GPS接收儀檢定指標及觀測資料品質之研究

Abstract

為了探討GPS觀測資料品質與基線解算精度間之關聯性，本研究採用了五項觀測資料品質指標，分別為接收儀內部時鐘的穩定度、接收儀內部時鐘與GPS時鐘的平均偏差量、『觀測資料的筆數』除以『週波脫落的數目』、L1載波的多路徑效應、L2載波的多路徑效應。 為了消除不同環境因素對定位精度所造成的影響，本項測試選在國家GPS校正場進行，將六部儀器同時整置在GPS校正基樁上，於2004年1月5日至1月8日連續同步接收72小時。以Bernese 4.2版軟體及Teqc軟體來進行觀測資料品質的解算，並蒐集IGS日本USUD站、台灣TWTF以及內政部北港PKGM站的GPS觀測資料，約制上述三衛星追蹤站坐標作為主站，以Bernese 4.2版軟體進行不同距離的基線解算。 整體來看，以接收儀內部時鐘頻率穩定度影響定位精度為最大，次之為週波脫落及多路徑效應，最後則為接收儀內部時鐘偏移量。在內部時鐘頻率穩定度及週波脫落這兩項指標上表現較佳的接收儀，其坐標重現性的定位精度也較其它接收儀來得好。

For discussing the relation between the data quality and the precision of the baseline. In this project , five indexes are chosen for discussing GPS data quality. They are clock offset, clock stability, multipath on L1, multipath on L2 and observations by cycle slips (o/slips). For reducing common errors, six types of GPS receivers are chosen and set up at Ultra-Short Distance Network of NML (National Measurement Laboratory, Taiwan) during three days. The first three indicators are calculated by Teqc software and the last two indicators are solved by Bernese software. Moreover, the observations of three GPS tracking stations are obtained through internet, short baseline (about 25 km), middle baseline (about 150 km) and long baseline (around 2000 km) are processed by Bernese software. We found that clock stability and o/slips were very important factors for the positioning. Clock offset and multipath effects would not be the critical factors to influence the GPS results. We hope the information is helpful for GPS users when they decide to purchase any GPS receiver and to process GPS data.