This is the Global Positioning System or International Positioning System as it is known internationally.
It was originally developed in the 1970s by the US Department of Defense for military purposes, and over the last fifteen years has found a variety of applications for political activities.
The system offers global coverage, 24-hour usage and uses a common WGS84 / IIRF coordinate system.
It consists of 3 sections:
- The Satellite section, which includes about 28 satellites moving in a circular orbit at an altitude of about 20200 Km. Of the 28, 25 are immediately usable while (3) are in reserve. The period of rotation of each satellite is 12 hours in astral time, ie they appear above the horizon of a place about 4 mm earlier each day.
- The control department which includes 1 main earth station and 5 secondary stations and is responsible for the monitoring of the satellites.
- The part of the users that includes the satellite signal receivers, who receive, process and record the measurements.
The basic principle of the system is based on measuring the distance between satellite and receiver.
Specifically, satellites are “stations” with controlled orbits and are “reference points” used to locate the earth.
Distances to satellites are measured by time-dependent “codes”.
Each satellite transmits a number of signals. The mark includes:
A. Two carrier waves at frequencies L 1: 1575.42 MHz and at frequency L 2: 1227.60 Hz
B. Two codes: The P-code (Precision Code) configured on both frequencies L1 & amp; L2 and which provides an accurate measurement of the signal transmission time. The C / A – code (Coarse Acquisition Code) which is configured only in the frequency L1 and which provides information for the download of the P-code.
C. A satellite message (D-code), known as a Navigation Message, which provides information on the position of the satellites of the signal transmission time of each signal.