Automatic on-orbit adjusting TDI stages of intelligent space camera based on sun zenith angles

Xingxing Wu; Lingjie Wang; Fucheng Liu; Liang Yang; Jinguo Liu; Dong Xu; Boyan Zhang

doi:10.1117/12.2579286

5 November 2020 Automatic on-orbit adjusting TDI stages of intelligent space camera based on sun zenith angles

Xingxing Wu, Lingjie Wang, Fucheng Liu, Liang Yang, Jinguo Liu, Dong Xu, Boyan Zhang

Proceedings Volume 11570, AOPC 2020: Telescopes, Space Optics, and Instrumentation; 115700C (2020) https://doi.org/10.1117/12.2579286
Event: Applied Optics and Photonics China (AOPC 2020), 2020, Beijing, China

Abstract

Time delay and integration (TDI) CCD or CMOS sensors are widely used in space cameras to realize high resolution. Fixed TDI stages are often used when space cameras are working to avoid image saturation. As a result images obtained have problems such as short of digital number levels. In this paper an automatic on-orbit adjusting TDI stages method of space camera based on sun zenith angles was put forward. In this method radiance at entrance pupil of space camera was calculated in real time by nonlinear function fitting according to sun zenith angles of ground targets. Then optimal time of exposure could be obtained. Line transfer time for image compensation was calculated at the same time. Finally TDI stage was acquired by optimal time of exposure and line transfer time. In this way real-time calculation and adjustment of TDI stages were realized. Results of comparison of simulation by STK and computation by MODTRAN indicate that standard deviation of radiance fitting errors is about 0.175W/m² ∙s and relative radiance fitting error is no more than 0.93% as sun zenith angle belongs to [5°, 65°]. Dynamic changes of SNR along with changes of time and sun zenith angle using adjusting TDI stages method and fixed TDI stages method were compared and analyzed. Results of analysis indicated that SNR would be improved from 23 dB to 39dB as sun zenith angle was 88.2° when automatic on-orbit adjusting TDI stages method was used in comparison with fixed TDI stages method.

Citation Download Citation

Xingxing Wu, Lingjie Wang, Fucheng Liu, Liang Yang, Jinguo Liu, Dong Xu, and Boyan Zhang "Automatic on-orbit adjusting TDI stages of intelligent space camera based on sun zenith angles", Proc. SPIE 11570, AOPC 2020: Telescopes, Space Optics, and Instrumentation, 115700C (5 November 2020); https://doi.org/10.1117/12.2579286

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KEYWORDS

Cameras

Sun

Signal to noise ratio

Photography

Reflectivity

Detection and tracking algorithms

Light sources and illumination

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