Showing papers in "Artificial Satellites in 2013"

Detecting Meaconing Attacks by Analysing the Clock Bias of Gnss Receivers

Abstract: Existing Global Navigation Satellite Systems offer no authentication of their satellite signals towards their civilian users. As a consequence, several types of GNSS-related attacks, including meaconing, may be performed and remain undetected. In the scope of the project “Developing a prototype of Localisation Assurance Service Provider”, which is funded by ESA and realised by the company itrust consulting and the University of Luxembourg, a methodology to visualise the beginnings and the ends of meaconing attacks by monitoring the clock bias of an attacked receiver over time was developed. This paper presents an algorithm that is based on this attack visualisation technique and is capable of detecting meaconing attacks automatically. Experiments in a controlled environment confirmed that the chosen methodology works properly. In one of these tests, for example, six meaconing attacks were simulated by using a GNSS signal repeater. The algorithm was able to detect the beginnings and the ends of all six attacks, while resulting in no more than two false positives, even though the average delay introduced by the meaconing stations (repeater) was just 80 nanoseconds.

On Egnos Monitoring in Local Conditions

Abstract: Any SBAS system should deliver to the user corrections to pseudoranges as well as information about the system integrity. In theory, as soon as the system is permanently monitored by RIMS stations, it is impossible to deliver the fault information to the user. However many observations shows that accuracy of EGNOS service in the same time are different in different places, which shows the influence of local conditions on them. In addition evidences on possibilities in jamming or spoofing of GPS signals should be seriously taken into account. According to many sources of information, among them observations of authors, present accuracy of EGNOS service has better than declared. In fact EGNOS accuracy is about 1,5m (95%), but availability of the service happens still controversial and it has random character. According to reports essential differences as well as lack of correlation of this parameter in the different point of observations has been observed. So in author’s opinion Local Monitoring of EGNOS service can contribute to better confidence of local users, especially in critical operations, like for example berthing of big ships or in landing operations with EGNOS procedures. An example of such system which works in real time has been elaborated in Polish Naval Academy and will be presented. Paper presented at the Conference on "SATELITARNE METODY WYZNACZANIA POZYCJI WE WSPO�CZESNEJ GEODEZJI I NA WIGACJI" (2012, Warsaw, Poland)

A Comparison Between Numerical Differentiation and Kalman Filtering for a Leo Satellite Velocity Determination

Abstract: The kinematic orbit is a time series of position vectors generally obtained from GPS observations. Velocity vector is required for satellite gravimetry application. It cannot directly be observed and should be numerically determined from position vectors. Numerical differentiation is usually employed for a satellite’s velocity, and acceleration determination. However, noise amplification is the single obstacle to the numerical differentiation. As an alternative, velocity vector is considered as a part of the state vector and is determined using the Kalman filter method. In this study, velocity vector is computed using the numerical differentiation (e.g., 9-point Newton interpolation scheme) and Kalman filtering for the GRACE twin satellites. The numerical results show that Kalman filtering yields more accurate results than numerical differentiation when they are compared with the intersatellite range-rate measurements.

Analysis of Current Position Determination Accuracy in Natural Resources Canada Precise Point Positioning Service

Abstract: Abstract Precise Point Positioning (PPP) is a technique used to determine highprecision position with a single GNSS receiver. Unlike DGPS or RTK, satellite observations conducted by the PPP technique are not differentiated, therefore they require that parameter models should be used in data processing, such as satellite clock and orbit corrections. Apart from explaining the theory of the PPP technique, this paper describes the available web-based online services used in the post-processing of observation results. The results obtained in the post-processing of satellite observations at three points, with different characteristics of environment conditions, using the CSRS-PPP service, will be presented as the results of the experiment. This study examines the effect of the duration of the measurement session on the results and compares the results obtained by working out observations made by the GPS system and the combined observations from GPS and GLONASS. It also presents the analysis of the position determination accuracy using one and two measurement frequencies

Gnss signal processing in gpu

Abstract: Signal processing of the global navigation satellite systems (GNSS) is a computationally demanding task due to the wide bandwidth of the signals and their complicated modulation schemes. The classical GNSS receivers therefore utilize tailored digital signal processors (DSP) not being flexible in nature. Fortunately, the up-to-date parallel processors or graphical processing units (GPUs) dispose sufficient computational power for processing of not only relatively narrow band GPS L1 C/A signal but also the modernized GPS, GLONASS, Galileo and COMPASS signals. The performance improvement of the modern processors is based on the constantly increasing number of cores. This trend is evident not only from the development of the central processing units (CPUs), but also from the development of GPUs that are nowadays equipped with up to several hundreds of cores optimized for video signals. GPUs include special vector instructions that support implementation of massive parallelism. The new GPUs, named as general-purpose computation on graphics processing units (GPGPU), are able to process both graphic and general data, thus making the GNSS signal processing possible. Application programming interfaces (APIs) supporting GPU parallel processing have been developed and standardized. The most general one, Open Computing Language (Open CL), is now supported by most of the GPU vendors. Next, Compute Unified Device Architecture (CUDA) language was developed for NVidia graphic cards. The CUDA language features optimized signal processing libraries including efficient implementation of the fast Fourier transform (FFT). In this paper, we study the applicability of the GPU approach in GNSS signal acquisition. Two common parallel DSP methods, parallel code space search (PCSS) and double-block zero padding (DBZP), have been investigated. Implementations in the C language for CPU and the CUDA language for GPU are discussed and compared with respect to the acquisition time. It is shown that

The Algorithm for Determining the Coordinates of a Point in Three-Dimensional Space by Using the Auxiliary Point

Abstract: ABSTRACT During the process of satellite navigation, and also in the many tasks of classical positioning, we need to calculate the corrections to the initial (or approximate) location of the point using precise measurement of distances to the permanent points of reference (reference points). In this paper the authors have provided a way of developing Hausbrandt's equations, on the basis of which the exact coordinates of the point in two-dimensional space can be determined by using the computed correction to the coordinates of the auxiliary point. The authors developed generalised equations for threedimensional space introducing additional fixed point and have presented proof of derived formulas.

Rosborough formulation in satellite gravity gradiometry

Abstract: Following the launch of CHAMP, a new era was born in the gravity field determination from satellite observations. Many methods have been proposed and applied for the recovery of the Earth's gravity field from the observations of the satellite missions CHAMP, GRACE and GOCE. This paper deals with the Rosborough formulation in gravity field modelling. This formulation is derived from the transformation of time-wise representation from the orbital into the spherical coordinate systems. Base functions of the Rosborough formulation depend on the type of the functional of the gravity field and the inclination of the orbit. Unlike the space-wise approach, the Rosborough approach can easily deal with both isotropic and non-isotropic functionals. The proposed formulation is implemented on the GOCE data in order to show its efficiency. Numerical results show that the Rosborough formulation is a powerful and efficient tool in the case of GOCE gradiometry data processing.

Spectral Analysis of Borowiec SLR Data For Spin Determination Of Geodetic Satellite EGP

Abstract: Borowiec 10 Hz Satellite Laser Ranging (SLR) station is capable to measure spin of the Japanese Experimental Geodetic Satellite (EGP). Spectral analysis of 391 passes measured from March 10, 1994 to November 27, 2009 gives frequency signal representing the 3 rd and the 6 th harmonics of the satellite spin rate. Analysis of this signal, corrected for the apparent effects, indicates en exponential slowing down of the satellite: the spin rate decreases according to the equation f = 671.115907 · exp(-4.08324 x 10 -5 · D) (mHz), where D is a day after launch. More than 15 years of the SLR measurements allowed investigating the initial spin rate of the satellite fini = 671.116, RMS = 0.203 (mHz) (initial spin period Tini = 1.49006, RMS = 0.0007 (s)).

Symmetric Neutral-Atmosphere Mapping Functions: A Review of the State-Of-The-Art

Abstract: The aim of this paper is to review of six recent symmetric mapping functions. The mapping function can be largely used for GPS meteorological measurements, InSAR atmospheric corrections and precise measurements of very long baseline interferometry (VLBI). These spacebased techniques use radio signal that propagate through the Earth's atmosphere. The electrically-neutral region, predominantly the troposphere, affects the speed and direction of travel of radio waves leading to existence of excess path. The mapping function models the elevation angle dependence of the delay. Within the past decade, significant improvements have been achieved in order to use of Numerical Weather Models (NWM) for geodetic positioning. Ray-tracing algorithms have been performed through refractivity shells retrieved from NWMs in order to relate zenith delays to slant delays. Therefore, there seems to be a real need for deep review of recent developments in the mapping function domain. This paper proposes a comprehensive review of the symmetric mapping functions state of the art, their spatio-temporal variations and used NWM and generic models. Niell Mapping Function (NMF), Vienna Mapping Function (VMF1), University of New Brunswick-VMF1 (UNB-VMF1) mapping functions, Global Mapping Function (GMF) and Global Pressure and Temperature (GPT2)/GMF are reviewed in this paper.

Construction of the Numerical and Semi-Analytical Solutions of the Rigid Earth Rotation at a Long Time Intervals

Abstract: This research is the continuation of our studies of the rigid Earth rotation at a long time intervals (Pashkevich V.V. and Eroshkin G.I., 2005). The main purpose of this investigation is the construction of the new high-precision Rigid Earth Rotation Series 2012 (RERS2012), dynamically adequate to the JPL DE406/LE406 ephemeris (Standish E. M., 1998). The dynamics of the rotational motion of the rigid Earth is studied numerically by using Rodrigues-Hamilton parameters over 2000 and 6000 years. The numerical solution of the rigid Earth rotation is implemented with the quadruple precision of the calculations. The orbital motions of the disturbing celestial bodies are defined by the DE406/LE406 ephemeris. The initial conditions of the numerical integration are taken from SMART97 (Bretagnon P. et al., 1998) and S9000 (Pashkevich V.V. and Eroshkin G.I. 2005). The results of the numerical solutions of the problem are compared with the semi-analytical solutions of the rigid Earth rotation (SMART97 and S9000, respectively) with respect to the fixed ecliptic of epoch J2000. The investigation of these discrepancies is carried out by the least squares and spectral analysis methods for the relativistic (Kinematical) case, in which the geodetic perturbations (the most essential relativistic perturbations) in the Earth rotation are taken into account. As a result, the Rigid Earth Rotation Series (RERS2012) is constructed, which is dynamically adequate to the DE406/LE406 ephemeris over 2000 and 6000 years. The discrepancies between the new numerical solutions and the semi-analytical solutions of MRS2012 do not surpass 12 μas over 2000 year time interval and 2 mas over 6000 year time interval. Thus, the result of the comparison demonstrates a good consistency of RERS2012 series with the DE406/LE406 ephemeris.

Influence of Ephemeris Error on GPS Single Point Positioning Accuracy

Abstract: Abstract The Global Positioning System (GPS) user makes use of the navigation message transmitted from GPS satellites to achieve its location. Because the receiver uses the satellite's location in position calculations, an ephemeris error, a difference between the expected and actual orbital position of a GPS satellite, reduces user accuracy. The influence extent is decided by the precision of broadcast ephemeris from the control station upload. Simulation analysis with the Yuma almanac show that maximum positioning error exists in the case where the ephemeris error is along the line-of-sight (LOS) direction. Meanwhile, the error is dependent on the relationship between the observer and spatial constellation at some time period.

Egnos Limitations over Central and Eastern Poland - Results of Preliminary Tests of Egnos-Eupos Integration Project

Abstract: Abstract The problem of insufficient accuracy of EGNOS correction for the territory of Poland, located at the edge of EGNOS range is well known. The EEI PECS project (EGNOS EUPOS Integration) assumes improving the EGNOS correction by using the GPS observations from Polish ASG-EUPOS stations. One of the EEI project tasks was the identification of EGNOS performance limitations over Poland and services for EGNOSS-EUPOS combination. The two sets of data were used for those goals: statistical, theoretical data obtained using the SBAS simulator software, real data obtained during the measurements. The real measurements were managed as two types of measurements: static and dynamic. Static measurements are continuously managing using Septentrio PolaRx2 receiver. The SRC permanent station works in IMAGE/PERFECT project. Dynamic measurements were managed using the Mobile GPS Laboratory (MGL). Receivers (geodetic and navigation) were working in two modes: determining navigation position from standalone GPS, determining navigation position from GPS plus EGNOS correction. The paper presents results of measurements’ analyses and conclusions based on which the next tasks in EEI project are completed

Testing the Number of IGS Stations Required for Accurate Alignment of the Thai GPS Network and ITRF2005 Using the Gipsy Software

Abstract: Since its introduction in 1990s, the GPS Precise Point Positioning (PPP) technique has been widely used for many high precision positioning applications such as the study of tectonic plate motion, establishment of national and regional reference frames and so on. Among the GPS PPP software packages, the GIPSY-OASIS II software package is the one of the most popular software package used by many research institutes worldwide. The processing of GPS data with the GIPSY-OASIS II software requires three main steps. The first step is to compute a daily GPS solution for each station and the second step is to combine daily GPS solutions into a multi-day averaged solution. The final step is to transform these multi-day averaged solutions into the International Terrestrial Reference Frame (ITRF) coordinate solution and this step generally requires the use of available International GNSS service (IGS) stations to compute the required transformation parameters. In order to obtain high precision ITRF coordinate solutions, an investigation on a selection of IGS stations used for aligning the multi-day averaged solution into ITRF is therefore needed. This study aims to investigate the effect of number of IGS stations used for aligning the multi-day averaged solutions into the final ITRF coordinate solution in Thai region. Data from two different GPS campaigns (with epochs before and after the 2004 SumatraAndaman earthquake) measured by the Royal Thai Survey Department (RTSD) were used in this investigation. By varying the number of IGS station used in the alignment step, results indicate that the use of at least 16 IGS stations in the alignment process can produce reliable and accurate ITRF solutions especially those impacted by the large earthquake.

Evaluation of symmetric neutral-atmosphere mapping functions using ray-tracing through radiosonde observations

Abstract: The aim of this paper is to compare the validity of six recent symmetric mapping functions. The mapping function models the elevation angle dependence of the tropospheric delay. Niell Mapping Function (NMF), Vienna Mapping Function (VMF1), University of New BrunswickVMF1 (UNB-VMF1) mapping functions, Global Mapping Function (GMF) and Global Pressure and Temperature (GPT2)/GMF are evaluated by using ray tracing through 25 radiosonde stations covering different climatic regions in one year. The ray-traced measurements are regarded as “ground truth”. The ray-tracing approach is performed for diverse elevation angle starting at 5 o to 15 o .� The results for both hydrostatic and non-hydrostatic components of mapping functions support the efficiency of online-mapping functions. The latitudinal dependence of standard deviation for 5 o is also demonstrated. Although all the tested mapping functions can provide satisfactory results when used for elevation angles above 15 o , for high precision geodetic measurements, it is highly recommended that the online-mapping functions (UNBs and VMF1) be used.� The results suggest that UNB models, like VMF have strengths and weaknesses and do not stand out as being consistently better or worse than the VMF1. The GPT2/GMF provided better accuracy than GMF and NMF. Since all of them do not require site specific data; therefore GPT2/GMF can be useful as regards its ease of use.

Effect of the glonass-specific receiver antenna phase center corrections on the results of european regional gnss network

Abstract: In the paper I investigated the effect of the GLONASS-specific receiver antenna phase center corrections on the results of a regional permanent GNSS network. I made anal- ysis, using Bernese GPS Software 5.0, of GPS-only and GPS-GLONASS (GNSS) observations collected at permanent sites in Europe. Two types of GNSS solutions were computed: with GPS phase center corrections used for observations of both systems, and with the system spe- cific corrections for observations of the respective system. The Bernese software was modified accordingly to use GLONASS specific corrections for GLONASS measurements. The results, i.e., coordinates and tropospheric zenith delays were analyzed and compared between computed solutions. Introducing GLONASS-specific receiver antenna phase center corrections did not im- prove the repeatability of the GNSS coordinate time series. Differences of coordinates between the two GNSS solutions were highly repeatable but offsets (biases) were observed; maximum bias for horizontal component was 1 mm and 4 mm for up component. Similar biases were observed for stations with the same antenna models. Periodic signal with a period of 1/3-year was found in difference time series between GPS and GNSS solutions for north component with a maximum peak-to-peak amplitude 2.8 mm. The periodic signal was attributed to GLONASS.

Development of an Integrated Digital Elevation Model for Safe Takeoff and Landing of the Aircraft

Abstract: . The article describes preliminary results of the augmentation of Global Navigation Satellite System/Inertial Navigation System positioning (GNSS/INS) by Digital Elevation Model (DEM) based on the data from the Shuttle Radar Topography Mission (SRTM) and data from field survey. The prototype software is developed to refer the position of the aircraft to DEM and informs the user about the current relevant flight parameters. The number of the parameters may be arbitrarily increased, however, currently we investigate the altitude above the terrain and the aircraft position relative to the descent path and airfield. The study provides some information on the local SRTM accuracy in relation to the field survey of the airfield "Dajtki" – Aeroclub of Warmia and Mazury in Olsztyn. Keywords: GNSS, GNSS/INS, air navigation, STRM – Shuttle Radar Topography Mission, DEM – Digital Elevation Model. 1. INTRODUCTION It is estimated that about one-third of serious accidents involving aircraft transport is the result of hitting the Earth's surface by a plane performing completely smooth and normal flight plan, run by well-prepared and efficient staff, these accidents are commonly called CFIT - Controlled Flight Into Terrain. One of the tragic example of CFIT accident is a crash of a Polish Air Force Tupolev Tu-154M aircraft in Smolensk (Russia), killing 96 people including President of Poland and his wife in April 2010. Since the beginning of commercial jet operations, more than 9,000 people have died worldwide because of CFIT. What’s more, CFIT accidents lead amongst all other air transport accident types and result in the greatest number of fatalities. It is estimated that CFIT accidents comprise about 25% of the total accidents and cause about 32% of the fatalities (ALAR Tool Kit, 2001). (ALAR stands for Approach and Landing Accident Reduction and it has been among the primary goals of the Flight Safety Foundation – FSF). It has also been estimated that about two-thirds of the accidents occur within eight miles of the runway with the majority of them occurring within three miles of the runway. Figure 1 presents vertical profiles of some recent CFIT accidents/incidents. In all of them there was a lack of vertical situation awareness. This leads