Vol 55, No 3 (2019)

Spatial-local algorithms for signal and image filtering are widely used in practice because they have one or several parameters whose values significantly determine a filtering error. The choice of these parameters from the filtering error minimum condition is a known problem that has not been acceptably solved yet. A statistical algorithm is proposed that makes it possible to quite accurately estimate the optimal parameters of two spatial-local filters. An efficient algorithm for estimating the measurement noise variance is presented.

Probability distribution density parameters determined using the maximum likelihood and moment methods are comparatively estimated according to their accuracy and complexity of estimation algorithms. Expressions determining the Nakagami distribution parameters by the maximum likelihood method are obtained. A method for estimating the Nakagami distribution parameters by the moment method in which the distribution moments are replaced by their estimates is described. It is noted that parameter estimation by the maximum likelihood method has a smaller variance and bias as compared to estimation by the moment method, especially with a small sample size. It is shown that, unlike energy parameter estimation, the real laws of Nakagami distribution are approximated using a large volume of statistical data that describe the signal.

Errors of laser interferometers using quadrature detectors depend not only on the interferometers themselves, but also on the electronic systems for processing quadrature signals. There are three sources of errors of quadrature detector signals that affect the displacement measurement error: the inequality of the amplitudes of quadrature signals, the phase shift of these signals (not equal to 90°), and the zero offset in each signal. A simple method for identifying and correcting these errors based on experimental data on signals obtained using analog-to-digital converters is considered. The proposed method is applicable to any interferometer with sinusoidal quadrature outputs.

It is experimentally demonstrated that the classification of fragments of a hyperspectral image with preliminary transformation of the spectral features of the image into the principal components and with the use of the Hilbert-Huang spectral transform is fairly effective in the case of vegetation types that are difficult-to-distinguish on the basis of hyperspectra. This classification is compared with traditional methods, where hyperspectral features transformed to the principal components without using spatial information are used. RBF neural networks are used in all methods at the final stage of the classification.

A constructive theory of the formation of images of one-dimensional binary objects in a partially coherent diffraction-limited projection system with an arbitrary ratio of the angular sizes of the light source and aperture diaphragm is developed. The solution of the two-dimensional problem for such objects can be reduced to a one-dimensional problem, i.e., to calculating the integral in the form of convolution of the object with a generalized aperture response whose spectrum has a tapered profile determined by system parameters. The convolution integral is further subjected to a nonlinear transformation whose level is defined by the ratio of the angular sizes of the source and aperture diaphragm. It is shown that the profile of images formed in partially coherent light is determined by the threshold characteristic of the system that ensures reliable detection of the binary object boundaries. An approximation of this characteristic is proposed. The theory admits a simple physical interpretation of phenomena that occur in partially coherent projection systems.

The dependence of the piezo-optical strain sensor gauge factor on the geometric parameters of the photoelastic element is obtained by accurate numerical simulations. It is shown that the piezo-optical gauge sensitivity to the applied force is more dependent on the photoelastic element shape than the sensitivity to deformation. A comparative analysis of the gauge factors and other parameters of strain-resistive, piezoelectric, fiber-optic, and piezo-optical strain gauges was carried out. Strain-resistive and fiber-optic sensor gauge factors are three orders of magnitude lower than those of piezo-optical sensors. Correctly calculated piezoelectric sensor gauge factors are also two-three orders of magnitude inferior to those of piezo-optical sensors. A comparison of the basic properties and parameters of modern commerical strain gauges based on different physical principles is presented.

The effect of linear acceleration on the characteristics of an optoelectronic vibration ring angular velocity transducer is analyzed taking into account the stiffness of the ring resonator supports. A method for compensating for the effect of linear acceleration on the characteristics of the angular velocity transducer is proposed.