| In recent years, wide field of view has become an important development trend of optical remote sensing instruments. In order to meet the exploration request of ultra wide field of view(FOV), wide spectral coverage and high resolution of tropospheric monitoring instrument, off-axial two-mirror and three-mirror telescopes which can gain high-quality wide-scene image are studied and designed.Firstly, the remote sensing principle of the instrument is introduced. According to the requirements of instrument’s spectral resolution and signal-to-noise ratio(SNR), the relationship between F number of optical system and SNR is numerically analyzed to determine the fore optical system’s parameters including F number, FOV and focal length with the help of atmospheric radiative transfer model MODTRAN.According to the above indicators and requirements of lightweight, compact off-axial two-mirror fore objective consisting of two concave mirrors is studied and designed. Based on Gaussian optics and Young’s formulas, the approach to determine its initial structural parameters is presented. And the impact of various X-Y polynomials on its pupil aberration is analyzed for elimination of too large smile effect. An off-axial two-mirror fore telescopic objective with FOV of 108° across-orbit direction, F number of 10, focal length of 34 mm and working wavelength range from 0.27 to 2.4μm is optimally designed, which both the primary and the secondary are freeform mirrors. The designed objective has many advantages of simple and compact structure, imagery telecentricity, near diffraction-limited imaging quality and small smile effect.Then, off-axial three-mirror fore objective consisting of one convex mirror and two concave mirrors which can achieve ultra wide FOV and middle relative aperture is studied and designed. By analyzing astigmatism characteristics of convex-concave two-mirror telecentric telescopic objective, the approach to determine its initial structural parameters gradually is presented. An off-axial three-mirror fore telescopic objective with FOV of 108° across-orbit direction, F number of 4, focal length of 17 mm and working wavelength range from 0.27 to 2.4μm is optimally designed, which the primary is spherical mirror and the secondary and the tertiary are aspherical mirrors. The designed objective has the same advantages as the above off-axial two-mirror fore objective.Finally, tolerances of the designed optical systems of imaging spectrometer with ultra wide FOV and high resolution are optimally allocated. The allocation results in line with actual processing requirements are acquired.Both of the designed optical systems have good imaging quality inside wide FOV and wide waveband, and can be used as the fore telescopic objective of spaceborne imaging spectrometers with high temporal resolution which can achieve daily global coverage to monitor the temporal and spatial variation of earth’s tropospheric atmospheric composition and detect global carbon sources and sinks. |
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