Showing papers in "Annual of Navigation in 2016"

A Navigation Message Authentication Proposal for the Galileo Open Service

Abstract: GNSS vulnerabilities have become evident in the last decade. Authentication of the GNSS signals and data can be an important building block contributing to mitigating these vulnerabilities. This paper presents a Navigation Message Authentication (NMA) scheme based on the Timed Efficient Stream Loss-tolerant Authentication (TESLA) protocol and a novel concept based on a single one-way chain for all senders and cross-authentication. The paper presents an NMA implementation in the Galileo Open Service (OS) navigation message that should provide similar navigation performance to data-authenticated users and standard non-authenticated users in terms of time to first fix, accuracy, and availability even in difficult reception conditions. The proposal also maintains a high level of signal unpredictability to help receivers protect against replay attacks. The scheme and implementation proposed yield significant improvements compared to the state of the art, offering the opportunity for Galileo to become the reference GNSS in civil navigation authentication. Copyright © 2016 Institute of Navigation

Comparison of Estimation Accuracy of EKF, UKF and PF Filters

Abstract: Abstract Several types of nonlinear filters (EKF – extended Kalman filter, UKF – unscented Kalman filter, PF – particle filter) are widely used for location estimation and their algorithms are described in this paper. In the article filtering accuracy for non-linear form of measurement equation is presented. The results of complex simulations that compare the quality of estimation of analyzed non-linear filters for complex non-linearities of state vector are presented. The moves of maneuvering object are described in two-dimensional Cartesian coordinates and the measurements are described in the polar coordinate system. The object dynamics is characterized by acceleration described by the univariate non-stationary growth model (UNGM) function. The filtering accuracy was evaluated not only by the root-mean-square errors (RMSE) but also by statistical testing of innovations through the expected value test, the whiteness test and the WSSR (weighted sum squared residual) test as well. The comparison of filtering quality was done in the MATLAB environment. The presented results provide a basis for designing more accurate algorithms for object location estimation.

A Robust GNSS LOS/NLOS Signal Classifier

Abstract: GNSS signal classification to LOS and NLOS signals is of great value for conventional ranging-based and shadow matching algorithms. The most common attribute for performing this classification is the signal strength. Alas, such classification is often insufficient, in particular, in urban environments. In this paper, we present a novel approach for LOS/NLOS classification utilizing supervised machine learning algorithms. Provided with a sufficiently large labeled training set, the proposed approach is able to predict with high certainty (>85 percent) the satellites’ visibility status in dense urban regions. This achievement was possible due to the vast raw measurements supplied for the algorithm and using sophisticated feature-selection techniques.

Absolute Positioning Using the Earth's Magnetic Anomaly Field†

Abstract: Achieving worldwide dependable alternatives to the Global Positioning System is a challenging engineering problem. Current Global Positioning System alternatives often suffer from limitations such as where and when the systems can operate. Navigation using Earth’s magnetic anomaly field, which is globally available at all times, shows promise to overcome many of these limitations. We present a navigation framework that uses Earth’s magnetic anomaly field as a navigation signal to aid an inertial navigation system in an aircraft. The filter utilizes ultra-accurate optically pumped cesium magnetometers to make scalar intensity measurements of Earth’s magnetic field and compare them with a map using a particle filter approach. The accuracy of these measurements allows observability of not only the inertial navigation system errors but also the temporal effects of Earth’s magnetic field, which corrupt the navigation signal. These temporal effects are thoroughly analyzed, and we present a simple model that allows near worldwide use of the navigation filter. We analyze the dependencies on altitude and magnetic storm activity in a realistic simulation using data from test flights and magnetic observatories.

Autonomous Vehicle Dynamic Model‐Based Navigation for Small UAVs

Abstract: This paper presents a novel approach to autonomous navigation for small UAVs, with no extra sensor added to the conventional INS/GNSS setup. The proposed method significantly increases the accuracy and reliability of autonomous navigation, especially for small UAVs with low-cost IMUs. This improvement is of special interest in the case of GNSS outages, where inertial coasting drifts very quickly. In the proposed architecture, the VDM provides the estimate of position, velocity, and attitude, which is updated within a filter based on available observations, such as IMU data or when available, GNSS measurements. The filter is capable of estimating wind velocity and dynamic model parameters, in addition to navigation states and IMU sensor errors. Monte Carlo simulations reveal major improvements in navigation accuracy compared to conventional INS/GNSS systems during GNSS outages of 5 min. A discussion on the observability is also presented at the end. Copyright (C) 2016 Institute of Navigation.

The Effect of Correlator and Front‐End Design on GNSS Pseudorange Biases for Geodetic Receivers

Abstract: GNSS satellite signal deformations cause individual biases in the pseudorange observable. These biases are typically mitigated by using external correction values. However, the biases are the result of the correlator's tracking response and thus depend on correlator and front-end design of the receiver. As a result, different receivers are likely to exhibit inconsistent biases, for which the available corrections may not be applicable. The residual errors lead to adverse effects for SPP and PPP applications with pseudoranges and can also hinder carrier-phase ambiguity resolution. Bias inconsistencies of modern GNSS receivers are studied in a zero-baseline test. Differential pseudorange biases between receivers are computed for GPS, GLONASS, Galileo, and BeiDou satellites for all commonly tracked signals. The effects on pseudorange-based positioning applications and carrier-phase ambiguity resolution are discussed.

The Limits of In-Run Calibration of MEMS Inertial Sensors and Sensor Arrays

Abstract: MEMS accelerometers and gyroscope triads now cost less than $10, potentially opening up many new applications. However, these sensors require calibration prior to navigation use. This paper determines the maximum tolerable sensor errors for in-run calibration techniques using a basic Kalman filter by developing criteria for filter failure and performing Monte Carlo simulations for a range of different sensor specifications, and both car and UAV motion-profiles. Gyroscope bias is found to be the most significant with the maximum tolerable value of its SD varying between 0.75 and 2.6 deg/s depending on the value of the specification of the other sensor sources. The paper shows that pre-calibration and smart array techniques could potentially enable in-run calibration to be applied to lower-quality sensors. However, the estimation of scale-factor cross-coupling and gyroscope g-dependent errors could potentially be critical. Armed with this knowledge, designers can avoid both unnecessary design complexity and computational load of over-engineering and the poor navigation performance of inadequate filters.

Fast Precise Point Positioning: A System to Provide Corrections for Single and Multi‐Frequency Navigation

Abstract: Fast Precise Point Positioning (Fast-PPP) provides Global Navigation Satellite System corrections in real-time. Satellite orbits and clock corrections are shown to be accurate to a few centimeters and a few tenths of a nanosecond which, together with the determination of the fractional part of the ambiguities, enable global high-accuracy positioning with undifferenced Integer Ambiguity Resolution. The new global ionospheric model is shown to provide corrections accurate at the level of 1 Total Electron Content Unit over well-sounded areas and Differential Code Biases at the level of tenths of a nanosecond. These corrections are assessed with permanent receivers, treated as rovers, located at 100 to 800 kilometers from the reference stations of the ionospheric model. Fast-PPP achieves decimeter-level of accuracy after few minutes, several times faster than single- and dual-frequency ionospheric-free solutions, using a month of Global Positioning System data close to the last Solar Maximum and including equatorial rovers.

Zero-baseline Analysis of GPS/BeiDou/Galileo Between-Receiver Differential Code Biases (BR-DCBs): Time-wise Retrieval and Preliminary Characterization

Abstract: When sensing Earth's ionosphere using multiple Global Navigation Satellite Systems (GNSSs), special care needs to be taken with the receiver differential code bias (DCB) contributions to the error budget. We propose a method that is able to time-wisely retrieve the Between-Receiver DCBs (BR-DCBs) from code measurements collected by a zero-baseline setup, thereby eliminating most common error sources. We base our investigations on dual-frequency GPS (L1 + L2), BeiDou (B1 + B2), and Galileo (E1 + E5a) measurements collected in 2013 with a 30 second sampling rate by four multi-GNSS receivers of three types connected to one common antenna. For each receiver-pair, we determine the time-wise estimates of GPS/GEO/IGSO/MEO/Galileo BR-DCBs from the corresponding code measurements. We confirm that (1) the time-wise estimates of BR-DCBs for all tested receiver-pairs exhibit good intra-day stability and (2) the daily weighted average (DWA) estimates of GEO/IGSO/MEO BR-DCBs are inconsistent for receiver-pairs of mixed type, due to the presence of BeiDou code inter-satellite-type biases (ISTBs). We also identify likely factors accounting for variability in DWA estimates of BR-DCBs over a one-year interval. Copyright © 2016 Institute of Navigation Copyright © 2016 Institute of Navigation

Estimation of Galileo Uncalibrated Hardware Delays for Ambiguity-Fixed Precise Point Positioning

Abstract: Ambiguity fixing in Precise Point Positioning (PPP) has been extensively studied in recent years. The provision of uncalibrated hardware delays (UHDs) to the PPP algorithm, on top of precise orbits and clocks, allows the recovery of the integer values of the carrier-phase ambiguities. Experimental results show that integer ambiguity resolution increases the accuracy in the position domain. Most of the research so far has been done on GPS, where the wide- and narrow-lane approach for ambiguity resolution has proven successful. In the context of multi-GNSS PPP, the aim of this study is to extend the method to Galileo. Initial results for UHD estimation for Galileo satellites are presented. The contribution of ambiguity-fixing to GPS+Galileo PPP is assessed.

Assessing the Occurrence Pattern of Large Ionospheric TEC Gradients over the Brazilian Airspace

Abstract: We investigate the occurrence pattern of equatorial plasma bubbles and the corresponding ionospheric gradients over a section of the Brazilian airspace in 2014/2015. The GPS-derived total electron content (TEC) data from a chain of receiver stations were used in this study to compute the TEC gradients along the southern crest of the equatorial ionospheric anomaly region over Brazil. Here, we present a few illustrative examples to delineate the general qualitative features of equatorial plasma bubbles in this region, and the varying degree of TEC gradient magnitudes associated with these bubbles. We also inferred the overall probability distribution function of the computed TEC gradient magnitudes in this region, which extend up to 1000 mm/km at the GPS L1 frequency. Copyright © 2016 Institute of Navigation.

Tracking Error Modeling in Presence of Satellite Imperfections

Abstract: Modeling both nominal distortions and signal anomalies (i.e. Evil waveforms, ICAO threat models) is crucial for an accurate user error budget for SBAS and GBAS (multi- frequency, multi-constellation). Such analysis of particu- lar interest for the ongoing standardization work of L1- L5 SBAS services. In this paper we propose a method to jointly estimate the analogue and the digital distortions. This comes very useful in those cases in which the esti- mates of the two satellite imperfections are interdependent, e.g. when the time-bandwidth product is small. The impact of both satellite imperfections on the ranging performance of a GNSS receiver is assessed by means of analytical for- mulas which make use of the Cross-Power Spectrum (CPS) between the distorted and the ideal signal, and of the Power Spectral Density (PSD) of the nominal (ideal) signal.

3D Multi-Copter Navigation and Mapping Using GPS, Inertial, and LiDAR

Abstract: As the use of unmanned aerial vehicles has become more prevalent, the need for a reliable three-dimensional positioning and navigation capability is required to enable operation in challenging environments where the Global Positioning System (GPS) may not be available. For many of these environments, there may not be one particular method to solve the positioning navigation problem. Therefore, we have selected a set of dissimilar sensor technologies and implemented an integrated navigation method that can support reliable operation in an outdoor and structured indoor environment. The integrated navigation design is based on three types of sensors: a GPS receiver, an inertial measurement unit, and three laser scanners. This paper will show that decimeter-level relative positioning accuracies can be achieved for structured indoor operations and that when segments are included where GPS is available, the platform's trajectory is globally anchored with meter-level accuracy. A secondary goal of the proposed method is the generation of a three-dimensional map of the environment. Copyright © 2016 Institute of Navigation Copyright © 2016 Institute of Navigation

A Comparative Analysis of Adaptive Notch Filtering and Wavelet Mitigation against Jammers Interference

Abstract: Global Navigation Satellite System (GNSS) receivers are vulnerable to the threats of unintentional interference generated by other communication systems and intentional interference known also as jamming. In particular, the intentional transmission of Radio Frequency (RF) interference with the goal of disrupting one or more of the received GNSS frequency bands can disrupt the operation of GNSS receivers over a wide target area. This paper provides a comparison between two interference mitigation techniques at the digital signal processing level. The traditional adaptive notch filtering has been compared with a more innovative technique based on the use of the Wavelet Packet Decomposition (WPD). Using simulated GNSS jammed scenarios and a software-defined GNSS receiver, results indicate the benefits of WPD relative to notch filtering. Further tests using love interference signals, and both a software and commercial hardware receiver, demonstrate the benefits of WPD in terms of signal quality and position domain metrics.

GNSS Integrity in The Arctic

Abstract: Growing activity in the Arctic calls for high integrity navigation in this region. This can be achieved using Global Navigation Satellite Systems (GNSS) in conjunction with Satellite Based Augmentation Systems (SBAS) or Advanced Receiver Autonomous Integrity Monitoring (ARAIM). Single frequency GPS-only SBAS is in service in some regions today and is reliant on ground and space infrastructure. ARAIM will be more autonomous and will rely on the multitude of signals and core constellations coming in the future. Here, we examine both SBAS and ARAIM in the context of aviation and maritime requirements in the Arctic. Results demonstrate that the introduction of multi-frequency and multi-constellation to these systems enables navigation safety in the Arctic. SBAS brings aircraft precision approach as well as precise maritime operations such as mapping. ARAIM also supports precision approach in addition to autonomous ice navigation at sea but falls short of precision maritime requirements.

Estimation of effective swath width for dual-head multibeam echosounder

Abstract: Abstract Many surveying companies and maritime institutions are now using multibeam systems for their operations, either offshore or in coastal and inland waters. Since the time the first multibeam echosounder appeared (late 1970s) the technology has advanced enormously. Modern systems now boast far greater angular coverage (typically 120°-150°) and form hundreds of beams. Dual-head multibeam systems can potentially cover the entire sector (180°) underneath the ship. However surveyors must be aware that the outer beams of these acoustic systems return the most errors causing that the effective swath width is shorter than what the manufacturers declare. The paper presents the methods of estimating of effective (usable) swath width of dual-head multibeam echosounder EM 3002D. Results of the hydrographic survey performed by the polish navy survey ship ORP ‘Arctowski’ have been showed in the article.

Dependence of GLONASS Pseudorange Inter‐frequency Bias on Receiver–Antenna Combination and Impact on Precise Point Positioning

Abstract: GLONASS pseudorange observations are affected by inter-frequency channel biases (ICBs) due to the frequency division multiple access (FDMA) satellite signal structure. This research estimated the GLONASS pseudorange inter-frequency channel biases using 350 IGS stations, based on 32 receiver types and over 11 antenna types over a period of 1 week, DOY 195 to 201 in 2013. An improvement of 19% and 1% was observed after calibrating out the pseudorange ICBs, in the horizontal and vertical components, respectively, considering a 20-min convergence period. Two major contributions are presented. The first contribution is the presentation of the four different scenarios involving varying different receiver and antenna types and how that variability affects the characteristics of ICBs. Attention is also drawn to the characteristics of the Analysis Center (AC) satellite common mean errors. In relation to the antipodal nature of the GLONASS satellites, the correlation of the GLONASS frequency numbers with the AC-satellite common mean errors is addressed.

GBAS Availability Assessment and Modeling of Ionospheric Scintillation Effects

Abstract: The Japan Aerospace Exploration Agency (JAXA) is promoting a research and development program named DREAMS (Distributed and Revolutionary Efficient Air-safety Management System) to contribute to the realization of next-generation air transportation systems. One of the most important targets of this program is a reliable, high-precision navigation system. This paper describes an investigation into the effects of ionospheric plasma bubbles on the availability of Ground-based Augmentation Systems (GBAS). Although the effects of ionospheric anomalies on GBAS integrity have been well researched, their effects on GBAS availability have not received much attention. Since ionospheric plasma bubbles occur much more frequently than the Storm-enhanced Density (SED) phenomenon in regions at low magnetic latitude, their effects on availability as well as on integrity should be investigated.

Algorithms of Position and Velocity Estimation in GPS Receivers

Abstract: Abstract Processing of signals in Global Positioning System (GPS) receivers includes numerous signal and data operations leading to calculation of coordinates and velocities of satellites in global Earth-Centered Earth-Fixed (ECEF) frame of reference as well as pseudoranges and delta-ranges between the user and all the tracked GPS satellites. Further processing of these data consists in estimation of the user’s position, velocity and time (PVT) and nowadays it is usually realized by means of an Extended Kalman Filters (EKF). The choice of measuring data processed by the Kalman filter significantly influences the accuracy of navigation solution. In simpler GPS receivers, the estimation of user’s position and velocity is based on pseudoranges only, whereas in more advanced ones delta-ranges are also applied. The paper describes both possible solutions and compares the accuracy of estimation of the user’s position and velocity in both cases. The comparison is based on simulation results, which are included in the paper.

Methods of improving the jamming resistance of GNSS receiver

Abstract: Abstract Jamming of GNSS signals can be both a consequence of accidental activities and an intentional act. This issue is lately discussed as an essential threat for the use of satellite navigation systems. This is especially dangerous in the face of common usage of GPS - like systems in everyday life and the great belief of everyday users in the truth of devices indications. In spite of the legal prohibition of using them, jammers are commonly accessible, especially in the Internet. Until recently even specialists have shared the conviction that the broadband GPS signal is not a subject of disturbances in contrast to older wireless communication techniques because its power level is below natural level of noises and in addition it is randomly coded. But nowadays jammers are very often successfully applied, which is confirmed in many reports. The average user has not the suitable knowledge about the specificity of the jamming and has no technical possibilities of the detection of jammer signals. Receivers, which can indicate the presence of perturbative signals, became accessible a few months ago only. Presently accessible jamming monitors can also determine the direction of interferer signal transmission. There are also specially designed receivers with anti-jamming mechanism, which are, however, not commonly accessible. The possible way of countermeasure the jamming in the GNSS receiver are discussed in this paper.

Peculiarities of zigzag behaviour in linear models of ship yaw motion

Abstract: Abstract The present survey, as part of larger project, is devoted to properties of pure linear models of yaw motion for directionally stable ships, of the first- and second-order, sometimes referred to as the Nomoto models. In rather exhaustive way, it exactly compares and explains both models in that what is being lost in the zigzag behaviour, if the reduction to the simpler, first-order dynamics (K-T model) is attempted with the very famous [Nomoto et al., 1957] approximation: T = T1 + T2 - T3. The latter three time constants of the second-order model, more physically sound, are strictly dependent on the hydrodynamic coefficients of an essential part of the background full-mission manoeuvring model. The approximation of real ship behaviour in either of the mentioned linearity orders, and the corresponding complex parameters may facilitate designing and evaluating ship steering, and identifying some regions of advanced nonlinear models, where linearisation is valid. As a novel outcome of the conducted investigation, a huge inadequacy of such a first- -order model for zigzag simulation is reported. If this procedure is used for determining steering quality indices, those would be of course inadequate, and the process of utilizing them (e.g. autopilot) inefficient.

Global Satellite Navigation Systems at High Latitudes, Visibility and Geometry

Abstract: Abstract Since few years the significance of the navigation at high latitudes (60° and more), increases incessantly, e.g. northern passages between Atlantic and Pacific Waters. In these regions the user’s position can be obtained mainly from global satellite navigation systems (SNS). Nowadays (September 2016) two systems, American GPS and Russian GLONASS, are fully operational, two next, Galileo in Europe and BeiDou in China, are under construction. As the error of user’s position obtained from these systems depends on geometry factor DOP (Dilution Of Precision) among other things the knowledge of the number of satellites visible by this user above given masking elevation angle Hmin and the distributions of DOP coefficient values, GDOP in particular, is very important. The lowest and the greatest number of satellites visible in open area by the user at high latitudes for different Hmin, the percentage of satellites visible above angle H, distributions of satellites azimuths and GDOP coefficient values for different Hmin for all these four SNSs at different user’s latitudes (beginning from 60°) and other distributions are presented in the paper. All calculations were made for constellation of BeiDou 27 MEO satellites, Galileo 24 satellites, GLONASS 24 and GPS 31 satellites.

Accuracy of positioning Autonomous Biomimetic Underwater Vehicle using additional measurement of distances

Abstract: Abstract The article describes a study of problem of estimating the position coordinates of Autonomous Biomimetic Underwater Vehicle (ABUV) using two methods: dead reckoning (DR) and extended Kalman filter (EKF). In the first part of the paper, navigation system of ABUV is described and scientific problem with underwater positioning is formulated. The main part describes a way of estimating the position coordinates using DR and EKF and a numerical experiment involving motion of ABUV along the predetermined test distance. The final part of the paper contains a comparative statistical analysis of the results, carried out for assessing the accuracy of estimation of the position coordinates using DR and EKF methods. It presents the generalized conclusions from the research and the problems relating to the proper placement of the components of the system measuring distances.

Extending Required Navigation Performance to Include Time Based Operations and the Vertical Dimension

Abstract: New Air Traffic Management (ATM) concepts aim at enabling an increase in air traffic while at the same time maintaining the same or a better level of safety. Key enablers for these new ATM concepts are evolving technologies which are successively included in aircraft guidance and control functions. Some components of theses evolving ideas were already introduced in the ATM environment– such as Required Navigation Performance (RNP) - or are in the process of being researched and tested such as Required Time of Arrival (RTA) or advanced RNP. Moreover, with the evolution of air to ground datalink communications, full four-dimensional trajectories could be negotiated between air traffic control and the aircraft and flown in free route airspace [0]. While research into datalink communications, the trajectory management process and conflict resolutiosn are actively being pursued by the ATM research community, so far no requirements for a continuous four dimensional airborne navigation performance have been investigated or specified. Four-dimensional navigation requirements would describe the minimum capability of the aircraft to adhere to the trajectory that was assigned by or negotiated with ATC in the cross-track, along track, vertical and temporal dimension. As such, they would define a 4D RNP concept evolving from the current cross-track RNP specifications [1]. Presently, RNP is a designator for an area navigation system for use within a performance based navigation concept. RNP also includes continuous monitoring of navigation performance and alerting of the pilot in case of failure [1]. Only lateral (or cross-track) RNP accuracy is indicated by a number following the letters RNP, (i.e. RNP 0.3 for 0.3 nm accuracy). In this case, accuracy relates to the Total System Error (TSE) which is a combination of the Flight Technical Error (FTE) and the Navigation Sensor Error (NSE), and designates the 95% uncertainty bounds. Vertical guidance during an RNP operation is accomplished using barometrical vertical navigation (Baro VNav). Limiting factors for vertical navigation are the barometric uncertainty of the altimeter and the human factor in determining the pressure value for the pilot to set in the airplane and no monitoring or position error estimation exists for such Baro VNav systems. In the work presented here, we derive requirements for the missing dimensions vertical, along track and time from high level ICAO prerequisites and presently applicable separation standards. In addition, we introduce new algorithms based on augmented GNSS that continuously monitor the system performance in those additional dimensions. A four dimensional RNP concept needs to be seen as an extension of the current RNP definitions and must include a required navigation performance for the vertical and the along track dimension as well as for time. The along-track or longitudinal component is tightly connected to the time component by means of speed and the RTA at each given waypoint. Thus, from a top-down point of view, it makes sense to define requirements jointly for the along-track / longitudinal component and time through the concept of required time of arrival and speed control. Vertical Required Navigation Performance (vRNP) could be specified as a separate component, since it is largely independent of the other dimensions. Vertical performance requirements are already formulated to some degree for legacy systems. Attachment A to Volume 2 of [1] describes the accuracy requirements of the altimeter system for Baro VNav approach operations. The ICAO documentation on Reduced Vertical Separation Minimums (RVSM) [2] specifies the integrity requirements for altitude in a high density enroute traffic environment. For the vertical RNP, we merge the existing requirements from both documents. Assuming a zero mean Gaussian distribution for the altitude error, a system with a standard deviation of 5.05 m can fulfill this requirement. The limiting factor is the accuracy required by [1], whilst [2] would allow a tail heavy distribution. It is notable that RVSM requires about the same error probability for a vertical error exceeding 90m which the PBN manual requires for an error exceeding 15m during instrument approach. In order to complete the requirement for vRNP, we suggest a monitoring and alerting function which warns the pilot in the case of malfunctions of the barometric altimeter. The monitor performance must also comply with the previously defined error curve. We show that an algorithm using a GNSS solution augmented by a regional augmentation system such as WAAS or EGNOS can be used for monitoring the barometric altitude. The suggested system is capable of monitoring altitude deviations in level flight and up to a certain descent or climb path angle. In the case of longitudinal and time navigation performance no such prerequisites as for vertical RNP exist. Same track separations considerations are largely based on collision risk models that are specifically tailored to a target airspace. Here, for along track RNP and the desired target level of safety given by ICAO, we define requirements for arrival at any point on a trajectory at a given time. Required arrival time accuracy at waypoints is be closely linked to a minimum along track separation requirement as well as separation requirements at merging points of trajectories. We found that the required along track accuracy depends largely on the number of aircraft on a specific route and their respective speed. Results show that, for example, in order to reach a target level of safety of 5x10^-9 with 10 aircraft per hour on a given route crossing a given point, an along track accuracy of 2875 m is needed. With a speed of 400 knots this is equivalent to a required temporal accuracy of 13.5 s assuming no uncertainty on the speed. Along –track position and velocity monitoring is already accomplished by the algorithm for receiver autonomous integrity monitoring (RAIM). The onboard clock needs to be synchronized to a common time base, preferably UTC as it is already used as common reference time for aviation. Since satellite navigation systems are time based, the navigation solution already incorporates clock synchronization with the GNSS time base accurately up to a few milliseconds. Therefore, if the flight management computer is synchronized with GPS time, a precise time reference is always assured, as long as a navigation solution is available. Regional augmentation systems can support the clock accuracy by detecting common system biases in the satellite navigation system that would otherwise map to the clock correction. For redundancy of the clock monitoring, we recommend that two independent systems are used to derive separate clock solutions. One form of cross checking can be a comparison of the UTC time derived from GPS with the UTC time derived from EGNOS or Galileo.

Operational Scenarios for Maritime Safety in the Baltic Sea

Abstract: The project Enhanced Situational Awareness to Improve Maritime Safety in the Baltic (BONUS ESABALT) studies the feasibility of data crowdsourcing among marine stakeholders in the Baltic Sea for enhancing maritime safety. This paper describes the system architecture, and by use of practical maritime scenarios demonstrates the system utility. These scenarios are categorized under maritime safety, intelligent navigation, and environmental monitoring with cross-border cross-sector operability. The paper also summarizes the validation campaign performed onboard Viking Line’s cruise ship M/S Amorella, operating between Turku and Stockholm. Analysis of the vessel-generated data and end-user requirements recorded during this voyage is expected to enable distillation of the most critical information for crowdsourcing in the maritime scenario. Finally, the paper compares the BONUS ESABALT project with the state-of-the-art and provides the estimated economic and policy impact of the proposed system in the Baltic Sea Region.