應用NDVI與地景指標評估林地利用的衝擊－以苗栗獅潭地區多期福衛二號影像為例

Using NDVI and Landscape Metrics to Assess Impacts of Forest Land-Use in Shitan, Miaoli with Multi-Temporal FORMOSAT-2 Images

謝漢欽(Han-Ching Hsieh) ； 黃俊元(Chun-Yuan Huang)

《台灣林業科學》 35卷2期 (2020/06) Pp. 173-191

https://doi.org/10.7075/TJFS.202006_35(2).0005

摘要

為能有效提供公私有林邊際土地利用變動與森林覆蓋分布狀況的科學數據，本研究選擇苗栗縣獅潭地區公私有森林覆蓋地為研究試驗區，蒐集2005年至2014年間8個年期無雲的福衛二號影像。為提高分析結果的可靠度，運用數值高程模型求算各期影像的太陽入射共同陰影區，濾除共同陰影區，建立各年期影像的NDVI影像。以物件為基礎的平均值調整影像分割法，萃取非植生區塊分布圖層，8個年期的萃取總體精度皆達81%以上。另以地景生態指標分析技術，分析各年期土地利用型之非植生覆蓋區塊空間分布格局。透過兩個層級的地景結構指標變遷分析，評估本區域之森林地景破碎化程度，有逐年變大趨勢。從個別年期坐落於主要土地利用型，區塊平均坡度大於等於16°之非植生覆蓋區塊面積比率進行比較，結果顯示非植生覆蓋區塊發生比率依序於果樹、裸露地、旱田的面積比較大；發生於混淆林、闊葉林、竹林與檳榔的面積比有逐年小幅度增加趨勢。此外應用地區性的空間統計指標，分析各年期非植生覆蓋區塊空間分布圖，可顯示兩個非植生覆蓋區塊熱點區位。以上研究的方法與結果可提供淺山地區土地利用管理的空間決策資訊。

關鍵字

福衛二號 ； 植生指標 ； 地景指標 ； 土地利用 ； 影像分割

並列摘要

To effectively provide scientific-based data of forest cover changes on public and private land-use types, in this study, forestland in Shitan District of Miaoli County was selected as the research experimental area, and 8 cloud-free FORMOSAT-2 (FS2) images from 2005 to 2014 in the area were collected. To improve the reliability of the analyses, a digital elevation model (DEM) was used to calculate the common shadow areas of the sun incident geometry of each date's FS2 image, and after filtering out common shadow areas from each image, the normalized difference vegetation index (NDVI) of each FS2 image was established. Image segmentation with an object-based mean shift algorithm was applied to extract non-vegetation-covered patches (NVCPs). The overall accuracy of the 8-date NVCP extractions exceeded 81%. Combined with analysis of geoprocessing and landscape metrics, the spatial distribution pattern of NVCPs in each land-use type was evaluated. To measure the degree of forest landscape fragmentation, 2 levels of landscape metrics (class and landscape) were selected to access landscape structural changes during these years. Comparing the ratio of the area of NVCPs, the average slope which was more than 16° and occurred with main land-use types in individual images, results showed that the ratios of the area of NVCPs were larger in the order of land-use types of fruit trees, bare land, and dry land, and the ratios of mixed forests, broadleaf forests, bamboo forests, and betel nut (areca) plantations slowly increased year to year. In addition, utilizing a local spatial statistical indicator to analyze the spatial distribution of NVCPs during the 10 years, 2 hotspots of NVCPs were detected. The methods and outcomes of this study can provide spatial decision-making information for managing forest land-use in shallow mountain areas.

並列關鍵字

FORMOSAT-2 ； NDVI ； landscape metrics ； land use ； image segmentation