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顾及Vis-NIR光谱指数时序统计特征的红层荒漠化场景分类

Classifying red-bed desertification scenes considering time-series statistical features of Vis-NIR spectral indices

  • 摘要: 荒漠化调查是区域土地修复、植被恢复与水土保持等农业整治工程的基础工作。而在东南丘陵区红层荒漠化的多光谱遥感监测中,仅依靠单一时相影像有限的光谱特征,难以表征和区分红层区复杂地表覆盖类型。针对该问题,该研究以湘赣北部交界的红层出露带为研究区,提出一种顾及Vis-NIR光谱指数时序统计特征的红层荒漠化场景多尺度分层分类方法。研究首先在典型地表覆盖敏感指数基础上,基于时序统计分析方法,增强红层目标与其他地物覆盖的可分性;然后结合面向对象影像分析技术和决策树分类方法,先后从像元尺度和对象尺度完成红层区纯净地物覆盖和荒漠化混合场景覆盖分类;最后与随机森林(random forest,RF)和支持向量机(support vector machine,SVM)分类模型进行对比分析。结果表明:敏感光谱指数的时序统计分析能够有效增强红层区典型覆盖场景的可分性;结合时序统计增强与面向对象空间优化的分层决策模型相较于RF和SVM两类分类模型总体分类精度提高了3.04%、3.52%;其中对裸岩的提取精确率为86.15%,召回率为89.31%,F1分数为0.88, F1分数相较于RF和SVM分别提高了4.76%和6.02%,有效地减少了裸岩错分漏分,提高了红层荒漠化场景分类精度。该研究为荒漠化遥感调查提供了一种简单有效的技术方案,也为赣西北红层荒漠化区域的土地修复等相关农业整治工作提供可靠的空间数据支持。

     

    Abstract: Desertification has posed a serious threat to regional land restoration, vegetation recovery, as well as soil and water conservation in agricultural remediation. Considerable attention has been paid to desertification monitoring in northwest and southwest China. However, it is still lacking on the investigation of desertification in the red-bed hilly areas of southeast China. Multi-spectral remote sensing can be expected to monitor the areas of the red-bed desertification. It is also challenging to characterize and distinguish the complex surface cover types in the red-bed areas using only limited spectral features. This study aims to classify the red-bed desertification scenes considering the time-series statistical features of Vis-NIR spectral indices. The study area was taken as the red-bed exposure zone in the northern part of the Hunan-Jiangxi border area, China. Firstly, the sensitive spectral indices were constructed using the spectral features of different land cover types. Then the time series analysis was performed on these indices, including the Max, Min, Mean, Median, StdDev, and Variance. The optimal set of features was selected using the Jeffries-Matusita (J-M) distance. A hierarchical decision tree (DT) model was constructed for the typical surface cover scenes in the red-bed areas. The spatial constraints were used to optimize using expert knowledge, such as the object-based image analysis (OBIA), buffer zones, and mathematical morphology filtering. The confusion was reduced among bare rock, cultivated land, and building. Finally, the enhanced features were obtained to combine the spectral index features with the time series statistical features. The results indicated that the differentiation of the various land cover types was effectively improved in the red-bed desertification scenes. The J-M distances between the categories to be classified and the rest were mostly greater than 1.8 under the enhanced features. The temporal analysis of sensitive spectral indices was effectively enhanced to separate the typical cover scenes in the red-bed areas. The spatial pattern of the bare rock was also optimized to classify the hierarchical decision model. After that, the spatially optimized hierarchical decision model was improved the overall accuracy (OA) by 3.04%, 3.52%, and 2.87%, respectively, compared with the random forest (RF), support vector machine (SVM) models, and the original DT model. The extraction accuracy of the bare rock was 86.15%, with a recall rate of 89.31% and an F1 score of 0.88. The F1 score shared an improvement of 4.76% and 6.02%, respectively, compared with the RF and SVM. The overall accuracy of classification was significantly improved for this land cover type, compared with the rest. The misclassification and omission of bare rock were effectively reduced to optimize the mixed pixels among bare rock, building, and cultivated land. Ultimately, the classification accuracy was enhanced in the red-bed desertification scenes. A highly precise and scalable remote sensing classification can be expected to monitor the land degradation. The finding can offer a simple, effective technical solution to the desertification remote sensing. The reliable spatial data can deliver for the land restoration and agricultural remediation in the red-bed desertification areas.

     

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