Cost-Effective GNSS Hardware for High-Accuracy Surveys and Its Prospects for Post-Processed Kinematic (PPK) and Precise Point Positioning (PPP) Strategies

This dissertation determines for the first time the vertical accuracy achievable with low-cost mass-market multi-frequency, multi-GNSS (LM3GNSS) receivers, and antennas in the context of Ellipsoid Reference Survey (ERS), usually employed in bathymetric operations aboard survey platforms. LM3GNSS receivers are relatively new in the market, and their emergence is driven by the automobile industry and several mass-market applications requiring location-based solutions at high accuracies. It is foreseeable that emerging hydrographic survey platforms such as autonomous surface vehicles, small unmanned aircraft, crowd-sourced bathymetric platforms, and offshore GNSS buoy will find LM3GNSS receivers attractive since they are power- and cost-effective (often less than $1,000 per unit). Previous studies have shown that some mass-market GNSS receivers\u27 positioning accuracy is at the sub-meter level in some positioning strategies, but the authors rarely discussed the vertical accuracy. In rare cases where attention is given to the vertical component, the experiment design did not address the dynamic antenna scenario typical of hydrographic survey operations and the positioning performance that meets the hydrographic survey community\u27s aspirations. The LM3GNSS receivers and low-cost antennas considered in this dissertation achieved vertical accuracies within 0.15 m at a 95% confidence level in simulated precise point positioning (PPP) and post-processed kinematic positioning strategies. This dissertation characterizes the signal strength, multipath, carrier-phase residuals, and code residuals in the measurement quality assessment of four LM3GNSS receivers and four low-cost antennas. The dissertation investigates the performances of the LM3GNSS receivers and low-cost antennas in different antenna-receiver pairings, relative to a high-grade GNSS receiver and antenna in simulated-kinematic and precise point positioning (PPP) strategies. This dissertation also shows that solutions with an uncalibrated antenna improve with a cloned ANTEX file making the results comparable to those achieved with high-end GNSS antenna. This dissertation also describes a GNSS processing tool (with graphic user interface), developed from scratch by the author, that implements, among others, orbit interpolation and geodetic computations as steps towards multipath computation and analysis. The dissertation concludes as follows: (1) The LM3GNSS hardware considered in this dissertation provides effective alternative positioning and navigation performance for emerging survey platforms such as ASV and sUAS. (2) LM3GNSS hardware can meet vertical positioning accuracy on the order of 0.15 m at a 95% confidence level in PPP strategy on less dynamic platforms. (3) LM3GNSS receivers can provide PPK solutions at medium (30 – 40 km) baselines with a vertical positioning accuracy better than 0.15m at a 95% confidence level. (4) LM3GNSS receivers in PPP strategy should meet IHO S-44 order-1 and order-2 in shallow waters. (5) Zephyr3 antenna, being a high-end GNSS antenna, may not always offer the best performance with the LM3GNSS receiver, especially in a dynamic environment. (6) Given the current tracking capabilities, the measurement quality, and positioning performances of LM3GNSS receivers relative to the geodetic grade receiver, it is foreseeable that the distinction between high-end GNSS and LM3GNSS receivers will most likely fade away as GNSS hardware technology advances. (7) Maximizing an LM3GNSS receiver in PPK strategy requires a multi-constellation-enabled reference station and high (i.e., 1 Hz) data tracking rate; otherwise, the PPK solutions will likely drift up to 20 cm

Methodology and consistency of slant and vertical assessments for ionospheric electron content models

The final publication is available at Springer via http://dx.doi.org/10.1007/s00190-017-1032-zA summary of the main concepts on global ionospheric map(s) [hereinafter GIM(s)] of vertical total electron content (VTEC), with special emphasis on their assessment, is presented in this paper. It is based on the experience accumulated during almost two decades of collaborative work in the context of the international global navigation satellite systems (GNSS) service (IGS) ionosphere working group. A representative comparison of the two main assessments of ionospheric electron content models (VTEC-altimeter and difference of Slant TEC, based on independent global positioning system data GPS, dSTEC-GPS) is performed. It is based on 26 GPS receivers worldwide distributed and mostly placed on islands, from the last quarter of 2010 to the end of 2016. The consistency between dSTEC-GPS and VTEC-altimeter assessments for one of the most accurate IGS GIMs (the tomographic-kriging GIM ‘UQRG’ computed by UPC) is shown. Typical error RMS values of 2 TECU for VTEC-altimeter and 0.5 TECU for dSTEC-GPS assessments are found. And, as expected by following a simple random model, there is a significant correlation between both RMS and specially relative errors, mainly evident when large enough number of observations per pass is considered. The authors expect that this manuscript will be useful for new analysis contributor centres and in general for the scientific and technical community interested in simple and truly external ways of validating electron content models of the ionosphere.Peer ReviewedPostprint (author's final draft

PERFORMANCE ANALYSIS OF WEB-BASED RELATIVE AND PRECISE POINT POSITIONING TECHNIQUES WITH DIFFERENT SATELLITE VISIBILITY CONDITIONS

The Global Navigation Satellite System (GNSS) is used for precise positioning applications, such as surveying and geodesy. The aim of the present work is to evaluate the effectiveness of web-based relative positioning (RP) and precise point positioning (PPP) GNSS post-processing services using measurements of different satellite visibility obstacles. Within this framework, static GNSS observations were conducted at three control benchmarks selected taking the impact of natural and human-made obstacles on satellite signals into consideration. 3 hours of static GNSS observations in Istanbul, Turkey were repeatedly obtained from three control BMs over six days and were evaluated through two RP (AUSPOS, OPUS) and three PPP (CSRS-PPP, Magic-PPP, GAPS-PPP) web-based GNSS post-processing services. The 6-day average of the three control benchmark coordinates computed using the Bernese GPS software v5.0, and were accepted as true results. They were compared to the local coordinates acquired through the RP and PPP web-based GNSS post-processing services. The different satellite visibility conditions were found to have significant effects on the GNSS point positioning solutions. We also found that web-based GNSS post-processing services provide easy and effective solutions for geodetic positioning applications

Submillimetric GPS distance measurement over short baselines: noise mitigation by global robust estimation

The potential use of GPS technology for precise length determination is currently a topic of extensive research. A prior work was dedicated to submillimetric length determination over short baselines and under ideal conditions of data availability and a clear environment. This paper presents a new computation method suited to the less favourable working conditions that are usually encountered in practice. It is based on both robust estimation theory and the use of an ambiguity-free estimation method. As the experimental comparisons with the standard procedure based on least-squares ambiguity determination show, it provides more stable values and permits results to be obtained significant to the submillimetre level with time spans of a few hours.This research is funded by the Spanish Ministry of Science and Innovation (AYA2011-23232).Baselga Moreno, S.; García-Asenjo Villamayor, L.; Garrigues Talens, P. (2014). Submillimetric GPS distance measurement over short baselines: noise mitigation by global robust estimation. Measurement Science and Technology. 25(10):1-6. https://doi.org/10.1088/0957-0233/25/10/105004S162510Altamimi, Z., Collilieux, X., & Métivier, L. (2011). ITRF2008: an improved solution of the international terrestrial reference frame. Journal of Geodesy, 85(8), 457-473. doi:10.1007/s00190-011-0444-4Amiri-Simkooei, A. R., & Tiberius, C. C. J. M. (2006). Assessing receiver noise using GPS short baseline time series. GPS Solutions, 11(1), 21-35. doi:10.1007/s10291-006-0026-8Baire, Q., Bruyninx, C., Legrand, J., Pottiaux, E., Aerts, W., Defraigne, P., … Chevalier, J. M. (2013). Influence of different GPS receiver antenna calibration models on geodetic positioning. GPS Solutions, 18(4), 529-539. doi:10.1007/s10291-013-0349-1Baselga, S. (2007). Global Optimization Solution of Robust Estimation. Journal of Surveying Engineering, 133(3), 123-128. doi:10.1061/(asce)0733-9453(2007)133:3(123)Baselga, S. (2010). Global optimization applied to GPS positioning by ambiguity functions. Measurement Science and Technology, 21(12), 125102. doi:10.1088/0957-0233/21/12/125102Baselga, S. (2014). Ambiguity-Free Method for Fast and Precise GNSS Differential Positioning. Journal of Surveying Engineering, 140(1), 22-27. doi:10.1061/(asce)su.1943-5428.0000111Baselga, S., & García-Asenjo, L. (2008). GNSS Differential Positioning by Robust Estimation. Journal of Surveying Engineering, 134(1), 21-25. doi:10.1061/(asce)0733-9453(2008)134:1(21)Baselga, S., & García-Asenjo, L. (2008). Multipath Mitigation by Global Robust Estimation. Journal of Navigation, 61(3), 385-392. doi:10.1017/s0373463308004803Baselga, S., García-Asenjo, L., & Garrigues, P. (2013). Submillimetric GPS distance measurement over short baselines: case study in inner consistency. Measurement Science and Technology, 24(7), 075001. doi:10.1088/0957-0233/24/7/075001Dow, J. M., Neilan, R. E., & Rizos, C. (2009). The International GNSS Service in a changing landscape of Global Navigation Satellite Systems. Journal of Geodesy, 83(3-4), 191-198. doi:10.1007/s00190-008-0300-3Griffiths, J., & Ray, J. R. (2012). Sub-daily alias and draconitic errors in the IGS orbits. GPS Solutions, 17(3), 413-422. doi:10.1007/s10291-012-0289-1Huber, P. J. (1981). Robust Statistics. Wiley Series in Probability and Statistics. doi:10.1002/0471725250Koivula, H., Häkli, P., Jokela, J., Buga, A., & Putrimas, R. (2011). GPS Metrology: Bringing Traceable Scale to a Local Crustal Deformation GPS Network. International Association of Geodesy Symposia, 105-112. doi:10.1007/978-3-642-20338-1_13Niu, X., Chen, Q., Zhang, Q., Zhang, H., Niu, J., Chen, K., … Liu, J. (2013). Using Allan variance to analyze the error characteristics of GNSS positioning. GPS Solutions, 18(2), 231-242. doi:10.1007/s10291-013-0324-xRay, J., Altamimi, Z., Collilieux, X., & van Dam, T. (2007). Anomalous harmonics in the spectra of GPS position estimates. GPS Solutions, 12(1), 55-64. doi:10.1007/s10291-007-0067-7Snay, R. A., & Soler, T. (2008). Continuously Operating Reference Station (CORS): History, Applications, and Future Enhancements. Journal of Surveying Engineering, 134(4), 95-104. doi:10.1061/(asce)0733-9453(2008)134:4(95)Wieser, A., & Brunner, F. K. (2002). Short Static GPS Sessions: Robust Estimation Results. GPS Solutions, 5(3), 70-79. doi:10.1007/pl00012901Yang, Y. (1999). Robust estimation of geodetic datum transformation. Journal of Geodesy, 73(5), 268-274. doi:10.1007/s001900050243Yang, Y., Song, L., & Xu, T. (2002). Robust estimator for correlated observations based on bifactor equivalent weights. Journal of Geodesy, 76(6-7), 353-358. doi:10.1007/s00190-002-0256-

ANALYSIS OF WEB-BASED ONLINE SERVICES FOR GPS RELATIVE AND PRECISE POINT POSITIONING TECHNIQUES

ABSTRACT Nowadays, Global Positioning System (GPS) has been used effectively in several engineering applications for the survey purposes by multiple disciplines. Web-based online services developed by several organizations; which are user friendly, unlimited and most of them are free; have become a significant alternative against the high-cost scientific and commercial software on achievement of post processing and analyzing the GPS data. When centimeter (cm) or decimeter (dm) level accuracies are desired, that can be obtained easily regarding different quality engineering applications through these services. In this paper, a test study was conducted at ISKI-CORS network; Istanbul-Turkey in order to figure out the accuracy analysis of the most used web based online services around the world (namely OPUS, AUSPOS, SCOUT, CSRS-PPP, GAPS, APPS, magicGNSS). These services use relative and precise point positioning (PPP) solution approaches. In this test study, the coordinates of eight stations were estimated by using of both online services and Bernese 5.0 scientific GPS processing software from 24-hour GPS data set and then the coordinate differences  between the online services and Bernese processing software were computed. From the evaluations, it was seen that the results for each individual differences were less than 10 mm regarding relative online service, and less than 20 mm regarding precise point positioning service. The accuracy analysis was gathered from these coordinate differences and standard deviations of the obtained coordinates from different techniques and then online services were compared to each other. The results show that the position accuracies obtained by associated online services provide high accurate solutions that may be used in many engineering applications and geodetic analysis.

BDS GNSS for Earth Observation

For millennia, human communities have wondered about the possibility of observing phenomena in their surroundings, and in particular those affecting the Earth on which they live. More generally, it can be conceptually defined as Earth observation (EO) and is the collection of information about the biological, chemical and physical systems of planet Earth. It can be undertaken through sensors in direct contact with the ground or airborne platforms (such as weather balloons and stations) or remote-sensing technologies. However, the definition of EO has only become significant in the last 50 years, since it has been possible to send artificial satellites out of Earth’s orbit. Referring strictly to civil applications, satellites of this type were initially designed to provide satellite images; later, their purpose expanded to include the study of information on land characteristics, growing vegetation, crops, and environmental pollution. The data collected are used for several purposes, including the identification of natural resources and the production of accurate cartography. Satellite observations can cover the land, the atmosphere, and the oceans. Remote-sensing satellites may be equipped with passive instrumentation such as infrared or cameras for imaging the visible or active instrumentation such as radar. Generally, such satellites are non-geostationary satellites, i.e., they move at a certain speed along orbits inclined with respect to the Earth’s equatorial plane, often in polar orbit, at low or medium altitude, Low Earth Orbit (LEO) and Medium Earth Orbit (MEO), thus covering the entire Earth’s surface in a certain scan time (properly called ’temporal resolution’), i.e., in a certain number of orbits around the Earth. The first remote-sensing satellites were the American NASA/USGS Landsat Program; subsequently, the European: ENVISAT (ENVironmental SATellite), ERS (European Remote-Sensing satellite), RapidEye, the French SPOT (Satellite Pour l’Observation de laTerre), and the Canadian RADARSAT satellites were launched. The IKONOS, QuickBird, and GeoEye-1 satellites were dedicated to cartography. The WorldView-1 and WorldView-2 satellites and the COSMO-SkyMed system are more recent. The latest generation are the low payloads called Small Satellites, e.g., the Chinese BuFeng-1 and Fengyun-3 series. Also, Global Navigation Satellite Systems (GNSSs) have captured the attention of researchers worldwide for a multitude of Earth monitoring and exploration applications. On the other hand, over the past 40 years, GNSSs have become an essential part of many human activities. As is widely noted, there are currently four fully operational GNSSs; two of these were developed for military purposes (American NAVstar GPS and Russian GLONASS), whilst two others were developed for civil purposes such as the Chinese BeiDou satellite navigation system (BDS) and the European Galileo. In addition, many other regional GNSSs, such as the South Korean Regional Positioning System (KPS), the Japanese quasi-zenital satellite system (QZSS), and the Indian Regional Navigation Satellite System (IRNSS/NavIC), will become available in the next few years, which will have enormous potential for scientific applications and geomatics professionals. In addition to their traditional role of providing global positioning, navigation, and timing (PNT) information, GNSS navigation signals are now being used in new and innovative ways. Across the globe, new fields of scientific study are opening up to examine how signals can provide information about the characteristics of the atmosphere and even the surfaces from which they are reflected before being collected by a receiver. EO researchers monitor global environmental systems using in situ and remote monitoring tools. Their findings provide tools to support decision makers in various areas of interest, from security to the natural environment. GNSS signals are considered an important new source of information because they are a free, real-time, and globally available resource for the EO community

Satellite Positioning

Satellite positioning techniques, particularly global navigation satellite systems (GNSS), are capable of measuring small changes of the Earths shape and atmosphere, as well as surface characteristics with an unprecedented accuracy. This book is devoted to presenting recent results and development in satellite positioning technique and applications, including GNSS positioning methods, models, atmospheric sounding, and reflectometry as well their applications in the atmosphere, land, oceans and cryosphere. This book provides a good reference for satellite positioning techniques, engineers, scientists as well as user community