以精密單點定位技術估計GPS追蹤站之絕對位移速度

Absolute Site Velocity Estimation Using the GPS Precise Point Positioning Technique

陳志嘉(Jhih-Jia Chen) ； 楊名(Ming Yang)

《航測及遙測學刊》 16卷2期 (2011/06) Pp. 115-126

https://doi.org/10.6574/JPRS.2011.16(2).3

摘要

全球定位系統（Global Positioning System, GPS）被廣泛應用在控制網的建立、追蹤站位移速度估計等應用上。傳統上，以相對定位估計追蹤站位移速度，所直接得到的往往是各追蹤站間的相對位移速度；而以IGS（International GNSS Service）精密星曆、時鐘產品定位的精密單點定位（Precise Point Positioning, PPP）技術則具有可直接獲得在國際參考框架（International Terrestrial Reference Frame, ITRF）下的絕對位置解等優勢。但由於上述IGS產品為各分析中心產品之弛約制解的加權平均，其原點和地心間存在差異，連帶影響了PPP的定位成果。因此PPP所得的追蹤站位移速度之精確度，也就值得探討。本研究以均勻分布全球的33個IGS追蹤站於2002年至2010年的資料，以PPP方式估計其位移速度，並與在ITRF下的位移速度相比。在ITRF2000時期，其差異在E、N、H三方向各為0.22±1.34mm/yr、-0.93±0.89mm/yr、4.82±2.20mm/yr，藉由Helmert七參數轉換，差異降至-0.07±1.29mm/yr、-0.25±0.57mm/yr、-0.00±2.22mm/yr。而在ITRF2005時期，差異在三方向各為-0.07±0.73mm/yr、-0.28±0.53mm/yr、2.50±2.04mm/yr，經過轉換後則為0.05±0.64mm/yr、-0.33±0.42mm/yr、0.00±2.01mm/yr，僅在高程方向差異有所改善。代表隨著參考框架更新，IGS產品品質的提升，在ITRF2005時期以PPP方式估計追蹤站的之絕對水平位移速度其精確度已在1mm/yr以內。

關鍵字

精密單點定位 ； 追蹤站位移速度估計 ； 國際參考框架

並列摘要

Global Positioning System (GPS) has been widely used in various applications such as geodetic control networks and site velocity estimation. Traditionally, site velocities have been determined using relative GPS positioning. However, the obtained velocity results are thus relative in nature. In recent years, the precise point positioning (PPP) technique, which uses International GNSS Services (IGS) products - precise satellite ephemerides and clocks - to directly estimate site positions in the International Terrestrial Reference Frame (ITRF), has become a promising tool for absolute site velocity estimation. Nevertheless, the PPP-derived site positions have been reported to be partially biased as a result of the fact that the above IGS products are based on the loosely constrained IGS analysis centre (AC) solutions. So it is an interesting issue to examine the accuracy of PPP-derived site velocities.In this research, we computed a set of PPP-derived velocity solutions for 33 evenly distributed IGS global tracking stations from 2002 to 2010, and compared them with their respective quantities defined in the ITRF. During the ITRF2000 period, the velocity differences in the east, north, and up directions are 0.22±1.34, -0.93±0.89, 4.82±2.20 mm/yr, respectively. After performing the 7-parameter Helmert transformation to absorb the systematic biases between the PPP results and the ITRF, the differences are significantly reduced to -0.07±1.29, -0.25±0.57, -0.00±2.22 mm/yr, respectively. During the ITRF2005 period, the velocity differences in the east, north, and up directions are -0.07±0.73, -0.28±0.53, 2.50±2.04 mm/yr, and 0.05±0.64, -0.33±0.42, 0.00±2.01 mm/yr after Helmert transformation. Only the vertical component is notably improved by the transformation. This indicates that the quality of IGS products improves with time so the biases existed in the PPP solutions are gradually diminishing. It is concluded that under the current ITRF2005, one can reliably use the PPP technique to obtain highly accurate, on the level of sub-mm/yr, absolute horizontal site velocities.

並列關鍵字

Precise point positioning ； site velocity estimation ； International Terrestrial Reference Frame