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Since the lever arm between the receiving antennae is known, the angle between the

lever arm vector and the line-of-sight vector in the plane containing the satellite can be

found. This process may be extended to received signals from multiple satellites (with

multiple lines of sight) and to multiple receivers enabling the determination of all attitu-

des. The distance

involves the phase difference

Δφ

and can be calculated as follows:

Δφ

= +

(1)

0, 053

deg

360

(2)

Here

is wave length; it can be

∞

19 cm, as in Ref. /2/.

GPS is a form of information technology using systems of hardware, software and

information (time and ephemeris) transmitted from satellites to provide derived infor-

mation (time, position, and velocity) to users. The derived information may be combined

with other systems to perform a variety of tasks. As a distribution system for precision

time signals GPS helps to synchronize global information networks of fiber optics,

communication satellites, radio, coaxial cable, and copper wire.

2.1. The applications of global positioning system

GPS has been tested for surveying large structures since the late 1980s. The past ten

years have seen dramatic reductions in hardware cost coupled with significant increases

in performance, so market pressure caused manufacturers to focus more attention on the

development of low-cost, high-accuracy GPS antennas, and prices are greatly reduced

during last two decades /3/. Recent advances in GPS technology have made it a cost-

effective tool for monitoring safety and performance of bridges: the price of the GPS

receivers employed in structural monitoring systems is below $5,000.

Fields of GPS application are now numerous. GPS is used in all phases of

highway

construction

. Survey data is used to design construction projects. Real-time GPS data is

used to provide precision management of heavy machinery during construction.

Bridge

monitoring

is becoming increasingly important for traveler safety and for maintenance

during life of bridge. The problem is ageing of bridges, since many of them are carrying

greater loads than predicted by design. High accuracy GPS survey receivers are installed

at critical locations on bridges to measure deflection and deformation. This data is used to

ensure bridge integrity and safety.

Train control and collision avoidance

is being imple-

mented in the United States through the deployment of a nationwide differential GPS

network based on vacated Air Force emergency communication sites. A GPS-based sepa-

ration system is being developed that will help trains avoid collisions. Using GPS infor-

mation, the fully automated separation system will activate a warning the trains that they

are too close to one another.

Earthquake monitoring and prediction

is the next field of

successful application of GPS system. High-accuracy GPS surveying receivers are being

used to monitor the earth’s crustal movements preceding earthquakes. In Japan, a network

of hundreds of GPS stations is monitoring shifts of a few millimeters in fault lines. In the

United States, GPS systems gather data for geology research projects related to land mass

movement. GPS is applied for

mining and infrastructure

development and/or manage-

ment in order to obtain public safety, precise location for mine surveying, cost-cutting

and increased productivity in open cut mines, precision location for mining explosives,

oil pipeline development and monitoring.

Public safety

and emergency services

are

benefiting from GPS through better resource management and vehicle dispatch. GPS