TABLE OF CONTENTS Terrestrial positioning systems are position location system that uses land-based transmitters or reference points to act as reference points for the calculation of position information. Some of the terrestrial based positioning systems include long range aid to navigation (LORAN), dead reckoning (DR) and inertial navigation systems (INS).
Long range aid to navigation is a radio positioning system that provides location information by using the time difference between receptions of radio signals from two or more high power fixed transmitters.
The LORAN system uses a master transmitter and secondary transmitters. The secondary transmitters emit their timing pulses (time of emission TOE) at a fixed time after the master transmitter sends its timing pulses. By knowing the position of the transmitters and relative time that it takes for each of the signals to be received, a line of position arc can be mapped for each transmitter.
Line of position (LOP) is sequence of points that represent the solution to the timing function from the transmitter time of emission. The LOP is determined by measuring the amount of time that has elapsed (time delay) for the reception of a pulse transmission. Where the LOP arcs cross is the location of the LORAN receiver.
The transmission of these timing pulses is repeated. Group repetition interval is time duration of a sequence of signals or pulses. GRI is used in the LORAN system to hold a sequence of timing pulses that include a master and secondary pulses.
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