Obtaining high spatial resolution remote sensing images has always been one of the goals pursued in the field of remote sensing imaging. When the angular resolution of the remote sensor is constant, the closer the imaging distance, the higher the spatial resolution. For the remote sensor, the ground sample distance (GSD) at the nadir is closely related to the orbital height. Generally, the lower the orbital height, the easier it is to achieve high spatial resolution. With the rapid development of the ion thruster, spacecraft attitude adjustment technology and heat-resistant and corrosion-resistant materials, the use of ultra-low orbits to deploy micro-satellite, for earth observation and network collaborative information exchange has become an important direction in the development of aerospace technology. Based on the analysis of the development overview of typical foreign low-orbit satellites, combined with the analysis of orbit characteristics, this article summarizes the requirements of low-orbital satellites for remote sensor optical system. To meet the specific requirements, through comparative analysis of existing commonly used optical system forms, a new V-shaped high compression ratio optical system form is proposed, which greatly compresses the axial distance, and the focal length/length ratio is close to 10:1. A design example is given. Its technical specifications are as follows: focal length 4285mm, field of view angle 1.2°, F Number 8, the spectral range is 0.45 microns to 0.8 microns, the MTF value in the full field of view and the full spectrum is greater than 0.32 at the Nyquist frequency (83lp/mm), and the relative distortion is less than one ten thousandth. The simulation analysis results show that the imaging quality of the new V-shaped high compression ratio optical system proposed in this article is close to the diffraction limit, and the processing and assembly tolerance requirements are moderate. The engineering of the optical system is highly achievable, and it can well meet the application needs of low orbit.
Due to the diffraction limit of optical system and detector fabrication technology, super-resolution imaging has been an important means to achieve high spatial resolution in remote sensing. One super-resolution imaging method based on sub-pixels is explored in the paper, the mechanism and image reconstruction of the method are mainly studied. Taking one remote sensor as a sample, registration accuracy of homonymous points, which matters to super-resolution image reconstruction, and its influencing factors, are analyzed, showing that, the image resolution can be improved about 1.5 times when the registration accuracy of homonymous points is better than 0.12 pixels.
The star sensor is an important means of satellite on-orbit attitude measurement, and its angle measurement accuracy directly determines the satellite attitude measurement accuracy. The optical system is an important part of the star sensor, and its image quality evaluation method, aberration control and optimization design method are different from the traditional imaging system. Starting from the working principle of the star sensor, this paper analyzes the main factors that affect the accuracy of angle measurement and the imaging characteristics of the energy detection system, and then puts forward the control elements and aberration correction requirements at the lens design level, and finally discusses the difference from the Programming language Method, using various operands provided by optical design software to constrain various aberration. Finally, for an optical system with a focal length of 250mm, an entrance diameter of 125mm, a field of view of 8°, and a spectral range of 400nm to 800nm, the constraint method proposed in this paper is used to optimize the design at the system level, and the finally imaging quality meets the shape of spot, centroid position deviation, enclosed energy, relative distortion, lateral chromatic aberration and other special requirements, and in the temperature range -10℃~40℃, the imaging quality is almost unchanged. The simulation results show that the optimized control method proposed in this paper has important guiding significance for the optical design of the very high-precision star sensor, and it is also suitable for energy detection systems such a point target detection system.
The polarization characteristic of ocean or atmospheric optical sensor is one of the important factors affecting the accuracy of radiation measurement and quantitative inversion. According to polarization ray tracing algorithm, a calculating model of the polarization sensitivity based on the Muller pupil is proposed. A complete coastal zone remote sensor with low polarization sensitivity is designed, optimized and controlled, by the cooperative design of optical configuration compensating and coating. The result shows that the linear polarization sensitivity is less than 2.5% at B1, and below 1.5% for other four bands respectively.
The optical-mechanical model of the off-axis optical system with oscillating mirror is established. The stray light path is analyzed on the basis of the simulation results. According to various types of stray light paths, the main path of stray light are determined and the influence of important surfaces and illumination surfaces on stray light of the camera are clarified. Effective restraint measures are proposed without blocking the imaging light. After re-simulation, the veiling glare indexes of the two imaging channels are greatly reduced. PST (Point Source Transmittance) is used as an index to test the validity of stray light suppression measures. When the off-axis angle is 30 degrees, the PST of the camera reaches 10-8, which meets the design requirements.
Mars is the most similar planet as the Earth in the solar system. So it is the most studied planets in the solar system. U.S.A., Russia and E.U. have launched more than 43 satellites or spacecraft. China has realized to surround and land on the Moon, but has never been to explore Mars.
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