開源軟體RTKLIB解算GPS連續站資料精度：地球科學應用探討

An Investigation of Earth Science Applications Using RTKLIB, an Open-Source Freeware

GPS連續觀測陣列（Continuous GPS array）是近年來監測活動構造與其變形的有效工具之一。台灣現有的高密度GPS連續觀測陣列，在地震發生後常被用來計算地震的同震位移，後續更可用來協助解算震源機制與地體動力模型反演等工作。在眾多GPS解算軟體中，RTKLIB為一款開源（open-source）自由軟體（freeware），有圖形化介面、便於安裝、操作簡易等特色，同時具有主要的GPS/GNSS資料處理與導航功能，然而軟體本身並非專為地球科學應用來開發。再加上開源的特性，與一般地球科學常用的專業軟體，例如GAMIT/GLOBK、Bernese GPS等相比，有價格、取得容易、操作簡單的優勢；與其他線上精密單點定位服務（Precise Point Position, PPP）軟體相比有可控制的參數多、批次處理、無需網路即可解算等優勢，尤其有利於教學與初學者的需要。本文包含兩個主軸：一、利用RTKLIB以單基線相對定位解算2016年2月美濃地震前後三天的GPS資料，估算同震位移，結果顯示使用RTKLIB 2.4版解算的同震位移與GAMIT/GLOBK的結果相近，各站相關係數都達0.8以上，同震位移的南北與東西向較差分別為0.5與0.8mm，合乎地科估算同震位移的需求。二、以RTKLIB精密單點定位解算嘉南地區三站2013年的速度場，結果無法滿足地殼變形後續分析。整體而言，以此版本的測試結果，採用單基線相對定位方法可以有效看出地震同震，精密單點定位用於速度場計算方面雖然還有待改進，但應足以滿足公寸等級的工程應用精度。本文也提出相應的RTKLIB解算配置，以版本2.4而言，同震估算成果可以相當接近專業軟體GAMIT/GLOBK的結果。 The Continuous GPS (CGPS) array has been proved to be one of the effective tools for active deformation monitoring. One typical application of a CGPS array in Taiwan is to estimate coseismic displacements for the inversions of geodynamic models. Among the specialized GPS processing software packages, RTKLIB is an open-source freeware that provides fundamental GPS/GNSS data processing capability with a graphic user interface and is easy to install and operate. Compared to the specialized software packages such as GAMIT/GLOBK or Bernese, its cost-effectiveness is obvious. On the other hand, when it compares to the on-line Precise Point Positioning (PPP) services, it is flexible and opens up more control options to the users with the capability of batch processing. These advantages are essential for the beginners to learn. We analyzed the coseismic displacement of the Meirong earthquake happened on February 6, 2016 with RTKLIB using relative positioning and compared the results to that estimated by GAMIT/GLOBK. The correlation for both estimations are >0.8 and the discrepancies are 0.5 and 0.8 mm in the easting and northing, respectively. In addition, we calculated the velocity field with 3 CGPS stations in 2013 with its PPP mode. However, the result is not as expected and can not support the requirement of crustal deformation. Overall, with the current tested version, v2.4, RTKLIB is effective in relative positioning and the use of it in determining coseismic displacement is successful. The result is nearly identical to that of GAMIT/GLOBK. We also reported the best configuration in doing this. On the other hand, its PPP mode is not accurate enough to support active deformation monitoring at this point but should be sufficient for engineering applications that require decimeter accuracy.

The Continuous GPS (CGPS) array has been proved to be one of the effective tools for active deformation monitoring. One typical application of a CGPS array in Taiwan is to estimate coseismic displacements for the inversions of geodynamic models. Among the specialized GPS processing software packages, RTKLIB is an open-source freeware that provides fundamental GPS/GNSS data processing capability with a graphic user interface and is easy to install and operate. Compared to the specialized software packages such as GAMIT/GLOBK or Bernese, its cost-effectiveness is obvious. On the other hand, when it compares to the on-line Precise Point Positioning (PPP) services, it is flexible and opens up more control options to the users with the capability of batch processing. These advantages are essential for the beginners to learn. We analyzed the coseismic displacement of the Meirong earthquake happened on February 6, 2016 with RTKLIB using relative positioning and compared the results to that estimated by GAMIT/GLOBK. The correlation for both estimations are >0.8 and the discrepancies are 0.5 and 0.8 mm in the easting and northing, respectively. In addition, we calculated the velocity field with 3 CGPS stations in 2013 with its PPP mode. However, the result is not as expected and can not support the requirement of crustal deformation. Overall, with the current tested version, v2.4, RTKLIB is effective in relative positioning and the use of it in determining coseismic displacement is successful. The result is nearly identical to that of GAMIT/GLOBK. We also reported the best configuration in doing this. On the other hand, its PPP mode is not accurate enough to support active deformation monitoring at this point but should be sufficient for engineering applications that require decimeter accuracy.