As a reentry vehicle traveling through atmosphere with a very high Mach number, the ultraviolet, visible light and infrared signatures, produced from its head shock-wave layer and wake, are the foundation of detecting...As a reentry vehicle traveling through atmosphere with a very high Mach number, the ultraviolet, visible light and infrared signatures, produced from its head shock-wave layer and wake, are the foundation of detecting and identifying for the ground monitoring and the antimissile controlling and guiding system. At the same time, the gas layer radiation is also an important source of heating flux to the wall. The absorption coefficients of high temperature gas in the head shock-wave layer are basic parameters for calculations of the target ultraviolet, visible light and infrared optical characteristics, the heat shield and the aerodynamic flow-field coupling with thermal radiation. In this paper, after the thermo-chemical non-equilibrium phenomenon of hypersonic rarefied flow during reentry stage is discussed, a three-temperature model (electronic temperature Te, vibrational temperature TV and rotational-transitional temperature TR) is used to characterize energy levels population of non-equilibrium air species in the shock-wave layer and the contribution of 11-species such as N2, N2+, N, N+, O2, O2+, O, O+, NO, NO+ and e- is directly calculated by using the atomic and molecular radiation theory. At last, a model is established, which calculates the absorption coefficient of high-temperature equilibrium or non-equilibrium air. The results are in good agreement with experimentally measured data in the visible region, but are slightly bad in the ultraviolet and infrared regions.展开更多
考虑到植被可见光-近红外的光谱吸收特征与光合有效辐射吸收率(fraction of absorbed photosynthetically active radiation,FAPAR)有很好的关联,综合"高光谱曲线特征吸收峰自动识别法"与"光谱吸收特征参量化法",...考虑到植被可见光-近红外的光谱吸收特征与光合有效辐射吸收率(fraction of absorbed photosynthetically active radiation,FAPAR)有很好的关联,综合"高光谱曲线特征吸收峰自动识别法"与"光谱吸收特征参量化法",提取对FAPAR敏感的高光谱吸收特征参数,借鉴可见光-近红外植被指数的数学形式,尝试用优化组合后的可见光-近红外光谱吸收特征参数替代光谱反射率,构建新型植被指数估算植被FAPAR,并利用2014年和2015年内蒙古自治区中部与东部地区天然草地典型群落冠层实测光谱数据进行FAPAR估算建模与验证。结果表明:新型植被指数"SAI-VI"不仅有效提高了单个光谱吸收特征参数在高、低覆盖区域估算FAPAR的精度,而且相比五种与FAPAR有较好相关性的具有不同作用类型的可见光-近红外植被指数,其与FAPAR值的相关性更高(存在最大相关系数=0.801),以其为变量的指数模型预测FAPAR精度更高且稳定性较好(建模与检验的判定系数均最高且超过0.75,标准误差与平均误差系数也相应最小)。研究表明:融入可见光-近红外高光谱吸收特征的新型植被指数"SAI-VI",强化了可见光波段与近红外波段光谱吸收特征的差别,相较单一光谱吸收特征参数,在降低土壤背景影响的同时增强了对FAPAR变化的敏感度。同时,"SAI-VI"有效综合了对植被FAPAR敏感的光谱吸收特征信息,相较原始光谱反射率,能表达植被光合有效辐射吸收特征的更多细节信息,可作为植被冠层FAPAR反演的新参数,一定程度上弥补当前植被指数法估算FAPAR的不足。展开更多
基金Chinese N ational Science Fund for Distinguished Young Scholars ( No.5 972 5 6 17) the National Natural Science Foun-dation of China ( No.5 980 6 0 0 3) and F ok Ying Tung Education Foundation ( No.710 5 3)
文摘As a reentry vehicle traveling through atmosphere with a very high Mach number, the ultraviolet, visible light and infrared signatures, produced from its head shock-wave layer and wake, are the foundation of detecting and identifying for the ground monitoring and the antimissile controlling and guiding system. At the same time, the gas layer radiation is also an important source of heating flux to the wall. The absorption coefficients of high temperature gas in the head shock-wave layer are basic parameters for calculations of the target ultraviolet, visible light and infrared optical characteristics, the heat shield and the aerodynamic flow-field coupling with thermal radiation. In this paper, after the thermo-chemical non-equilibrium phenomenon of hypersonic rarefied flow during reentry stage is discussed, a three-temperature model (electronic temperature Te, vibrational temperature TV and rotational-transitional temperature TR) is used to characterize energy levels population of non-equilibrium air species in the shock-wave layer and the contribution of 11-species such as N2, N2+, N, N+, O2, O2+, O, O+, NO, NO+ and e- is directly calculated by using the atomic and molecular radiation theory. At last, a model is established, which calculates the absorption coefficient of high-temperature equilibrium or non-equilibrium air. The results are in good agreement with experimentally measured data in the visible region, but are slightly bad in the ultraviolet and infrared regions.
文摘考虑到植被可见光-近红外的光谱吸收特征与光合有效辐射吸收率(fraction of absorbed photosynthetically active radiation,FAPAR)有很好的关联,综合"高光谱曲线特征吸收峰自动识别法"与"光谱吸收特征参量化法",提取对FAPAR敏感的高光谱吸收特征参数,借鉴可见光-近红外植被指数的数学形式,尝试用优化组合后的可见光-近红外光谱吸收特征参数替代光谱反射率,构建新型植被指数估算植被FAPAR,并利用2014年和2015年内蒙古自治区中部与东部地区天然草地典型群落冠层实测光谱数据进行FAPAR估算建模与验证。结果表明:新型植被指数"SAI-VI"不仅有效提高了单个光谱吸收特征参数在高、低覆盖区域估算FAPAR的精度,而且相比五种与FAPAR有较好相关性的具有不同作用类型的可见光-近红外植被指数,其与FAPAR值的相关性更高(存在最大相关系数=0.801),以其为变量的指数模型预测FAPAR精度更高且稳定性较好(建模与检验的判定系数均最高且超过0.75,标准误差与平均误差系数也相应最小)。研究表明:融入可见光-近红外高光谱吸收特征的新型植被指数"SAI-VI",强化了可见光波段与近红外波段光谱吸收特征的差别,相较单一光谱吸收特征参数,在降低土壤背景影响的同时增强了对FAPAR变化的敏感度。同时,"SAI-VI"有效综合了对植被FAPAR敏感的光谱吸收特征信息,相较原始光谱反射率,能表达植被光合有效辐射吸收特征的更多细节信息,可作为植被冠层FAPAR反演的新参数,一定程度上弥补当前植被指数法估算FAPAR的不足。
