基于HITRAN数据库的水汽折射率计算

Calculate the Refractive Index of Water Vapor Based on HITRAN Database

大气折射率的精确信息在光波传播研究中至关重要，水汽折射率是其研究的一个重点。利用HITRAN数据库提供的线谱信息计算了波长在0．3～20μm范围内标准条件下的水汽折射率，针对该数据库缺乏高能谱线的缺点，利用非线性拟合的方法创建了一条新的紫外伪谱，以表征水汽的紫外能谱及光致电离能谱，提高了水汽折射率的计算精度。计算结果表明，水汽在中红外波段有两个强吸收带：2．4～3．3μm，4．8～8．8μm。针对水汽这两个较强的吸收带，以Gross线形为原函数，拟合得到了一个波长覆盖范围比较广的标准水汽色散公式，比较实验测量数据和旧的色散公式可知，拟合公式和实验数据吻合比较好。

An accurate knowledge of the atmospheric refractivity is important for the study of light wave propagation, and the refractive index of water vapor plays an important role in the atmospheric refractivity. The linetransitions of water vapor in the latest HITRAN （high resolution transmission） database are used to calculate the refractive index of standard water vapor for wavelengths between 0.3 μm and 20 μm. Before the calculation, a pseudo-spectral is constructed from the measured data to represent the UV resonances and photo-ionization continuum with nonlinear least square method, since the HITRAN database does not provide a line-transition in UV bands. Calculation results show that strong absorbance by water vapor occurs at wavelengths around 2.9 μm and 7 μm in the mid-infrared. Then a simple dispersive formula at wavelengths from 0.3 ~m to 20 /~m for standard water vapor is given, where the Gross line shape is used. Finally the new dispersive formula is compared with the previous formulae against measurements of refractive index for wavelengths in visible bands and around 3.4 ~m, 10.6 Izm, which is in good agreement with the measuremental data.