The Study On Nadir-Limb Imaging Spectrometer For Space-Based Ionosphere Upper Atmosphere Remote Sensing

With the development of the remote sensing of atmosphere, the study of upperatmosphere (ionosphere) remote sensing is becoming the priority research areas inthe earth and space science. It is significant for human beings activities to study thespectral radiance of the particles, build the model of the distribution in upperatmosphere, and realize the space environment weather forecasting. The nadir-limbimaging spectrometer for the observation is a new kind of space-based opticalremote sensing instrument. The present article introduced a program in applicationtowards the observation based on requirements of the ionosphere and upperatmosphere observation. We designed and fabricated the principle verificationsystem of the imaging spectrometer. The observation method that is combined ofnadir observation and limb observation is adopted. The spectral range covers130nmto180nm. We designed two compact optical structures for the spectrometer based onpresent foreign advanced programs of instruments. These optical systems are bothcomposed of the telescope with an off-axis parabolic mirror and the spectral imagingsystem. The spectral imaging system in the first design is an advancedCzerny-Turner system and the other is a single toroidal grating system. In the firstdesign, the dispersion element is a plane grating. On the analysis of aberrations inthe classic Czerny-Turner system, perfect imaging conditions in broadband wereobtained. The performances of the design showed that aberrations in the broadbandwere all corrected and the design met the requests of the spectrometer excellently.The system doesn't need to be applied complicate grating technique of manufacture, and is ease in fabrication and alignment. In the second design, the toroidal grating isadopted as the dispersion element. We obtained the aberrations corrected conditionsin details based on the analysis of the optical path functions and aberrations.According to these conditions, we optimized the toroidal grating by the geneticalgorithm and obtained the optimum parameters of the optical structure. The systemhas the fewest mirrors and the highest transmission.Because the toroidal grating is complicate and expensive in the introduction, theprinciple verification system of the spectrometer adopts the off-axis parabolic mirrorwith the Czerny-Turner system in convenient of fabrication, alignment andexperiment. The spectral transmission characteristics were studied, and thetransmission efficiency and the signal-to-noise ratio of the optical system wereanalyzed. The results indicated that the system satisfied the requests of thefar-ultraviolet waveband observation. The principle verification system weredesigned and fabricated with the corresponding detector integrated. We built avacuum experiment system to do performance evaluation and calibration of it. Theirradiance responsivity of the system was calibrated and the composite uncertainty is7.7%. The space resolution is0.7mrad, the spectral resolution is1.76nm (at161nm).The development of the far-ultraviolet spectrometer principle verification systemsatisfied the request of the design and validated the feasibility of the program. It fillsup blank of the corresponding research and provides foundations for the applicationof the spectrometer in the space-based project on the weather satellite in our country.