Acta Agriculturae Zhejiangensis ›› 2021, Vol. 33 ›› Issue (11): 2116-2127.DOI: 10.3969/j.issn.1004-1524.2021.11.14

• Environmental Science • Previous Articles     Next Articles

Phenological period identification of oilseed rape based on time-series PolSAR image and decision tree model

LI Shitaoa(), ZHANG Wangfeib,*(), ZHAO Lixianb, WANG Xiyuanb   

  1. a. School of Geography and Ecotourism, Southwest Forestry University, Kunming 650224, China
    b. Forest College, Southwest Forestry University, Kunming 650224, China
  • Received:2020-12-15 Online:2021-11-25 Published:2021-11-26
  • Contact: ZHANG Wangfei

Abstract:

Crop phenological period identification plays an important role in agricultural condition monitoring. Timely and accurate crop phenological period identification is of great significance for evaluating crop growth trend and improving the agricultural information management level effectively.In this study, we selected oilseed rape as an example and proposed a crop phenological period identification method through polarimetric synthetic aperture radar (PolSAR) data and decision tree algorithms. First, polarimetric SAR parameters were extracted through three popular polarimetric decomposition methods. Their dynamic responses to oilseed rape phenological periods were also analyzed. Then, the parameters extracted by the three polarimetric decomposition methods were used to train and validate the decision tree models, five oilseed rape phenological periods were identified. Finally, confusion matrices were used to verify feasibility of the constructed decision models.The results showed that polarimetric SAR decomposition parameters, including scattering angle(Alpha), eigenvalue(L2, L3), pseudo-entropy(P2) and target azimuth (Beta1) parameters from H/A/alpha decomposition method; ground scattering (Ground) and odd scattering (Odd) parameters from Freeman-Durden decomposition method; odd scattering (Odd_Y) and helix scattering (Helix) parameters from Yamaguchi decomposition method showed great sensitivity to changes of oilseed rape phenological period.The decision tree models were more accurate to classify the phenology of rapeseed. Among the results, primitive decision tree model established based on the combination of extracted parameters from three polarimetric decomposition methods had the highest classification accuracy, the overall classification accuracy was 94%. The results also showed the sensitivity of PolSAR parameters to phenological changes of oilseed rape and the effectiveness of decision tree model in identification of oilseed rape phenological period.

Key words: rape, phenological identification, Radarsat-2, polarimetric decomposition, decision-tree

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