Navigation Satellite Research Articles

Application of Kalman filter in wharf surface displacement of Beidou automatic monitoring

To meet the requirements for real-time dynamic monitoring of wharf surface displacement, an automatic monitoring system based on Beidou satellite navigation was constructed, and it was applied to monitor the surface displacement of a wharf in Tianjin Port. Next, the sensible system noise of the Kalman filter state equation was determined by the simulation experiment. Finally, the monitoring data were processed and analyzed by Kalman filter. The results show that the accuracy of the monitoring data can be improved by more than 30% by Kalman filtering, particularly the elevation direction accuracy can reach more than 40%. The plane and elevation accuracy can be less than 1.5mm, after the Beidou automatic monitoring data has been processed by Kalman filtering, and this meets the needs for most engineering deformation monitoring. In a word, the Beidou automatic monitoring system is characterized by continuity, real-time and high precision, and can be applied to most engineering deformation monitoring requirements.

Interaction of Satellite Navigation Signals with Forest and Snow-Ice Layers

Interaction of Satellite Navigation Signals with Forest and Snow-Ice Layers

Processing of retransmitted GPS signals in the problem of measuring the total electron content in the ionosphere

Objectives. For a method for estimating the total electron content in the ionosphere based on the retransmission of the L1 GPS navigation signal by a repeater nanosatellite (SR) to the frequencies of 150/400 MHz allocated for geophysical research and their reception at a ground-based receiving point (RP), it is necessary to develop the algorithms for coherent accumulation of received relayed signals and measurement of the difference between their delays at observation intervals up to a few seconds.Methods. The proposed algorithms provide phase demodulation of the received signals at each of the relay frequencies in accordance with the dynamics of the mutual spatial movement of the navigation satellite (NS), SR and RP; multiplying the result by the estimate of the navigation message combined time delay, generated by the receiver of the direct navigation signal on the NS-RP route, intra-period processing over the entire duration of the observation in a filter matched with the signal of the navigation satellite, and inter-period coherent accumulation of the results of intra-period processing at a single-valued range interval. Coherent accumulation, taking into account a random uncontrolled shift in the frequency of the retransmitted signal, is implemented by discrete Fourier transform of the vectors formed for each resolution element in the delay time from inter-period readings of the results of intra-period processing, taking into account the range migration during the mutual movement of the NS, SR and RP.Results. It is shown that by the output signal of the coherent accumulator makes it is possible to detect retransmitted signals at each of the retransmission frequencies, to measure accurately the difference in delay times, and estimate the total electron content on the SR-RP path. The results of modeling are presented, confirming the efficiency of the proposed algorithms in estimating the total electron content on the SR-RP route.Conclusion. An algorithm for coherent accumulation of received retransmitted signals and measurement of the difference between their delays is developed, and its simulation is performed. The algorithm can be used for estimating TEC based on the retransmission of signals from GPS.

An enhanced outlier processing approach based on the resilient mathematical model compensation in GNSS precise positioning and navigation

The abnormal measurements are widely existent in Global Navigation Satellite System (GNSS) precise positioning and navigation mainly because of the diffraction, reflection, refraction, and even non-line-of-sight reception. However, when multiple outliers exist in GNSS measurements, traditional methods including test procedure or robust estimation usually cannot work well. This study proposed an enhanced outlier processing approach based on the resilient mathematical model compensation. Specifically, first, to avoid excessive deletion, the total number of measurements is considered in the adaptive test procedure with the help of a scale factor. Second, in adaptive robust estimation, the total number of remaining measurements is also considered, thus making it more compatible with the adaptive test procedure. In addition, to overcome the potential inappropriate reweighting operator, different shrinking factors are adopted for code and phase measurements according to their precision, respectively. To verify the effectiveness of the proposed method, one static monitoring experiment and one kinematic vehicle experiment were conducted, where the method without outlier processing, traditional test procedure, traditional robust estimation, and the proposed method were all used. For the static experiment, the ambiguity resolution and positioning solutions of the proposed method perform best. The positioning accuracy of the float and fixed solutions can be improved by approximately 67.4% and 77.6% on average under challenging environments, respectively. For the kinematic experiment, the performance is also the best in terms of positioning availability and accuracy by using the proposed method.

A Spatial Registration Method for Multi-UAVs Based on a Cooperative Platform in a Geodesic Coordinate Information-Free Environment

The satellite navigation system of Unmanned Aerial Vehicles (UAVs) is susceptible to external interference in a complex environment, resulting in the loss of their own geodetic coordinate information. A spatial registration method for multi-UAVs based on a cooperative platform in a geodesic coordinate information-free environment is proposed to solve this problem. The mutual observation information between UAVs is approximated by the observation information of the cooperative platform. Indirect observation information of the target can be obtained on account of mutual observation. On the basis of this, a close-range spatial registration algorithm without the geodetic coordinate information of UAVs is designed by means of the right-angle translation method. Finally, the Kalman filtering technique is used to track maritime targets. In this paper, the proposed method is verified by a simulation experiment and a practical experiment. The proposed method is 90% effective in reducing systematic errors. The tracking accuracy after alignment is significantly better than that of the original trajectory.

Opportunistic navigation applied to integration of alternative positioning and electronic mapping based on spline technology

The problem of vulnerability and local incapacity of global satellite navigation systems is formulated. The expediency of alternative positioning methods to create a precedent for high-precision location determination in the satellitedenied environment is revealed. The hypothesis about the impossibility of a separate alternative to meet the requirements of full autonomy of modern navigation when it is necessary to comprehensively solve geolocation scenarios based on the combinatorics of various technologies is put forward. An assumption about the probable advantage of combining data from several information sources to compensate for the disadvantages of each option when predicting an increase in the overall reliability and accuracy of navigation parameters is made. An opportunistic navigation paradigm with the objective function of obtaining location information from mixing additional radio frequency signals with simultaneous visualization of a spline positioning map to determine the location inside a graphic fragment is proposed. The confidence that the approach from the standpoint of spline functions expands the horizon of possibilities of the concept of opportunistic navigation from the purely technical synergetics of the landscape of «signals of opportunity» to the creation of a perspective positioning system using effective electronic mapping is expressed. It is determined that the positioning accuracy of navigation systems is practically necessary to build an optimal trajectory for the safe routing of the vessel. Attention is focused on understanding the optimality of the trajectory as a multi-way planning strategy within the framework of the «receding horizon» paradigm with the obligatory condition that a waypoint with a user-defined probability is achievable by a moving object. It is noted that the modeling of optimal trajectories is implemented by a method similar to the technology of interpolation of navigation contours based on the composition of a B-spline with the provision of an attribute parameter to maintain the same value at each point as a result of the analysis of the spatial anisotropy of the source data. The synthesis of threedimensional spreading of magnetic map anomalies has been tested to create a mapping standard based on a hybrid approximation algorithm as an implementation of a method for computer rendering a geometric primitive of a function of two variables. The postulate of increasing the potential of high-precision localization of the position of any mobile object in space is interpreted, provided that the ontology of opportunistic navigation is applied in practice as the realization of situational awareness of interdependent technical systems in order to maximize the reliability of observation.

SOME LEGAL ASPECTS OF INTERNATIONAL LIABILITY FOR DAMAGE CAUSED BY MALFUNCTIONING OF SATELLITE NAVIGATION SYSTEMS

International liability is one of the most difficult legal issues related to satellite navigation applications. The 1972 Liability Convention provides that a launching State shall be absolutely liable to pay compensation for damage caused by its space objects on the surface of the Earth or to aircraft flight, and liable for damage due to its fault in space. The legal situation of artificial satellites, including navigation satellites, is determined by their assignment to space objects. Unfortunately, the term “space object” is also not specifically defined in international space law. The main purpose of this article is to determine whether damage caused by satellite navigation systems can be covered by the Liability Convention, whether the Convention refers only to direct physical damage resulting from the fall or collision of space objects or whether it also encompasses damage resulting from the malfunctioning of a navigation space object and intangible electromagnetic waves. It seems that the present regulations of the Outer Space Treaty and the Liability Convention do not apply to satellite navigation and do not cover the damage caused by navigation’s intangible signals. Unfortunately, it is rather clear that the international community is unlikely to adopt uniform rules on liability for satellite navigation signals in the near future. However, the United Nations and its Committee on the Peaceful Uses of Outer Space remain to be the best platform to work on establishing the principles governing the issue of liability for damage caused by malfunctioning of satellite navigation systems and their signals.

Unveiling the Core Patterns of High-Latitude Electron Density Distribution at Swarm Altitude

The ionosphere has distinctive characteristics under different solar and geomagnetic conditions, as well as throughout the seasons, and has a direct impact on our technological life in terms of radio communication and satellite navigation systems. In the pursuit of developing highly accurate ionospheric models and/or improving existing ones, understanding the various physical mechanisms that influence electron density dynamics is critical. In this study, we apply the Multivariate Empirical Mode Decomposition (MEMD) method to the electron density distribution in the mid-to-high latitude (above 50° magnetic latitude) regions in order to identify the dominant scales at which these mechanisms operate. The data were collected by the Swarm mission in the Northern Hemisphere. MEMD allows us to separate the main intrinsic modes and assess their relative contributions to the original one, thereby identifying the most important modes and the spatial scales at which they exert influence. Our study spanned the period from 1 January 2016 to 31 December 2021, which was characterized by low solar activity levels. This choice allowed for a more focused investigation of other variables influencing electron density distribution under similar solar activity conditions. We specifically examined the variations of the resulting modes in relation to different seasons and geomagnetic activity conditions, providing valuable insights into the complex behavior of the ionosphere in response to various external factors.

Retrieval of tropospheric delays from multi-GNSS observations in the polar region: effect factors and performance

Precise point positioning (PPP) technique is practical in estimating the zenith tropospheric delay (ZTD). To comprehensively study the factors affecting its accuracy in the polar region, different elevation cutoff angles for each single system and multi-system combination, different tropospheric mapping functions, tropospheric gradients and also seasonal variations are assessed. Meanwhile, European Centre for Medium-Range Weather Forecasts (ECMWF) products are adopted to validate the accuracy of PPP-derived ZTD. The results show that the root mean square (RMS) value of the estimated ZTD and ECMWF products is around 4 mm when the elevation cutoff angle is set to 10 degrees or less. From the view of system combination, it improves the ZTD accuracy in comparison with each individual system. The dual-system combination has 21.8%, 19.0% and 19.1% improvements in its ZTD accuracy compared with the Global navigation satellite system (GLONASS), Beidou navigation satellite system (BDS) and Galileo satellite navigation (GAL) systems. The four-system combination can reach 7.7% further improvement in ZTD estimation than that of the dual-system. For mapping functions, Vienna mapping function 3 (VMF3) function has the best accuracy among the four mapping functions of Niell mapping function (NMF), global mapping function, VMF1 and VMF3, while NMF does not perform as well as others. Considering the tropospheric gradients could get higher accuracy in ZTD estimation than ignoring them. The tropospheric delay estimated in winter is more accurate than that in summer and specifically the RMS value in winter is about 0.9 mm lower than that in summer. Overall, from investigation the estimation of ZTD in the polar region can be optimally handled with a multi-system and VMF3 mapping function at an elevation cutoff angle of 7°, considering the tropospheric gradients.

Civil Aviation Satellite Navigation Integrity Monitoring with Deep Learning

Civil Aviation Satellite Navigation Integrity Monitoring with Deep Learning

Assisted-GNSS positioning algorithm based on one-way fuzzy time information

In order to solve the problem that the accuracy of approximate position and approximate time information is limited by the traditional auxiliary positioning algorithm, this paper analyzes the problem that the calculation amount may increase and fail when these auxiliary information exceeds the precision requirement range and puts forward a positioning algorithm based on one-way fuzzy time assistance that is suitable for the positioning solution of GNSS satellite navigation receivers under the condition of fuzzy time information, such as the rotation condition. Methods using the reference information in the ephemeris information, the relatively accurate approximate time information can be reasonably searched and verified so as to achieve the effect of obtaining the positioning result with less calculation. The experimental results show that this method can accurately calculate the exact position even if there is an error in the approximate position information under the condition of one-way time assistance, which not only solves the problem that it cannot be positioned under the conditions of rotation but also does not increase the additional calculation amount and has practical engineering value.

Satellite Interference Source Direction of Arrival (DOA) Estimation Based on Frequency Domain Covariance Matrix Reconstruction.

Direction of arrival (DOA) estimation is an effective method for detecting various active interference signals during the satellite navigation process. It can be utilized for both interference detection and anti-interference applications. This paper proposes a DOA estimation algorithm for satellite interference sources based on frequency domain covariance matrix reconstruction (FDCMR) to address various types of active interference that may occur in the satellite navigation positioning process. This algorithm can estimate the DOA of coherent signals from multiple frequency points under low signal-to-noise ratio (SNR) conditions. The signals received from the array are transformed from the time domain to the frequency domain using a fast Fourier transform (FFT). The data corresponding to the frequency point of the target signal is extracted from the signal in the frequency domain. The frequency domain covariance matrix of the received array signals is reconstructed by utilizing its covariance matrix property. The spatial spectrum search method is used for the final DOA estimation. Simulation experiments have shown that the proposed algorithm performs well in the DOA estimation under low SNR conditions and also resolves coherency. Moreover, the algorithm's effectiveness is verified through comparison with three other algorithms. Finally, the algorithm's applicability is validated through simulations of various interference scenarios.

Using Software-Defined radio receivers for determining the coordinates of low-visible aerial objects

The object of this study is the process of determining the coordinates of low-visible aerial objects. The main hypothesis of the research assumed that the signals emitted by airborne systems of airborne objects that are not visible to radar stations have a greater power than the signal reflected from the airborne object. This, in turn, could improve the signal/noise ratio and, accordingly, the accuracy of determining the coordinates of low-visible aerial objects. It is suggested to use Software-Defined Radio receivers to receive such signals emitted by on-board systems of low-visible aerial objects. It was established that the main sources of signals for Software-Defined Radio receivers are signals of command, telemetry, target channels, manual control channels, and satellite navigation. It was established that an additional distinguishing feature when determining the coordinates of low-visible aerial objects is the uniqueness of their spectra and spectrograms. The method of determining the coordinates of low-visible aerial objects when using Software-Defined Radio receivers has been improved, which, unlike the known ones, involves: – the use as signals for Software-Defined Radio of signal receivers of on-board equipment of low-visible aerial objects; – the use of a priori coordinate values of a low-visible aerial object; – conducting additional spectral analysis of signals of on-board systems of low-visible aerial objects. The spectra and spectrograms of signals of on-board systems of aerial objects when using non-directional and directional antennas were experimentally determined. The experimental studies confirm the possibility of using the Software-Defined Radio receiver to receive signals from airborne equipment and improve the signal-to-noise ratio. The accuracy of determining the coordinates of aerial objects when using Software-Defined Radio receivers was evaluated. A decrease in the error of determining plane coordinates by the Software-Defined Radio system of receivers compared to the accuracy of determining coordinates by the P-19 MA radar station was established by an average of 1.88–2.47 times, depending on the distance to the aerial object

Electronic Warfare Theory and Strategy: Focusing on the Threat of North Korea’s Electronic Warfare

Purpose: The importance of electronic warfare in modern warfare is increasing day by day. In particular, North Korea has a relative weakness of conventional weapons systems, and has focused on developing asymmetric weapons systems and electronic warfare as a way to overcome them. North Korea is currently expected to further expand its application to some aircraft and guided weapons operations under satellite navigation systems such as GPS, GLONASS, COMPASS and Beidou.
 Method: This study studied the prior theory of electronic warfare at home and abroad. Prior research examined the military doctrines of the United States and trends in Europe. In particular, I studied the doctrines of the United States Joint Navigation Center (Navigation Warfare Center, JNWC) and the Education Command. Based on these prior research materials and literature reviews, I wanted to specifically review North Korea's electronic warfare cases and present our response in terms of legal and institutional aspects.
 Results: The South Korean military should recognize the importance of navigation warfare (part of electronic warfare) that protects our troops' location, navigation and square information so that they can be used without interruption, prevent the enemy's use of related information, and ensure the peaceful use of such information outside the light bulb In addition, we need to build an electronic warfare simulator and continue to promote training based on various scenarios.
 Conclusion: Efforts to train and support professionals are urgently needed. In parallel with these efforts, joint efforts to develop electronic technologies between the civilian and military should be preceded. To win a high-tech war in the 21st century, it is essential, among other things, to have precision weapons and original electronic warfare support capabilities. In addition, it is necessary to foster R&D and defense companies to secure domestic technology.

Evaluation of Best Satellite-Receiver Geometry for Improved IRNSS/GPS Position Accuracy

A GPS-IRNSS combined navigation system is emerging in India. It is possible to increase the accuracy of the receiver or user's position at any time and under any weather conditions with a combined system. It is possible to use these navigation systems for finding the precise location of receivers in civil aviation, precision applications such as surveying, disaster management, and other applications. Usually, satellite navigation systems are based on a geometric relationship between satellite and receiver, with errors caused by atmospheric conditions, multipath, and other factors affecting accuracy. Geometry of satellite receivers is measured by the Dilution of Precision (DOP), a unit less quantity. This paper investigates the possibility possible to obtain better accuracy by combining GPS and IRNSS constellations. This improved accuracy is typically useful for precision applications such as surveying and disaster management.

Vision-Aided Localization and Mapping in Forested Environments Using Stereo Images.

Forests are traditionally characterized by stand-level descriptors, such as basal area, mean diameter, and stem density. In recent years, there has been a growing interest in enhancing the resolution of forest inventory to examine the spatial structure and patterns of trees across landscapes. The spatial arrangement of individual trees is closely linked to various non-monetary forest aspects, including water quality, wildlife habitat, and aesthetics. Additionally, associating individual tree positions with dendrometric variables like diameter, taper, and species can provide data for highly optimized, site-specific silvicultural prescriptions designed to achieve diverse management objectives. Aerial photogrammetry has proven effective for mapping individual trees; however, its utility is limited due to the inability to directly estimate many dendrometric variables. In contrast, terrestrial mapping methods can directly observe essential individual tree characteristics, such as diameter, but their mapping accuracy is governed by the accuracy of the global satellite navigation system (GNSS) receiver and the density of the canopy obstructions between the receiver and the satellite constellation. In this paper, we introduce an integrated approach that combines a camera-based motion and tree detection system with GNSS positioning, yielding a stem map with twice the accuracy of using a consumer-grade GNSS receiver alone. We demonstrate that large-scale stem maps can be generated in real time, achieving a root mean squared position error of 2.16 m. We offer an in-depth explanation of a visual egomotion estimation algorithm designed to enhance the local consistency of GNSS-based positioning. Additionally, we present a least squares minimization technique for concurrently optimizing the pose track and the positions of individual tree stem[s].

Variability and distribution of nighttime equatorial to mid latitude ionospheric irregularities and vertical plasma drift observed by FORMOSAT-5 Advanced Ionospheric Probe in-situ measurements from 2017 – 2020

Irregularities in ionospheric plasma distribution can result in severe scintillation and disruption to the radio frequencies utilized for satellite communications and navigation. In the low and mid latitudes, these irregularities can include Equatorial Plasma Bubbles (EPBs) and Travelling Ionospheric Disturbances (TIDs). EPBs are irregularities manifesting in low latitude nighttime ionosphere plasma density that can extend along magnetic field lines with zonal scales on the order of 100 km or less, while TIDs are propagating wave disturbances. High frequency in-situ measurements of ionospheric plasma aboard spacecraft in Low Earth Orbit (LEO) are a direct measurement of irregularities in plasma density and are therefore valuable for resolving EPB and TID occurrences, variability, and relation to other ionospheric parameters that are believed to play a driving role in the formation of such irregularities. In this study, we utilize observations taken over a three-year period between 2017 and 2020 by the Advanced Ionospheric Probe (AIP) carried aboard the FORMOSAT-5 satellite to examine the spatial, seasonal, and interannual variability of equatorial to mid latitude ionospheric irregularities and vertical ion drift during this time. AIP provides in-situ measurements of ion density and vertical ion drift in the equatorial to mid latitude ionosphere at approximately 720 km altitude with local times between 22:00 – 23:00 local time. Our global scale results resolve distinct and inter-annually recurrent seasonal patterns in the distribution of nighttime ionospheric irregularities and vertical plasma drift during this time. Elevated occurrences of ion density irregularities are resolved along the Equatorial Ionization Anomaly (EIA) latitudes, while notable occurrences with variability consistent with EPBs also observed along the low and equatorial magnetic latitudes. Zonal variability of equatorial irregularities consistent with the signatures of nonmigrating atmospheric tides are observed. It is also notable that the occurrences and geographic distribution of ion density irregularities showed a considerable level of interannual variability, especially at mid latitudes over the South Atlantic and Southern African sectors, which showed much higher levels of irregularities in 2017–––2018, compared to 2019 and 2020. In comparison, the spatial and interannual variation of the co-located vertical ion drifts were much more consistent during the years examined, indicating that the driver for the observed interannual variability in ion density irregularities cannot be attributed to the vertical ion drift at the same time and location of the observations. This highlights the need for in-situ instruments distributed across multiple satellites in different local time zones.

High-Gain Dual-Band Aperture-Shared CP Patch Antenna With Wide AR Beamwidth for Satellite Navigation System

This paper presents a compact dual-band, high-gain, light-weight, circularly polarized (CP) microstrip patch antenna with wide axial ratio (AR) beamwidth for multiple satellite communication, positioning and navigation systems The antenna consists of a main dual-frequency coplanar metal frame radiator, a circular metal capacity-loaded radiator, and some coaxial feeding probes. Due to the use of air dielectric, the maximum right-hand circularly polarized gain of the antenna is up to 6.2 dBic in the lower bands and 6.3 dBic in the upper bands. By utilization of dual-frequency coplanar patch and metal capacity-loaded technology, the dimensions of the aperture-shared CP antenna are only 0.38 λ × 0.38 λ × 0.04 λ. To increase the 3-dB AR beamwidth, a novel vertically grounded shorting sheet is introduced. The 3-dB AR beamwidth ranges from −120° to 100° at 1.227 GHz and from −90° to 95° at 1.575 GHz. As a result, the proposed antenna is an excellent candidate for high gain, wide AR beamwidth and compact air dielectric antenna.

Smoothened Absolute Kinematic Position Estimation Of Leo Satellite Using Gps Observables

In this paper, our objective is to use the navigation signals (pseudorange and carrier phase measurements) from GPS to kinematically estimate the absolute position of a low Earth orbit satellite and its receiver clock biases. GPS observables can estimate the precise position of a satellite in near real time. The GPS satellite navigation file is downloaded from Scripps Orbit and Permanent Array Centre (SOPAC) website for starting epoch of 01-01-2016 00:00 UT. The observables are then generated for a Low-Earth-Orbit (LEO) satellite at an altitude of 901.4 km. The absolute position is estimated using pseudorange measurements. The accuracies obtained are (5.68 8.04 6.17) m in ECEF frame. This estimated absolute position is then smoothened with the time-differenced carrier phase measurements. The Kalman filter gains are computed in near real time. The smoothened accuracies obtained are (2.24 2.60 2.6982) m in ECEF frame, thus showing improved estimated absolute position accuracy.

Dysregulated Signalling Pathways Driving Anticancer Drug Resistance.

One of the leading causes of death worldwide, in both men and women, is cancer. Despite the significant development in therapeutic strategies, the inevitable emergence of drug resistance limits the success and impedes the curative outcome. Intrinsic and acquired resistance are common mechanisms responsible for cancer relapse. Several factors crucially regulate tumourigenesis and resistance, including physical barriers, tumour microenvironment (TME), heterogeneity, genetic and epigenetic alterations, the immune system, tumour burden, growth kinetics and undruggable targets. Moreover, transforming growth factor-beta (TGF-β), Notch, epidermal growth factor receptor (EGFR), integrin-extracellular matrix (ECM), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), phosphoinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR), wingless-related integration site (Wnt/β-catenin), Janus kinase/signal transducers and activators of transcription (JAK/STAT) and RAS/RAF/mitogen-activated protein kinase (MAPK) signalling pathways are some of the key players that have a pivotal role in drug resistance mechanisms. To guide future cancer treatments and improve results, a deeper comprehension of drug resistance pathways is necessary. This review covers both intrinsic and acquired resistance and gives a comprehensive overview of recent research on mechanisms that enable cancer cells to bypass barriers put up by treatments, and, like "satellite navigation", find alternative routes by which to carry on their "journey" to cancer progression.