基于VDVI-DPM模型的秦岭生态修复区植被覆盖度反演与成效分级研究

Inversion and restoration effect grading of fractional vegetation cover in ecological restoration areas in the Qinling Mountains based on the VDVI-DPM model

  • 摘要: 针对无人机可见光影像植被覆盖度反演在小尺度复杂地物区存在端元定标不稳定、分级方法缺失的技术难点,以秦岭生态修复区为案例,通过像元二分模型构建了一套兼顾精度与效率的植被覆盖度反演与分级方法,研究量化了非正态特征在空间聚合过程中对植被覆盖度估算的系统性偏移,对比了可见光波段差异植被指数(VDVI)、超绿指数(EXG)、差异增强植被指数(DEVI)三种指数在不同异质背景下的鲁棒性。结果表明:遥感估算植被覆盖度具有尺度依赖性,图像在聚合过程中因趋向正态分布导致端元值收敛,使植被覆盖度随聚合倍数呈线性上升趋势(R2>0.86),每聚合1倍产生0.07%~0.23%的系统性增长。VDVI的总体分级精度为76%~80%,Kappa系数为0.713~0.772,明显优于EXG(54%~79%)和DEVI(65%~81%),是小尺度、复杂景观下植被覆盖度反演与分级的最优通用指标;该方法适用于地物类型复杂的人工恢复区,为无人机可见光影像在小微尺度生态监测及精细化土地覆被识别中提供了精度与成本、效率间平衡的实用化路径。

     

    Abstract: Aiming at the bottlenecks of unstable endmember calibration and the lack of classification methods in fractional vegetation cover (FVC) retrieval from unmanned aerial vehicle (UAV) visible images in small-scale and complex land feature areas, this study took the Qinling ecological restoration area as a case study, and constructed a retrieval and classification method of FVC balancing accuracy and efficiency via the dimidiate pixel model. It quantified the systematic bias of FVC estimation induced by non-normal characteristics in the process of spatial aggregation. It also compared the robustness of three indices, namely visible-band difference vegetation index (VDVI), EXG (excess green index) and DEVI (difference enhanced vegetation index), under different heterogeneous backgrounds. The results showed that remote sensing estimation of FVC was scale-dependent. During image aggregation, endmember values converged as the data tended toward a normal distribution, resulting in a linearly increasing trend of FVC with the aggregation factor (R2>0.86) and a systematic increase of 0.07%-0.23% per doubling of aggregation. The overall classification accuracy of VDVI achieved 76%-80%, with a Kappa coefficient of 0.713-0.772; both were significantly better than those of EXG (54%-79%) and DEVI (65%-81%). This indicated that VDVI was the optimal general index for FVC retrieval and classification in small-scale and complex landscapes. The proposed method was suitable for artificial restoration areas with complex land cover types, providing a practical approach balancing accuracy, cost and efficiency for the application of UAV visible imagery in small and micro-scale ecological monitoring and refined land cover identification.

     

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