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基于物候知识和贝叶斯网络的江汉平原种植模式制图

Mapping of cropping patterns on the Jianghan Plain based on phenological knowledge and Bayesian networks

  • 摘要: 农作物空间分布图是进行耕地利用方式监测、种植强度模拟、粮食估产以及农业可持续发展评估的基础数据。现有作物制图方法主要采用机器学习算法,对样本依赖度高且算法可移植性差。深度学习方法需要大量的训练样本,数据依赖的问题比较突出。而可靠的、大量的标记样本缺乏一直是深度学习方法的短板。农作物的生长过程有着相对稳定的周期性的节律并能被时序遥感数据捕捉到。该研究提出一种新的基于作物物候知识和贝叶斯网络的种植模式制图方法。通过提取作物的关键物候期特征,利用少量样本,对作物物候知识进行概率编码,构建种植模式制图的贝叶斯网络。选取种植模式较为复杂的区域进行实证研究,结果表明:1)在物候知识的引导下,不依赖样本(或仅利用少量样本),即可获得模型参数,且分类精度较高,制图总体精度达92%以上;2)该文提出的贝叶斯网络方法具有“弱学习-强推理”的能力,消解了推理过程中精度较低的拟合,将机器学习方法对数据的依赖程度降低了42%,有效增强了分类模型的可解释性,具有较好的鲁棒性和可移植性。

     

    Abstract: A spatial distribution map of crops is often required in a wide range of agricultural and environmental applications, including the land use patterns, cropping intensity, and grain yields in sustainable agriculture. Current crop mapping techniques can rely primarily on machine learning algorithms due to the training data and portability. Deep learning can also require large amounts of training data, with the data dependency. However, the reliable, accurate, sufficiently large, and labeled datasets have consistently been limited for the data-driven tasks in the large-scale or heterogeneous agricultural regions. The high-quality training data can be compounded by cloud contamination in the optical remote sensing, inconsistent field surveys, and phenological variability over the landscapes, leading to the persistent challenge of scalable crop mapping. Crops can often follow a relatively stable and biologically driven growth rhythm under environmental and agronomic practices. The growth cycle can be divided into characteristic phenological stages (e.g., emergence, vegetative growth, flowering, and maturity). The time-series remote sensing data can be expected to systematically capture and quantify the vegetation indices, such as the NDVI or EVI. These temporal dynamics can also reduce the dependence on the large training data. Expert phenological knowledge can be encoded into computational models. In this study, a cropping pattern mapping was introduced to incorporate the crop phenology knowledge into the classification framework using Bayesian Networks. Key phenological features were extracted at the critical growth stages, according to a small number of the representative training samples. Knowledge probabilistic encoding was also performed to define the conditional dependencies. A Bayesian Network was constructed to tailor to the phenology-driven crop type classification. Empirical experiments were conducted to validate the effectiveness of the model in a region with highly complex cropping patterns. The results demonstrate that: 1) The model parameters were established either without training data or with only a limited number of samples, particularly with the phenological knowledge as a guiding framework. Thus, the accuracy was maintained under conditions of sample scarcity, with an overall mapping precision of over 92%. The prior knowledge effectively served as a data surrogate in knowledge remote sensing; 2) The Bayesian Network classification framework exhibited a 'weak learning - strong inference' performance, whereby the overfitting was avoided for the limited samples rather than the domain-specific knowledge structures for the inference. The highly precise fitting was observed in the data-driven models during the inference phase. The dependency of the machine learning on data was reduced by 42%. As a result, the data dependency and overfitting were avoided to enhance the interpretability, transparency, and portability of the classification in the machine learning models. The strong robustness was also achieved to generalize under the different temporal and spatial contexts, especially with the sparse or costly training data. The domain knowledge was then integrated with the probabilistic graphical modeling. A promising pathway can represent crop mapping in data-constrained environments. The finding can offer a practical alternative to fully data-driven approaches in the classification tasks during remote sensing. A geospatial data layer can also support decision-making in agricultural planning and food security evaluation.

     

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