GPS接收儀資料品質監控系統及校正系統之建立

Abstract

在台灣地區，由內政部、中研院、氣象局、地調所及各學術團體所設置的GPS固定站已超過100座，未來若有了法定地位的賦予，將很有可能取代現有一等衛星控制點的功能。因此，各衛星追蹤站觀測資料品質的好壞就更形重要。此外，為了更能確保各型GPS接收儀其定位結果能否符合原預期之準確度，應用高準確度校正網，並追溯連繫至國際IGS固定站ITRF坐標系，依校正程序對GPS接收儀進行評估應是有效的方法。本文即構想建立一套GPS接收儀資料品質監控系統及校正系統。 首先，本研究採用了五項觀測資料品質指標，並探討這些指標與基線解算精度間之關聯性。結果發現，以接收儀內部頻率穩定度的影響最大，其次為週波脫落，再其次為多路徑效應。吾人即根據此一結果建立GPS資料品質自動化計算系統，針對內政部各衛星追蹤站觀測資料品質進行管制，希望能夠藉由此一監控流程，當儀器發生故障或追蹤站環境發生變化時，能早期發現問題儘早處理異常狀況，藉以確保各追蹤站觀測資料的品質。 此外，並建立高準確度校正網及校正程序，依ISO建議方法，評估校正場坐標之不確定度。成果顯示該校正場固定站TNML之ITRF坐標，在95%信賴水準，三向度擴充不確定度為33.2 mm。超短距離校正場各校正點，相對固定站TNML（基線距離約50 m），在95%信賴水準，相對位置之三向度擴充不確定度為2.2 mm；若相對固定站TWTF（基線距離約25 km），在95%信賴水準，相對位置之三向度擴充不確定度為13.4 mm。而短距離校正場各校正點，相對固定站TNML（基線距離約5 km），在95%信賴水準，相對位置之三向度擴充不確定度為17.6 mm。此校正網各校正點之坐標不確定度，將作為相關校正服務之主要依據，藉以確保GPS接收儀之定位品質及可靠度。

In Taiwan, there are more than one hundred GPS tracking stations maintained by Ministry of the Interior (MOI), Academia Sinica, Central Weather Bureau and Central Geological Survey. In the further, they may be instead of the GPS controlling points after giving the lawful status. Therefore, the data qualities of the tracking stations are more and more important. For maintaining and ensuring the positioning accuracy of the GPS receivers, an accurate and efficient system for calibrating the GPS receivers must be established. A highly accurate GPS calibration network, tied to the ITRF coordinates of IGS stations, can be effectively used to evaluate the performance of GPS receivers. This study addresses the feasibility of establishing a system for monitoring and calibrating GPS receivers. First, five data quality indexes were adopted and the relationships of the indexes and the positioning precision were found. The frequency stability of GPS receiver is the most importand index, the cycle slip is the second index, and the mutlipath is the third index. According to the results, the auto-analytical system of GPS data quality was established and the MOI’s tracking stations were monitored. When the receiver got some problem or the station’s environment changed, we hope to find and resolve the problems earlier to make sure the high data quality of the tracking stations. Moreover, uncertainties of the GPS calibration network are evaluated based on the method suggested by the ISO (International Organization for Standardization). Analytical results indicate that the 3-D expanded uncertainty of the main station TNML in the ITRF system is around 33.2 mm at the 95% confidence level. The 3-D expanded uncertainties of the calibration points of ultra-short distance network are evaluated to be about 2.2 mm in relation to the main station TNML (the distance are around 50 m) at the 95% confidence level. The 3-D expanded uncertainties of the calibration points of ultra-short distance network are evaluated to be about 13.4 mm in relation to the main station TWTF (the distance are around 25 km) at the 95% confidence level. The 3-D expanded uncertainties of the calibration points of short distance network are evaluated to be about 17.6 mm in relation to the main station TNML (the distance are around 5 km) at the 95% confidence level. The uncertainties of the network’s coordinates are obtained and used as a basis for calibration. The precision of the coordinates suffices to calibrate GPS receivers to ensuring the precision and reliability of positioning.