Chapter 1

Chapter 1 introduces the reader to the generic term “navigation” and introduces its subtleties with relevance to everyday life. It starts with the formal definition of the term followed by the history of navigation from its prehistoric beginnings to the current state of the art. The development of navigation techniques over the years is described in a concise manner. It then explains the different forms of navigation with a brief description of one system for each of these kinds. Prerequisite topics of the reference frame and coordinate system are also discussed and elaborated on with reference to the geodetic shape of the earth.

1.1 Introduction?1

1.1.1 Organization of this book?2

1.2 Navigation?4

1.2.1 History of navigation?4

1.2.2 Types of navigation?8

1.2.2.1 Guidance?8

1.2.2.2 Dead reckoning?8

1.2.2.3 Piloting?9

1.3 Referencing a position?9

1.3.1 Reference frame?11

1.3.1.1 Heliocentric reference frame?12

1.3.1.2 Geocentric reference frames?12

1.3.1.3 Local reference frames?17

1.3.1.4 Conversions between coordinate systems?17

1.4 Radio navigation system?21

1.4.1 Piloting system?22

1.4.2 Guidance system?23

1.4.3 Dead reckoning system?24

Conceptual questions?25

References?25

Navigation is a basic need for anyone who wants to move with a purpose. Navigation is the art of moving in a suitable direction in order to arrive at a desired location. Thus, even in prehistoric times, when the most primitive form of animals started moving on earth, the art of navigation existed in its most ancient form. Even today, when humans, the most evolved species on earth, move by flying in the most technologically advanced aircraft or by driving a car, or by riding a bicycle or simply walking, with a desire to reach somewhere, we perform some sort of navigation.

You may have noticed that when we move without the aid of instruments and the route to our destination is known to us, we generally use some sort of mental map, which is mostly pictorial in the form of landmarks and connected paths. On this map, we identify our positions and apply our previous experience to guide us and decide the course of our movement. However, this method does not work for a new destination or for places where such landmarks are not present, which is the reason why people get lost in deserts or on the oceans. In such situations, we paper or digital maps, which give similar information. However, whether paper or digital, or as mental pictures including other geographical information, these maps are aids to navigation that enable us to locate and relate our positions with respect to our destinations and show different possible ways to reach there. The decisions we make in choosing the course of our movement by comparing our position with the available information on these maps is called navigation.

Thus, it is apparent that we first need to know our position to identify correctly where we are, and then to make an appropriate decision about where to move. Satellite navigation is a method that provides us with the correct position on or off the earth for this purpose. Here, signals transmitted from navigation satellites are used to derive the required set of position parameters by a navigation receiver. In turn and in conjunction with the additional information, these parameters are used to further decide the course of movement.

However, positions are not sought only for movement. Sometimes our exact position is also required to be correlated with other facts or to derive ancillary information. For example, if we know our position on the earth's surface, we can easily figure out the kind of climate we must expect. Knowing precise positions of a network of points on the earth will also let one obtain the exact shape of the earth or its derivatives, such as tectonic or other crustal movements. There are many other interesting applications of navigation, which we will discuss in Chapter 10. There, we shall come to know how this knowledge about position and its derivatives can be used for many exciting applications.

The general requirement of the estimation of position is global; for that, we need to represent positions uniquely. Positions are hence represented in terms of global standards such that positions of all the points on and near the earth can be expressed by a certain unique coordinate based on a common reference. It is like the unique identity of that position. Thus, finding the position of a person is simply a matter of determining the unique identity of the place where he or she is currently located. These coordinates are hence chosen to specify the positions in a convenient manner. In later subsections of this chapter, we will learn about reference frames and coordinate systems, which forms the basis for representing the positions. Nevertheless, the definition of these coordinates assumes the existence of certain geodetic parameters.

The philosopher Socrates said “Know thyself.” At the outset of learning navigation, we can update this to say, “Know (the position of) thyself.” Thus, our entire endeavor throughout this book will be to understand the fundamentals of how modern space technology is used to fix our own position, aided by advanced techniques and effective resources. Details about existing systems currently being used for this purpose will be discussed post hoc.

However, it is also important to know how the information is organized in this book. The more logically things are developed here, the more easy it will be to understand them. Thus, it is a good idea to first have a holistic view of how the different aspects of a satellite navigation system are gradually introduced in the chapters in this book. We therefore suggest that readers continue to pursue this section describing the overall organization of this book, about which many of us have a general apathy and a tendency to want to skip this explanatory material.

The first chapter of this book is informative. We will start by introducing the term ‘navigation’ and getting a feel for the real development of a navigation system through a chronological description from their inception up to the current state of the art. We will first learn about the historical development of the navigation system. Whilst to some history may sound boring according to Sir Francis Bacon “Histories make men wise”. We will therefore take a look at the history of satellite navigation before we gear up to understand the technological aspects of the subject. Then, before we move on to the topics of satellite-based navigation, a brief introduction to its predecessors, including other forms of navigation, should prove helpful. All of these will be covered in this chapter, and reading it, we hope, will be as interesting as the technology in subsequent chapters. Chapter 2 is also information based, primarily regarding the overall architectural segments of the whole satellite navigation system. Although we will only learn in detail about the control segment in this chapter, other elements will be discussed in the following chapters. Enjoyment of this book will intensify in Chapter 3, where we describe the space segment of the architecture. From this chapter onward, there will be frequent Matlab activities illustrating the current topic. We suggest that readers attempt these activities as they come across them, rather than leaving them to the end. Chapter 4 details the satellite signals used for navigation purposes and transmitted by satellites. Their characteristics will be described and the rationale for their use explained. Chapter 5 describes the user segment and will provide the working principles of a navigation receiver and the different aspects of it. We will explain how signals are used in receivers to derive the parameters required to fix a position. Chapter 6 explains the algorithms for the derivation of the navigation parameters i.e. position, velocity, and time, by using the measurements and estimations performed in the receivers. Receiver errors in such estimations with their sources and effects are discussed in detail in Chapter 7. Chapter 8 contains the topic of differential navigation system. It is a vast subject that could easily fill a book the same size as this or even bigger. However, we have accommodated it here into a single concise chapter of only few pages. Chapter 9 looks at special topics such as the Kalman filter and the ionosphere, both of which have large implications for navigation systems. Readers may skip reading this particular chapter if they wish, without loss of continuity. However, that would be at the cost of some very interesting material. Finally, Chapter 10 provides details of some important applications of satellite navigation.

Navigation is related to the art of getting from one place to another, safely and efficiently. Although, the word ‘navigation’ stems from the Latin word Navigare, which means ‘to sail or drive a ship,’ its...