利用Google街景影像進行地形遮蔽下之衛星可視性分析

Utilizing Google Street View Images for Satellite Visibility Analysis of Topographic Obstructions

近年來，隨著世界各國接連發展衛星系統，GNSS定位系統於焉成形，提升全球衛星覆蓋率與衛星定位技術的使用層面。GNSS定位技術與地面動態載台結合以快速獲取空間資訊之應用逐漸興起，而隨著地面動態載台於街道巷弄間移動，環境地形因素對於衛星訊號之傳遞影響將更為複雜。鑒於Google街景影像其獲取之拍攝範圍與地面動態載台路徑之高重疊率，加以使用者可大量且免費地獲取該影像，本研究以Google街景影像為材料，進行地形遮蔽效應影響之衛星可視性分析。研究成果顯示，在15分鐘衛星取樣時間的軌道資料中，透過Google街景影像進行地形遮蔽效應影響之衛星可視性分析，其誤差值最大為2.8979°，小於容許視角誤差。本研究方法與流程之最終Sky Plot成果圖與1日每小時PDOP值折線圖可提供使用者預先評估接收站選站品質良窳，並規劃適當的觀測時間，以提升整體測量外業之品質與效益。

GNSS enhances the global coverage of satellites as well as the application of satellite positioning. When combining satellite positioning technique and inertial navigation system on the terrestrial mobile platform, the positional information can be acquired easily. However, the GNSS positioning in dense urban areas is usually unreliable because of topographic occlusion or multipath interference. Therefore, topographic effects must be taken into account for operating satellite visibility analysis. Yet, there are many inconveniences existing in current approaches to the analysis of topographic effects, neither these methods can acquire data with high accuracy. For this reason, this research aims to develop a solution, which can simultaneously possess an efficient and reliable data acquisition. Based on the high coverage and accessibility of Google Street View Service, this study developed an image-based approach for topographic effect analysis by using Google Street View images. The results show that the maximum error of proposed method is less than the tolerance error of orbit data in 15 minutes’satellite sampling time. Moreover, the sky plot and the daily PDOP result graphs of this research can provide useful information, such as available satellite number and the appropriate observation time of the corresponding GNSS receiving station.