大气色散对航空双谱段高分辨率斜视成像影响

Influence of Atmospheric Chromatic Dispersion on Aerial Dual-band High Resolution Standoff Imaging

航空双谱段高分辨率斜视成像载荷作为重要的成像手段,具有焦距长、分辨率高等特点,由于大气层上疏下密的分层特性,光线在大气中斜视传播时,导致光谱展宽并产生色散和畸变,严重影响系统成像分辨率和目标定位精度。文章分析了斜视成像的几何特性;利用MODTRAN软件仿真分析了斜视成像时大气透过特性和光谱散射特性;通过光线追踪法定量分析了大气色散对可见光和中波红外谱段的光线弯曲和光谱色散的影响,并提出了基于多光谱ZnS楔形窗口补偿方法。结果表明,远距离斜视成像可见光近红外0.50~0.95μm透过率高,散射小;中波3.70~4.80μm散射和路径辐射效应较小,光线斜视传播时,光线弯曲角度基本一致;大气色散对可见光谱段影响较大,航高20km斜视120km时,成像分辨率由0.375m退化至4.2m,大气色散对中波红外谱段影响较小;色散补偿后,可见光谱段色散角度下降为原来的1/2,中波红外谱段不受影响,在提升可见光成像品质的同时,保持中波红外谱段色散特性不变。

As an important product in imaging, the aerial dual-band high resolution standoff imaging payload has the characteristics of long focus length and high resolution. However, spectra are broadened with the layer effects of atmospheric density variation when light transmitted obliquely, which results in chromatic dispersion, distortion, resolution degradation and targeting error. In this paper, geometric characteristics of standoff imaging are analyzed. Characteristics of transmittance and scattering effects are simulated with MODTRAN. Ray tracing method is adopted to quantitatively analyze the influences of light ray deflection and chromatic dispersion. A dispersion compensation method is proposed based on multispectral ZnS window wedge. The results show as followed: 1) visible near infrared (VNIR) 0.5~0.95μm has good transmittance and low scattering, and middle wave infrared (MWIR) 3.7~4.8μm has lower scattering and path radiation effects;2) visible and middle wave infrared spectral bands have similar deflection angle;3) visible spectral band is influenced more seriously by dispersion than middle wave infrared, and the ground resolution degraded from 0.375m to 4.2m for altitude 20km standoff range 120km imaging;4) after adopting compensation method, dispersion angle is greatly reduced in visible band, with about half of the original value, and has no effect in middle wave infrared band.