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 And Ranging) 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

starting day of 1970’s. This new concept found success in fulfilling all requirements related to 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

for eliminating the use of Laplace correction for conversion of astronomic to 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 the NAVSTAR GPS of U.S., during the cold war time of last decades of twentieth century. At present, it is complementary as well as alternative option for operational navigation system with related precision and full coverage. The modern age GPS receivers are compatible to both NAVSTAR and GLONASS, thus providing more flexibility of positioning and better accuracy.

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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.

Initially GPS was designed for military use for US Department of Defense to give positioning 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:-

o 22 m & 27.7 m Horizontal & Vertical accuracy respectively. o UTC accuracy of 200 ns time.

SPS (Standard Positioning Service):- This service has been used by civilians without any restrictions but accuracy has been degraded by DOD for Selective Availability.

Estimated Accuracy:-

o 100 m & 156 m Horizontal & Vertical accuracy respectively. o UTC 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 orbit at about 36,000 km; 27 satellites at 21,500 km in 3 orbital planes

regional mode.

QZSS Japan 3 3 satellites in elliptical orbit at about 40,000 km t 32,000 km in different orbital planes

Regional Project not operational yet.

IRNSS India 7 3 satellites in geostationary orbit at 36,000 km; 4 satellites in inclined geosynchronous orbit at about 36,000 km

Regional Project not operational yet.

Different level of above accuracy can be achieved by using different types of receivers with different positioning methods.

Initially most of civilian applications were in marine navigation and surveying. But in modern era, applications e.g. truck fleet management via car navigation, and automation of machinery via construction etc. has become very popular.