Scope for application of GPS in Indian Coal Industry  A . Venkateshwar Singareni Collieries Company Ltd Andhra Pradesh, India. sccl@ap.nic.in Introduction Before we get onto the core issue , let us try to recap as to when and where GPS started. The first one called NAVSTAR GPS (Navigation Satellite Timing and Ranging Global Positioning System) was (and still is) a satellite-based radio navigation and surveying system providing precise three dimensional position, navigation and time information to suitably equipped users everywhere on a continuous basis. The system consists of 24 satellites including three active spares , placed in near circular orbits in six orbital planes of 55 o inclination at height of about 20,200 km. There are often more than 24 operational satellites as new ones are launched to replace older satellites. The orbit altitude is such that the satellites repeat the same track and configuration over any point approximately every 24 hours. The satellites have 12-hour periods so that atleast 4 satellites are available for observations for positioning on ground, sea and air at any time throughout the year anywhere in the world. GPS provides specially coded satellite signals that can be processed in a GPS receiver, enabling the receiver to compute position, velocity and time. Signals from four satellites are required to compute the four dimensions of X, Y, Z (position) and Time at any point on Earth. GPS was developed and funded by the U. S. Department of Defence (DOD) during early 1970s primarily for military applications with limited access to civilian users. Virtually all of the development of GPS equipment was under contract from the DOD (US). Many of the contractors to the government also had commercial involvement in similar technologies, especially receivers. This meant that by the early eighties, commercial interest in GPS began to blossom. By 1990, although the system was not fully implemented, it was sufficiently reliable to make general commercial and even personal use viable. The system has now been completed and is in full commercial use GPS Applications GPS receivers have been developed which observe signals transmitted by the satellites and achieve upto 2cm accuracy horizontally and 3cm vertically anywhere on earth’s surface. They have the following advantages over conventional methods of navigation or surveying:
Time and frequency dissemination, based on the precise clocks on board the satellites and controlled by the monitor stations, is another use for GPS. Astronomical observatories, telecommunications facilities, and laboratory standards can be set to precise time signals or controlled to accurate frequencies by special purpose GPS receivers. Research projects have used GPS signals to measure atmospheric parameters.Now, there is an increasing confidence in adapting GPS to other commercial and social applications. GPS Accuracy GPS achieves integrity and protects users against system anomalies and failures by relying on satellite self-checks and , as well as signal assessment by users. Thus, GPS has both integral and independent mechanisms to assure integrity.Augmented GPS systems have additional built-in integrity monitoring that can benefit GPS users. Differential GPS (DGPS) and Real time Kinematic (RTK) systems, such as the network operated by the U.S. Coast Guard (USCG), use an onsite integrity monitor to check satellite-signal validity and provide an independent assessment of satellite health. Because of the real-time capability, continuous availability and the high accuracy potential, GPS usage is very broad and is still growing.
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