Coherent Change Detection Using Passive GNSS-Based BSAR: Experimental Proof of Concept

This tutorial presents a state-of-the-art survey of advanced applications of Synthetic Aperture Radar (SAR). Applications include: the detection and recognition of targets in SAR imagery, and the detection of targets under trees (and in the open) using change detection (coherent change detection, full-polarization change detection, etc). A fully polarimetric SAR sensor is described. Models of clutter and targets are developed from analysis of full-polarization SAR imagery. Algorithms for optimum (GLRT) processing of full-polarization data are derived, including the polarimetric whitening filter (PWF) and the polarimetric matched filter (PMF). Polarization-based discrimination features (polarization entropy, anisotropy, etc.) are developed and applied to SAR image terrain classification. Model-based and template-based target recognition systems are described and classifier performance results versus resolution and polarization are summarized for 10-and 20-target classifiers. Super-resolution algorithms are applied to SAR imagery and target recognition performance improvements demonstrated. Multi-polarization and multi-pass change detection algorithms are developed and demonstrated using UHF SAR imagery of targets under trees; fusion of multi-polarization coherent and non-coherent change detection algorithms is demonstrated. The effect of SAR image compression on change detection performance is quantified. Change detection performance using multi-pass VHF SAR imagery of targets under trees is demonstrated using data gathered by the Swedish CARABAS SAR system.

With the capability to record Global Navigation Satellite Systems (GNSS) data at high-rate, at sampling rates typical for seismological applications, experiments are needed to quantify the response of GNSS to shaking from earthquakes. There have been a few studies that examine the response of GNSS to strong shaking. Recently, Ebinuma and Kato (2012) used a global positioning system (GPS) simulator to electronically test several GNSS receivers and obtain the receiver characteristics at three frequencies: 1, 2, and 5 Hz. The results showed that the amplitude of 5-Hz displacements recorded by the GPS was, depending on the receiver model, between 30 and 125 percent more than the displacement input to the simulator. At low frequencies, the GPS displacement was nearly equal to the input displacement. In addition, Ebinuma and Kato (2012) examined how each receiver model amplified an earthquake displacement record in the 2–8 Hz band. The study discussed here builds on the tests by Ebinuma and Kato (2012), but rather than using electronic simulation, the tests are setup outdoors and closer to actual field installations of GNSS equipment. The authors used a one-dimensional shake table capable of 400 mm of displacement and high acceleration; the shake table also is constrained by a precision linear slider to have very low tilt that would affect inertial sensors. In addition, the stage position can be accurately monitored independent of the GNSS hardware and, importantly, provides a reference to compare with the estimated displacements from the GNSS data. The tests spanned a greater frequency range from 0.2 to 20 Hz and used equipment from three different manufacturers covering five different combinations of receivers and antennas. In addition, the authors have been able to simulate the frequency response of the GNSS equipment using a simple, causal filter. The quality of the filter was tested using additional test data where a step function in displacement was applied to the shake table. The observed displacements from the GNSS data show an overshoot in displacement at the time of the step or transition of the stage. That overshoot was accurately predicted using the filter design derived from the sinusoidal displacement tests.

Global navigation satellite systems (GNSS) historically been known as one of the newest technologies since the 1970s.GNSS originally developed for military purposes in the USA (GPS -Global Position System).There are several satellite systems in the world.Satellites, International Research Base Stations, regional/national and local base stations form a permanent geodetic frame.Research on the size and shape of the Earth-planet, climate, sea, urban planning.In geodesy, a network of global positioning base stations makes it possible to assess the movements of continents, land plates at international level.GNSS is an important technology in navigation, logistics, economics, land surveying and other "geo" sectors.GNSS equipment/receivers and their manufacturers are applying new designs and electronics.Initially, GNSS instruments were used with single frequency signal reception, later expanding the number of GNSS signal channels to two frequencies.Such technological improvements nowadays improve the certainty, reliability and accuracythe overall quality of GNSS measurements.The GNSS base station enables the surveyors to determine coordinates with an accuracy of two centimeters in real time (RTK) and with an accuracy of five millimeters using the accumulated post-processing data.Various types of factors hamper GNSS measurements.The GNSS signal (radio wave) travels in airspace, in urban environments and is a physical parameter.Any obstacletree, building walls, and atmospheric effectmakes GNSS measurements less accurate.The GNSS signal must be strong and free from attenuation and suppression effects.This study develops GNSS models that show the comparison, certainty and reliability of GNSS measurements using different types of GNSS techniques.Evaluation of Latvian Global Positioning Reference Station Network -LatPos system measurements against a corresponding RTK solution method using Latvian Global Positioning Network geodetic point (G2 class).

Since the beginning of the International Global Navigation Satellite System (GLONASS) Experiment, IGEX, in October 1998, the Center for Orbit Determination in Europe (CODE) has acted as an analysis center providing precise GLONASS orbits on a regular basis. In CODE's IGEX routine analysis the Global Positioning System (GPS) orbits and Earth rotation parameters are introduced as known quantities into the GLONASS processing. A new approach is studied, where data from the IGEX network are combined with GPS observations from the International GPS Service (IGS) network and all parameters (GPS and GLONASS orbits, Earth rotation parameters, and site coordinates) are estimated in one processing step. The influence of different solar radiation pressure parameterizations on the GLONASS orbits is studied using different parameter subsets of the extended CODE orbit model. Parameterization with three constant terms in the three orthogonal directions, D, Y, and X (D = direction satellite–Sun, Y = direction of the satellite's solar panel axis), and two periodic terms in the X-direction, proves to be adequate for GLONASS satellites. As a result of the processing it is found that the solar radiation pressure effect for the GLONASS satellites is significantly different in the Y-direction from that for the GPS satellites, and an extensive analysis is carried out to investigate the effect in detail. SLR observations from the ILRS network are used as an independent check on the quality of the GLONASS orbital solutions. Both processing aspects, combining the two networks and changing the orbit parameterization, significantly improve the quality of the determined GLONASS orbits compared to the orbits stemming from CODE's IGEX routine processing.

Built-up city 'urban canyons' offer an environment which challenges the physical limitations of modem real-time GPS positioning systems and, yet, is perhaps the one environment where the successful application of GPS technology could benefit most users. With a view to the next generation of Real Time Kinematic (RTK) positioning systems, this paper highlights the limitations imposed on current RTK systems operating in the urban canyon using GPS visibility trials conducted in the urban canyon of the Perth Central Business District (CBD). Furthermore, following the recent release of receivers capable of integrating the Global Positioning System (GPS) and the Russian equivalent, the Global Navigation Satellite System (GLONASS), the advantages of integration of both GPS and GLONASS systems are demonstrated using GLONASS visibility simulations at selected points in the Perth CBD.

Tropospheric delay accounts for one source of error in global navigation satellite systems (GNSS). To better characterize the tropospheric delays in the temporal and spatial domain and facilitate the safety-critical use of GNSS across China, a method is proposed to generate a grid-based tropospheric product (GTP) using the GNSS network with an empirical tropospheric model, known as IGGtrop. The prototype system generates the GTPs in post-processing and real-time modes and is based on the undifferenced and uncombined precise point positioning (UU-PPP) technique. GTPs are constructed for a grid form ( $$2.0{^{\circ }}\times 2.5{^{\circ }}$$ latitude–longitude) over China with a time resolution of 5 min. The real-time GTP messages are encoded in a self-defined RTCM3 format and broadcast to users using NTRIP (networked transport of RTCM via internet protocol), which enables efficient and safe transmission to real-time users. Our approach for GTP generation consists of three sequential steps. In the first step, GNSS-derived zenith tropospheric delays (ZTDs) for a network of GNSS stations are estimated using UU-PPP. In the second step, vertical adjustments for the GNSS-derived ZTDs are applied to address the height differences between the GNSS stations and grid points. The ZTD height corrections are provided by the IGGtrop model. Finally, an inverse distance weighting method is used to interpolate the GNSS-derived ZTDs from the surrounding GNSS stations to the location of the grid point. A total of 210 global positioning system (GPS) stations from the crustal movement observation network of China are used to generate the GTPs in both post-processing and real-time modes. The accuracies of the GTPs are assessed against with ERA-Interim-derived ZTDs and the GPS-derived ZTDs at 12 test GPS stations, respectively. The results show that the post-processing and real-time GTPs can provide the ZTDs with accuracies of 1.4 and 1.8 cm, respectively. We also apply the GTPs in real-time kinematic GPS PPP, and the results show that the convergence time of the PPP solutions is shortened. These results confirm that the GTPs can act as an efficient information source to augment GNSS positioning over China.

The localization system is the most important part of the overall drone navigation system. The Global Positioning System (GPS) or Global Navigation Satellite System (GNSS) is the main device commonly used in a drone. However, under certain conditions, GPS or GNSS may not function optimally, such as in situations of signal jamming or enclosed environments. This paper implemented a new approach to address this issue by combining GNSS data with Visual Odometry (VO) through Machine Learning (ML) methods. The followed process consists of three main stages. First, performing speed and orientation estimation using VO. Second, performing left and right feature separation on the images to generate a more stable and robust estimation of speed and rotation. Third, refining speed and orientation estimation by integrating GNSS data through ML-based data fusion. The proposed method strives to enhance drone localization accuracy, despite disruptions or unavailability of GNSS signals. The research results indicate that the introduced method significantly reduces Absolute Translation Error (ATE) compared to utilizing VO or GNSS separately. The average ATE produced reached 4.38 m and an orientation of 8.26°, indicating that this data fusion approach provides a significant improvement in drone localization accuracy, making it reliable in operational scenarios with limited GNSS signals.

A Global Navigation Satellite System (GNSS) concept based on an open system architecture (OSA) has been developed by the authors. As described in this paper, this GNSS OSA concept utilizes the Global Positioning System (GPS) signal-in-space interface as the foundation for its interoperability standards. So long as each GNSS component adheres to these interoperability standards, synergy is enabled at the individual satellite level and the overall whole becomes much more than the simple sum of its components. The biggest beneficiaries of this GNSS OSA concept are those military and civil/commercial users of satellite navigation services who already have equipment compatible with the GPS signal-in-space interface (i.e., dual use). With the recent decisions in Europe to proceed with the civil Galileo system, on-going international development of space-based augmentation systems, and several industry announcements of plans to build commercial regional positioning systems, the dual-use GNSS OSA concept described in this paper provides a technical roadmap for the future global evolution of satellite navigation.

Versions of this paper were first presented at the Royal Institute of Navigation GNSS Vulnerabilities and Solutions Conference held at Baska, Croatia in September 2008 and the Royal Institute of Navigation NAV 08 Conference held at Church House, Westminster, London in October 2008.The US Global Positioning System (GPS) is currently the primary source of Position, Navigation and Timing (PNT) information in maritime applications, whether stand-alone or augmented with additional systems. This situation will continue in the future with GPS, possibly together with other Global Navigation Satellite Systems (GNSS) e.g. Galileo, being the core PNT technology for e-Navigation – the future digital maritime architecture. GPS signals, measured at the surface on the Earth, are very weak. As such, the system is vulnerable to unintentional interference and jamming, resulting in possible denial of service over large geographical areas. The result of such interference could be the complete failure of the mariner's GPS receiver or, possibly worse, the presentation to the mariner of hazardously misleading information (HMI) for navigation and situational awareness, depending on how the GPS receiver reacts to the jamming incident. Recognising this, the General Lighthouse Authorities of the United Kingdom and Ireland (GLA), in collaboration with the UK Ministry of Defence (MOD) Defence Science and Technology Laboratory (DSTL), have conducted a series of sea-trials with the aim of identifying the full effects of GPS jamming on safe navigation at sea.This paper presents the key findings of these trials and provides important information on the effect of GPS denial. The GLA are playing a pivotal role in the establishment of eLoran as an independent source of PNT, taking advantage of eLoran's complementary nature, having dissimilar failure modes to GPS and the future GNSS. This paper provides information on the performance of an eLoran receiver in an area of GPS service denial. The paper presents the rationale for the work, details the system architecture employed, the data gathering efforts and finally the data analysis procedures, results and conclusions.

Precise Orbit Determination (POD) is an integral part for analyzing measurements from space geodetic techniques such as Satellite Laser Ranging (SLR) and Global Navigation Satellite Systems (GNSS) such as the Global Positioning System (GPS). In the last two decades, POD based on GPS data has furthermore been established as one of the standard techniques to derive trajectories of satellites in the low Earth orbit (LEO) with highest accuracy. Since the launch of dedicated gravity missions, GPS sensors are not only used as a key tracking system for LEO POD, but also for extracting the long wavelength part of the Earth’s gravity field (together with SLR to spherical satellites). This chapter introduces SLR and GNSS measurements collected by the terrestrial networks of the International Laser Ranging Service (ILRS) and the International GNSS Service (IGS) as the observational basis for the realization of a terrestrial reference frame from satellite data. On this foundation, the basic equations and mathematical methods of orbit determination are introduced and extensively discussed. Pseudo-stochastic orbit modeling techniques are eventually presented as a general and efficient concept to determine satellite trajectories of highest quality even in presence of deficient force models, covering the full range between dynamic and purely kinematic solutions. Selected results from the application of the discussed orbit determination techniques are highlighted for GPS LEO data. Special emphasis is also put to present orbit determination in the context of more general orbit determination problems, where satellite trajectories are simultaneously determined with other parameters encompassing (at maximum) all pillars of geodesy, i.e., the shape, rotation, and gravity field of the Earth.

The Global Navigation Satellite System (GNSS), the US Global Positioning System (GPS) at its core but the Russian GLONASS and other systems also at play, is destined to be the basic infrastructure of the forthcoming information age, producing vast civil applications and markets. With the whole world going to be reliant on the GPS that is still owned and operated by the military of a single nation (as also is GLONASS), concerns are being raised in various circles as to the adequacy of the civil world becoming wholly reliant on those military systems. Awareness is increasing worldwide of navigation satellites’ implications as a foremost 21st century issue that transcends civil and national security boundaries. The European Union has embarked on the development of Galileo as an independent, non-military, GNSS. Various meetings have been held between Japanese and US Governments since 1996 on GPS issues, the most recent being the second annual “Japan-US GPS Plenary Meeting” held in October 2002.This paper addresses such issues with a focus on the Japanese situation, especially those surrounding the Japan-US GPS meetings, in the hope that they may serve the purpose of promoting first, the recognition of these issues by other people, and second, the understanding of the situation peculiar to Japan, the world’s second largest economy and perhaps the largest civil GPS user nation. The special Japanese sensitivity to space and national security issues, a survey of developments of Japan-US GPS meetings, and reports of discussions of related topics in other international forums are all discussed. It is apparent that there is a barrier in Japan between the civil and national security views, which is especially conspicuous in the Japan-US GPS meetings, and that international discussions point to the responsibility of user nations to deny the GNSS service to “hostile users”. All concerned, whether in Japan or elsewhere, should transcend the vertical “turfs” to come to grips with the whole GNSS issue as their own responsibility, to recognize and be prepared for the threat of a 21st century “Navigation War”.KeywordsGlobal Position SystemGlobal Navigation Satellite SystemGlobal Navigation Satellite SystemNational SecurityTechnical InteractionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Conventional Synthetic Aperture Radar (SAR) Coherent Change Detection (CCD) has been found to be of great utility in detecting changes that occur on the ground. The CCD procedure involves performing repeat pass radar collections to form a coherence product, where ground disturbances can induce detectable incoherence. However there is usually a difference in the radar collection geometry which can lead to incoherent energy noise entering the CCD. When sensing flat terrain in a far-field regime, the incoherence due to collection geometry difference can be removed through a conventional global Fourier image support trimming process. However, it has been found that when the terrain is either in a near-field regime or contains non-flat topography, the optimal trimming process is substantially more involved, so much so that a new per-pixel SAR bistatic back-projection imaging algorithm has been developed. The new algorithm removes incoherent energy from the bistatic SAR CCD collection pair on a per-pixel basis according to the local radar geometry and topography, leaving a higher coherence CCD product. In order to validate the approach, change detection measurements were conducted with GB-SAR, a ground-based indoor radar measurement facility.

In this paper we present a new generalized family of change detection algorithms for SAR imagery that includes traditional non-coherent and coherent processing as special cases. The parameterized family of algorithms, referred to as partially coherent change detection (PCCD), allows the user to select the level of coherence desired in the change detection algorithm. This and other settings of the algorithm enable one to specify the types of changes that are significant, thereby reducing the number of false alarms due to insignificant changes—such as foliage motion. Algorithm settings may also be applied spatially in order to support spatially varying levels of coherence based on scene content. Examples from synthetic and measured imagery demonstrate the efficacy of the new family of algorithms.

This paper provides an overview of Global Navigation Satellite System (GNSS) signals. Today, GNSS comprises two major constellations: (1) the United States' Global Positioning System (GPS), and (2) the Russian Federation's Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS). Two other major constellations are being deployed. Additionally, regional systems have been deployed or are planned. Whereas most GNSS timing receivers today rely only upon the legacy GPS signals, it is anticipated in the near future that multi-system receivers will become the norm. This paper describes the characteristics of each of the GNSS signals, and highlights the performance benefits that will be provided to the precise time and frequency community as the GNSS evolves.

Global navigation satellite systems (GNSSs) are widely utilized in various scientific domains such as agriculture, health monitoring, weather forecasting, and crop health detection. GNSS is a satellite network utilized in positioning and navigation including location-based services and precise orbit determination. The satellite navigation system offers various advantages such as real-time location and temporal synchronization. The Global Positioning System (GPS) is one of the well-known GNSSs, operated by the United States. Some of the other examples may include GPS; Galileo; Russia’s GLONASS, known as the Global Navigation Satellite System; and the BeiDou Navigation Satellite System (BDS). GNSS has found many applications in the field of precision agriculture, timing and synchronization in telecommunication, search and rescue operations, military and defense purposes, Earth observation, construction, and weather forecasting. However, GNSS has also been explored in the accurate and reliable positioning and timing information for climate change analysis and modeling. Therefore, it is essential to examine the potential of GNSS in climate monitoring and modeling. This chapter will present a review of GNSS types, GNSS remote sensing applications, and challenges faced by GNSS. Additionally, this chapter also explores the meta-analysis of the publications or research contributions made by different authors in the field of GNSSs.