Correlation-extremal Navigation Systems Research Articles

Applying spline interpolation to increase accuracy of correlation-emergency navigation systems

Relevance. Spline interpolation is used to improve the accuracy of correlation-extreme navigation systems. A two-stage algorithm for combining images in correlation-extreme navigation systems is proposed. At the first stage, the surface of the decision function of the algorithm is constructed in the vicinity of its extremum using a quadratic interpolator by six points and its Gaussian curvature and extremum coordinates are estimated. These parameters are used to determine the optimal value of the parameter of the cubic spline interpolator used in the second stage in order to refine the rough estimate of the coordinates and improve the positioning accuracy of the navigation system. Purpose of the work: The purpose of the work is to develop an algorithm for aligning images in correlation-extreme navigation systems, which makes it possible to realize a cubic spline parameter close to the optimal value for each of the possible shifts of the current image relative to the reference image and, as a result, to increase the accuracy of determining the coordinates. Materials and methods. In correlation-extreme navigation systems, the coordinates of the aircraft are determined by calculating the mutual shift of the current image obtained using the sensor of the Earth's physical field and the reference image, which is known in advance. At the same time, the alignment accuracy of discrete current and reference images, which are usually used in practice, does not exceed half a pixel. Therefore, the problem of improving the accuracy of navigation systems is of great importance. One of the possible ways to solve this problem is to use methods for approximating the decision function of the image alignment algorithm in the vicinity of its global maximum.Results: To illustrate the gain in the accuracy of the positioning of navigation systems, statistical tests of the algorithm with a 6-point interpolator and the above-described two-stage procedure for minimizing the decision function containing spline interpolation at the second stage were carried out. A typical image was used as a reference image. The coordinates of the center of the current and reference images were played randomly in accordance with the two-dimensional normal distribution law, the average value of which coincided with the center of the reference image; the standard deviation is also found. Then the current image was formed. The constructed current image was noisy with additive white Gaussian noise with zero mean value and the same standard deviation for each element . Image alignment was assumed to be correct if the following conditions were met: , where – is the shift estimate generated by the algorithm. Then, the algorithms were repeatedly run with different realizations of the noise component of the current image, and the dependences of the root-mean-square error in each direction on the mean-square value were plotted . The figures in the article show the dependencies for the algorithm with a 6-point interpolator (upper curve) and for a two-stage algorithm (lower curve). Analysis of the graphs allows us to conclude that the second algorithm wins in the accuracy of determining the coordinates of the shift by about 5 times. The dependencies for both algorithms practically coincide with those shown in the figure. It should be noted the weak dependence of the positioning accuracy on the change in the parameter in the area . Conclusions: It is shown that the optimal value of the parameter of the cubic spline interpolator depends to a lesser extent on the magnitude of the local shift of the images and, to a greater extent, on the correlation interval of the reference image in the vicinity of the image alignment point, which is proposed to be estimated using the Gaussian curvature parameter.

Optimization of the number of channels of a multichannel radiometric receiver

Background: Improving the positioning accuracy of passive radiometric correlation-extreme navigation systems (RM CENS) of aircraft (AC) by landmarks depends on the ability of information RM sensors of systems to form two-dimensional images of ground objects in real time. The use of matrix RM sensors, which are based on multichannel RM receivers of the millimeter wave range (MMW), makes it possible to realize the required speed of the CENS Objectives: The aim of the work is to optimize the number of multiplexed channels per one amplifying-converting path of a multi-channel RM receiver with linear multiplexing and separation of channels according to the form of signals. Materials and methods: As an optimization criterion in this work, it is proposed to use the gain in sensitivity obtained as a result of the use of a multichannel RM receiver with linear multiplexing and signal waveform separation in comparison with the sensitivity of a RM receiver with time division multiplexing. Results: As a result of the analysis of the process of functioning of a multichannel RM receiver with time division multiplexing in this work a relation was obtained for the sensitivity of an individual channel of a RM receiver with time division multiplexing. Conclusions: It can be concluded that it is optimal to create a matrix RM receiver based on combining 16 RM channels of the superheterodyne type into one amplifier-conversion path. In this case, the total number of amplifying-converting paths is equal to four. The sensitivity of each channel remains high enough.

Evaluation of accuracy of radiometric correlation-extreme navigation systems

Background: The use of passive matrix radiometric sensors of the millimeter wave range in aircraft navigation systems, which make it possible to form a radiometric image of a ground navigation object under conditions of high-speed flight of aircraft, is one of the effective ways to ensure high accuracy in measuring the coordinates of objects and, ultimately, leads to an increase in the probability of positioning aircraft [1]. In work [2], analytical relationships were obtained and quantitative estimates of the accuracy of positioning of aircraft equipped with a matrix radiometric navigation system were made. It is shown that the use of matrix radiometric sensors makes it possible to realize the required high (up to units - tens of meters) positioning accuracy of high-speed aircraft. Objectives: The purpose of this article is to develop a method for increasing the accuracy of a radiometric correlation - extreme system based on the use of a matrix radiometric millimeter-wave receiver with channel compaction. Materials and methods: In this paper, we used the method of linear multiplexing with channel separation according to the waveform using orthogonal Walsh functions. In this case, the sensitivity for each channel corresponds to the sensitivity of the modulation radiometer, and in comparison with the sensitivity of the compensation radiometer, it decreases by about two times. Taking into account the orthonormality of the Walsh functions, the signal at the output of each channel is proportional to the intensity (power) of the signal at the input of this channel. Results: In this work, it is shown that the optimal number of combined channels is a multiple . The analysis of the results of the calculations shows that the combination of 64 channels into one amplifier-conversion path leads to an increase in inter-channel interference and, as a consequence, to a deterioration in the sensitivity of each channel. Conclusions: In this case, it is expedient to limit the number of channels to be sealed per one amplifying-converting path. So, when 16 channels are combined into one path, the sensitivity of each channel remains quite high: about 1 K – for a super heterodyne radiometric receiver, and less than 1 K – for a direct amplification radiometric receiver. In this case, the number of amplifying-conversion paths with the total number of channels in the matrix 64 is equal to four.

The Creation of the Database for Mobile Robots Navigation under the Conditions of Flexible Change of Flight Assignment

The necessity to find a rational way of creating a database regarding the sighting surface taking into consideration the features of construction and functioning of correlation-extreme navigation systems (CENS) of aerial mobile robots (MR), including in particular the conditions of flexible change of flight assignment, is shown in the article. It is proposed to use invariants, which have been obtained based on a correlation analysis of the scene according to the brightness index with the subsequent and allowing to form selective images, as a database information content. The results of the evaluation of the quality of formed selective reference image (RI) for scenes with various object impletion under conditions of limitations in time and number of calculations are given

Synthesis of an optimal digital filter of a compensation radiometer for radiometric correlation-extreme navigation systems of unmanned aerial vehicles

The expediency of using a compensation radiometer (CR) with periodic absolute calibration as a sensor for preprocessing the information of correlation-extreme navigation systems (CENS) of unmanned aerial vehicles (UAV) was shown. This is determined by the possibility of obtaining and using the estimates of gain fluctuations obtained in previous frames which will provide an increase in the radiometer sensitivity. In addition, due to the accumulation of information, an increase in accuracy of measurement of the elements of the current image formed by the CENS will be provided. The algorithm of processing the obtained calibration estimates during linear processing corresponds to a certain digital filter (DF). By defining a set of the DF weight coefficients, it is possible to improve the CR fluctuation sensitivity by reducing the gain fluctuations. Up to 1.8-time gain in sensitivity can be reached for typical frequency and time parameters of the compensation radiometer of UAV CENS. The problem of synthesis of a digital filter was set. A solution to the problem of synthesizing an optimal digital filter was proposed. Its use in a CR will improve the fluctuation sensitivity. In its turn, this will make it possible to improve the quality of a current image generated by the system when siting by means of sighting surfaces with low-contrast objects taking into account fluctuations in radio-brightness temperature. It was found that the gain in sensitivity when using the optimal digital filter increases with an increase in the operating period of the radiometer and an increase in the digital filter order. Improvement of fluctuation sensitivity of the CENS data preprocessing system is important for UAV location in low-contrast areas

The Criterion and Evaluation of Effectiveness of Image Comparison in Correlation-Extreme Navigation Systems of Mobile Robots

The Criterion and Evaluation of Effectiveness of Image Comparison in Correlation-Extreme Navigation Systems of Mobile Robots

Optimizing Strap-down Inertial Navigation Systems Characteristics and External Correction Sensors for Autonomous Navigation of Different UAV Classes

Currently, unmanned aerial vehicles (UAVs) can be used in topographic works, condition monitoring and diagnostics of extended engineering structures, delivering goods to hard-to-reach places, etc. To provide the widespread UAVs applications and raise the number of tasks to be solved through their using, it is necessary to increase their autonomy degree in terms of navigation support, in particular. Unmanned aerial vehicles (UAV) control systems for autonomous navigation use the strap-down inertial navigation systems (SINS) based on various types of gyroscopes. SINS based on the laser gyroscopes, which have a large mass, have the best accuracy. UAVs with a payload mass that is commensurable with the mass of navigation equipment require optimization of SINS characteristics. An optimization method has been developed to enable obtaining a Pareto set for the mass and accuracy of SINS based on laser gyroscopes. A comprehensive assessment of the characteristics of SINS and UAV carrier with different payload mass has been performed. Various SINS correction methods are considered when satellite navigation is unavailable.For overland flights, the correlation-extreme navigation systems (CENS) and SLAM methods (for simultaneous localisation and mapping) can be used. CENS require a reference lay-of-the-land description and a sufficient density of landmarks. In navigation based on SLAM algorithms, there is no need in the reference lay-of-the-land description, and the initial data can be obtained through the optical sensors under appropriate condition of the atmospheric path.Regardless of the condition of the atmospheric path, type of the underlying surface and its information available in detail, the UAV coordinates can be determined by Doppler dead reckoning using a Doppler system (DISS). At low and medium altitudes SINS correction is possible, only heading sensor data are needed to calculate the path angle.In combining with DISS and 3D Flash Ladar sensors (for implementing SLAM algorithms), it is more optimal to use low-accuracy SINS based on fibre-optic gyroscopes rather than laser gyro-based systems.The results obtained can be used when developing navigation systems for medium, light and heavy-medium UAVs.

Evaluation of the Potential Accuracy of Correlation Extreme Navigation Systems of Low-Altitude Mobile Robots

Evaluation of the Potential Accuracy of Correlation Extreme Navigation Systems of Low-Altitude Mobile Robots

Formation of reference images and decision function in radiometric correlation­extremal navigation systems

Methods for formation of reference images (RI) and unimodal decision function (DF) have been developed to ensure efficient functioning of radiometric correlation­extreme navigation systems (CENS) of flying machines (FM). The methods were developed for the conditions of CENS position finding on the surfaces of sighting (SS) with a highly developed infrastructure at insignificant altitudes of flight of the flying machine which leads to formation of current images (CI) with a non­stationary structure. Non­stationarity of CI arises when geometric conditions of sighting the three­dimensional objects change. The method of RI formation is based on the use of a set of three­dimensional stationary objects with the highest radio­brightness temperature, their contouring and determination of mean radiobrightness temperature. A method for forming a unimodal DF of radiometric CENS which takes into account three­dimensional form of SS objects, spatial position and orientation of the FM was developed. The method is based on CI pre­processing which consists in its layering with respect to the mean radiobrightness temperature of background and determination of a set of objects with the highest radiobrightness temperature. The set of objects defined by their contouring is used as a geometric invariant with an informative attribute in the form of average radiobrightness temperature. It was established by simulating the process of formation of DF that pronounced unimodal DFs are formed at signal­to­noise ratio (q=5...10) at the output of the radiometric channel. At the same time, the possibility of correct localization of the binding object in TI is close to unity and reduction of influence of perspective and scale distortions of images on accuracy of CENS location is ensured. The simulation results have confirmed effectiveness of the proposed methods of formation of RI and DF for location of radiometric CENS on the sighting surfaces with complex three­dimensional objects leading to formation of a non­stationary CI.

Спосіб комплексування зображень різних діапазонів хвиль з метою створення універсальних еталонів для комбінованих кореляційно-екстремальних систем навігації

To ensure the accuracy of navigation and aiming of modern unmanned aerial vehicles and cont-rolled means of destruction in any weather conditions and time of day, in conditions of interference, the most promising is the joint use of sensors of various physical nature for the detection and identification of targets (objects to be defeated). In this case, combined correlation-extremal systems are used to solve the problems of navigation (guidance). For the operation of such systems, it is advisable to form universal reference images. The methods for integrating digital images of a different range of waves to create universal reference images used in combined correlation-extremal navigation systems are analyzed. To form a universal reference image it is necessary to solve the problem of obtaining a «combined» image on the basis of seve-ral initial images of the same section of the terrain in different wave ranges. In this case, the problem of integrating images for the subsequent synthesis of a universal reference image is conveniently reduced to the task of combining in one image the characteristics common to the optical and radar images — the original images. That is why there is proposed a method for integrating radar and grayscale optical images which allows to create digital grayscale image combining the main informative signs of images of both ranges. The use of this method leads to an increase of the brightness and contrast of common fragments of the original images, does not lead to the destruction of correlation links, therefore the resulting composite images can use to form universal reference images.

Aeromagnetic Gradiometry and Its Application to Navigation

Modern methods of airborne magnetic field measurements are described. A stochastic algorithm to compensate the deviations between the indications of an aeromagnetometer and an aeromagnetic gradiometer is considered. An integration algorithm for the inertial and correlation-extremal navigation systems is briefly described. An advantage of using magnetic field gradient measurements as navigational data is justified. The performance of the integration algorithm is illustrated by numerical simulation.

A method for localizing a reference object in a current image with several bright objects

To ensure the effective functioning of the correlation-extreme navigation systems (CENSs), a method is developed to localize a reference object (RO) in a current image (CI) with several bright objects. The peculiarity of the method consists in converting the CI to a binary unit by determining the average value of the background and setting it for the threshold of the image quantization, which in turn determines the amount of probabilities of errors of the first and second kinds as well as entails assigning the objects of the viewing surface (VS) and the backgrounds to two classes: the RO and the background. The CI model is represented by the brightness values of the corresponding objects and backgrounds of the VS in the differentiation elements. In the model of the current image, the RO has the highest brightness. Other objects that are similar in brightness and commensurate with the RO are categorized as false. The reference image (RI) is set by the contrast mark and the geometrical shape of the object, and it is binary. An algorism has been developed for localizing the RO in an image by searching for a fragment of a binary CI with a maximum value of units that coincides with the RI. The peculiarity of the algorithm consists in adapting the application procedure for the threshold conversion of a CI with an unknown value of the signal-noise ratio. A method has been developed to clarify the maximum value of the DF and to determine the coordinates of the RO in the field of the CI matrix. The method consists in the summation of the number of units of different sections and finding the highest value of the DF. The highest value of the DF coincides with the full match between the CI and the RI. An analytical expression has been obtained for the estimation of the probability of localizing the RO. The expression establishes dependence of the probability of localizing the RO on the parameters that are specified in the stages of solving the problem of localizing the RO, which are the identification, the multi-threshold selection, and the specification of the maximum DF. By modeling the process of forming the DF, numerical estimates have been obtained for the probability of localizing the RO. The research results indicate the feasibility of using the proposed method in a CENS in relation to a VS with several bright objects.

The research of image segmentation algorithms based on Vilenkin-Crestensen functions

The problem of Vilenkin-Crestenson functions (VCF) application to process aerospace images is considered. Theoretical grounds of VCF basis and its construction in the field of m-based numeric systems with operation of inversion by Walsh are discribed. Examples of basic functions system building on the basis of VCF with different bases and their application to image segmentation are shown. Avdvantages of using image segmentation algorithm based on VCF basis are discribed. Band pass spectrum restriction possibilities to highlight borders and edge the regions of similar density are given. Different forms of VCF spectrum restriction and its combinations with thier impact to image segmentation results are shown. Technical vision system application of sugested algorithm are shown. VCF basis abbility to highlight objects to be used in correlation-extreme navigation systems are shown. The experimental results of using VCF in comparasing with traditional Fourie basis are given.

Analysis of modern correlation extreme navigation systems

Methods of classification of correlation extremal navigation systems and geophysical fields are examined. The block diagram of correlation extremal navigation systems, which works in risk conditions of current navigational and mapping information, is introduced. The block of efficient mapping is set in the diagram; it realizes famous approach of simultaneous positioning and mapping on the base of recurrent Bayes estimation. It is shown, that block allows obtaining more precise mapping information during the flight process

Algorithm of inertial navigation system correction on the bases of range information

In the work possibilities of correction of inertial navigation systems from correlation-extremal navigation systems, which work with use of field of place’s relief, are examined. Recurrent-search method was used for correlation-extremal navigation systems, Kalman filtering was chosen for evaluation of field’s relief. It is shown that the accuracy of evaluation and correction increases significantly, especially during continuous and simultaneous use of system.

Theoretical Efficiency Estimate of a Hierarchical Correlation Algorithm of Image Overlapping in Correlation-Extremal Navigation Systems

Theoretical Efficiency Estimate of a Hierarchical Correlation Algorithm of Image Overlapping in Correlation-Extremal Navigation Systems

Correlation-Extremal Systems for Navigation and Location of Mobile Objects

The paper reviewed the studies of Tomsk researchers in the area of correlation-extremal navigation systems with emphasis on analysis and design of the systems of extremal passive location.

Airborne Magnetometric Navigation Systems and the Prospects for Their Practical Use

Consideration was given to the problems of aeromagnetic measurements of the data used in the information channels of a new class of the airborne correlation-extremal navigation systems. Approaches to them were studied and methods and algorithms were proposed and checked experimentally with the aim of using these systems in self-acting high-precision navigation systems based on various magnetic fields.