Analysis and Compensation of Ionospheric Time-Variant Tec Effect on Geo Sar Focusing

Abstract

Compared to low Earth orbit (LEO) synthetic aperture radar (SAR), geosynchronous (GEO) SAR has a larger coverage and shorter revisit period. However, due to its longer integration time it will be affected by ionospheric time-variant total electron content (TEC), which introduces a phase error into the SAR azimuth signal. Using U.S. total electron content (USTEC) data, TEC variation with time on GEO SAR track is analyzed. It is shown that quadratic phase error caused by time-variant TEC is main effect on image focusing compared to higher order errors. Therefore, contrast optimization autofocus (COA) algorithm can be used for compensation. The key steps of COA are given. Simulations based on scenes derived from PALSAR2 data demonstrate the effectiveness of COA.

Compensation of Background Ionospheric Effect on L-Band Geosynchronous SAR with Fully Polarimetric Data

“…With the change rate of TEC(t), different orders of the phase error will lead to distortions of the azimuth signal, among which the first-order term causes the overall offset, and the second and higher orders cause defocusing [16]. The related error analysis and numerical simulations have been discussed by many scholars, particularly in [16,17,24].…”

“…Guarnieri et al prove the effectiveness of PGA when dealing with atmospheric phase distortion but specifically for wet tropospheric interference [23]. Furthermore, Li et al use contrast optimization autofocus (COA) to compensate for the time-variant ionospheric effect on GEO-SAR focusing, but the requirement of a strong target in the image is still indispensable [24]. Hu and Ding have applied autofocus processing based on minimum entropy to compensate for the ionospheric effects on GEO-SAR imaging, but Hu mainly concentrates on scintillation compensation [25], and Ding's method considers the different types of imaging errors as a whole including the ionosphere [26].…”