應用魚眼物像對應模式於雨量計顯露度測量

Abstract

雨量計所處環境之遮蔽程度將影響降雨觀測的準確性，過度遮蔽恐造成量測結果偏差。為確保降雨資料具代表性，雨量計應架設於開闊場域，並定期檢視其周圍遮蔽情形。 針對雨量計周遭環境之遮蔽程度測量，本研究提出一套影像式雨量計顯露度測量方法，使用魚眼鏡頭拍攝雨量計上方之天空影像，結合基於魚眼投影幾何之嚴密物像對應模式，並依據顯露度幾何條件，定義相關參數並推導誤差改正方法，以符實務應用要求。 為驗證所提方法之可行性與應用價值，本研究設計模擬實驗與實際實驗，透過前者掌握重要影響因子，而後依據模擬實驗成果，於實際場域獲取實際觀測資料，進行顯露度解算與成果分析。 實驗成果顯示，經由本研究研擬之顯露度測量程序，配合各階段之率定演算法與誤差分析及處理機制，解算所需參數同時控管其品質，最終可提供誤差1度以內之仰角測量品質，滿足雨量計顯露度測量之精度需求。

The operation of rain gauges is influenced by environmental shielding, where excessive obstruction may lead to precipitation measurement biases. To ensure the representativeness of measurement results, rain gauges should be installed in open areas and their surrounding conditions should be regularly monitored. In response to this practical need, this study proposes an image-based method for exposure measurement of rain gauges. By capturing upward-looking sky images using a fisheye lens, and applying an object-image correspondence based on rigorous fisheye projection geometry, relevant parameters are defined according to the geometric conditions of exposure. Additionally, an error correction method is derived to account for potential measurement deviations. To verify the feasibility and practical applicability of the proposed method, this study designed simulation and field experiments. The simulation experiments were conducted to identify key influencing factors in exposure measurement, while the field experiments acquired real observation data based on the simulation results, followed by parameter computation and analysis. Experimental results indicate that the proposed exposure measurement procedure, combined with calibration algorithms and error correction mechanisms at various stages, can effectively derive the required parameters and control their quality. The final outcomes demonstrate that the measurement method can achieve elevation angle error within 1 degree, thereby fulfilling the accuracy requirements for rain gauge exposure measurement.