FDOA-based passive source localization: a geometric perspective

2018 Fall.Includes bibliographical references.We consider the problem of passively locating the source of a radio-frequency signal using observations by several sensors. Received signals can be compared to obtain time difference of arrival (TDOA) and frequency difference of arrival (FDOA) measurements. The geometric relationship satisfied by these measurements allow us to make inferences about the emitter's location. In this research, we choose to focus on the FDOA-based source localization problem. This problem has been less widely studied and is more difficult than solving for an emitter's location using TDOA measurements. When the FDOA-based source localization problem is formulated as a system of polynomials, the source's position is contained in the corresponding algebraic variety. This provides motivation for the use of methods from algebraic geometry, specifically numerical algebraic geometry (NAG), to solve for the emitter's location and gain insight into this system's interesting structure

Exploiting Structural Signal Information in Passive Emitter Localization

The operational use of systems for passive geolocation of radio frequency emitters poses various challenges to single sensor systems or sensor networks depending on the measurement methods. Position estimation by means of direction finding systems often requires complex receiver and antenna technique. Time (Difference) of Arrival methods (TDOA, TOA) are based on measurements regarding the signal propagation duration and generally require broadband communication links to transmit raw signal data between spatially separated receivers of a sensor network. Such bandwidth requirements are particularly challenging for applications with moving sensor nodes. This issue is addressed in this thesis and techniques that use signal structure information of the considered signals are presented which allow a drastic reduction of the communication requirements. The advantages of using knowledge of the signal structure for TDOA based emitter localization are shown using two exemplary applications. The first case example deals with the passive surveillance of the civil airspace (Air Traffic Management, ATM) using a stationary sensor network. State of the art airspace surveillance is mainly based on active radar systems (Primary Surveillance Radar, PSR), cooperative secondary radar systems (Secondary Surveillance Radar, SSR) and automatic position reports from the aircraft itself (Automatic Dependent Surveillance-Broadcast, ADS-B). SSR as well as ADS-B relies on aircrafts sending transponder signals at a center frequency of 1090 MHz. The reliability and accuracy of the position reports sent by aircrafts using ADS-B are limited and not sufficient to ensure safe airspace separation for example of two aircrafts landing on parallel runways. In the worst case, the data may even be altered with malicious intent. Using passive emitter localization and tracking based on multilateration (TDOA/hyperbolic localization), a precise situational awareness can be given which is independent of the content of the emitted transponder signals. The high concentration of sending targets and the high number of signals require special signal processing and information fusion techniques to overcome the huge amount of data. It will be shown that a multilateration network that employs those techniques can be used to improve airspace security at reasonable costs. For the second case, a concept is introduced which allows TDOA based emitter localization with only one moving observer platform. Conventional TDOA measurements are obtained using spatially distributed sensor nodes which capture an emitted signal at the same time. From those signals, the time difference of arrival is estimated. Under certain conditions, the exploitation of signal structure information allows to transfer the otherwise only spatial into a spatial and temporal measurement problem. This way, it is possible to obtain TDOA estimates over multiple measurement time steps using a single moving observer and to thus localize the emitter of the signals. The concept of direct position determination is applied to the single sensor signal structure TDOA scheme and techniques for direct single sensor TDOA are introduced. The validity and performance of the presented methods is shown in theoretical analysis in terms of Cramér-Rao Lower Bounds, Monte-Carlo simulations and by evaluation of real data gained during field experiments

Validation Technique for Modeled Bottomside Ionospheres via Ray Tracing

A new method for validating ionosphere models using High Frequency (HF) angle of arrival (AoA) data is presented. AoA measurements from a field campaign held at White Sands Missile Range, New Mexico, USA in January 2014 provide the actual elevation angle, azimuth and group delay results from 10 transmitter-receiver circuits. Simulated AoAs are calculated by ray tracing through the electron density profiles predicted from the ionosphere models hosted by NASA\u27s Community Coordinated Modeling Center: IRI-2016, USU-GAIM, GITM, CTIPe, TIE-GCM, and SAMI3. Through the implementation of metrics including Mean Absolute Error, Prediction Efficiency, Correlation Coefficient, and others, we are able to compare and analyze model performance using this new model validation approach. The wide variety of metrics determine model performance quantitatively and qualitatively by analyzing behavior over time

Seaglider observations of biogeochemical variability in the Iberian upwelling system.

Seasonal upwelling events along the Galician coastline of the North Atlantic furnish the upper watercolumn with nutrients, resulting in strong summer phytoplankton blooms and the sustenance of one of Europe’s largest fisheries. The episodic nature of these upwelling events result in considerable challenges studying the region using traditional shipboard observations. This thesis demonstrates an alternative sampling technique, providing high spatial and temporal resolution biogeochemical data through the use of an autonomous underwater gliderthe Seaglider. SG510 “Orca” was outfitted with sensors to measure dissolved oxygen, temperature, salinity, chlorophyll a (chl a), coloured dissolved organic material (CDOM) and optical backscatter. Deployed for 113 days over summer 2010, Orca completed 17 zonal transects across the shelf, continental slope and open ocean at 42.1° N. Data collected during the campaign was used to assess both the physics of the watercolumn, and the effect these physical processes have on the region’s biogeochemistry. As part of this biogeochemical study, a novel attempt at calculating net community production (NCP) was completed using an oxygen inventory technique. Two major phytoplankton bloom events occurred during the deployment period, with respective peak Chl a concentrations of 9.65 and 11.23 mg m3. During these bloom events, NCP varied between (net autotrophic) values of 25 and 123 (±17 ) mmol m2. d1. Negative values of NCP were only observed twice for 24 and 60 hours respectively, with a maximum heterotrophy of 44 (±17) mmol m2 d1. Overall, the summer season featured a net autotrophic metabolic balance of +27 mmol m2 d1 .thus highlighting the importance of the region for net carbon sequestration. Finally, this thesis also demonstrates the success of using autonomous glider platforms for sustained biogeochemical and physical observations within a highly dynamic and challenging operational environment with strong currents and considerable shipping traffic

Evaluation of the potential accuracy of the pulsed radio signals source coordinate determination by the positioning system using a single UAV-sensor

An approach to determining the coordinates of pulsed radio signals sources by the positioningsystem in the application of a single unmanned aerial vehicles sensor is shown in this article. Therange-difference location method allows to determinate an informative coordinate parameter withoutretransmission and internal synchronization of receiving points. The result is achieved by improving thewell-known scientific and methodological apparatus with considering some features of the operationmode of pulsed radio signals sources. Presenting results of the simulation allow to estimate theinfluence of main input factors on the potential accuracy of the pulsed radio signal source coordinatedetermination

A Portfolio Approach to NLOS and Multipath Mitigation in Dense Urban Areas

Non-line-of-sight (NLOS) reception and multipath interference are major causes of poor GNSS positioning accuracy in dense urban environments. They are commonly grouped together. However, both the mechanisms by which they cause position errors and many of the techniques for mitigating those errors are quite different [1]. For example, correlation-based multipath mitigation has no effect on the errors caused by NLOS reception. University College London (UCL) has investigated the performance of a number of multipath and/or NLOS mitigation techniques in dense urban areas, including C/N0-based solution weighting [2], advanced consistency checking [3], dual-polarization NLOS detection [4] and vector tracking [5]. In this paper, we present a new multipath detection technique based on comparing the measured C/N0 on multiple frequencies and also new dual-polarization results. Meanwhile, other researchers have demonstrated NLOS detection using a panoramic camera [6, 7] or 3D city model [8, 9] and detection of NLOS and multipath using an antenna array [10]. All of these techniques bring some improvement in positioning performance in urban environments, but none of them eliminate the effects of both NLOS reception and multipath interference completely. As the different techniques are largely complementary, best performance is obtained by using several of them in combination, a portfolio approach. This paper comprises three parts. The first presents a feasibility study on a new multipath detection technique using multi-frequency C/N0 measurements. Constructive multipath interference results in an increase in the measured C/N0, whereas destructive multipath interference results in a decrease. As the phase of a reflected signal with respect to its directly received counterpart depends on the wavelength, the multipath interference may be constructive on one frequency and destructive on another. Thus, by comparing the difference in measured C/N0 between two frequencies with what would normally be expected for that signal at that elevation angle, strong multipath interference may be detected. However, the converse is not true because, depending on the path delay, the phase of the multipath interference may also be consistent across the two frequencies. Consistency across three frequencies in the presence of multipath interference is much less likely than consistency across two. Therefore, by comparing C/N0 measured across three (or more) frequencies, the chance of detection is improved substantially, noting that reliability is less critical as part of a portfolio approach to multipath detection than for a stand-alone technique. Experimental results are presented demonstrating the potential of this approach using GPS and GLONASS data collected in Central London. The second part of the paper presents the results of the first multi-constellation test of the dual-polarization NLOS detection technique pioneered at UCL [4]. This separately correlates the right hand circularly polarized (RHCP) and left hand circularly polarized (LHCP) outputs of a dual-polarization antenna and differences the resulting C/N0 measurements, producing a result that is positive for directly received signals and negative for most NLOS signals. Data was collected at six different sites in Central London and NLOS reception of both GPS and GLONASS signals was detected. Position solutions with the NLOS signals removed are compared with the corresponding all-satellite solutions. The final part of the paper addresses the portfolio approach to NLOS and multipath mitigation. Each technique is assessed qualitatively for its ease of implementation and its efficiency at detecting or directly mitigating both NLOS reception and multipath mitigation. A compatibility matrix is then presented showing which techniques may be combined without conflict. Suitable portfolios are then proposed both for professional-grade and for consumer-grade user equipment. References [1] Groves, P. D., Principles of GNSS, inertial, and multi-sensor integrated navigation systems, Second Edition, Artech House, 2013. [2] Jiang, Z., P. Groves, W. Y. Ochieng, S. Feng, C. D. Milner, and P. G. Mattos, “Multi-Constellation GNSS Multipath Mitigation Using Consistency Checking,” Proc. ION GNSS 2011. [3] Jiang, Z., and P. Groves, “GNSS NLOS and Multipath Error Mitigation using Advanced Multi-Constellation Consistency Checking with Height Aiding,” Proc. ION GNSS 2012. [4] Jiang, Z., and P. D. Groves, “NLOS GPS Signal Detection Using A Dual-Polarisation Antenna,” GPS Solutions, 2012, DOI: 10.1007/s10291-012-0305-5. [5] Hsu, L.-T., P. D. Groves, and S.-S. Jan, “Assessment of the Multipath Mitigation Effect of Vector Tracking in an Urban Environment,” Proc ION Pacific PNT, 2013. [6] Marais, J., M. Berbineau, and M. Heddebaut, “Land Mobile GNSS Availability and Multipath Evaluation Tool,” IEEE Transactions on Vehicular Technology, Vol. 54, No. 5, 2005, pp. 1697-1704. [7] Meguro, J., et al., “GPS Multipath Mitigation for Urban Area Using Omnidirectional Infrared Camera,” IEEE Transactions on Intelligent Transportation Systems, Vol. 10, No. 1, 2009, pp. 22-30. [8] Obst, M., S. Bauer, and G. Wanielik, “Urban Multipath Detection and mitigation with Dynamic 3D Maps for Reliable Land Vehicle Localization,” Proc. IEEE/ION PLANS 2012. [9] Peyraud, S., et al., “About Non-Line-Of-Sight Satellite Detection and Exclusion in a 3D Map-Aided Localization Algorithm,” Sensors, Vol. 13, 2013, pp. 829-847. [10] Keshvadi, M. H., A. Broumandan, and G. Lachapelle, “Analysis of GNSS Beamforming and Angle of Arrival Estimation in Multipath Environments," Proc ION ITM, San Diego, CA, January 2011, pp. 427-435

An Assessment of Regional ICESat-2 Sea-Level Trends

Sea-level rise is an important indicator of ongoing climate change and well observed by satellite altimetry. However, observations from conventional altimetry degrade at the coast where regional sea-level changes can deviate from the open-ocean and impact local communities. With the 2018 launch of the laser altimeter onboard ICESat-2, new high-resolution observations of ice, land, and ocean elevations are available. Here we assess the potential benefits of sea level measured by ICESat-2 by comparing to data from Jason-3 and tide gauges. We find good agreement in the linear rates computed from the independent observations, with an absolute average residual of 3.60 ± 0.03 cm yr−1 between global ICESat-2 and Jason-3 observations at a 1° posting. The recent La Niña is clearly evident in ICESat-2 observations, as well as small-scale features. By demonstrating the quality of the ICESat-2-measured sea level, we provide support for integrating it into the existing suite of sea-level observations

Multi-Sensor Methods for Mobile Radar Motion Capture and Compensation.

Ph.D. Thesis. University of Hawaiʻi at Mānoa 2017