Satellite radar altimeters play a key role in numerous space missions for the remote Earth sensing. The data they provide are used in solving various fundamental and applied problems of geophysics, oceanography, meteorology, etc. In many modern measuring systems the altimeter data is processed in several stages. One of them is the ground-based retracking of the information streamed from the spacecraft. The goal of this work is to study altimeter parameter estimators in the course of the satellite altimeter data retracking by ground-based complex. The main task of delay-lock loop onboard a satellite carrier is a reliable keeping of received echo-signal within the tracking window. More accurate estimates of information parameters are worked out by the ground segment where data from the satellite is delivered via telemetry. Retracking can be performed either without using any physical echo model, or relying on some mechanism under generation of response of an illuminated surface to the probing signal. In the latter case, the measuring results become more trustworthy. The paper deliberations are based on the model close to the classical Brown’s one, they include algorithms of its parameters statistical fitting to the observation and computer simulation of fitting according to the maximal likelihood (ML) and the least squares (LS) methods. The results obtained are compared to the potential attainable and show that while LS fitting yields noticeably to the potential, experimental accuracy of ML-fitting practically coincides with the potential one.

When ensuring aviation safety, the outboard environment awareness of the crew in low visibility conditions is especially important. The information about the runway condition and availability of any obstacles is crucial. There are ground-based obstacle detection systems, but currently only large airports are equipped with them. There are Enhanced Vision Systems designed for application on aircraft in low visibility conditions. The main goal of this research is to develop the means of runway obstacle recognition in low visibility conditions, which are to improve the capabilities of Enhanced Vision Systems. The research covers only the methods for static image object detection. The analysis of the runway markings, objects and possible obstacles is performed. Targets for acquisition are defined. The simulation of runway images is performed on full-flight simulator in low visibility conditions. The requirements for features descriptors, recognition and detection methods are defined and methods for research are defined. The paper provides evaluation of method applicability to runway pictures taken in poor visibility conditions above and below the decision height taking into account various characteristics. The covered methods solve the problem of detecting objects of the runway in low visibility conditions for static image. Conclusions about the possibility to use the studied methods in Enhanced Vision Systems are made. Further development of optimization methods is required to perform detection in video sequences in real time. The results of this work are relevant to the tasks of avionics, computer vision and image processing.

A new method based on direct frequency conversion is developed for measuring complex reflection coefficient of microwave two-poles. The method is based on the use of quadrature synchronous detection of the signal branched by omnidirectional probe with subsequent quadrature processing of the detected signal components. Such approach makes it possible to solve measuring task by simultaneously analyzing both amplitude and phase distribution of the field in transmission line which leads to redundancy. In addition, the use of direct frequency conversion provides the detection linearity in considerably higher dynamic range of the levels of the signal forwarded from the transmission line. So, both of these factors can improve the measurement accuracy. The method is performed by excitation of probing harmonic microwave oscillation in transmission line and formation of reference microwave oscillation with the same frequency. The reference signal and the signal branched from the transmission line by omnidirectional mobile probe are fed to the inputs the quadrature synchronous detector. At its outputs, I and Q components of the detected signal are formed. By means of these components, the amplitude and phase field distribution in the trans-mission line is obtained. It is followed by calculation of module and phase estimations using the expressions presented in the paper. The measurement result is obtained as arithmetic average of these estimations. A mathematical model of the proposed method is developed. The relations for the module and phase of the complex reflection coefficient are derived based on the analysis of both the amplitude and phase distribution of electromagnetic field in the transmission line. The paper describes the experimental unit in the form of vector measuring line that implements the quadrature method of measurement. The experimental analysis of the amplitude and phase distribution of the field in microwave path is carried out for standard loads with different parameters. Based on the analysis results, the estimations of measured parameters are calculated and measurement errors are defined. It is shown that highprecision measuring instruments can be designed using the proposed method.

Nowadays the interest in search of ways of improving the efficiency of small radar cross-section aerial objects detection and localization rises against the background of widespread use of light and unmanned aerial vehi-cles. As a result, researchers pay attention to radar systems (RS) with continuous linear frequency modulation (linear FM) signal. The use of such signals gives the measurable opportunity to reduce radar system peak-speech power and to cut the cost and weightsize parameters of the RS. The paper observes low-power ground based radar implementation prospects for purposes of detection and estimation of motion rates of small-sized aerial objects. The proposed algorithm of radar signals processing enables to simplify the detection of such tar-gets. The paper reveals the structure and defines the steps of the algorithm. The fundamental for the algorithm under consideration is the method of the range-Doppler image composition of the scanned area using digital signal processing. The paper presents the results of the algorithm operation in the low-power RS of C-band radar, obtained by processing of quadrotor echo-signals during the real experiment. The results show successful solvation of the applied problem of detection and tracking on the small-sized aerial object with the radar cross-section equal to less than 0.5 m2 and the spectrum of secondary radiation characterized by the expressed multimodality. The results of the experiment validate the application of the algorithm and demonstrate the possibility of the algorithm implementation in design of portable RS and automated target acquisition centers for detecting and tracking of the small-sized aerial targets (both, single as multi agent) with the information display on operator control panel.

The change in characteristics of ultrasonic waves’ transmittion in solid rotating media is the basis for the operation of acoustic angular velocity sensor. The transmission coefficient of the sensing element (SE) of the acoustic path deter-mines the level of angular velocity sensor informative signal based on detecting changes in characteristics of bulk acoustic waves in solid media. In this regard, the efforts aimed at obtaining maximum transmission coefficient are relevant and represent an important stage in the design of such devices. The sensitive element of the acoustic path consists of radiating and receiving plate piezoelectric transducers, propagation medium (acoustic duct), contact layers and electrical load. The coefficient is identical to the path of ultrasonic delay lines on bulk acoustic waves. Although, many sources present the theoretical analysis of the path of this type, they carry out the analysis in so-called one-dimensional approximation, i.e. they perform the analysis without taking into account the limited transverse dimensions, whereas the path of the sensing element should have limited lateral dimensions, which can affect the value of transmission coefficient. The above-mentioned sources do not present the results of experiments. Thus, it is necessary to conduct a complex of simulation and experiments to analyze the acoustic path transmission coefficient of the angular velocity sensor. Authors of the paper developed a pathmodeling program in Mathcad software to perform simulation. For implementation of the experiment, authors created the installation, as well as a number of proto-types with transducers made of piezoelectric quartz and piezoelectric ceramics. The results demonstrate that fundamental statements developed for one-dimensional approximation one can use to determine the transmission coefficient of the acoustic path with limited dimensions. Besides, the use of the matched electrical load gives the opportunity to increase the transmission coefficient. For example, in case of Y-cut piezoelectric quartz converter prototype the increase reached 20 dB.

The well-known method of image reconstruction by projections in magnetic resonance imaging uses spin echo excited by two sinc pulses. The further processing involves forming of the spin echo signal two quadrature components converting them into a digital format and the subsequent Fourier transform. The proposed modified method is based on the second sinc radio pulse substitution for the linear FM pulse. In this case, the mentioned projections are formed by amplitude detection of the spin echo envelope, which significantly simplifies the processing procedure. The aim of the research is to analyze the modified method resolution. The mathematical model is based on Bloch equations. Their solution is carried out on the basis of the device of the spin system state transition matrices. For their calculation, the stepped approximation of the excitation pulse complex envelopes is used. It makes possible to convert the system of linear differential equations with variable coefficients (Bloch equations) to the system of linear differential equations with piecewise constant coefficients. In this case, the equations have analytical solution. Following the obtained solution, the analysis of the method resolution not previously investigated, is performed by means of modeling the spin echo excitation. The conditions are specified when no dynamic distortions influencing received image quality exist. It is shown that resolution is determined by the size of the scan area, the magnitude of the gradient of the applied magnetic field, the pulse duration with linear frequency modulation, as well as gyromagnetic ratio of the core type used. The developed method eliminates the need for Fourier transform over the spin echo signal and pro-vides resolution comparable to the conventional one.