Proceedings Article | 30 January 2019
KEYWORDS: Imaging systems, Tolerancing, Airglow, Optical filters, Lens design, Image analysis, Earth's atmosphere, Manufacturing
The middle and upper atmosphere is an important part of atmosphere of the earth. In this region, there are many photochemical phenomena and dynamical processes. One of the photochemical phenomena is airglow. When excited atmospheric molecule or atom transmits to lower level, the light with some wavelength will emit. The light is referred to as airglow. Airglow is therefore a powerful tool in investigations of atmospheric composition, temperature, and density in the emission region, and mass and energy movements to or from this region. Tracing the airglow emission, all-sky airglow imagers are widely used for imaging the atmospheric airglow. The characters of the imager are: wide field of view, fast, high resolution, low cost. This paper systematically studies the basic principle of the imager, completes the calculation of the key parameters, designs the optical system structure of the imager and optimizes the system image quality to obtain an ideal design result. The main contents can be list as follow. All-sky imaging technology records the optical phenomena in the 180° range above the ground plane with imaging and storage media. Use the fisheye lens to realize the 180° of the field of view. Different airglow layers correspond to different radiation peak heights. In order to obtain the atmospheric airglow signal at a certain height, it is necessary to filter the airglow radiation of different bands. The intensity of airglow information using narrow-band filter extraction feature height region of the upper atmosphere. High-sensitivity CCD were used to record all-sky airglow intensity distributions. The system consists of fisheye lens, telecentric imaging lens, filter, imaging lens and CCD. Through the analysis of recorded images, obtained observation data of regional atmospheric fluctuations of airglow height. The central wavelength of the imaging system is 630.5 nm, the bandwidth is 2 nm, the field of view is 180° the focal length is 5 mm, and the relative aperture is 1:1.9; The modulation transfers function (MTF) is more than 0.75 at the Nyquist spatial frequency of 37 lp/mm. The root-mean-square (RMS) radius of spot diagram is less than half of the pixel. 80% of the energy is enclosed in a pixel, and the uniformity of image illumination is 89%. The design requirements are satisfied. And based on the final design, the lens is simplified and the glass material is simplified. Finally, optimization of tolerance analysis is used to guide actual production. The final system structure compact, low cost, high resolution, suitable for airglow atmospheric radiation detection.
