Shadow Information Analysis of Digital Aerial Images and Its Application of Forestland Classification

航攝數位影像陰影資訊分析及其在林地分類之應用

謝依達(Yi-Ta Hsieh) ； 鍾玉龍(Yuh-Lurng Chung) ； 陳朝圳(Chaur-Tzuhn Chen)

《航測及遙測學刊》 21卷3期 (2016/11) Pp. 139-149

https://doi.org/10.6574/JPRS.2016.21(3).1

摘要

Forest resource inventory plays a key role in forest management and monitoring. Using photogrammetry and remote sensing techniques in forest resource inventory has obtained significant results such as getting the spatial information of forest. However, during the image capturing process, numerous influential factors hinder the quality of these images, such as the shadows caused by the different angle of the sun, terrain features, and surface object occlusion. Furthermore, the shadows in optical remote sensing images are regarded as image nuisances in numerous applications, specifically, change detection and image classification frequently affecting the accuracy of analytical results. Therefore, research on shadow processing in images is highly valued. In recent years, airborne multispectral aerial image devices have been developed high radiometric resolution data, including Leica ADS-40, Intergraph DMC. These devices are capable of capturing radiometric resolution images of 12 bits or higher, for example, a 12-bit digital number (DN) ranged from 0-4,095. The increased radiometric resolution of digital imagery provides more radiometric detail of potential use in classification or interpretation of land cover of shadow areas. Therefore, the classification of the shadow areas was tested by using four compensation methods (Method 1, used 13-bit spectral information in shadow area for classification; Method 2 used Linear Correlation Correction (LCC) before the classification; Method 3 used Histogram Matching (HM) before the classification, and Method 4 used Multi-Source Data Fusion (MSDF) to aid in classification of shadows.), and compared the benefits of those shadow compensation methods. The results indicated that Method 1 (13-bit high radiometric resolution images; no treatment) and method 2 (LCC) presented better land cover classification results and possessed significant accuracy (over 90% of overall accuracy), and this result further demonstrates that the 13 bit high radiometric resolution images (ADS-40) have sufficient information to satisfy classification of shadow areas.

關鍵字

high radiometric resolution ； land cover classification ； shadow detection ； shadow compensation

並列摘要

森林資源調查扮演森林經營管理與監測的重要關鍵，隨著空間資訊獲取方法的日新月異，利用航遙測分析技術於森林資源調查與監測已有具體成效。然而在遙測影像在拍攝過程中，會受太陽角度、地形起伏、地物遮蔽等因素影響而產生陰影，並影響影像品質。事實上，在航遙測光學影像中，陰影一直被視為變遷分析與影像分類等應用層面的影像雜訊，經常導致分析結果之準確度受到影響，因此影像陰影區域處理為被視為一項重要的研究課題。近年來空載多光譜遙測儀器可獲取高空間、高輻射解析力資料，如Leica ADS-40、Intergraph DMC等多光譜航測影像，皆可獲得12-bit以上的輻射解析力(Digital Number: 0–4,095)，輻射解析力的增加對於陰影區域之解釋提供了極高的潛力。有鑑於此，本研究進行陰影區域的土地覆蓋分類，並採用四種陰影補償技術輔助後續分類（方法1，13-bit陰影光譜資訊；方法2，線性相關校正陰影補償技術；方法3，值方圖匹配陰影補償技術；方法4，多元資料融合陰影補償技術），並比較各方法之優劣。研究結果指出，在進行陰影區域的土地覆蓋分類的結果中，其中方法1（13-bit陰影光譜資訊）與方法2（線性相關校正陰影補償）所得結果較佳（90%以上的總體精確度），成果證明13-bit的高輻射解析力航攝數位影像具有足夠資訊勝任陰影區域土地覆蓋分類。

並列關鍵字

高輻射解析力 ； 土地覆蓋分類 ； 陰影偵測 ； 陰影補償