L-band geosynchronous SAR imaging degradations imposed by ionospheric irregularities

Abstract

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.