A Study on the Relationship between Seasonal Tropospheric Variation and Positioning Accuracy by GPS

季節性對流層變化影響GPS衛星定位精度之研究

王傳盛(Chuan-Sheng Wang) ； 劉說安(Yuei-An Liou)

《航測及遙測學刊》 11卷2期 (2006/06) Pp. 191-200

https://doi.org/10.6574/JPRS.2006.11(2).6

摘要

GPS在大地網型測量的定位精度，在近二十年來已被改進相當的多，主要的誤差或錯誤來源，像是電離層折射、軌道精度、天線相位中心模擬、環境造成的訊號多路徑效應與散射、對流層折射等，都逐漸的被降低或消除。在大地測量最先進的GPS資料分析方法中，水平坐標的定位精度約在1-2mm左右，垂直坐標的定位精度約在5-10mm左右。垂直定位精度較差的理由有兩個。第一因為衛星在天空中的分佈狀況有其理論上的幾何極限值，且截止仰角通常設在15度。第二，由於對流層折射的影響，特別是水氣所造成的訊號遲延。
因台灣位於溫濕之亞熱帶，大氣中水氣含量高且隨著季節呈現相當大的變化；故本研究利用台灣（工業技術研究院量測技術發展中心）、關島、日本、新加坡及中國大陸（武漢）IGS固定站、內政部衛星追蹤站、氣象局GPS觀測站之GPS衛星觀測資料，並採取大氣經驗模式，配合參數估計求取對流層遲延殘差的方式，計算點位橢球高程變化與季節性氣候變化的關係。並分析Saastamoinen model與Hopfield model兩種不同大氣模式應用於GPS定位精度之比較。本研究結果顯示在2003年7月和12月份相同點位橢球高程的月平均值最大可相差20mm，每日求解成果，則可達約60mm；而Saastamoinen model與Hopfield model兩種大氣模式，對相同的資料進行計算則發現橢球高程後者會較前者多出4mm的偏差量。

關鍵字

全球定位系統 ； 橢球高程 ； 對流層效應

並列摘要

The positioning accuracy of the Global Positioning System (GPS) has been improved considerably during the past two decades. The main error sources such as ionospheric refraction, orbital accuracy, antenna phase center variation, signal multipath, and tropospheric delay have been reduced substantially, if not eliminated. In this study, seasonal effect on the GPS positioning accuracy is investigated. Taiwan is chosen for her unique geographic location and complex topography with abound water vapor in the air but spatially and seasonally dependent. The GPS data were collected from continuously operating reference stations by the Ministry of the Interior (MOI), Central Weather Bureau (CWB), and Industrial Technology Research Institute (ITRI) of Taiwan, and International GPS Service (IGS). The investigation of the relationship between variance of the vertical coordinate and change of climate is carried out by computing the GPS data collected in July and December 2003 to represent summer and winter, respectively. In addition, the comparison in results by using the Saastamoinen model and Hopfield model for correcting the influence of the atmospheric path delay is presented. It is found that the maximum difference in the monthly average ellipsoid height between the two months is about 20 mm. The corresponding daily maximum difference is 60 mm. Also, the ellipsoid height derived by using the Saastamoinen model is smaller than that by using the Hopfield model.

並列關鍵字

GPS ； ellipsoid height ； tropospheric effect