and local contrast were used to compare and analyze the processing results of different image enhancement methods. The subjective and objective evaluation results showed that the proposed method can effectively suppress the noise in terahertz detection signals, enhance the ability of defect detection and positioning, and improve the accuracy of detection. The proposed method in this paper is expected to play a positive role in improving the practicability of terahertz imaging detection technology and expanding its application fields.

Temporal integration for amplitude modulation in childhood: Interaction between internal noise and memory factors

It is still unclear whether the gradual improvement in amplitude-modulation (AM) sensitivity typically found in children up to 10 years of age reflects an improvement in “processing efficiency” (the central ability to use information extracted by sensory mechanisms). This hypothesis was tested by evaluating temporal integration for AM, a capacity relying on memory and decision factors. This was achieved by measuring the effect of increasing the number of AM cycles (2 vs 8) on AM-detection thresholds for three groups of children aged from 5 to 11 years and a group of young adults. AM- detection thresholds were measured using a forced-choice procedure and sinusoidal AM (4 or 32 Hz rate) applied to a 1024-Hz pure-tone carrier. All age groups demonstrated temporal integration for AM at both rates, that is significant improvements in AM sensitivity with a higher number of AM cycles. However, both 5- 6 years and adults exhibited similar levels of temporal integration, while 7-8 and 10- 11 years showed less integration. This is because at both rates: (i) the youngest group (5-6 years) displayed the worst thresholds with 2 AM cycles but similar thresholds with 8 cycles compared to older children groups, and (ii) adults showed the best thresholds with 8 AM cycles but similar thresholds with 2 cycles compared to older children groups. Computational modelling indicated that higher levels of internal noise combined with poorer short-term memory capacities in children accounted for the developmental trends. Improvement in processing efficiency may therefore account for the development of AM detection in childhood.

Equivalent noise characterization of human lightness constancy

A goal of visual perception is to provide stable representations of task-relevant scene properties (e.g. object reflectance) despite variation in task-irrelevant scene properties (e.g. illumination, reflectance of other nearby objects). To study such representational stability in the context of lightness representations in humans, we introduce a threshold-based psychophysical paradigm. We measure how thresholds for discriminating the achromatic reflectance of a target object (task-relevant property) in rendered naturalistic scenes are impacted by variation in the reflectance functions of background objects (task-irrelevant property). We refer to these thresholds as lightness discrimination thresholds. Our approach has roots in the equivalent noise paradigm. This paradigm relates signals to internal and external sources of noise and has been traditionally used to investigate contrast coding. For low variation in background reflectance, lightness discrimination thresholds were nearly constant, indicating that observers' internal noise determines threshold in this regime. As background object reflectance variation increases, its effects start to dominate performance. We report lightness discrimination thresholds as a function of the amount of variability in the background object reflectance to determine the equivalent noise - the smallest level of task-irrelevant (i.e. background reflectance) variation that substantially corrupts the visual representation (i.e. perceived object lightness) of the task-relevant variable (i.e. achromatic reflectance). A linear receptive field model, which employs a single center-surround receptive field tailored to our stimulus set, captures human behavior in this task. Our approach provides a method for characterizing the effect of task-irrelevant scene variations on the perceptual representation of a task-relevant scene property.