Optical Design for Satellite Camera with Online Optical Compensation Movements

Jo, Jeong-Bin; Hwang, Jai-Hyuk; Bae, Jong‐Sup

doi:10.5139/jksas.2015.43.3.265

Cited by 4 publications

References 6 publications

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Tilted-secondary mirror (TSM) for forward motion compensation in high resolution earth observation satellite cameras

Yilmaz,

Kılıçaslan,

Selimoğlu

2024

Earth Observing Systems XXIX

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The most important difficulty encountered in obtaining high-resolution and quality images from earth observation satellites is the image motion that occurs in the focal plane of the optical system due to the orbital movement of the satellite. The orbital motion of satellites requires optical systems to perform their tasks on a fast-moving platform. As a result of this, smear occur in the obtained ground images, this reduces the image quality and is resulting in blurred images. By keeping the exposure time short so that images of the desired region can be captured in a short time to reduce blur, however, in this case, the signal-to-noise ratio of the image and its contrast are reduced, resulting in noisy and poor-quality images. Forward Motion Compensation (FMC) methods make it possible to obtain high quality images by limiting the focal plane image motion caused by the forward motion of satellites. In this research, it has been extensively analyzed why the secondary mirror of RC telescope has been chosen to apply tilt motion for the purpose of FMC, and the best location of the pivot point has been analyzed by using Zemax OpticStudio program. When tilting the secondary mirror, it is important to avoid causing de-focus. In addition, the pivot point must be located in the optical axis directly behind the secondary mirror, and results have shown that a pivot point distance of 24 mm is also sufficient for the mechanical design of the piezo tilt stage. Approximately 52 pixels can be shifted by moving the secondary mirror by 0.015 degrees. This movement allows for an increase in the image exposure time by 52 times. TSM to compensate for forward motion allows high-resolution images to be obtained without degrading image quality by limiting focal plane image motion and still maintaining the diffractionlimited performance of the optical system. This research has been proposed to develop new method to increase the exposure time without need of additional optical element to apply tilt motion, such as scanning mirrors or high cost TDI sensors.

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Tilted-secondary mirror (TSM) for forward motion compensation in high resolution earth observation satellite cameras

Yilmaz,

Kılıçaslan,

Selimoğlu

2024

Earth Observing Systems XXIX

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Adaptive thermal refocusing system for a high-resolution space camera

Zhao

et al. 2022

Appl. Opt.

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To solve the problem of camera imaging quality degradation caused by defocusing during on-orbit operation, we propose an adaptive thermal refocusing system for high-resolution space cameras—the system comprising active and passive thermal refocusing. Using a space camera with a Ritchey–Chretien optical system as an example, the secondary mirror assembly was determined to be a passive thermal refocusing system, the primary mirror assembly being an active thermal refocusing system. We analyzed the system through structure/thermal/optics performance simulation when temperature variation Δ T was 5°C, 10°C, and 15°C; thermal vacuum experiments verified that the axial displacement of the active system was 0.0032, 0.0061, and 0.0090 mm, and the passive system was 0.00015, 0.00030, and 0.00069 mm, respectively. The data demonstrated the adaptive refocusing system theory to be consistent with the simulations and experiment, exhibiting high stability and reliability.

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Online refocusing algorithm for a satellite camera using stellar sources

Hwang

Bae

2016

Opt. Express

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In this study, an online refocusing algorithm is proposed for a satellite camera performing an Earth observation mission. Satellite cameras are vulnerable to misalignment in orbit because of their severe launching environments and the thermal vacuum environment in space. The proposed online refocusing algorithm is able to guarantee high quality images by aligning the satellite camera in real time. This alignment is achieved by precisely adjusting the movement mechanism of the secondary mirror (M2) and the focal plane. The target optical system used in this study was originally designed for the purposes of algorithm development. The system uses a Schmidt-Cassegrain-type satellite camera with a 200-mm diameter primary mirror (M1). The ground sampling distance (GSD) is 3.8 m from an altitude of 700 km. A fourth-order equation model is derived for the modulation transfer function (MTF) variation tendency for M2 de-spacing. Following this, the proposed online refocusing algorithm for the target optical system is developed. The algorithm is able to assess the de-space position from the MTF measurements using stellar sources. It is determined from the simulation that any misaligned satellite camera can be refocused within a ± 0.5μm M2 de-space error by applying the proposed refocusing algorithm in real time.

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Optical Design for Satellite Camera with Online Optical Compensation Movements

Cited by 4 publications

References 6 publications

Tilted-secondary mirror (TSM) for forward motion compensation in high resolution earth observation satellite cameras

Tilted-secondary mirror (TSM) for forward motion compensation in high resolution earth observation satellite cameras

Adaptive thermal refocusing system for a high-resolution space camera

Online refocusing algorithm for a satellite camera using stellar sources

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