The Study On Limb Imaging Spectrometer For Space-based Atmospheric Remote Sensing

Atmospheric sounding and research are the hot subjects which the earth and space scientific communities pay attention together. Limb imaging spectrometer for space-based atmospheric remote sensing is a new type space optics remote sensing instrument. In this paper, according to the application requirement to sound earth limb atmosphere on spatial platform, a compact optical system of limb imaging spectrometer is designed. It is composed of fore optical system and spectral imaging system. The spectral range is from 540nm to 780nm (using 1st order of the grating) and from 270nm to 390nm (using 2nd order of the grating). The limb imaging spectrometer records images of atmospheric limb from 540nm to 780nm when the visible filter is in place and from 270nm to 390nm when the UV filter is in place. The fore optical system not only covers a wide band (from 270nm to 780), but also includes UV band. The reflective and refractive fore optical systems are designed. The plane grating is choosed as the dispersion element of spectral imaging system. The traditional Czerny-Turner configuration is modified in broad band aberration correction simultaneity and astigmatism correction based on the study on the aberration correction in Czerny-Turner spectral imaging system. The spectral imaging system is designed using the modified Czerny-Turner configuration. Optical systems of limb imaging spectrometer are designed with reflective and refractive fore optical systems matched with the modified Czerny-Turner spectral imaging system. Both schemes can satisfy the design requirement. The refractive fore optical system can avoid of using aspheric surface, therefore it is advantagesous for fabrication and alignment. The reflective fore optical system can reduce the amount of optical elements, so the energy usage ratio is high, but its fabrication is difficult.For the convenience of fabrication and alignment, the limb imaging spectrometer prototype uses the refractive fore optical system matched with the modified Czerny-Turner spectral imaging system. The spectroradiometric transfer characteristic of optical system is researched, and the SNR of the prototype is analyzed and estimated. The data acquisition and processing software is programmed, and the mechanism is designed. The limb imaging spectrometer prototype is developed, and performance evaluation, wavelength calibration and radiometric calibration are performed. The spatial resolution is 0.44mard, spectral resolution is 1.3nm (at 632.8nm), and wavelength calibration precision is 0.12nm. Using an integrating sphere, the spectral radiance responsivities of the prototype is calibrated. The effect of the uncertainties in measurements of bidirectional reflectance distribution function (BRDF) of the diffuser is eliminated and the composite uncertainty is 2.4%, so high precision radiometric calibration of limb imaging spectrometer for space-based remote sensing is achieved. The performance evaluation and calibration results satisfy requirements. The successful development of the prototype fills up domestic blank, and provides technical foundations for development of engineering prototype and application of limb imaging spectral technique in space-based atmospheric remote sensing in our country in future.