Understanding satellite navigation

391 Pages·2015·16.7 MB·English

by  Rajat Acharya

Understanding
Satellite Navigation
Rajat Acharya
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Preface
IwasverymuchmotivatedtowriteabookonSatelliteNavigationPrincipleswhen
mybookletpublishedinternallyinISROonthissubjectfortheSatelliteNavigation
Course by the Centre for Space Science and Technology Education-Asia Pacific
(CSSTE-AP) was much appreciated by my students. From the feedback I received
from people from a wide spectrum of professions and countries and represent both
commercialandstrategicusers,aswellasresearchers,itwasclearthatabook was
neededwhichwasacceptableequallyintermsofeaseofunderstandingandpertinent.
Itwasobviousthatagoodintroductorybookwithaselectiveassortmentofsubjects
and explanations simple enough for new learners was necessary. So, this book has
been written with the aim of introducing the subject to beginners, coming from
different backgrounds, in a very congenial form, so that the subject can be learned
fromscratch.
Oneofthemainfeaturesofthisbookisthatitexplainsthebasicworkingprin-
ciples right from a foundation level with just the necessary mathematics and no
complex-looking equations. This book is written keeping in mind the undergradu-
ates and all those readers who are being introduced to the subject for the first
time. It is expected that the simplistic approach developed from the first principle
yetincorporatingalltechnicalities,willnotonlyservethemwellbutalsobeasource
of enjoyable learning.
Thisbookwillcoverthebasicworkingprinciplesofthegenericsatellitenaviga-
tion system, instead of concentrating on any particular existing system. It will
emphasize the build up of fundamental ideas for each involved process based on
elementary physics added to rational common sense. Every basic principle is fol-
lowed by mathematical substantiation, but using only as much mathematics as is
deemed necessary for target readers. In addition, this book employs MATLAB as
a visualisation tool, for every important new concept that is introduced. This will
allow readers to corroborate all that they have learned through simulation, which
we believemakesthis book unique.
Finally, it is worth mentioning that all the relevant topics on the subject have
beenencompassedinacomprehensivemanner.Howevertheviewsandtheopinions
presentedherearethoseoftheauthoranddonotnecessarilyreflecttheviewsofhis
employer, northe Government ofIndia.
RajatAcharya
XIII
Acknowledgment
IwishtoextendmysinceregratitudetotheUniversityofCalcuttaandespeciallyto
personalities like Prof. Asish Dasgupta, Prof. Apurba Datta and Prof. Bijoy
Banerjee, who have always been my inspiration. I am also grateful to the, Space
Applications Centre (SAC-ISRO) for the supportit has providedme. Thecourtesy
extended by Dr Bijoy Roy, Dr Chandrashekhar, Mr Suman Aich, and Mr Ananya
RoyofSACbyagreeingtoreviewandcommentontheearlyversionsofthemanu-
script are also very much appreciated. Thanks are due to Dr Suman Ganguly of
CFRSI for his kind cooperation. I also acknowledge the generous gestures of
Dr M R Sivaraman, Dr Kalyan Bandyopadhyay, Mr Vilas Palsule and the whole
team of the CSSTE-AP. I would also like to thank the entire Elsevier team and
the peer reviewers of this book. Last but not the least, I sincerely thank my wife
Chandrani,mysonAnubrata,andmyparents,fortheirinspirationandfortherelent-
lesssacrificestheymadeduringthewritingofthisbookinordertomakethiseffort
a success.
XV
CHAPTER
1
Introduction to Navigation
CHAPTER OUTLINE
1.1 Introduction.........................................................................................................1
1.1.1 Organizationofthisbook.....................................................................2
1.2 Navigation...........................................................................................................4
1.2.1 Historyofnavigation...........................................................................4
1.2.2 Typesofnavigation.............................................................................8
1.2.2.1 Guidance.....................................................................................8
1.2.2.2 Deadreckoning............................................................................8
1.2.2.3 Piloting.........................................................................................9
1.3 Referencingaposition..........................................................................................9
1.3.1 Referenceframe...............................................................................11
1.3.1.1 Heliocentricreferenceframe.......................................................12
1.3.1.2 Geocentricreferenceframes.......................................................12
1.3.1.3 Localreferenceframes...............................................................17
1.3.1.4 Conversionsbetweencoordinatesystems....................................17
1.4 Radionavigationsystem.....................................................................................21
1.4.1 Pilotingsystem................................................................................22
1.4.2 Guidancesystem..............................................................................23
1.4.3 Deadreckoningsystem.....................................................................24
Conceptualquestions................................................................................................25
References...............................................................................................................25
1.1 Introduction
Navigationisabasicneedforanyonewhowantstomovewithapurpose.Navigation
istheartofmovinginasuitabledirectioninordertoarriveatadesiredlocation.Thus,
eveninprehistorictimes,whenthemostprimitiveformofanimalsstartedmovingon
earth,theartofnavigationexistedinitsmostancientform.Eventoday,whenhumans,
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,
withadesiretoreachsomewhere,weperformsomesortofnavigation.
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
1
UnderstandingSatelliteNavigation.http://dx.doi.org/10.1016/B978-0-12-799949-4.00001-4
Copyright©2014ElsevierInc.Allrightsreserved.
2 CHAPTER 1 Introduction to Navigation
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
anddecidethecourseofourmovement.However,thismethoddoesnotworkfora
new destination or for places where such landmarks are not present, which is the
reasonwhypeoplegetlostindesertsorontheoceans.Insuchsituations,wepaper
ordigitalmaps,whichgivesimilarinformation.However,whetherpaperordigital,
orasmentalpicturesincludingothergeographicalinformation,thesemapsareaids
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,itisapparentthatwefirstneedtoknowourpositiontoidentifycorrectly
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 derivethe 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 ofmovement.
However, positions are not sought only for movement. Sometimes our exact
positionisalsorequiredtobecorrelatedwithotherfactsortoderiveancillaryinfor-
mation.Forexample,ifweknowourpositionontheearth’ssurface,wecaneasily
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
oritsderivatives,suchastectonicorothercrustalmovements.Therearemanyother
interestingapplicationsofnavigation, which wewilldiscussinChapter10. There,
weshallcometoknowhowthisknowledgeaboutpositionanditsderivativescanbe
used for manyexcitingapplications.
Thegeneralrequirementoftheestimationofpositionisglobal;forthat,weneed
to represent positions uniquely. Positions are hence represented in terms of global
standardssuchthatpositionsofallthepointsonandneartheearthcanbeexpressed
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
ofdeterminingtheuniqueidentityoftheplacewhereheorsheiscurrentlylocated.
Thesecoordinatesarehencechosentospecifythepositionsinaconvenientmanner.
Inlater subsections ofthischapter, wewill learn about reference frames andcoor-
dinate systems, which forms the basis for representing the positions. Nevertheless,
the definition of these coordinates assumes the existence of certain geodetic
parameters.
1.1.1 Organization of this book
ThephilosopherSocratessaid“Knowthyself.”Attheoutsetoflearningnavigation,
wecanupdatethistosay,“Know(thepositionof)thyself.”Thus,ourentireendeavor
throughout thisbookwillbetounderstand thefundamentals ofhowmodern space
1.1 Introduction 3
technologyisusedtofixourownposition,aidedbyadvancedtechniquesandeffec-
tiveresources.Detailsaboutexistingsystemscurrentlybeingusedforthispurpose
will be discussed post hoc.
However, it is also important to know how the information is organized in this
book.Themorelogicallythingsaredevelopedhere,themoreeasyitwillbetoun-
derstandthem.Thus,itisagoodideatofirsthaveaholisticviewofhowthedifferent
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
describingtheoverallorganizationofthisbook,aboutwhichmanyofushaveagen-
eral apathy and atendency towant toskip this explanatorymaterial.
Thefirstchapterofthisbookisinformative.Wewillstartbyintroducingtheterm
‘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
theart.Wewillfirstlearnaboutthehistoricaldevelopmentofthenavigationsystem.
WhilsttosomehistorymaysoundboringaccordingtoSirFrancisBacon“Histories
makemenwise”.Wewillthereforetakealookatthehistoryofsatellitenavigation
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
ofthesewillbecoveredinthischapter,andreadingit,wehope,willbeasinteresting
asthetechnologyinsubsequentchapters.Chapter2isalsoinformation based,pri-
marilyregardingtheoverallarchitecturalsegmentsofthewholesatellitenavigation
system.Althoughwewillonlylearnindetailaboutthecontrolsegmentinthischap-
ter, other elements will be discussed in the following chapters. Enjoyment of this
bookwillintensifyinChapter3,wherewedescribethespacesegmentofthearchi-
tecture. From this chapter onward, there will be frequent Matlab activities illus-
trating the current topic. We suggest that readers attempt these activities as they
comeacrossthem,ratherthanleavingthemtotheend.Chapter4detailsthesatellite
signals used for navigation purposes and transmitted by satellites. Their character-
isticswillbedescribedandtherationalefortheiruseexplained.Chapter5describes
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
toderivetheparametersrequiredtofixaposition.Chapter6explainsthealgorithms
for the derivation of the navigation parameters i.e. position, velocity, and time, by
usingthemeasurementsandestimationsperformedinthereceivers.Receivererrors
insuchestimationswiththeirsourcesandeffectsarediscussedindetailinChapter7.
Chapter8containsthetopicofdifferentialnavigationsystem.Itisavastsubjectthat
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
looksatspecial topics suchastheKalmanfilterandtheionosphere,bothofwhich
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 ofsatellite navigation.
4 CHAPTER 1 Introduction to Navigation
1.2 Navigation
Navigationisrelatedtotheartofgettingfromoneplacetoanother,safelyandeffi-
ciently.Although,theword‘navigation’stemsfromtheLatinwordNavigare,which
means ‘to sail or drive a ship,’ its contemporary meaning is the art of providing
position and/ordirection toanyoneon land orsea or inspace (Elliot et al. 2001).
1.2.1 History of navigation
Theartofnavigationpredatedtheadventofmankind.Prehistoricanimalsmovedin
search of food using their innate navigation skills. Figure 1.1, however, is only
indicative.
Humanshavebeenusingdifferenttechniquesofnavigationfromtheearlyages
of civilization. Primitive people living in caves had to hunt deep in the forest in
search of food when geographical movement was not easy and finding their way
back was difficult. Thus, they made special marks on trees or erected stone pillars
tocreatelandmarksinordertofindtheirwaybackhome.Theuseofsoundorsmoke
signalswereanothercommonmeansoffindingtheirwayback.Wewilllookmoreat
theformalclassificationslater,butitisworthmentioningherethatthesemostprim-
itivemethods ofnavigation were oftheguidance type.
Navigationdevelopedatsea,withmostdevelopmentsinthemodernnavigation
systemoccurringintheprocessofguidingseavehicles.Inancienttimes,seafaring
explorers started traveling across the oceans in search of new lands, in order to
increase trade and colonize. Development in the field became necessary in order
to cater to the needs of voyages and the constant effort to improve them.
FIGURE1.1
Primitivenavigation.
1.2 Navigation 5
Asmentionedbefore,mappingtheseaalongsideitsadjacentlandsisnotnavigation,
butderivingonesownpositionfromitandthusdecidingthedirectionofmovement
toward a certain destination is. However, both systems were developed simulta-
neously and are sometimes treated as the same thing. In this section, we restrict
our discussion tonavigation only.
Thefirstkindofseanavigatingwasprobablydonebyskirtingaroundthecoast,
andthusbystayinginsightofland.Pictorialmapswerecreatedduringthistimeby
sailorswhowoulddrawwhattheycouldseealongthecoast.Usingthese,theycould
return or retrace their course on subsequent journeys. The first known coastal and
river maps were from China in around 2000 B.C. and indicated sailing directions
(Wellenhof et al. 2003). However, whenvoyages ventured further out into the sea,
the only means of navigating was by observing the position of the sun and stars.
This kind of navigation is termed celestial navigation. Some experienced sailors
could also navigate by understanding the winds or determining the depth of the
seabed,fromwhichtheycouldestimatetheirdistancefromtheland.Thiswasprob-
ably the earliest form ofbathymetric navigation.
WrittenrecordsofcelestialnavigationdatebacktothethirdcenturyB.C.Some
oftheseaccountsareavailableinHomer’sepic,TheOdyssey(HistoryofNavigation,
2007).Theastrolabe,whichmeasurestheelevationofthesunandthestars,asshown
inFigure1.2(a)becamethemaininstrumentforpositioningandwasapparentlyused
evenbefore600BC(Kayton,1989).HeronandVitruviousgaveadetaileddescrip-
tion of the odometer, an instrument to measure distance (Wellenhof et al. 2003).
During thistime, Greek andEgyptian sailors started using the polarstars andcon-
stellationstonavigatebecausetheydidnotdisappearbelowthehorizonthroughout
thenight.However,movementusingpolestarsneededtobecorrectedwithtimeas
the stars change their positions because of the wobbling of the earth on its axis.
Measurementsoftheinstrumentswere aidedbynauticalcharts.Ptolemyproduced
the first world map, which remained in use for many years during sea voyages.
Textual descriptions for sailing directions have been in use in one form or another
since then.
Themiddleagesinnavigationweremarkedbythediscoveryoflodestone.With
this,navigationbecameeasierforsailors,whostartedtouseitforitsmagneticprop-
erties. Comparing it with detailed maps of the period, they could find their way
easily evenwith unfavorable skyconditions allowing sailors tonavigate evenwith
limited visibility. The first true mariner’s compass was invented in Europe toward
the beginning of the thirteenth century A.D. Thus, when Christopher Columbus
set out on his transatlantic voyage in 1492, he had only a compass, a few dated
measuringinstruments,amethodtocorrectforthealtitudeofPolaris,andsomerudi-
mentarynautical charts astools for navigation.
Fromthemiddleofthesixteenthcentury,navigationsawarapiddevelopmentin
relatedtechnologywhenanumberofinstrumentsandmethodswereinvented.This
was when the Europeans started to settle colonies in different countries, and they
used sea routes to navigate to these new lands. The improvement of navigational
techniques became mandatory and the mathematical approach toward navigation