Preparation And Properties Of Spectral Characteristic Simulation Materials Of Plant Leaves

Hyperspectral remote sensing imaging can obtain a continuous spectral curve of the target in the Vis-NIR band(380-2500nm)to identify the spectral difference between the target and the background.Therefore,to effectively combat hyperspectral detection,it is necessary to simulate not only the color of the background,but also the spectrum of the background.Vegetation environment is one of the most commonly backgrounds which targets are located,it is significant for improving the stealth ability of targets by developing spectrum simulation materials for plant background.From the structure and composition of plant leaves,this paper studied the reflection spectral characteristics of different plant leaves,analyzed and demonstrated the relationship between the leaf structure composition and the spectral characteristics.Based on the above research,two kinds of plant background spectrum simulation materials were developed,and the influencing factors of its spectral characteristics were explored.The specific research contents are as follows:1.The Vis-NIR reflectance spectra of ten common plant leaves(Magnolia gradiflora,Peach,Oriental Cherry,Ligustrum lucidum,Callicarpa bodinieri,Ilex corallina Franch,Bamboo,Midget crabapple,Photinia serrulate,Osmanthus fragrans)were studied.The results showed that all different leaves exhibit four spectral characteristics:green peaks,red edges,near-infrared plateaus,and water absorption valleys.The spectral characteristics of leaves with different health(green fresh leaf,yellow fresh leaf,chlorophyll removed leaf,green dead leaf,dead and dried leaf)was compared.The results show that chlorophyll,healthy and complete mesophyll tissue and water in the leaves are the decisive factors to form the above spectral characteristics.2.Polyurethane based plant background spectrum simulation materials(PU-SSM)were designed and prepared.Polyurethane foam with three-dimensional porous structure was used as bionic porous substrate(BPS)to simulate mesophyll tissue in plants,and the relationship between pore structure(size,open porosity and volume density)and near-infrared plateau in spectrum was also studied.Vat dyes or organic pigments was used to simulate chlorophyll,and the green apex and red edge characteristics in the visible region were further adjusted by the chlorophyllin sodium copper salt.The effect of water content of PU-SSM on the intensity of water absorption valley was also studied.The results show that BPS with low density(<0.10g/cm~3)and high open porosity(>90%)can form the similar near-infrared plateau to leaves,and the spectra similarity in visible region can be improved by chlorophyllin sodium copper salt.PU-SSM with 100-120%water contents can simulate four key spectral characteristics of natural leaves.The performance of PU-SSM was characterized by spectral correlation coefficient,three-dimensional profile,contact angle,and thermal infrared imaging.The results show that the spectral correlation coefficient between PU-SSM and natural leaves reach 0.983,and it is universally applicable for simulation of different leaves.Thermal infrared images show that PU-SSM can be well integrated in the background,and the average radiation temperature difference between PU-SSM and natural leaves within 24 hours is only 0.25?,suggesting it can simulate the thermal infrared performance of leaves.Moreover,the PU-SSM can be combined with textiles to obtain composite fabric,the strength of the composite fabric is748.07N,and the green apex of composite fabric weaken after exposure outdoor environment for 72 h,and PU-SSM exhibit poor durability that it needs to add water during application.3.In order to solve the problem of water retention,polyhydroxyethyl methacrylate-based plant leaf spectrum simulation material(PHEMA-SSM)was designed and prepared.The film with high transparency in the Vis-NIR region was used to encapsulate PHEMA-SSM to improve its water retention and durability.Organic pigments were used to simulate the green apex and red edge of leaves in visible region,the effect of the amount of pigments on the spectrum of PHEMA-SSM was studied.Nano titanium dioxide was used to improve the reflectance in the near infrared plateau,and the effect of the amount of nano titanium dioxide on the near-infrared plateau was studied.The results show that the spectral correlation coefficient between PHEMA-SSM and natural leaves reach 0.972 when the amount of pigment is 4%and the amount of nano titanium dioxide is 0.01%.PHEMA-SSM was vacuum encapsulated by films to improve its water retention.The results show that the PE/PA and PET/CPP encapsulating films slightly affect the reflectance spectrum of PHEMA-SSM.The encapsulated PHEMA-SSM still exhibit four spectral characteristics of natural leaves after exposure in the outdoor natural environment for one month,and the tensile strength of the encapsulated PHEMA-SSM is increased by 39 times.