外文翻譯---gps全球衛(wèi)星定位系統(tǒng)(已修改)
2025-01-29 23:23 本頁(yè)面
【正文】 英文文獻(xiàn)The Global Positioning SystemThe global Positioning System (GPS) is revolutionizing surveying technology, Like its predecessor , the TEANSIT Doppler system, GPS shifts the scene of surveying operations from groundtoground measurements to groundtosky , with obvious implications : intervisibility of marks is no longer a criteion for their location 。 operations are possible in nearly all kinds of weather and be performed during day or night 。 and the skills required to utilise the technology are different both in field operations and data processing . But GPS is not merely a replacement for TRANSIT . The simultaneous visibility of multiple satellites allows effective cancellation of the major sources of error in satellite observations , with the result that with GPS, relative positioning accuracies of one part per million(ppm) or better over distances from one kilometer to thousands of kilometers are possible . This means that GPS can pete with terrestrial techniques over short distances, and can achieve more accurate results in less time than TRANSIT observations over longer distances . GPS was designed primarily as a navigation system, to satisfy both military and civilian needs for realtime positioning. This positioning is acplished through the use of coded information, essentially clever timing signals, transmitted by the satellites. Each GPS satellite transmits a unique signal on two Lband frequencies: A at MHz and B at MHz(equivalent to wavelengths of approximately 19 and 24 cm, respectively).The satellite signals consist of the Lband carrier waves modulated with a Standard orS code (formerly called the C/A code),a Precise or P code and a Navigation Message containing, amongst other things ,the coordinates of the satellites as functions of timethe Broadcast Ephemerides. The S code which is intended mainly for civilian use , yields a range measurement precision of about 10 meter, The navigation service provided by this code is referred to as the Standard Positioning Service, The p code is intended for military and selected civili
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