Optical Design Of Imaging Spectrometer With Very High Spectral Resolution And For Atmospheric CO₂ Detection

CO2 is the most important greenhouse gases. In recent decades, climate problem due to its increasing emission has become one of major and globally concerned environmental problems. In order to study its effects on global climate change and ecosystem, it is necessary to measure spatial and temporal changes of atmospheric CO2 on the global scale with high accuracy. In this thesis, optical system of imaging spectrometer being spaceborne on low cost mini-satellites is studied for this purpose.Firstly, the principle of remotely measuring the atmospheric CO2 column concentration is introduced. Through analysis of the relationship among measurement accuracy, spectral resolution and the required signal to noise ratio(SNR) with help of the Line-By-Line Radiative Transfer Model(LBLRTM), these performances and then the relative aperture and other specifications of the instrument are determined. Based on the proposed specifications and miniaturization requirement, an imaging spectrometer scheme composed of a Schwarzchild telescope and an off-axis Three-Mirror anastigmat(TMA) Littrow spectroscopic mount with an immersion echelle grating is studied. The optical paths of its three bands share the same optical system, and so it is compact.Then, starting from the half of TMA Littrow mount due to its symmetry, its initial configuration parameters are solved with its primary aberration formula. The compact optical system of imaging spectrometer with F/4 and 21000 spectral resolving power is designed with the commercial optical design software.In order to reduce size of the imaging spectrometer,the principle and method of immersion grating improving spectral resolving power and reducing spectroscopic mount size are studied and analyzed. Study and optical design show that size of spectroscopic mount with an immersion echelle grating reduced to 40% of the original.Finally, tolerances of the designed immersion echelle grating optical system are optimally allocated. The allocation results in line with actual processing requirements are acquired. Baffle structures are designed, and stray light analysis shows that the system has low stray light characteristic.The compact optical system of imaging spectrometer for measuring atmospheric CO2 column concentration with 2ppm sensitivity is designed. It lays the foundation for development of atmospheric CO2 sensor prototype being spaceborne on low cost mini-satellites.