2022 | Buch

# Introduction to GNSS Geodesy

## Foundations of Precise Positioning Using Global Navigation Satellite Systems

verfasst von: Clement A. Ogaja

2022 | Buch

verfasst von: Clement A. Ogaja

Introduction to GNSS Geodesy is a concise reference for beginners and experts in GNSS-based satellite geodesy. It covers all of the important concepts in almost a third of the space of the other GNSS books. Th e book begins with a case study in Augmented Reality to set the stage for what is to come and then moves on to the key elements of GNSS geodesy that make accurate and precise geopositioning possible. For example, it is important to understand the geodetic reference systems and the associated GNSS data processing strategies that enable both accurate and high-precision geopositioning. Chapter 2 gives an overview of GNSS constellations and signals, highlighting important characteristics. Chapter 3 then introduces reference systems in geodesy, covering such topics as time systems, geodetic datums, coordinate systems, coordinate conversions and transformations, and International Terrestrial Reference Frame. Th is lays the framework for the rest of the book.

Chapters 4 and 5 dig deep into mathematical formulation of GNSS parameter estimation and observation models. All the concepts are presented clearly and concisely, with diagrams to assist reader comprehension. Chapter 6 describes Continuously Operating Reference Station (CORS) networks and their role in geodesy and definition of reference frames. Various global and regional CORS networks are presented in this section. Th e chapter also covers GNSS data and common formats such as RINEX and RTCM. Chapter 7 introduces the whole cycle of GNSS data processing, including preprocessing, ambiguity fixing, and solution reprocessing methods as commonly used in both epoch solutions and time series data. Th e book concludes with appendices on orbit modelling, GNSS linear combinations, application examples, and an example linear model.

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Abstract

This chapter introduces Augmented Reality (AR) as a special case example to highlight the important role of geodetic GNSS in a cutting-edge technology application. It discusses AR, for example, as used in project sites to overlay digital information such as graphical annotations, construction designs, and 3D models of invisible underground utilities, in their real-world position, on an image of the site being viewed through a device such as a smartphone camera. The AR concept is explained, and why GNSS Geodesy is important in supporting it, followed by a brief discussion of high-accuracy AR applications in the construction industry and other areas such as utilities, oil and gas pipelines, and land development.

Abstract

This chapter is an overview of GNSS constellations and signals. It focuses on highlighting the important characteristics of constellations with global satellite coverage, even though other regional augmentation systems also exist. It also highlights some of the key components and characteristics of multi-frequency GNSS signals for positioning, navigation, and timing. Such multi-frequency signals allow for several possible combinations when developing models for high-precision geodetic quality positioning. For example, both dual-frequency and triple-frequency data processing models can be developed through the various combinations of the signals.

Abstract

Accurate and well-defined time and coordinate reference systems are the basis for GNSS geodesy, where positions are computed from radio signal travel time measurements and provided as a set of coordinates. This chapter contains a review of the time systems and coordinate systems (and reference frames). The aim is to provide only the necessary background information, and references for a more detailed understanding of the pertinent concepts and equations are provided.

Abstract

There are several parameter types in geodesy that have to be estimated, but whose values are interesting only for some special studies. GNSS phase ambiguities, clock parameters, and troposphere are examples of such parameter types. Moreover, if the user is interested only in one or particular type of parameters, all the others can be ignored after estimating them. On the basis of the definition of geodesy, (Geodesy, is the Earth science of accurately measuring and understanding Earth’s geometric shape, orientation in space, and gravitational field. The field also incorporates studies of how these properties change over time and equivalent measurements for other planets (https://en.wikipedia.org/wiki/Geodesy).) geodetic parameters include, but are not limited to, station position coordinates and velocities; satellite position coordinates and velocities; baseline vectors; heights and height systems; the Earth’s orientation and its geocenter, the geoid, and other related quantities from gravity field measurements. These geodetic quantities (parameters) are derived (estimated) using precise measurements and the exact science of geodesy, for which GNSS is one of the widespread, globally accessible tools. This chapter is a quick overview of the concepts.

Abstract

This chapter summarizes the necessary information to understand GNSS measurement and observation models. Section 5.1 presents the underlying observation equations for GNSS signals, while signal propagation errors and correction methods are introduced in Sects. 5.2 and 5.3. Specifically, receiver and satellite antenna phase center modeling is summarized in Sect. 5.3.2.3, and other topics such as phase wind-up and Earth deformation effects on station coordinates are also, respectively, discussed in Sects. 5.3.2.4 and 5.3.2.6. Such discussions are provided with the assumption that the reader is primarily interested in understanding the concepts applicable in achieving high precision for geodesy and similar applications. Pertinent references are provided as necessary for further background understanding.

Abstract

From definitions of a geodetic CORS system to examples of tracking networks around the world and raw data exchange formats, this chapter highlights the ground-based infrastructure for collecting continuous tracking data from the earth-orbiting satellites. Such infrastructure, having increased over the years, is run by various agencies, organizations, and institutions to enable the science and practice of GNSS geodesy. The primary product from the CORS infrastructure is the satellite tracking data, archived in standard raw data exchange formats such as RINEX, for subsequent modeling and estimation of station coordinates and velocities, satellite orbits, clock products, reference frames, and other related products.

Abstract

This chapter discusses the typical processing workflow for estimating geodetic parameters from GNSS data. The scope is limited to post-processed data from relative static positioning, and the processing starts with raw GNSS observables. However, in the case of data reprocessing, normal equations become the starting point of the processing workflow. The chapter starts with preprocessing step that is common in GNSS software packages and is meant for quality control of data before the actual processing occurs. This is followed by a section focused on ambiguity fixing for precise positioning (and other parameter estimations). The chapter concludes with a section on reprocessing and data combinations from normal equations.