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Arid Land Geography ›› 2022, Vol. 45 ›› Issue (6): 1847-1859.doi: 10.12118/j.issn.1000-6060.2022.119

• Earth Information Sciences • Previous Articles     Next Articles

Extraction of cotton planting area based on Sentinel-2 time series data and phenological characteristics

Mihray MOYIDIN1(),Mamat SAWUT1,2,3(),LI Jinzhao1   

  1. 1. College of Geography and Remote Sensing Science, Xinjiang University, Urumqi 830046, Xinjiang, China
    2. Xinjiang Key Laboratory of Oasis Ecology, Xinjiang University, Urumqi 830046, Xinjiang, China
    3. Key Laboratory of Smart City and Environment Modelling of Higher Education Institute, Xinjiang University, Urumqi 830046, Xinjiang, China
  • Received:2022-03-23 Revised:2022-05-16 Online:2022-11-25 Published:2023-02-01
  • Contact: SAWUT Mamat E-mail:mihray_m@163.com;korxat@xju.edu.cn

Abstract:

Cotton is an important economic crop in China and is cultivated on a large scale in Xinjiang. The timely and accurate acquisition of cotton planting areas is significant to agricultural policy formulation and economic development. This study takes the Ugan River-Kuqa River delta oasis cotton as the main research object and uses the Sentinel-2 data of 36 scenes from 2018 to 2020 (1 scene/month) to construct a normalized vegetation index (NDVI) and red-edge normalized vegetation index (RENDVI) time-series data; The Savitzky-Golay filtering method is used to smooth and reconstruct the time-series data, and 11 phenological features are extracted. The out-of-bag method is used to optimize the 11 phenological features. Time-series data NDVI Fit and RENDVI783 Fit, phenological feature RENDVI783 Ph, and phenological feature optimization were combined to construct six different feature datasets, which were classified and extracted by random forest classification (RFC). The maximum likelihood and support vector machine were used to verify the classification effect. The results are as follows: (1) The changing trends of NDVI and RENDVI783 time-series data are relatively consistent. Cotton has an obvious upward trend from May (seedling stage) to early August (blooming stage) and reaches a peak from the end of August to September (flowering and boll stage). Compared with NDVI, the peak value of the RENDVI783 time-series curve composed of the red-edge band is increased from 0.7 to 0.9, and the cotton discrimination effect is better. (2) Among the 11 phenological features, the maximum value of the fitting function, the length of the growing season, the amplitude of the growing season, the end of the growing season, the large integral of the growing season, and the small integral of the growing season contributed the most to the classification effect, with importance scores of 1.43, 1.40, 1.23, 1.16, 1.02, and 1.01, respectively. (3) The RFC method has the best classification accuracy for the feature dataset (RENDVI783 Fit + phenological feature optimal combination). The overall accuracy and Kappa coefficient are 92.20% and 0.92, respectively. (4) The cotton classification accuracy in the study area reached 91.02%, and the planting area was approximately 3424 km2, accounting for 24.67% of the total area of the study area.

Key words: NDVI time-series, RENDVI time-series, phenological characteristics, out-of-bag error method, random forest classification