Using negative soil adjustment factor in soil-adjusted vegetation index (SAVI) for aboveground living biomass estimation in arid grasslands.
Using negative soil adjustment factor in soil-adjusted vegetation index (SAVI) for aboveground living biomass estimation in arid grasslands.
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土壤调节植被指数(SAVI)中负土壤调节因子在干旱草原地上生物量估算中的应用
DOI：
10.1016/j.rse.2018.02.068
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发表时间：
2018-05
影响因子：
13.5
通讯作者：
H. Ren;Guangsheng Zhou;Feng Zhang
中科院分区：
文献类型：
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作者：
H. Ren;Guangsheng Zhou;Feng Zhang
土壤调节植被指数（SAVI）中土壤调节因子（L）从0到1的所有值在植被覆盖稀疏的干旱地区都是不可取的。我们假设SAVI中的负土壤调节因子在干旱地区是令人满意的。在这项研究中，我们探讨了潜在的负土壤调节因子在SAVI对一组在2009年生长季在内蒙古荒漠草原，中国的实地测量。正如假设的那样，负的土壤调节因子被发现可以提供令人满意的土壤背景噪声的降低。萨维（L =-0.2）（R2= 0.64，RMSE = 18.4 g m−2，rRMSE = 25.5%，n = 120）提供了比最佳NDVI显著的改善（归一化植被指数）（即SAVI（L = 0））（R2= 0.44，RMSE = 22.7 g m−2，rRMSE = 31.4%，n = 120）进行地上生物量（AGB）估算。还探讨了负土壤调节因子的物理基础。结果表明，荒漠草原近似植被等值线与土壤线之间的交点位于近红外（near-infrared）平面第一象限的正值和红色区域内，植被等值线的斜率随着AGB的增大而增大，使原点向正交点移动，从而产生负因子。这与报告的SAVI植被等值线行为背道而驰，SAVI的植被等值线行为中，点位于第三象限的负NIR值和红色区域。负因子在荒漠草原绿色覆盖率（PGC）估测中也有较好的表现。我们进一步提出了一个概念模型来描述干旱草原植被等值线的行为。本文的研究结果将补充广泛使用的土壤调节因子。需要进一步研究来验证负土壤因子，并在其他干旱草地上测试概念模型。
All values of soil adjustment factor (L) from 0 to 1 in the soil-adjusted vegetation index (SAVI) were found to be undesirable in arid areas with sparse vegetation cover. We hypothesized that the negative soil adjustment factor in the SAVI would be satisfactory in arid areas. In the study, we explored the potential of negative soil adjustment factor in the SAVI against a set of field measurements during the growing season of 2009 in the desert steppe of Inner Mongolia, China. As hypothesized, negative soil adjustment factor was found to give satisfactory reduction of soil background noise. SAVI (L = −0.2) (R2= 0.64, RMSE = 18.4 g m−2, rRMSE = 25.5%, n = 120) provided dramatic improvements over optimal NDVI (normalized difference vegetation index) (that is, SAVI (L = 0)) (R2= 0.44, RMSE = 22.7 g m−2, rRMSE = 31.4%, n = 120) for aboveground living biomass (AGB) estimation among tested vegetation indices. A physical basis for the negative soil adjustment factor was also explored. Results showed that, the intersected points between approximate vegetation isolines and soil line were situated in the domain of positive values of NIR (near-infrared) and red in the first quadrant of NIR-red plane, and the slopes of vegetation isolines increased with increasing AGB in the desert steppe, thus resulting in negative factor by shifting the origin toward positive intersected points. This runs counter to reported vegetation isolines behavior for SAVI, in which the intersected points were situated in the region of negative values of NIR and red in the third quadrant. The good performance of negative factor was also observed for percent green cover (PGC) estimation in the desert steppe. We further proposed a conceptual model to describe vegetation isolines behavior in arid grasslands. Our findings will complement widely used soil adjustment factor. Further study is needed to validate the negative soil factor and test the conceptual model in other arid grasslands.