Lecture-1 CHAPTER 2 INTRODUCTION TO GPS 2.1 History of GPS GPS is a global navigation satellite system (GNSS). It is the commonly used acronym of NAVSTAR (NAVigation System with Time AndRanging) GPS (Global Positioning System) operated by US DOD (Department of Defence). It helps the user to know his position anywhere on the earth by giving solution to the problem-Where on earth am I? Four GPS coded satellite signals make possible the computation of position in 3- dimensional form, velocity and time offset via receiver clock. It could be contributed on ease of use and cost reduction in hardware simultaneously. GPS surveys provides following advantages:- 3- Dimensional with no need of site Intervisibility.All weather and day or night operation.Data processing with high speed having Common Reference System. High quality control with achieving high precision. Less labor but skilled persons are needed. A new beginning in new project of GPS has been proposed by US Department of Defense in the startingdayof1970s.Thisnewconceptfoundsuccessinfulfillingallrequirementsrelatedto position determination accurately at any time in any weather conditions for US government. After Post processing the data , following values would be possible to visualize:- State Plane coordinates with latitude, longitude, geodetic height. Cartesian Coordinates X, Y, Z.Forward & backward geodetic azimuth with geodetic or slope distances of baselines foreliminatingtheuseofLaplacecorrectionforconversionofastronomicto geodetic azimuth.Point to point varying vertical angle. Accuracy depends upon the quality of known points having baseline components in survey. There are two other Global systems for determination of positions, GLONASS and GALILEO. GLONASS (Russian Navigation Satellite System): Global Navigation Satellite System by Russian Aerospace Defence Forces is a space-based satellite navigation system. It provided an alternative to theNAVSTARGPSofU.S.,duringthecoldwartimeoflastdecadesoftwentiethcentury.At present,itiscomplementaryaswellasalternativeoptionforoperationalnavigationsystemwith relatedprecisionandfullcoverage.ThemodernageGPSreceiversarecompatibletoboth NAVSTAR and GLONASS, thus providing more flexibility of positioning and better accuracy. GinsyecsasareorprteM GALIcollabGPS, TGlaprTorOacholaGGinwsyGLONASS wan 1982 until tystemwasnconomicmelatellites are toatellites. It wiequisite numbrbits.Duringrogram as seeerritory by 20Many upgradeILEO (Euroboration of Euhigh precisioThesystemisGermany may aunchedare roject is in PrThe system is rbit (27 operaOctober2011.chieveIOC orizontal & vatitudesproveGalileo satellitGlobal Searchnitiated via rewill possible bystem at the sas conceived the constellatnotoperationlt-downofRo be launcheill make the sber of satellitthelate200en in third bud010. 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ISRO ).This gnals. ionary ith the hestsaa elp of footpritep in the fielave operators very importaFiint of its signld of modern time and moant role by climigure 2.3: IRNFignal. The opercommunicationey of airlinemb, descent aNSS Architecturgure 2.4: Satellrational SBAion, air traffices, a flight maand engine pe re (source: wwlite constellatioAS implementc control & management onerformance mww.spacealliancon of IRNSS ted by AAIsmanagement an the basis of management oce.ro, 2015) s efforts tendand navigatioGAGAN wilf aircrafts. s to a on. To ll play FiguAll the nanavigationin all condlater the adone the authorizedand calamgiven in TName NAVSTAGLONASGalileo Beidou ure 2.5: Controavigational sanal satellite bditions. It maapplications aservice over d users only. mity are a maTable 2.1. TabCountryARU.S. SSRussia Europe China ol and Space setellite systemy a country gay be noted thare extended a specific regTherefore avajor concern. ble 2.1: CompayNo. of Satellites 24 24 27 35 egment architecms have their sgives it advanthat navigationfor civilian ugion as well vailability of A comparisoarison of globaAl20,200 km19,100 km23,200 km5 satellitesat 36,000 k ctures of GAGspecific consttage of indepnal satellite syuse, but still as can use enservices of thon of global al navigation saltitude/ Orbim in 6 orbital pm in 3 orbital pm in 3 orbital p in geostationkm; GAN and IRNStellations and pendence as wystems are inithe country cncrypted signhe system at navigation saatellite systemsits planes planes planes nary orbit SS (Rao & Lachd other charactwell as availabitially designecontrolling thnal having concrucial timesatellite systems of the world Global/ Regional Global Global Global Global hapelle, 2013)teristics. Ownbility of the syed for militaryhe system cannditional accs including wms of the woOther informatiProject is operational. widely used.Project is operational.Project not operational yProject is operational ining a ystem y use, n shut ess to warfare orld is ion Most . yet. in 2.2 GPS Design Objectives GPS (NAVSTAR) is a satellite based navigation system that provides accurate positioning on the basis of constellation of 24 satellites and navigational facilities to the users. InitiallyGPSwasdesignedformilitaryuseforUSDepartmentofDefensetogivepositioning information at any weather conditions and anywhere on the surface portion of earth. Later it was made available for civilians use also. GPS Positioning Services according to Radio Navigation Plan:- PPS (Precise Positioning Service):- This service can use by approved U.S. Government agencies and specified civil users. Estimated Accuracy:- o22 m & 27.7 m Horizontal & Vertical accuracy respectively. oUTC accuracy of 200 ns time. SPS(StandardPositioningService):-Thisservicehasbeenusedbycivilianswithoutany restrictions but accuracy has been degraded by DOD for Selective Availability.Estimated Accuracy:- o100 m & 156 m Horizontal & Vertical accuracy respectively. oUTC accuracy of 340 ns time. The requirements of accuracy may be different for various users- Moving vehicle, accuracy of about 50 m. Soldier or hiker based users in desert, accuracy of about 15 m. Ship based users in coastal waters, accuracy of about 5 m. Land surveying based users, accuracy of about 1 cm or less. 3 satellites in inclined geosynchronous orbitat about 36,000 km; 27 satellites at 21,500 km in 3 orbital planes regional mode. QZSSJ apan33 satellites in elliptical orbit at about 40,000 km t 32,000 km in different orbital planes RegionalProject not operational yet. IRNSSIndia73 satellites in geostationary orbit at 36,000 km; 4 satellites in inclined geosynchronous orbitat about 36,000 km RegionalProject not operational yet. Differentlevelofaboveaccuracycanbeachievedbyusingdifferenttypesofreceiverswith different positioning methods. Initially most of civilian applications were in marine navigation and surveying. But in modern era, applicationse.g.truckfleetmanagementviacarnavigation,andautomationofmachineryvia construction etc. has become very popular.