Evaluation of topographic effects on vegetation indices
- 作者：Gao-Long ZHUJ.M. ChenWei-Min JUYi-Bo LIUBai-Ling XINGJing-Fang ZHU
- 会议时间：2011-08-01
- 关键词：vegetation index ; topographic effect ; topographic correction ; band ratio
- 作者单位：Gao-Long ZHU(International Institute for Earth System Sciences, Nanjing University, Nanjing 210093, China Department of Geography, Minjiang University, Fuzhou 350108, China)J.M. Chen,Wei-Min JU,Yi-Bo LIU,Bai-Ling XING(International Institute for Earth System Sciences, Nanjing University, Nanjing 210093, China)Jing-Fang ZHU(International Institute for Earth System Sciences, Nanjing University, Nanjing 210093, China Department of Geography, University of Toronto, Toronto, Ontario, Canada M5S 3G3)
- 母体文献：第五届海峡两岸遥感遥测会议论文集
- 会议名称：第五届海峡两岸遥感遥测会议
- 会议地点：哈尔滨
- 主办单位：中国地理学会
- 语种：chi
- 分类号：S5;P4
摘要
Topographic influence on vegetation indices (Vis) is an inevitable issue and usually neglected in their large scale applications. In this study, the topographic effects on SR (simple ratio), NDVI (normalized difference vegetation index), RSR (reduced simple ratio), MNDVI (modified normalized difference vegetation index), and MAVI (moisture adjusted vegetation index) derived from Landsat TM data over a mountainous forest area are evaluated. Two simple methods, the cosine correction and c-correction models, with different treatments of the influence of the diffuse irradiance on reflectance, are used to remove the topographic effects on the selected Vis. The results indicate that the topography affects strongly vegetation indices which are not expressed as band ratios, such as RSR and MNDVI, resulting in negative biases on sun-facing slopes and positive biases on sun-backing slopes. As the slope increases, these biases increase rapidly. Therefore, the topographic effects should be removed before using these non-band-ratio vegetation indices for vegetation parameter retrieval. Vegetation indices which can be expressed as band ratios, such as SR, NDVI, MAVI, can greatly reduce the noise caused by topographical variations. However, these indices still include significant topographic effects on steep slopes. SR is more sensitive to topographical variations on steep slopes than NDVI and MAVI, because the reflectances in the near infrared (NIR) and shortwave infrared (SWIR) bands are more sensitive to topographical variations than that in the red band. Diffuse radiance from the sky in the red band can moderates the variations of red band reflectance with topography, while this moderation is absent in the NIR and SWIR bands. The c-correction model is much better than the cosine correction model in removing topographic effects on Vis, especially on steep slopes.