利用水氣微波輻射儀提升GPS定位精度之研究

Enhancing the precision of GPS positioning by using the measurements from water vapor radiometer

GPS水平坐標的精度約在1~2mm，高程坐標的精度約在5~10mm。垂直定位精度較差的理由除了衛星在天空中的分佈有其理論上的極限值，造成垂直方向的衛星分布情況較差；也由於對流層折射的影響，特別是水氣所造成的訊號遲延量無法有效的消除，至今仍是GPS定位需要克服的重要課題之一。本研究利用水氣微波輻射儀（Water Vapor Radiometer, WVR）的觀測資料，配合不同長度的基線及不同的天候狀況來進行定位精度的評估，結果發現在計算中若使用Neill模式配合水氣微波輻射計觀測資料來進行誤差改正，在未降雨的時候只需先將WVR原始觀測資料透過亮溫修正程式進行校正，即可提升5%的定位精度；但若未將WVR資料進行校正，而直接導入WVR原始觀測資料來進行改正，反而會降低GPS基線解算的精度。此外，在降雨的時候不論WVR資料是否經過校正，皆無法利用此一觀測資料來修正GPS對流層誤差。 The horizontal precision of GPS positioning is 1~2 mm and the vertical precision of GPS positioning is 5~10 mm. The reason that the vertical precision is worse than the horizontal precision shall be the distribution of the GPS satellites. Moreover, the water vapor in the atmosphere can’t be eliminated effectively is also the important reason. In this study, the data of Water Vapor Radiometer (WVR) was adopted to correct the tropospheric delay for the GPS positioning in different weather. The results indicated that if the data of WVR after calibration was adopted to correct the tropospheric delay, the precision of GPS positioning can be enhanced about 5% in the period without rainfall. On the other hand, if the observation of WVR without calibration was employed, the precision of GPS positioning can’t be enhanced anymore. Moreover, whatever the WVR data was calibrated or not in the period with rainfall, we can’t use this observation to correct the tropospheric delay for the GPS data processing.

The horizontal precision of GPS positioning is 1~2 mm and the vertical precision of GPS positioning is 5~10 mm. The reason that the vertical precision is worse than the horizontal precision shall be the distribution of the GPS satellites. Moreover, the water vapor in the atmosphere can’t be eliminated effectively is also the important reason. In this study, the data of Water Vapor Radiometer (WVR) was adopted to correct the tropospheric delay for the GPS positioning in different weather. The results indicated that if the data of WVR after calibration was adopted to correct the tropospheric delay, the precision of GPS positioning can be enhanced about 5% in the period without rainfall. On the other hand, if the observation of WVR without calibration was employed, the precision of GPS positioning can’t be enhanced anymore. Moreover, whatever the WVR data was calibrated or not in the period with rainfall, we can’t use this observation to correct the tropospheric delay for the GPS data processing.