基于合成孔径雷达数据的农作物长势监测研究进展

Research Progresses of Crop Growth Monitoring Based on Synthetic Aperture Radar Data

[目的/意义]农作物长势监测能及时提供农作物的生长状态信息,对于加强中国作物生产管理、确保国家粮食安全具有重要的意义。卫星遥感技术的发展为大面积的作物长势监测提供了契机。然而,在雨热同期的作物生长旺季,光学遥感数据的获取经常受到天气的限制。因此,近年微波雷达遥感技术受到了广泛重视。[进展]梳理了利用合成孔径雷达(Synthetic Aperture Radar,SAR)数据进行农作物长势监测的国内外研究现状,从农作物长势SAR遥感监测指标、农作物长势SAR遥感监测数据和农作物长势SAR遥感监测方法3个方面对基于SAR数据农作物长势监测研究进展与标志性成果进行总结。在分析常用于农作物长势监测的方法及其适用性的基础上,对它们在长势监测中应用情况进行分析。[结论/展望]提出了4个国内外SAR监测农作物长势所存在的问题:1)基于SAR数据的农作物长势监测方法研究整体较少;2)微波散射特征挖掘不够,特别是对极化分解参数的长势监测应用研究还有待深入;3)针对农作物长势监测中的雷达植被指数相对较少,其应用尚未得到充分发挥;4)基于SAR散射强度的农作物长势监测主要采用经验模型,难以推广到不同地区和类型的农作物上。最后,展望未来的研究应聚焦于挖掘微波散射特征、利用SAR极化分解参数、发展和优化雷达植被指数以及深化散射模型来监测农作物长势。

[Significance]Crop production is related to national food security,economic development and social stability,so timely information on the growth of major crops is of great significance for strengthening the crop production management and ensuring food security.The traditional crop growth monitoring mainly judges the growth of crops by manually observing the shape,color and other appearance characteristics of crops through the external industry,which has better reliability and authenticity,but it will consume a lot of manpow‐er,is inefficient and difficult to carry out monitoring of a large area.With the development of space technology,satellite remote sens‐ing technology provides an opportunity for large area crop growth monitoring.However,the acquisition of optical remote sensing data is often limited by the weather during the peak crop growth season when rain and heat coincide.Synthetic aperture radar(SAR)com‐pensates well for the shortcomings of optical remote sensing,and has a wide demand and great potential for application in crop growth monitoring.However,the current research on crop growth monitoring using SAR data is still relatively small and lacks system‐atic sorting and summarization.In this paper,the research progress of SAR inversion of crop growth parameters were summarized through comprehensive analysis of existing literature,clarify the main technical methods and application of SAR monitoring of crop growth,and explore the existing problems and look forward to its future research direction.[Progress]The current research status of SAR crop growth monitoring were reviewed,the application of SAR technology had gone through several development stages:from the early single-polarization,single-band stage,gradually evolving to the mid-term multi-polarization,multi-band stage,and then to the stage of joint application of tight polarization and optical remote sensing.Then,the re‐search progress and milestone achievements of crop growth monitoring based on SAR data were summarized in three aspects,namely,crop growth SAR remote sensing monitoring indexes,crop growth SAR remote sensing monitoring data and crop growth SAR remote sensing monitoring methods.First,the key parameters of crop growth were summarized,and the crop growth monitoring indexes were divided into morphological indicators,physiological and biochemical indicators,yield indicators and stress indicators.Secondly,the core principle of SAR monitoring of crop growth parameters was introduced,which was based on the interaction between SAR sig‐nals and vegetation,and then the specific scattering model and inversion algorithm were used to estimate the crop growth parameters.Then,a detailed summary and analysis of the radar indicators mainly applied to crop growth monitoring were also presented.Finally,SAR remote sensing methods for crop growth monitoring,including mechanistic modeling,empirical modeling,semi-empirical mod‐eling,direct monitoring,and assimilation monitoring of crop growth models,were described,and their applicability and applications in growth monitoring were analyzed.[Conclusions and Prospects]Four challenges exist in SAR crop growth monitoring are proposed:1)Compared with the methods of crop growth monitoring using optical remote sensing data,the methods of crop growth monitoring using SAR data are obviously rela‐tively small.The reason may be that SAR remote sensing itself has some inherent shortcomings;2)Insufficient mining of microwave scattering characteristics,at present,a large number of studies have applied the backward scattering intensity and polarization charac‐teristics to crop growth monitoring,but few have applied the phase information to crop growth monitoring,especially the application study of polarization decomposition parameters to growth monitoring.The research on the application of polarization decomposition parameter to crop growth monitoring is still to be deepened;3)Compared with the optical vegetation index,the radar vegetation index applied to crop growth monitoring is relatively less;4)Crop growth monitoring based on SAR scattered intensity is mainly based on an empirical model,which is difficult to be extended to different regions and types of crops,and the existence of this limitation pre‐vents the SAR scattering intensity-based technology from effectively realizing its potential in crop growth monitoring.Finally,future research should focus on mining microwave scattering features,utilizing SAR polarization decomposition parameters,developing and optimizing radar vegetation indices,and deepening scattering models for crop growth monitoring.