绿色植被可见-近红外反射光谱模拟材料研究进展

Research Progress of Bionic Materials Simulating Vegetation Visible-Near Infrared Reflectance Spectra

成像光谱技术能够同时获取目标的图像特征和光谱特征,很容易识别与背景环境光谱特征区别较大的传统伪装材料。近年来,成像光谱得到了迅速发展,经历了多光谱技术到高光谱技术的跨越,传感器的探测波段数、光谱分辨率、空间分辨率的显著提高。得益于各国ISR无人机技术的应用,高光谱传感器由星载拓展到机载,可以在更近距离对军事伪装目标进行识别,对具有重要价值的军事目标的生存能力构成巨大挑战。目前,应对高光谱的伪装材料主要设计思路是,选择材料或材料体系具有与环境背景相似的颜色和光谱反射特征(传感器探测范围内)进行复合,目的是与环境背景达到“同色同谱”来躲避高光谱侦察。绿色植被是最常见的伪装背景,也是本领域绝大部分研究的光谱模拟对象,其反射光谱曲线在可见近红外波段具有:“绿峰”、“红边”、“近红外高原”和“水吸收带”四个主要特征,分别由叶片的组织结构以及叶绿素和水分产生。离体叶绿素光热稳定性较差,不能直接用作伪装材料,所以寻找和合成稳定性好、具有类叶绿素结构及光谱特征的分子是当前的研究热点之一。此外,铬绿和钴绿是常用的伪装颜料,具有类似绿色植被“绿峰”、“红边”和“近红外高原”光谱反射特性,研究者将其与高吸水填料复合来引入“水吸收峰”,大致模拟出绿色植被反射光谱,但是想要实现精确模拟,仍存在一些难以解决的问题。从绿色植被光谱特征出发,分别阐述了模拟绿色植被可见光区和近红外光区光谱特征的材料选择依据及体系;同时介绍了它们在精确模拟植被光谱时存在的问题,以及通过改性和复合来提升光谱相似度和耐候性的相关研究工作,总结并展望了绿色植被光谱模拟材料要解决的重难点问题和发展方向。

Imaging spectrum technology can obtain the image and spectral characteristics of the target at the same time,and it is easy to identify the traditional camouflage materials whose spectrum are different from the background spectrum.In recent years,imaging spectrum has been developed rapidly,which has experienced the leap from multispectral technology to hyperspectral technology.Owing to the application of ISR UAV technology in various countries,hyperspectral sensors are expanded from spaceborne to airborne,which can identify military camouflage targets in a closer range,and pose a huge challenge to the survival ability of military targets with important value.At present,the main design idea of hyperspectral camouflage materials is to composite materials with similar color and spectral reflection characteristics(within the detection range of sensors),so as to achieve“the same color and spectrum”with the environmental background to avoid the high spectrum reconnaissance.Green vegetation is the most common camouflage background,and it is also the spectral simulation object of most researches in this field.Its spectral reflection curve has four main characteristics in the visible near-infrared range:“green peak”,“red edge”,“near-infrared plateau”and“water absorption band”,assign to leaf tissue structure,chlorophyll and water.The photothermal stability of chlorophyll in vitro is poor,which cannot be directly used as camouflage material,so it is one of the current researches focuses on finding and synthesizing molecules with good stability,chlorophyll-like structure and spectrum.In addition,chrome green and cobalt green are commonly used camouflage pigments,which have spectral reflection characteristics similar to green vegetation,like“green peak”,“red edge”and“near-infrared plateau”.Researchers composited them with superabsorbent fillers to introduce“water absorption peak”,roughly simulating the reflection spectrum of green vegetation,but there are still some problems to be solved in order to achieve accurate simulation.Based on the Vis-NIR reflection spectra of green vegetation,this paper elucidated the material selection,which simulating spectrum properties of green vegetation in the visible and near-infrared region respectively,introduced the problems existing in the accurate simulation of the vegetation spectra,and the research work of improving the spectral similarity and weather ability through modification and composition.The prospects for the future developments are also discussed.