The Study On Detection Technology Of Cloud And Aerosol

Atmospheric aerosol is solid or liquid particle whose diameter ranges from 0.01 μm to 100 μm, and is one of the three active ingredients suspended in the atmosphere. Atmospheric aerosol has a great effect on the climate, environment and remote sensing, are becoming more signifcant for human life and social evelopment. Due to the great variation of aerosol in the time scale and spatial scale, it is very difficult to detect and retrieve aerosol. In this thesis, satellite remote sensing is chosen to detect aerosol in the global scale.There are three key problems for aerosol detection: the first is determining the area of clouds; the second is removing the surface reflection of the earth; the third is removing the signal of atmospheric molecular scattering. By means of the analysis on the features of cloud scattering, aerosol scattering, atmospheric molecular scattering and surface reflection, we can determine six channels(380 nm, 410 nm, 670 nm, 865 nm, 1610 nm and 2200 nm) in the cloud and aerosol detector.Based on the users’ requirements for aerosol detection, we designed a compact wide angle imaging system whose field of view is ±36° and the swath width is 1000 km with a ground resolution of 1000 m. This system takes the retrofocus optical structure which could meet the requirements of wide angle and long work distance at the same time. According to the interference principle of filter, telecentric structure is used to minimize the incidence angle of each chief ray on the filter, to avoid spectral response discrepancy at different field of angle, which is in favor of aerosol retrieval. The method of aberration vignetting is adopted to increase vignetting coefficient of off-axis field, which can improve the illuminance uniformity of the image plane.Based on configuration characteristics of the optical system, the test is made on the performance and calibration of the prototype. In the alignment process, a technical problem about alignment of optical axes parallelism in multi-optical system is solved and the accuracy of axis parallelism is up to 15". A focal plane array detector mounting device is designed, which can also be used to measure distortion and geometric calibration. By this method, the device’s precision of angle monitoring is less than 5″, and the distortion of prototype is less than 1.8%. Through the performance evaluation of the lens and the prototype, the test results of the prototype are consistent with the design results, which can meet the design requirement. A high precision spectral calibrationtesting device is designed. The precision of spectral calibration for the prototype is ±0.017 nm. By analyses, the difference between spectral response curve of each field is equal to 0.7 nm, verifying that the telecentric design can decrease the wavelength difference of each field. Base on the difficulty of radicance calibration for wide-field imager, the field segmental radiance calibration method is made on the prototype. Depending on the result of radiance calibration, the illumination uniformity of the prototype reached 84.5%, verifying the aberration vignetting method can effectively improve the image plane illumination uniformity.The result of the study is outlined as follows: a wide-angle low distortion aerosol detector was designed; the two problems about removing spectral difference and improving illumination uniformity are effectively solved; a new method for alignment of optical axes parallelism in multi-optical system is put forward; a qualified cloud and aerosol prototype is developed. It provides the foundation in technology for the development of new generation multi-channel cloud and aerosol detector.