基于像元物候曲线匹配的生长季内河北省冬小麦空间分布识别

    Spatial extraction of winter wheat in Hebei in growing season using pixel-wise phenological curve

    • 摘要: 及时、准确的农作物空间分布信息是进行作物长势监测、灾害评估与产量估计的基础。传统方法一般在作物收获期前后进行作物的识别,时间上滞后,难以满足农业生产的应用,时空泛化能力差,模型复用程度低。该研究以历史知识为支撑,提出冬小麦像元匹配模型(Pixel-Matched Model,PMM)进行冬小麦空间分布提取,旨在生长季内实现冬小麦空间分布的快速提取。研究结果表明,PMM能充分利用作物物候特征变化,排除冬小麦种植物候空间异质性的影响,能够在播种后2个月内实现冬小麦的准确提取,总体精度达到了95.49%,F1分数为0.83,且不随物候曲线的延伸而大幅提高精度。与传统参考曲线模型(Reference Curve Model,RCM)相比,PMM在消除区域内冬小麦生长物候差异方面具有优势,可在年际间实现冬小麦的准确识别,具有较强的时间泛化能力,能够实现冬小麦的自动化识别。

       

      Abstract: Timely and accurate information on geospatial distribution of crops in a growing season is critical for monitoring crop growth and forecasting the agricultural disaster and crop yield. Most remote sensing mapping methods were currently covered the crops images in the entire growing season. There was a time lag fail to meet the harsh requirement in the actual agricultural production. Moreover, the relatively generalization ability in time and space can make the crops mapping difficult to identify in most current approaches. The manual debugging in image acquisition has indicated the heavy workload and strong subjectivity, and thereby seriously prevents the automation of crop extraction in the threshold method. The changes of phenological characteristics in winter wheat gradually accumulate among years, and the time generalization ability of threshold can be mainly affected, with the continuous change of global climate. This study aims to propose a novel crops mapping method to rapidly acquire the specific knowledge in season, using the pixel-wise phenological curves. The reflectance imaging data in the growth period of 250 m winter wheat was used to construct the MODIS-NDVI time series data in 2017-2019. A Savizky-Glolay filter and moving average with dynamic step sizes filtering were used to reconstruct the time series datasets. The images of winter wheat during the stopping and jointing stage from Landsat-8 satellite were superimposed, and then the samples were selected to input the Support Vector Machine (SVM) for the extraction of wheat spatial distribution, serving as the prior knowledge and validation data. A Pixel-Matched Model (PMM) was designed to systematically extract the spatial distribution of winter wheat. The pixel similarity was calculated to compare between the prior winter wheat and current corresponding pixels, as well as the prior non-winter wheat pixels and standard curves. A standard deviation iteration method was used to optimize the threshold, in order to efficiently extract the spatial distribution of winter wheat in the growth period. The results showed that the PMM can fully utilize the change of crop phenological characteristics, and thereby to achieve high-precision extraction within the second month after sowing winter wheat. The obtained distribution from the SVM was set as the reference standard, where the overall accuracy of PMM extraction results was 95.49% and F1 score of 0.83. The high precision remained stable, with the deepening of winter wheat growth period, and the increasing of remote sensing data. The PMM can achieve the winter wheat distribution faster and well in large scale, compared with the Reference Curve Model (RCM), sharing the common phenological curve to extract crop distribution. The most advantage of PMM method was to significantly weaken the influence of phenological spatial difference of winter wheat planting, when extracting through the inter-annual comparison of the pixel own curve. The PMM can complete the identification of winter wheat across the years, indicating the strong time generalization ability to realize the automatic inference of winter wheat distribution using historical models. This approach can remarkably reduce the difficulty of extraction, while save the manpower investment in the extent extraction of winter wheat in growing season.

       

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