Journal of Agricultural Science and Technology ›› 2021, Vol. 23 ›› Issue (10): 107-116.DOI: 10.13304/j.nykjdb.2020.0268

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Prediction on the Vegetation Coverage of Tribulus terrestris L. Based on the Continuous Wavelet Transform

LIU Xin1, YANG Guang1*, LIN Qun2, ZHANG Longying1, CHEN Haoyu1, WANG Ning1, LIU Feng1, LIU Chen1   

  1. 1.College of Desert Management, Inner Mongolia Agricultural University, Hohhot 010018, China; 
    2.School of Computer and Information Technology, Shanxi University, Taiyuan 030006, China
  • Received:2020-03-30 Accepted:2020-05-11 Online:2021-10-16 Published:2021-10-11

基于连续小波变换的蒺藜植被覆盖度预测

刘昕1,杨光1*,林群2,张龙英1,陈昊宇1,王宁1,刘峰1,刘晨1
  

  1. 1.内蒙古农业大学沙漠治理学院, 呼和浩特 010018;  2.山西大学计算机与信息技术学院, 太原 030006
  • 通讯作者: 杨光 E-mail:yg331@126.com
  • 作者简介:刘昕 E-mail:865374825@qq.com
  • 基金资助:
    内蒙古自治区科技重大专项(2019ZD003)

Abstract:

The vegetation coverage is one of the most effective indicators to evaluate the desertification of land, and also is an important indicator for monitoring vegetation. Hyperspectral estimation of vegetation coverage can provide an important basis for vegetation monitoring. Tribulus terrestris L. fixed sand in the semi arid zone Togtoh County was as the research object, the spectral curve features of different vegetation coverages were analyzed; the correlation between the original spectral vegetation index of two wave bands and the vegetation coverage was extracted, and the optimal wave band combination was selected. The spectral reflectance ratio of vegetation was decomposed at the different scales by the continuous wavelet transform (CWT), and the optimal wave bands at the different decomposition scales were extracted. The vegetation coverage estimation models were established using the partial least square method (PLSR) and support vector machine (SVM) with the different independent variables. The results showed that: ① there was significant correlation between the original spectrum vegetation index and vegetation coverage with all the correlation coefficients above 0.55, and the optimal band combinations were DI (2 260 and 2 210 nm), RI (1 410 and 660 nm), NI (1 470 and 670 nm),RDVI(1 770 and 670 nm) and MSR(1 410 and 660 nm), respectively. ② There was also good correlation between the wavelet coefficient and vegetation coverage, which the correlation coefficients in the 1~10 scales of original spectral were high than 0.72 with the maximum correlation 0.788 9 in the sixth decomposition scale at the band 630 nm. The maximum correlation between the wavelet coefficient extracted from the first-order differential spectrum and the vegetation coverage was 0.806 9, and the correlations between the wavelet coefficient of 1~10 scale extracted from the second-order differential spectrum and the vegetation coverage were above 0.6 with the maximum correlation 0.781 8. ③Among the models established by using the original spectral vegetation index and wavelet coefficient extracted by CWT as the independent variables, the PLSR model input the second-order differential wavelet coefficient showed best precision and stability, which R2 was 0.905 9 and RMSE was 0.035 6, respectively. These results showed that the CWT algorithm could improve spectral characteristic information, which provided a technical method for the estimated inversion of vegetation coverage.

Key words: vegetation coverage,  , Tribulus terrestris , L., continuous wavelet transform, partial least square method, support vector machine

摘要: 植被覆盖度是评价土地是否荒漠化最有效的指标之一,也是植被监测的重要指标。通过高光谱估算植被覆盖度,可以为植被监测提供重要依据。以半干旱区托克托县的固沙植被蒺藜(Tribulus terrestris L.)为研究对象,分析了不同植被覆盖度光谱曲线特征的变化情况;提取两波段原始光谱植被指数并与植被覆盖度之间的相关性,选取最优波段组合;利用连续小波变换(continuous wavelet transform,CWT)对植被光谱反射率进行不同尺度分解,提取出不同分解尺度的最优波段;采用偏最小二乘法(partial least square,PLSR)和支持向量机(support vector machine,SVM)两种方法,以不同自变量建立植被覆盖度估算模型。结果表明:①原始光谱植被指数与植被覆盖度呈显著相关,相关系数均在0.55以上,最优波段组合为DI(2 260 nm,2 210 nm)、RI(1 410 nm,660 nm)、NI(1 470 nm,670 nm)、RDVI(1 770 nm,670 nm)、MSR(1 410 nm,660 nm);②小波系数也与植被覆盖度之间有良好的相关性,原始光谱中1~10尺度对应的相关系数均在0.72以上,在波段630 nm处第6分解尺度中,相关性最大为0.788 9;一阶微分光谱提取的小波系数与植被覆盖度的最大相关性为0.806 9;二阶微分光谱中1~10尺度小波系数与植被覆盖度的相关性均在0.6以上,其中最大相关性为0.781 8;③以原始光谱植被指数与不同导数变换的CWT提取的小波系数为自变量建立的模型中,输入量为二阶微分小波系数的PLSR模型精度最高,模型最稳定,R2为0.905 9,RMSE为0.035 6,这表明经过CWT算法处理后,可以提高光谱的特征信息,为植被覆盖度的估算反演提供技术方法。

关键词: 植被覆盖度, 蒺藜, 连续小波变换, 偏最小二乘法, 支持向量机

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