| Summary: | 博士 === 國立成功大學 === 地球科學系碩博士班 === 97 === GPS positioning has been widely applied in various fields, and provides all kinds of spatial positioning services and other information such as ionospheric delay which benefits the improvement of living, government public construction and scientific development. However, under the gradually out-of-date GPS systems and increasingly demand for high precision positioning, the United States have addressed Modernized GPS strategy since 2000. The Russian GLONASS system applies the spread spectrum format into Code Division Multiple Access (CDMA) mode, which is compatible with other positioning systems. The European Union (EU) has launched the primary Galileo satellite in 2006 and has launched two satellites at present under In-Orbit Validation (IOV) procedures. China has also announced to invest fund in developing the second generation Beidou navigation satellite system (Compass). The integration of various satellite positioning systems contracted as Global Navigation Satellite System (GNSS) will offer more efficient positioning information and capability in the very near future. At present, applications of GPS survey works utilize high cost dual frequency GPS receivers in Taiwan; therefore our research attempts to replace it with low cost navigation type receiver. We use single frequency receiver (L1 GPS) and combine the network of e–GPS RTK positioning system in Taiwan as virtual reference station. The results of zero baseline using L1 GPS receiver shows that approximately 96% baseline discrepancies are less then 1 mm for the baseline length. It is similar to the obtained test results of general dual frequency GPS receiver. The result reveals the stable and reliable quality of observation achievement. During the 1 hour static baseline test, within 7 km range, 72% of baseline reached fix solutions, which conform to general densified control point survey demand. When collocate with e-GPS system producing VRS data under static baseline test, 75% baselines are able to calculate fixed solutions in 10 km range and the maximum error is less than 3 cm. The results of combining VRS improve the baseline distance benefit of about 30%. When integrate the Single Frequency GPS with VRS observation data in 15m dynamic calculation, the obtained result can reach 90% success rate, horizontal positioning standard error of around 1cm. Nowadays, there are several L1 GPS and Galileo chips in the markets. We can expect the low cost GNSS L1 receivers with a competitive price. Their potential applications include the densification of a nation’s control network, and monitoring of hazardous area such as mountainside, mudflows, landslides, or volcano areas.
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