College of Electronic Science and Engineering, National University of Defense Technology, Changsha 410073, China
Corresponding author (email@example.com
It is well known that the ionospheric scintillation caused by small-scale ionospheric irregularities is a major distortion source for low-frequency spaceborne synthetic aperture radar (SAR) imaging. For L-band geosynchronous earth orbit (GEO) SAR, the orbit height is ultra-high and the integration time is ultra-long, thus ionospheric irregularities may cause more significant distortions on the imaging focusing. To evaluate this effect, the generalized ambiguity function (GAF) is employed to establish the analytical model. The imaging resolution can be studied by calculating the second moment of GAF. Furthermore, since the scanning velocity of the ionospheric penetration point (IPP) for GEO SAR is much slower than that of low earth orbit (LEO) SAR, the convection velocity of the ionospheric irregularities is no longer negligible. Taking this into account, we derive a more accurate expression of ionospheric irregularities' effect. The theoretical derivation is validated by numerical analyses and signal-level simulations.
This work was supported by National Natural Science Foundation of China (Grant Nos. 41271459, 61501477).
The geometric configuration of GEO SAR with the ionosphere.
(Color online) The IPP scanning velocity of GEO SAR.
(Color online) TFTPCF for different values of $ C_kL $. (a) TFTPCF versus space separation; (b) TFTPCF versus frequency separation.
Imaging resolution changed with the spectrum index. (a) Azimuth; (b) range.
Imaging resolution changed with the outer scale. (a) Azimuth; (b) range.
Imaging resolution changed with the scintillation strength. (a) Azimuth; (b) range.
Monte Carlo simulation results compared with the theoretical numeration. (a) Azimuth resolution; (b) range resolution; (c) peak power.
(Color online) TPCF versus time separation for different relative velocities.
Azimuth imaging resolutions versus the relative velocities operated via theoretical numeration and Monte Carlo simulation.
(Color online) Azimuth profiles for different relative velocity. (a) Monte Carlo simulations; (b) one realization.
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