隨著城市發展的快速擴張，大地電磁法（Magnetotelluric method， MT）在地下調查中的應用日益增加，範圍涵蓋水文地質研究至地熱能源探勘。然而，隨著城市地區持續擴張，城市化也對大地電磁測勘的設計與資料品質帶來重大挑戰。城市基礎設施的增長不僅會產生較高水準的電磁（EM）噪訊，掩蓋天然的大地電磁訊號，同時也降低了適合測點的可用性，常迫使測站必須遷移，進而影響空間解析度，並連帶影響地下成像的品質。儘管這些問題具有實務上的重要性，其對大地電磁結果的影響仍未被充分釐清，因此仍需更清楚地了解這些因素如何影響測勘成果。為回應此研究缺口，本研究提出一套以模擬為基礎的方法，用以檢視城市相關因素在貼近實際測勘環境的條件下，如何影響大地電磁的結果。具體而言，本研究聚焦於城市大地電磁測勘中常見的兩個面向，即噪訊條件下的大地電磁響應，以及測站間距對反演結果的影響。針對第一個面向，本研究利用一維正演模型生成合成大地電磁訊號，並施加不同的噪訊條件，再將所得響應與正演模型中已知的理想響應進行比較評估。針對第二個面向，本研究透過在不同測站間距配置下，施加一維與二維反演，探討測站間距對結果的影響。研究結果顯示，傳遞函數中的長週期區段普遍最容易受到噪訊影響，表現為視電阻率與相位上的散布情形，且隨著噪訊水準提高，此散布現象會擴展至更高頻率範圍。暫態噪訊所造成的損害程度高於高斯白噪訊。基於此發現，針對測站間距對反演結果影響的評估顯示，一維反演由於各測站皆為獨立反演，因此大致不受測站間距影響，但在個別測站層級仍容易受噪訊影響，因缺乏鄰近測站資料可供校正。相對而言，二維反演則明顯對間距敏感，較密的間距能提升結構解析度，但在噪訊條件下也容易產生假象，而較疏的間距則能提供較穩定但細節較少的結果。當測站分布不規則，特別是當偏移測站具有與周圍不同的地下地質條件時，二維反演的結果會進一步劣化，而此種情況對一維反演的影響則相對較小。本研究的發現為城市環境中進行的大地電磁測勘提供了實務參考，有助於評估測站可及性與地下成像品質之間可接受的取捨關係。這些成果旨在為持續調整大地電磁測勘方法，以因應持續擴張之現代城市環境的實際需求，貢獻一份力量。;With the rapid growth of urban development， the Magnetotelluric (MT) method has seen increasing application in subsurface investigations， ranging from hydrogeological studies to geothermal energy exploration. As urban areas continue to expand， however， urbanization also introduces significant challenges to MT survey design and data quality. The growth of urban infrastructure not only generates elevated levels of electromagnetic (EM) noise that obscure natural MT signals， but also reduces the availability of suitable measurement sites， often forcing station relocations that compromise spatial resolution and， in turn， the quality of subsurface imaging. Despite the practical relevance of these issues， their influence on MT results remains insufficiently characterized， and a clearer understanding of how these factors affect survey outcomes is still needed. In response to this gap， this study presents a simulation-based approach to examine how urban-related factors affect MT outcomes under conditions representative of real survey environments. Specifically， the study focuses on two aspects commonly encountered in urban MT surveys， MT response under noisy conditions and the effect of site spacing on inversion results. To address the first aspect， synthetic MT signals were generated using a 1D forward modeling approach and subjected to varying noise conditions， with the resulting responses evaluated against a known ideal response from the forward model. To address the second aspect， the effect of site spacing was investigated by applying 1D and 2D inversion under varying station distance configurations. The results show that the long period segment of the transfer function is generally most vulnerable to noise， observed as scatter in apparent resistivity and phase， with this scatter expanding into higher frequencies as noise levels increase. Transient noise causes more damage than Gaussian white noise. Building on this， the evaluation of site spacing effects on inversion results shows that 1D inversion is largely unaffected by site spacing， since each site is inverted independently， although it remains vulnerable to noise at individual sites with no neighboring data available to correct it. 2D inversion， by contrast， is clearly sensitive to spacing， with denser spacing improving structural resolution but introducing artifacts under noisy conditions， while wider spacing gives more stable but less detailed results. Irregular site distribution further degrades the 2D inversion， particularly when displaced sites carry different subsurface geology， a condition that 1D inversion tolerates well. The findings from this study provide a practical reference for MT surveys conducted in urban environments， helping to estimate acceptable trade-offs between site accessibility and subsurface imaging quality. These outcomes are intended to contribute to a broader effort to adapt MT surveying methodology to the realities of modern urban environments that continue to grow.
