GPS and GNSS Technology in Geosciences

By George P. Petropoulos and Prashant K. Srivastava

GPS and GNSS Technology in Geosciences offers an interdisciplinary approach to applying advances in GPS/GNSS technology for geoscience research and practice. As GPS/GNSS signals can be used to provide useful information about the Earth’s surface characteristics and land surface composition, GPS equipment and services for commercial purposes continues to grow, thus resulting in new expectations and demands. This book provides case studies for a deeper understanding of the operation and principles of widely applied approaches and the benefits of the technology in everyday research and activities.

• Presents processing, methods and techniques of GPS/GNSS implementation that are utilized in in-situ data collection in design and systems analysis
• Offers an all-inclusive, critical overview of the state-of-the-art in different algorithms and techniques in GPS/GNSS
• Addresses both theoretical and applied research contributions on the use of this technology in a variety of geoscience disciplines

• Language: English
• Publisher: Elsevier Science
• Release date: Feb 18, 2021
• ISBN: 9780128196939

Book preview

GPS and GNSS Technology in Geosciences

Editors

George p. Petropoulos

Assistant Professor of Geoinformatics, Department of Geography, Harokopio University of Athens, Greece

Prashant K. Srivastava

Assistant Professor Institute of Environment and Sustainable Development Banaras Hindu University, India

Table of Contents

Cover image

Title page

Copyright

Contributors

Foreword

I. General introduction to GPS/GNSS technology

Chapter 1. Introduction to GPS/GNSS technology

1. Background

2. Major segments of GPS

3. Functioning of GPS

4. GPS errors

5. GPS technologies

6. Global Navigation Satellite System

7. Applications of GPS/GNSS

8. Conclusions

Chapter 2. Fundamentals of structural and functional organization of GNSS

1. GNSS structural organization

2. GNSS functional organization

Chapter 3. Security of GNSS

1. Introduction

2. GNSS interference

3. GNSS jamming

4. GNSS self-jamming

5. GNSS meaconing

6. GNSS spoofing

7. The cloud-based GNSS spoofing detection

8. Some notation and definitions for detection of spoofing

9. GNSS spoofer DIY (Do It Yourself)

10. GNSS self-spoofing

11. Briefly about antispoofing

12. Summary and conclusions

13. Postscript

II. GPS/GNSS concept and algorithms

Chapter 4. GNSS multipath errors and mitigation techniques

1. Introduction

2. Multipath errors and their characteristics

3. Multipath mitigation techniques

4. Summary

Chapter 5. Antenna technology for GNSS

1. Introduction

2. Key antenna parameters for GNSS receivers

3. Antennas for GNSS

4. Final remarks

Chapter 6. Probing the tropospheric water vapor using GPS

1. Introduction

2. GPS error sources

3. Water vapor retrieval using GPS

4. Conclusions

Chapter 7. Probing the upper atmosphere using GPS

1. Introduction

2. Conclusions

3. Recommendations

Chapter 8. Video-based navigation using convolutional neural networks

1. Introduction

2. Proposed Super Navigation method

3. Implementation on low-power CNN accelerators

4. Experimental results

5. Conclusion and future work

III. Applications of GPS/GNSS

Chapter 9. GNSS monitoring natural and anthropogenic phenomena

1. Introduction

2. Earthquakes

3. Landslides monitoring

4. Crustal deformations

5. Challenges

6. Summary

Chapter 10. Environmental sensing: a review of approaches using GPS/GNSS

1. Introduction

2. Data collection

3. Data organization/analysis

4. Data visualization

5. Applications

6. Discussion and concluding remarks

Chapter 11. GNSS-derived data for the study of the ionosphere

1. The ionosphere

2. Ionosphere monitoring

3. Ionosphere modeling

4. TEC from GNSS

5. GNSS TEC for ionosphere studies

6. Final remarks

Chapter 12. Automatic pattern recognition and GPS/GNSS technology in marine digital terrain model

1. Introduction

2. Datasets description

3. Methodology implementation

4. The application of pattern recognition in marine pollution and structural studies

5. Conclusions

Chapter 13. Monitoring ionospheric scintillations with GNSS in South America: scope, results, and challenges

1. Introduction

2. Aspects of the climatology of ionospheric scintillations and their effects on GNSS-based applications in South America

3. Statistical modeling of amplitude scintillation

4. Low-cost instrumentation for ionospheric plasma bubbles monitoring

5. Discussion

6. Final remarks & future outlook

Chapter 14. The versatility of GNSS observations in hydrological studies

1. Introduction

2. Materials and methods

3. Results

4. Discussion

5. Conclusions & future outlook

Chapter 15. High-precision GNSS for agricultural operations

1. Introduction

2. GPS signal and structure

3. GPS positioning principle

4. Carrier-phase measurement

5. Real-time differential GPS correction

6. Applications of high-precision GNSS in agriculture

7. Conclusions and outlook

Chapter 16. An evaluation of GPS opportunity in market for precision agriculture

1. Introduction

2. GPS applications in precision agriculture

3. Challenges and future work

4. Conclusions and recommendations

Chapter 17. Use of GPS, remote sensing imagery, and GIS in soil organic carbon mapping

1. Introduction

2. Materials and methods

3. Methodology

4. Results

5. Discussion and conclusions

Chapter 18. GNSS and UAV in archeology: high-resolution mapping in Cephalonia Island, Greece

1. Introduction

2. Experimental setup

3. Methodology

4. Results

5. Discussion

6. Conclusions

IV. Challenges and future perspectives

Chapter 19. Accuracy and precision of GNSS in the field

1. Accuracy and precision of GNSS in the field

2. Conducting a survey: some examples

3. Conclusions

Chapter 20. Application of GPS and GNSS technology in geosciences

1. Introduction

2. Global navigation satellite system

3. Global Positioning System

4. Discussion

5. Conclusion

Chapter 21. Future pathway for research and emerging applications in GPS/GNSS

1. Introduction

2. Trends in GPS/GNSS technology, research, and applications

3. Vulnerabilities in existing technologies

4. Way forward

5. Concluding remarks

Index

Copyright

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Contributors

Christos Chalkias,     Department of Geography, Harokopio University of Athens, Athens, Greece

Prem Chandra Pandey,     Center for Environmental Sciences & Engineering, Shiv Nadar University, Uttar Pradesh, India

Alison de Oliveira Moraes,     Instituto de Aeronáutica e Espaço – IAE, São José dos Campos, SP, Brazil

Aspasia Efthimiadou,     Department of Soil Science, Institute of Soil and Water Resources, Hellenic Agricultural Organization – Demeter, Lycovrisi, Attiki, Greece

Antigoni Faka,     School of Environment, Geography and Applied Economics, Department of Geography, Harokopio University of Athens, Athens, Greece

Victor Hugo Fernandes Breder,     Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP, Brazil

V.G. Ferreira,     School of Earth Sciences and Engineering, Hohai University, Nanjing, Jiangsu, China

João Francisco Galera Monico,     Sao Paulo State University – UNESP, Presidente Prudente, SP, Brazil

Grigoris Grigorakakis,     Department of Geography, Harokopio University of Athens, Athens, Greece

Moisés José dos Santos Freitas,     Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP, Brazil

Kleomenis Kalogeropoulos,     Department of Geography, Harokopio University of Athens, Athens, Greece

Nikolaos Katsenios,     Department of Soil Science, Institute of Soil and Water Resources, Hellenic Agricultural Organization – Demeter, Lycovrisi, Attiki, Greece

Eleni Kokinou

Department of Agriculture, Hellenic Mediterranean University, Heraklion, Greece

Institute of Computer Science, Foundation for Research and Technology-Hellas, Heraklion, Greece

Amit Kumar,     Department of Geoinformatics, Central University of Jharkhand, Ranchi, Jharkhand, India

Pavan Kumar,     College of Forestry and Horticulture, Rani Lakshmi Bai Central Agricultural University, Jhansi, India

Sanjay Kumar,     Atmospheric Research Laboratory Department of Physics, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Shubham Kumar,     Department of Geoinformatics, Central University of Jharkhand, Ranchi, Jharkhand, India

Preet Lal,     Department of Geoinformatics, Central University of Jharkhand, Ranchi, Jharkhand, India

Lawrence Lau, PhD

Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hong Kong SAR, China

Department of Civil Engineering, The University of Nottingham Ningbo China, Ningbo, Zhejiang, China

Łukasz Lemieszewski,     Jakub Paradyż University, Faculty of Technology, Gorzów Wielkopolski, Poland

Kamil Maciuk,     AGH University of Science and Technology, Krakow, Poland

R.K. Mall,     DST - Mahamana Centre of Excellence in Climate Change Research (MCECCR), Banaras Hindu University, Varanasi, Uttar Pradesh, India

Jorge Martínez-Guanter,     Aerospace Engineering and Fluids Mechanics Department, University of Sevilla, Sevilla, Spain

Yenca O. Migoya-Orué,     The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy

H.D. Montecino,     Departamento de Ciencias Geodésicas y Geomática, Universidad de Concepción, Los Angeles, Biobío, Chile

Adam Narbudowicz

Trinity College Dublin, the University of Dublin, CONNECT Centre, Dublin, Ireland

Wroclaw University of Science and Technology, Telecommunications and Teleinformatics Department, Wroclaw, Poland

C.E. Ndehedehe,     Australian Rivers Institute and Griffith School of Environment & Science, Griffith University, Nathan, QLD, Australia

Evgeny Ochin,     Jakub Paradyż University, Faculty of Technology, Gorzów Wielkopolski, Poland

Manish Kumar Pandey,     Remote Sensing Laboratory, Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Zoi Papadopoulou,     Department of Natural Resources and Agricultural Engineering, Agricultural University of Athens, Athens, Greece

Alastair Pearson,     University of Portsmouth, School of the Environment, Geography and Geosciences, Buckingham Building, Lion Terrace, Portsmouth, UK

Manuel Perez-Ruiz,     Aerospace Engineering and Fluids Mechanics Department, University of Sevilla, Sevilla, Spain

George P. Petropoulos

Department of Geography, Harokopio University of Athens, Athens, Greece

School of Mineral Resources Engineering, Technical University of Crete, Kounoupidiana Campus, Greece

Sandro M. Radicella,     The Abdus Salam International Centre for Theoretical Physics (ICTP), Trieste, Italy

S.S. Rao,     Department of Physics, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Eurico Rodrigues de Paula,     National Institute for Space Research – INPE, São José dos Campos, SP, Brazil

Purabi Saikia,     Department of Environmental Sciences, Central University of Jharkhand, Ranchi, Jharkhand, India

Lucas Alves Salles,     Instituto Tecnológico de Aeronáutica – ITA, São José dos Campos, SP, Brazil

Martin Schaefer,     University of Portsmouth, School of the Environment, Geography and Geosciences, Buckingham Building, Lion Terrace, Portsmouth, UK

Hao Sha,     Gyrfalcon Technology Inc., Milpitas, CA, United States

Jyoti Kumar Sharma,     Center for Environmental Sciences & Engineering, Shiv Nadar University, Uttar Pradesh, India

A.K. Singh,     Atmospheric Research Laboratory Department of Physics, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, India

R.P. Singh,     Atmospheric Research Laboratory Department of Physics, Banaras Hindu University, Varanasi, Uttar Pradesh, India

Arpine Soghoyan,     Gyrfalcon Technology Inc., Milpitas, CA, United States

Panagiotis Sparangis,     Department of Soil Science, Institute of Soil and Water Resources, Hellenic Agricultural Organization – Demeter, Lycovrisi, Attiki, Greece

Prashant K. Srivastava

Remote Sensing Laboratory, Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, Uttar Pradesh, India

DST - Mahamana Centre of Excellence in Climate Change Research (MCECCR), Banaras Hindu University, Varanasi, Uttar Pradesh, India

Nikolaos Stathopoulos,     Institute for Space Applications and Remote Sensing, National Observatory of Athens, BEYOND Centre of EO Research & Satellite Remote Sensing, Athens, Greece

Baohua Sun,     Gyrfalcon Technology Inc., Milpitas, CA, United States

Prasoon Tiwari,     DST - Mahamana Centre of Excellence in Climate Change Research (MCECCR), Banaras Hindu University, Varanasi, Uttar Pradesh, India

Dimitris Triantakonstantis,     Department of Soil Science, Institute of Soil and Water Resources, Hellenic Agricultural Organization – Demeter, Lycovrisi, Attiki, Greece

Amit Kumar Tripathi,     Center for Environmental Sciences & Engineering, Shiv Nadar University, Uttar Pradesh, India

Andreas Tsatsaris,     Department of Surveying and Geoinformatics Engineering, University of West Attica, Athens, Greece

Konstantinos Tserpes,     Harokopio University, School of Digital Technology, Department of Informatics and Telematics, Athens, Greece

Shrini K. Upadhyaya,     Biological and Agricultural Engineering Department, University of California, Davis, CA, United States

Bruno César Vani,     Federal Institute of Education, Science and Technology of Sao Paulo – IFSP, Presidente Epitácio, SP, Brazil

Michalis Vidalis-Kelagiannis,     Department of Geography, Harokopio University of Athens, Athens, Greece

T. Xu,     Nanjing University of Information Science and Technology, Nanjing, Jiangsu, China

Lin Yang,     Gyrfalcon Technology Inc., Milpitas, CA, United States

P. Yuan,     Geodetic Institute, Karlsruhe Institute of Technology, Karlsruhe, Baden-Württemberg, Germany

Foreword

Although the Global Positioning System (GPS) technology, developed by the US Air Force to track their nuclear submarines, was ingeniously used by geoscientists in the 1990s to detect nano-strain deformation of the earth's surface, its potential applications in data-guided geo-science services to society began to sprout only after the US Government, in 2000, ended the selective availability of its error-free signals. This landmark decision, by dramatically reducing real-time location errors by an order of magnitude, fueled the design and development of a wide variety of progressively miniaturized receiver systems and algorithms for guiding management strategies, environmental monitoring, resource conservation, as well as individuals in planning their lives and works which, in turn, drove the evolution of new supportive public infrastructure. Concomitantly, the depoliticization of GPS signals catalyzed evolution of the transformative Global Navigation Satellite System (GNSS) which allows a civilian user to exploit the technical interoperability of the various national and regional satellite networks, notably the modernized GPS, the European Galileo, and the restructured Russian Glonass, to meet user demands for ever more precise estimations of earth coordinates and time. A commitment by GNSS to promote the development of and support to complementary systems that would continue to enhance location and time accuracy and also diversify the use of spatiotemporal data toward sustainable development offers a highly promising approach toward building a hazard resilient society.

This volume edited by scientists of proven credentials who have personally contributed to advancing the wavefront of GNSS applications from its initial tracking and time stamping uses to the Internet of Things has rightly identified the critical elements of scientific knowledge and the computational and technological challenges needed to translate these into knowledge products, to fashion its contents. These, contained in 27 chapters, systematically address the important links in the long chain of system structure and processes that reduce the end product of a highly sophisticated technological system into one of equally high social value. This book is thus admirably designed to inform, educate, and given the requisite motivation, empower both curious and dedicated individuals to professionally engage in aspects of the system that fire their interest.

icon

Vinod Gaur

Bangalore, February 10, 2021

I

General introduction to GPS/GNSS technology

Outline

Chapter 1. Introduction to GPS/GNSS technology

Chapter 2. Fundamentals of structural and functional organization of GNSS

Chapter 3. Security of GNSS

Chapter 1: Introduction to GPS/GNSS technology

Amit Kumar ¹ , Shubham Kumar ¹ , Preet Lal ¹ , Purabi Saikia ² , Prashant K. Srivastava ³ , ⁴ , and George P. Petropoulos ⁵ , ⁶       ¹ Department of Geoinformatics, Central University of Jharkhand, Ranchi, Jharkhand, India      ² Department of Environmental Sciences, Central University of Jharkhand, Ranchi, Jharkhand, India      ³ Remote Sensing Laboratory, Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi, Uttar Pradesh, India      ⁴ DST - Mahamana Centre of Excellence in Climate Change Research (MCECCR), Banaras Hindu University, Varanasi, Uttar Pradesh, India      ⁵ Department of Geography, Harokopio University of Athens, Athens, Greece      ⁶School of Mineral Resources Engineering, Technical University of Crete, Kounoupidiana Campus, Greece

Abstract

Satellite-based navigation systems are one of the most indispensable technologies in the present-day world that have made a vast improvement since the day of its inception due to global availability of signal and performance. It allows measuring positions in real time with an accuracy of up to a few centimeters on the Earth. The advent of Global Positioning System (GPS) has led to technological revolutions in highly accurate navigation, positioning, and time that is being applied in various civilian, military, and scientific purposes. GPS works on the radio waves that are being transmitted from a space-based group of satellites to the terrestrial GPS receiver to deduce the exact position of the Earth. Although there are various errors related to clock errors, multipath error, receiver noise, and antenna phase center variations at satellite as well as receivers end, it is being resolved through technological advancement and methods. Incorporating both GPS and GLONASS constellations in the navigation system may significantly improve the accuracy of the navigational solution. This chapter aims to discuss the various concepts of GPS, including working principle, various errors, various Global Navigation Satellite System technologies evolving from GPS to Quasi-Zenith Satellite System, and its vivid applications.

1. Background

The Global Navigation Satellite System (GNSS) has become a crucial player in terms of the country's capability to monitor real-time activities across the world. The rapid growth in GNSS was first observed through the development of commercial applications through building navigation satellites and associated equipment. The next-level progression was made in the positioning techniques using GNSS such as Global Positioning System (GPS), the infrastructure of the mobile network, and their integration for applications such as automatic vehicle location, tracking systems, navigation have drawn the attention of various countries such as the United States, India, and China. Satellite navigation system (SNS) is the system of offering real-time location service using navigation satellites to the users in air, sea, ground, or space [59]. It is most popular among other navigation technologies as it offers a real-time location in terms of position, velocity, and time (PVT) with very high precision. GNSS is a combined collection of satellite systems that directs to all the prevailing worldwide SNSs as well as regional and advanced navigational systems. These SNSs constitute several augmented systems to enhance system performance to achieve specific requirements. These are Japan's Multi-functional Satellite Augmentation System, United States of America's Wide Area Augmentation System, India's GPS-aided GEO augmented navigation (GAGAN), and Europe's European Geostationary Navigation Overlay Service (EGNOS).

Navigation is the science of providing directions from one place to another, based on landmarks or reference points, and the human sense of direction [5,26,58]. Using the Sun and the stars as reference for navigation on land as well as on ocean surfaces, (Hofmann-Wellenhof et al., 2003; [53]) have various limitations such as nonvisibility during cloudy conditions, the relative change in position of these references during various seasons, and position on the Earth [3]. With the advent of geographical coordinates (latitudes and longitudes) and altitude, the challenge with respect to two-dimensional and three-dimensional reference for terrestrial navigation has been resolved [4,14]. In the recent past, the radio signals have helped in the navigation to ensure safety during maritime and inland journeys [47]. Celestial navigation is based on the triangulation method, in which celestial bodies are used as reference points, and the GPS is based on the concept of trilateration, which uses GPS satellites' locations as reference [47]. GPS can measure the time, altitude, longitude, and latitude based on the available satellite signals above the horizon [50] and contributes in determining the precise positioning of an object on Earth that revolutionized the navigation and tracking applications [13,63]. It is one of the most popular satellite-based navigation radio systems due to the global availability of signal as well as performance. The fundamental operations of the GPS are one-way ranging that depends on satellite atomic clock predictability. GPS works in an integrated manner with various supporting parameters such as satellite geometry, communication link, the antenna of satellite and receiver, the position of the antenna, and decoding parameters [43]. It is independent of any weather conditions, and day or night limitations, and provides autonomous spatial positioning with global coverage. Real-time kinematic (RTK) GPS has high producibility, is comparatively more flexible, and is cost- and time-effective, which reduces the cost by ∼50% and time by ∼75% compared to traditional techniques. It allows measuring positions of an object in real time with an accuracy of a few centimeters [54].

The first GPS receivers were very simple, providing very basic information of latitude and longitude with monochrome screens and higher prices. Over the years, the next-generation SNS receivers brought more user-friendly map-based location devices with color screens with in-built multiple advanced features, at comparatively lower prices. GPS also operates independently, which makes it accessible by anyone and provides the ability to work freely with other GPS receivers. Nowadays, it is being used by civil, military, and commercial users vastly around the world with crucial information including speed, elevation, and geolocation with the added base map. The system has revolutionized today's technology by becoming more interactive, effective, and useful in multiple industries. This chapter will explore the basic principles of GPS, its various hardware that make it work in-depth, and the operation of the system, including the theoretical calculations for positioning, speed, bearing, and distance to destination.

The history of navigation goes back as early as the invention of the magnetic compass as mentioned by Ceruzzi [7]. The navigation in the later period was carried by a chronometer as given by Ceruzzi [8], which resolved the problem of longitude. This was replaced by Quartz oscillators in the 1920s. The next concurrent advancement was radio or the wireless. The next advancement was Omega and Loran, which were the radio-based inertial navigation systems. This was further taken over by satellite-based navigation systems in the 1960s. The evolution of GNSS as given in NASA (2020) is listed in Table 1.1.

Table 1.1

The commercial market of GPS emerged during 1983–95 [8], and the market converged during 1995–2015 [8]. From 1995 to 2005, GPS found its use in several areas ranging from research, surveying, military, and in hiking and hunting. In the second decade, from 2005 to 15, it drew public attention, and several new applications were created, which were never thought of earlier, for example, in cell phones, in drones, in a smartphone, tracking and privacy, etc., to name a few. The future market growth of GNSS could be estimated only after the full deployment of the Galileo and BeiDou satellite constellations is over. The European GNSS Agency projects the current value of six billion GNSS deployed devices to grow to over nine billion by 2023 (Jacobson, 2017). According to Research and Markets NASA (2020), the GNSS market is estimated to grow at a compound annual growth rate of around 9.0% during 2018–22. As per GNSS Market Outlook 2022 NASA (2020), market dynamics would be led by location-based services, transportation, surveying activities, and agriculture.

2. Major segments of GPS

GPS primarily consists of three different segments viz. (a) satellite constellation, (b) ground control stations, and (c) receivers [10]. The space segment consists of constellations of satellites that transmit pseudorandom noise (PRN)–coded signals, which are used for the true line-of-sight (LoS) range (speed∗time) along with various error sources including satellite clock error, atmospheric delays, receiver clock error, tracking errors, and receiver channel delays [40]. The coded signals comprise the information about the position of the satellite, which can be used by an unlimited number of users at a time [26]. The GPS satellite constellations in the space segment are being monitored and controlled by the GPS control segment (CS) by resolving satellite anomalies and collecting pseudorange and carrier-phase measurements at the control stations to ascertain and refurbish satellite clock rectification, almanac, and ephemeris at least once per day [49]. Additionally, the CS monitors the state of the satellite's health, controls its orbital position, and regulates the satellite bus and payloads [45]. The CS has three different physical components such as the master control station (MCS), monitor stations, and ground antennas. The receiver/user segment includes all military and civilian users using the GPS signal for various purposes [13]. Each GPS receiver processes the transmitted signals received from the satellites to determine the PVT of the receiver anywhere in the world.

3. Functioning of GPS

GPS works on the ranging and trilateration by combining various groups of satellites [34], functional in space as reference points. These satellites transmit a navigation message consisting of information related to almanac, i.e., the orbital information about the entire satellite constellation, general system status messages, as well as ephemeris, and the detail of the individual satellite's position to regulate the orbital position of satellites. A minimum of four common satellites are required in a group to determine the precise receiver's position at any time [21]. Only three distances to three simultaneously tracked satellites are needed to obtain the latitude, longitude, and altitude information. However, the fourth satellite accounts for the receiver clock offset and contributes in time rectification [27]. The GPS positioning is further improved at subcentimeter to a few meters with the deployment of two receivers simultaneously tracking the same GPS satellites [31]. GPS employs three basic binary codes viz, (PRN code including precision (P) code, Coarse Acquisition (C/A) code, and the navigation code. The PRN code is a sequence of very precise time marks that allow the receivers to estimate the transmission delay between the satellite and the control station [33,56].

The GPS satellites broadcast two carrier waves viz. L1 (390   MHz) and L2 (1500   MHz), which are modulated by the coded information signal that is transmitted by the satellites to communicate with the receivers. They are derived from the frequency of 10.23   MHz through a very precise atomic clock. The high-frequency signals transmitted from the satellites travel in a straight line and have very low power (50   W). It is very essential that the antenna of the GPS receiver should have a direct view of the satellite. L1 and L2 carrier waves are broadcasted at 1575.42   MHz and 1227.60   MHz, respectively. L1 carrier waves are modulated with the C/A code at 1.023   MHz and the P-code at 10.23   MHz, while the L2 carrier wave is modulated with only one code, i.e., P-code at 10.23   MHz. These coded signals are used to calculate the transmission time of radio signals from the satellite to the receivers on the Earth, i.e., the time of arrival, which is multiplied by the velocity of the signal to estimate the satellite range, which is the distance from the satellite to the receiver. The GPS signal contains a navigation message of a low frequency (50   Hz), which is modulated on the L1 and L2 carriers [16].

3.1. Pseudorange

Pseudorange is the measure of apparent signal propagation time from the satellite to the GPS receiver on the Earth. It is calculated by dividing the distance with the speed of light, which is denoted with c, i.e., a universal physical constant. The apparent signal propagation time is the deviation of signal reception by the receiver and the time of signal transmission by the satellite. In other words, it is the time delay between the clocks of GPS receivers and satellites on the Earth, determined from the P-code and C/A code. Generally, the signal from the satellite to the GPS receiver reaches in 0.06   s, if in case the satellite is in the overhead position of an observer. It is called pseudorange because the clocks in the GPS receiver and the satellite are not synchronized, and it is influenced by satellite orbital errors, user clock error, and ionospheric delay.

3.2. Carrier-phase measurement

The range between the carrier signal generated from the satellite and the carrier signal generated by a GPS receiver's internal oscillator can be obtained through the carrier-phase measurement. The ranges calculated with the carriers are much more accurate than those calculated with the pseudorange codes due to the better resolution of the carrier phase (19   cm) in the case of L1 frequency than that of the pseudorange codes [33].

3.3. GPS broadcast message, ephemeris, and almanac

The navigation message included three types of components (a) the current date, time, and the health of the satellite; (b) orbital information (ephemeris); and (c) the status of all the satellites in the GPS program (almanac). Each GPS satellite broadcasts microwave signals regarding clock corrections, system and satellite status, and its position or ephemeris data. The navigation message transmitted by the satellite contains the predicted satellite positions in real time referred to as broadcast ephemeris. Each GPS receiver is capable of acquiring either C/A code or P-code and can acquire the broadcast ephemeris in real time. This broadcast ephemeris is estimated using the past continuous tracking of the GPS satellites in space by ground station and analyzed by the MCSs. New parameters for the satellites are transmitted back to the GPS satellites on the hourly basis through a navigation message to predict new orbital elements. In contrast, the more accurate satellite positions are obtained by postprocessing of actual tracking of GPS satellite data, referred to as precise ephemeris, and are available at a later date [21,51].

Almanac data are transmitted from the satellite to the receivers and used to be stored in the GPS receiver's memory. The almanac consists of the data about the position of satellites in space at any given time including coarse orbit, status information of satellites' constellation, an ionospheric model, and information to relate GPS-derived time to Coordinated Universal Time. The entire almanac from a single satellite used to be received in ca. 12.5   min. GPS receivers in functional condition receive the latest corrected data within the last 4–6   h and are referred to as warm condition, whereas almanac data are not updated in case GPS receivers are not turned on for a long time and are referred to as cold receivers.

4. GPS errors

Both the GPS pseudorange and carrier-phase measurements are affected by different types of random and systematic errors (biases) [42]. Based on the source of its origin, it can be classified broadly into three categories, i.e., the ephemeris or orbital errors, satellite clock errors, and the errors originating at the satellites' end. The receiver clock errors, multipath error, receiver noise, and antenna phase center variations are the errors originating at the receiver end. The delays occurred during the GPS signal pass through the ionosphere and troposphere are the signal propagation errors, also called atmospheric refraction [28,29].

4.1. Satellite and receiver clock errors

The GPS satellite clocks are highly accurate but not perfect as their stability is about 1–2 parts in 1013 over a period of 1   day, which leads to the satellite clock error of ca., 8.64–17.28   ns/day. Cesium clocks have better stability compared to rubidium clocks and tend to perform better over a longer period [35]. Satellite clock errors can cause several GPS navigations errors that can be corrected through differencing between receivers. It may leave an error of the order of several nanoseconds, which translates to a range error of a few meters, as 1   nanosecond error is equivalent to a range error of about 30   cm [12]. In contrast, the inexpensive crystal clocks used in GPS receivers are much less accurate than the satellite clocks [29], and their errors can be rectified through differencing between the satellites.

4.2. Multipath error

The interaction of GPS signals with various surfaces including large buildings or other elevations surrounding the receiver antenna before being captured by the receiver causes multipath error in GPS signals. It distorts the original signal through interference with the reflected signals at the GPS antenna, which affects both carrier-phase and pseudorange measurements [56]. The reflected signal takes more time to reach the receiver than the direct signal resulting in errors in the range of a few meters that can be verified using a day-to-day correlation of the estimated residuals [21]. The pseudorange multipath error is reduced to several meters, even in a highly reflective environment with the help of new technology viz. Strobe correlator (Ashtech Inc.), and MEDLL (NovAtel Inc.), and multipath mitigation methods [55].

4.3. Ionospheric delay

Ionospheric propagation at the GPS L-band frequencies (1.2 and 1.6   GHz) is of great interest for GPS. The ionosphere is a dispersive medium with maximum electron density in layer F2 (210–1000   km). The altitude and thickness of those layers vary with time due to the changes in the solar radiation and the magnetic field of the Earth. The F1 layer disappears during the night and is more prominent in the summer than the winter [30]. This atmospheric layer bends the GPS signal path and causes a range error, particularly if the satellite elevation angle is greater than 5 degrees. It also causes a significant range error by speeding up the propagation of the carrier phase beyond the speed of light, in contrast by slowing down the PRN code and the navigation message at the same rate [21]. Ionosphere range delay on GPS signals is a major error source in GPS positioning and navigation [60]. Total electron content (TEC) of the ionosphere produces most of the effects on radio signals, and the GPS signal delays are caused by the ionosphere to be proportional to TEC along the path from the satellite to a terrestrial GPS receiver [60]. The highest TEC in the world occurs in the equatorial region, and it is maximum usually in the early afternoon and minimum usually just before sunrise. Variations in TEC along the slant path connecting GPS satellites and receivers represent irregularities and turbulence in ionospheric plasma density [46]. Conversely, the steep gradients of ionospheric plasma cause the navigation satellite signals scintillation in phase as well as amplitude. GPS is an effective tool to study the ionospheric disturbances and irregularities caused by space weather due to these scintillations [9,41,48]; Cherniak et al. (2018); [52].

4.4. Tropospheric delay

The electrically neutral troposphere (∼50   km from the surface of the Earth) acts as a nondispersive medium for radio frequencies below 15   GHz [19], which result in a longer satellite-to-receiver range than the actual geometric range. Temperature, pressure, and humidity in the signal path through the troposphere are the factors responsible for the tropospheric delay. The signals from satellites at low elevation angles travel a longer path through the troposphere than those at higher elevation angles. Therefore, the tropospheric delay is minimum in the user's zenith and maximum near the horizon [6]. The tropospheric delay is frequency independent and can be removed by the addition of a second C/A code on L2 as part of the modernization program [51].

4.5. GPS ephemeris errors

The position of each satellite in the constellation is a function of time because they keep on moving with respect to time. It is included in broadcast satellite navigation messages and predicted from previous GPS observations at the ground control stations. Typically, overlapping 4-h GPS data spans are used by the operational control system to predict fresh satellite orbital elements for each 1-h duration. The predicted satellite orbital information cannot consider the forces influencing the GPS satellites, which may lead to some errors in the estimated satellite positions (2–5   m) referred to as ephemeris errors. The ephemeris error for a particular satellite is identical to all GPS users worldwide [12].

4.6. Other limitations

GPS was originally designed in such a way that the real-time autonomous positioning and navigation with the civilian C/A code receivers would be less precise than military P-code receivers. The GPS signals were intentionally introduced by the United States to disrupt position, navigation, and time through either spoofing (making a GPS receiver calculate a false position) or jamming (overpowering GPS satellite signals locally so that a receiver can no longer operate). Antispoofing (A/S) is an encryption of the P-code induced to prevent the enemy from imitating a GPS signal. A/S does not pose a significant problem as precise GPS techniques rely on measuring the phase of the carrier signal itself, rather than the pseudoranges derived from the P-code. Modern geodetic receivers can, in any case, form two precise pseudorange observables on the L1 and L2 channels, even if A/S is switched on. However, the United States stopped the intentional degradation of GPS satellite signals in May 2000, thereby eliminating a source of uncertainty in GPS performance to civil GPS users worldwide [1].

The United States implemented the selective availability (SA) on Block II GPS satellites to deny accurate real-time autonomous positioning to unauthorized users to ensure national security. SA was officially activated on March 25, 1990 [21], to either the satellite clock or delta error or an additional slow varying orbital error or epsilon error. With SA turned on, nominal horizontal and vertical errors can be up to 100   and 156   m, respectively, at the 95% probability level [15]. The effect of signal spoofing in degrading the navigation solution can have serious impacts on both military and civilian applications, especially those related to safety-of-life services. Various techniques have been developed to detect and mitigate spoofing [25]. DGPS (to overcome the effect of the epsilon error) [12], signal quality monitor [38]; Ledvina et al., 2010), and vestigial signal defense [57] are being used for better accuracy than the standalone P-code receiver due to the elimination or the reduction of the common errors, including SA.

5. GPS technologies

There is a variety of methods employing GPS to improve the accuracy and increase the applicability of the system. RTK survey and differential GPS are few of them.

A differential GPS is an advanced form of GPS, providing very accurate and precise location-based services. In general, two receivers that are relatively closer (within 10–15   km) receive the signal from approximately the same GPS satellites and experience similar atmospheric errors. In DGPS, the difference between the concurrent coordinates with respect to known coordinates (base receiver) is estimated and applied to fix the concurrent coordinates of unknown locations (rover receiver). The corrected information can be applied to the roving receiver in real time in the field using radio signals or through postprocessing after data capture using special processing software. RTK surveying is a carrier phase–based relative positioning technique that employs two (or more) receivers simultaneously tracking the same satellites. RTK increases the accuracy while surveying a large number of unknown points located in the vicinity with reference to a known point, provided the area of investigation falls within 10–15   km to the known point, the connection between rover and static is established, and the LoS and the propagation path are relatively unobstructed [32]. In this method, the base receiver remains stationary over the known point and is attached to a radio transmitter. The rover receiver is normally carried in a backpack and is attached to a radio receiver. The base receiver measurements and coordinates are transmitted to the rover receiver through the communication (radio) link [33].

6. Global Navigation Satellite System

The GNSS is defined as the group of all SNSs and their augmentations. There are 195 countries across the globe, but very few countries host their own navigation system through a specific satellite (Jiang et al., 2013). Globally four countries host navigation systems: GPS (US), GLObal NAvigation Satellite System (GLONASS of Russia), Galileo (EU), and BeiDou (China). Additionally, two countries have regional navigation systems: Quasi-Zenith Satellite System (QZSS of Japan) and Indian Regional Navigation Satellite System (IRNSS) or Navigation Indian Constellation (NavIC of India). The GNSS constellation system is depicted in Fig. 1.1.

6.1. NAVSTAR

GPS is a commonly used acronym of NAVSTAR (NAVigation System Time and Ranging) and is the first SNS developed by the US Department of Defense in 1978. It is the first fully operational GNSS consisting nominally of a constellation of 24 operational satellites completed its initial operational capacity (IOC) on December 8, 1993 [21]. Its orbits are approximately circular with an inclination of about 55 degrees at the satellite altitude of about 20,200   km above the Earth's surface [36]. NAVSTAR GPS provides users with location-based services very precisely in very little time. The satellites in NAVSTAR constellation orbit the Earth in every 12   h transmitting continuous navigation signals in L1 and L2 frequencies. NAVSTAR has four generations of satellite constellation viz. Block I (1978–85), Block II (1989–90), Block II A (1990–97), Block II-R (1997–2004, Block IIR-M (2005–09), Block II-F (2010–16), Block III-A (2018-present). Each newer Blocks replaced older Blocks after completing their active service period (end of life) and are of the improved version. The satellites are orbiting at an altitude of ca. 20,200   km and arranged in a way that at least six satellites are always above the horizon everywhere on the globe (Fig. 1.2).

Figure 1.1 GNSS constellation systems. 

Adapted from Wu, J., Ta, N., Song, Y., Lin, J., Chai, Y., 2018. Urban form breeds neighborhood vibrancy: a case study using a GPS-based activity survey in suburban Beijing. Cities 74, 100–108. https://doi.org/10.1016/j.cities.2017.11.008; pp.1–29).

6.2. GLONASS

GLONASS is a satellite-based navigation system operated during the last decades of the twentieth century by the Russian Aerospace Defence as an alternative to the US-based NAVSTAR. At present, it is complimentary as well as an alternative option for an operational navigation system with related precision and full coverage [20]. The launching of satellites started in 1982 until the constellation was completed in 1995. The life cycle of GLONASS navigation satellites was 5–7   years, and the new satellites are to be launched after a specific time interval to fill the gap due to aging satellites [2,37,39]. In 2011, the full global coverage was established with upgraded satellite constellations under GLONASS-K. GLONASS consists of 24 satellites that are uniformly deployed in three approximately circular orbital planes at an inclination of 64.8 degrees to the equator at the satellite altitude of about 19,100   km above the Earth's surface. Each GLONASS satellite transmits standard and high accurate signals in L1 (1598.06–1604.40   MHz) and L2 (1242.94–1248.63   MHz) frequencies. The modern age GPS receivers are compatible with both NAVSTAR and GLONASS, thus providing more flexibility of positioning and better accuracy.

Figure 1.2 Satellite constellations and orbital altitude of major navigation systems.

6.3. Galileo

Galileo was developed by the collaboration of the European Union and European Space Agency in 2011, and the satellite constellation was completed in 2020 (https://ec.europa.eu/growth/sectors/space/galileo/launches_en) with 30 satellites in orbit (24 operational and 6 active spares) [11,18]. Additional satellites will be launched after in-orbit validation phase to achieve IOC. Galileo will give position measurements, i.e., horizontal and vertical, having the range of 1-meter precision. This positioning service even at high latitudes proves more efficient than other relatively positioning systems. The Galileo constellation is evenly distributed among three orbital planes inclined at 56 degrees relative to the equator with a nominal semimajor axis of about 30,000   km. Galileo will transmit radio navigation signals in E1 (1559–1594   MHz), E6 (1260–1300   MHz), E5a (1164–1188   MHz), and E5b (1195–1219   MHz) frequencies. The EGNOS provides an augmentation signal to the GPS standard positioning service (SPS). Global Search and Rescue function is a unique feature of Galileo. Apart from Russian GLONASS and US GPS, high precision has been achieved in the Galileo navigation and positioning system.

6.4. Compass/BeiDou

China developed its own navigation satellite system Compass/BeiDou with five geostationary satellites and 30 nongeostationary satellites to date. BeiDou-1 consists of three satellites and offers limited coverage (to users of China and their neighboring countries) and applications. The second generation of this navigation system, referred to as Compass, is a global SNS comprising 35 satellites. It has been operational with 10 satellites in orbit in China since December 2011. By 2020, it is expected to be available to all global customers [23,61]. It uses two different orbits with 55 degrees inclination for navigation satellites: (i) medium Earth orbit (21,500   km) and (ii) inclined geosynchronous orbit (36,000   km). It works on three channels: (i) B1: 1559.052–1591.788   MHz, (ii) B2: 1166.22–1217.37   MHz, and (iii) B3: 1250.618–1286.423   MHz frequencies. The system is providing two types of service at the global level: open service (with a positioning accuracy of 10   m, a timing accuracy of 20 nanosecond, and a velocity accuracy of 0.2   m/s) and authorized service (with a provision of more reliable PVT information and communications services as well as integrity information) [44].

6.5. Quasi-Zenith Satellite System

QZSS (also known as Michibiki) is a regional navigation satellite system developed by Japan. It is a combination of four satellites (now expanded to four satellites) that are inclined on orbital planes at 39 degrees–47 degrees on two altitudes, 39,581   km and 31,911   km, which provide navigation for East Asia, including Japan, and Oceania. The three satellites of this constellation were fully operational in 2013 and the fourth satellite of QZSS services was operational since November 1, 2018, and three more are satellites planned till 2023. The design and concept of QZSS are purely different from GPS and GLONASS systems due to the policy of national development [24]. QZSS is targeted to achieve communication-related services, i.e., audio, video, and data with location information, and is useful in mobile applications. QZSS is also termed as GNSS augmented service. It works on four frequency of signal: (i) L1 (L1 C/A and the L1-SAIF: center frequency 1575.42   MHz), (ii) L2 (center frequency 1227.6   MHz), (iii) L5 (center frequency 1176.45   MHz), and (iv) LEX (center frequency 1278.75   MHz) frequencies [62].

6.6. IRNSS/NavIC

IRNSS/NavIC is a regional SNS, developed by ISRO (Indian Space and Research Organisation). It would comprise of two services, i.e., SPS for civilian users and restricted service for authorized military users. Both services work on L5 (1176.5   MHz) and S-band (2492.08   MHz) frequencies. The proposed navigation system would have a constellation of seven satellites and a supported ground segment, and three satellites from the constellation will be kept as geostationary satellites. GPS with aided augmented navigation system is initiated in India with the collaborations of ISRO and Airport Authority of India (AAI), which is termed as GEO augmented system (GAGAN). This system is used to enhance the accuracy of a GNSS receiver based on reference signals. When GAGAN will be fully operational, it will fulfill the requirements of the three geostationary satellites (GAGAN will help to get more accuracy for IRNSS when it is fully completed and it will fulfill requirements of three geostationary satellites). The Indian subcontinent (India and neighboring countries) will be covered with help of the footprint of its signal. The operational Satellite Based Augmentation System implemented by AAI's efforts tends to be a step in the field of modern communication, air traffic control, and management and navigation (Table 1.2).

7. Applications of GPS/GNSS

7.1. Navigation

Navigation is of the most common uses of GPS, which aids in aviation, maritime, shipping, and rail and road transportation. It also supports the public in their day-to-day activities by providing the precise location with respect to the surroundings including geotagging, carpools, helping blind people navigate, safety and emergency assistance, security applications including tracking of vehicles, vehicle guidance, hiking, skiing, paragliding, skydiving, etc. (Jacobson, 2017).

7.2. Military services

The GPS of military services are far more precise than GPS used by civilians around the world. It uses dual-frequency equipment to avoid signal distortions that could jeopardize its mission or research. Although now dual frequencies are also used by government organizations and commercial services, commonly for civilians, it is single-frequency GPS receiver that makes a difference in precision too. It supports military operations, reconnaissance, and surveillance and to navigate the unfamiliar areas and enhance the awareness of GPS-guided missiles attack. Advanced GPS receivers are used for various military operations to achieve goals and diffuse enemy installations, including navigating to the target locations, tracking the movement of enemies, and supply delivery on the battlefield with precise computation.

Table 1.2

B1, 1561.1   MHz; B2, 1207.14   MHz; B3, 1268.52   MHz; GEO, geosynchronous; L1∗, 1602   MHz; L1, 1575.42   Mhz; L2∗, 1246   MHz; L2, 1227.60   MHz; L5, 1176.45   MHz; L6, 1278.75   MHz; MEO, medium Earth orbit; S, 2492.028   MHz.

7.3. Geodetic control surveys

A geodetic control survey is based on a network of monumented control points on the ground and a very precise survey method supporting mapping, construction, boundary surveys, etc. GPS emerged as a better alternative to these precise surveys. The static method is used in high-order geodetic control surveys, but for low-order control surveys such as in photogrammetric and other types of mapping, fast static techniques are used.

7.4. Cadastral