Gao Ying, Tang Bo, Lu Beibei, Ji Guojian, Ye Hong
Jiangsu Key Laboratory of Green Process Equipment, School of Petroleum Engineering, School of Energy, Changzhou University Changzhou 213164 People's Republic of China
Department of Thermal Science and Energy Engineering, School of Engineering Science, University of Science and Technology of China Hefei 230027 People's Republic of China
RSC Adv. 2021 Nov 18;11(59):37268-37275. doi: 10.1039/d1ra06056b. eCollection 2021 Nov 17.
Water is the main determinant of the leaf spectral characteristics in the shortwave infrared region, whereas only changing the water content in the PROSPECT model cannot accurately describe the solar spectrum reflectance and transmittance of the dehydrated leaf. To elucidate the effects of water loss, the solar spectrum reflectances and transmittances of the leaves in the fresh state, natural air-dry state and oven-dry state were measured, and the leaf parameters were predicted by the PROSPECT model inversion. The results revealed that the first effect was to increase the brown pigment content, which led to an increase in leaf absorption and change of the leaf absorption characteristics, and correspondingly, in the visible region, both the reflected and transmitted radiations were decreased and the reflection peak shifted towards a long wavelength. The other two effects were to increase the leaf structure index and refractive index, which resulted in an enhancement of the reflected radiation and an attenuation of the transmitted radiation over the range from 400 to 2500 nm. These findings suggest that if people consider the changes of leaf pigment content, structure and refractive index when water is lost from an actual leaf, it will be expected to improve the monitoring accuracy of the leaf water content based on leaf spectral remote sensing technology.
水是短波红外区域叶片光谱特征的主要决定因素，然而仅改变PROSPECT模型中的含水量并不能准确描述脱水叶片的太阳光谱反射率和透过率。为阐明水分损失的影响，测量了新鲜状态、自然风干状态和烘干状态下叶片的太阳光谱反射率和透过率，并通过PROSPECT模型反演预测叶片参数。结果表明，首要影响是增加褐色色素含量，这导致叶片吸收增加以及叶片吸收特性改变，相应地，在可见光区域，反射辐射和透射辐射均减少，且反射峰向长波长方向移动。另外两个影响是增加叶片结构指数和折射率，这导致在400至2500nm范围内反射辐射增强而透射辐射衰减。这些发现表明，如果人们在实际叶片失水时考虑叶片色素含量、结构和折射率的变化，有望提高基于叶片光谱遥感技术的叶片含水量监测精度。
