高程基準與高程系統研析與建議

Review and Recommendations for Vertical Datums and Height Systems

根據我國《國土測繪法》及《基本測量實施規則》，測量基準包括大地基準、高程基準、深度基準及重力基準，並分別配合相對應之參考系統，構成國家測繪之基本準據。我國現行法定高程基準為二○○一臺灣高程基準（TaiWan Vertical Datum 2001，TWVD2001），並已建立重力法大地起伏模型（TWGEOID2014）與混合法大地起伏模型（TWHYGEO2014），作為高程轉換與高程現代化之技術基礎。隨著全球導航衛星系統（Global Navigation Satellite System，GNSS）技術發展與高程現代化推動，國際間高程系統已逐步由傳統水準網導向以GNSS橢球高結合大地起伏模型計算正高之模式，並持續朝向物理一致性更高之重力法大地起伏模型發展。本文整理我國高程基準與高程系統現況，說明重力法與混合法大地起伏模型之建置與差異，並比較美國、歐盟、日本、澳洲及紐西蘭之高程基準發展趨勢，同時介紹美國NAPGD2022之制度與技術架構。綜合比較顯示，混合法大地起伏模型較有利於銜接既有工程成果與現行高程系統，重力法大地起伏模型則較具物理一致性、跨區域整合能力與長期發展潛力。考量臺灣位處板塊活動及地層下陷顯著區域，GNSS與水準測量之時空一致性對幾何大地起伏與混合法大地起伏模型精度具有關鍵影響，因此本文進一步提出GNSS與水準測量同步施測之必要性與分區分級作業建議。綜合制度延續性、工程實務需求及國際高程現代化趨勢，本文建議我國採行TWVD2001與GNSS結合重力法大地起伏模型並行之雙系統模式，並配合重啟海、陸、空重力測量、建立垂直速度場模型及完善新舊基準轉換機制，以作為未來高程現代化推動之方向。

According to Taiwan’s National Land Surveying and Mapping Act and its related regulations, the national surveying framework consists of the geodetic datum, vertical datum, chart datum, and gravity datum, together with their corresponding reference systems. Taiwan’s current legal vertical datum is the TaiWan Vertical Datum 2001 (TWVD2001), and the technical basis for height conversion and height modernization has been established through the gravimetric geoid model TWGEOID2014 and the hybrid geoid model TWHYGEO2014. With the rapid development of Global Navigation Satellite System (GNSS) techniques and the worldwide trend of height modernization, many countries have gradually shifted from traditional leveling-based height determination toward GNSS ellipsoidal heights combined with geoid models, and further toward gravimetric geoid models with stronger physical consistency. This paper reviews Taiwan’s present vertical datum and vertical system, explains the development and characteristics of gravimetric and hybrid geoid models, and compares the modernization strategies adopted in the United States, Europe, Japan, Australia, and New Zealand. The framework and technical implications of the U.S. NAPGD2022 are also introduced. The comparison indicates that hybrid geoid models are more practical for maintaining compatibility with existing engineering applications and legacy vertical systems, whereas gravimetric geoid models provide stronger physical consistency, better regional integration capability, and greater long-term potential. Because Taiwan is located in an area of active crustal deformation and significant land subsidence, the temporal consistency between GNSS and leveling observations is crucial for the accuracy of geometric geoid determination and hybrid geoid modeling. Therefore, this paper further discusses the necessity of synchronous GNSS and leveling observations and proposes a graded operational strategy based on regional deformation conditions. Considering institutional continuity, engineering practice, and international development trends, this study recommends that Taiwan adopt a dual-system framework in which TWVD2001 is maintained in parallel with a GNSS-based orthometric height system supported by a gravimetric geoid model. To support future height modernization, this framework should be accompanied by renewed terrestrial, airborne, and marine gravity surveys, the establishment of a vertical velocity model, and the development of transformation mechanisms between the old and new vertical systems.