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Ionosphere Spaceborne Sar Performance Impact

Posted on:2004-08-28Degree:MasterType:Thesis
Country:ChinaCandidate:Y FengFull Text:PDF
GTID:2208360092995216Subject:Signal and Information Processing
Abstract/Summary:PDF Full Text Request
Feng Yue (Signal & Information Processing) Directed by Professor Hong JunThe propagation characteristics of signals will be seriously affected by the ionosphere, especially the signals having a low band and large wideband. There has been increasing interest in the research of ionospheric effects on spaceborne synthetic aperture radar (SAR) these years in the world. However, works in this field have rarely been done in our country so far. Research on ionospheric effects on SAR is very important to develop spaceborne SAR technologies.In this paper, firstly, basic knowledge about ionosphere and some important ionospheric parameters which will affect the propagation of signals were introduced. Secondly, the model of ionospheric effects on spaceborne SAR was made based on Gauss envelope signals and rectangular envelope signals respectively. On the following, on the basis of formulas given above, three kinds of effects due to ionosphere are presented: image shift due to group delay which was caused by the difference between the group velocity and the velocity of light in the ionosphere; image distortion due to ionospheric dispersion which can create second phase error of LFM signals; the last, the phase perturbation caused by the irregularities of the ionosphere can reduce the coherent length and affect azimuthal resolution. Ionospheric effects can't be ignored if signals are at a low band and the bandwidth is large. To correct these effects, two methods were introduced in this paper: using weighted function to constrain second phase error caused by dispersion, and utilizing PGA algorithm to reduce the phase perturbation due to the irregularities of the ionosphere. Lastly, simulation of ionospheric effects on spaceborne SAR at L-band was made based on Chirp-Scaling algorithm. The simulation results show that, image will be severely degraded by phase fluctuations at typical conditions of the ionosphere, and can be well focused after calibration.
Keywords/Search Tags:Synthetic Aperture Radar(SAR), Ionosphere, PGA Calibration, SAR Simulation
PDF Full Text Request
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