Objectives The ionosphere, extending from about 60 km to 1000 km above the earth's surface, is an important part of the solar-terrestrial space environment. To better understand and characterize the ionosphere, it is necessary to observe the ionospheric parameters such as total electron content (TEC) and three-dimensional (3D) electron density. However, the three-dimensional electron density derived by the current methods is limited due to the low-spatial resolution. A new method combining of full-polarimetric synthetic aperture radar (SAR) and the international reference ionosphere (IRI) model is proposed to estimate high-spatial 3D electron density distribution.
Methods Firstly, we calculate Faraday rotation (FR) angles from full polarimetric SAR data.Then, we estimate vertical total electron content (VTEC) using FR angles and geomagnetic field information, and reconstruct 3D electron density distribution by combining IRI electron density profile with SAR-derived VTEC.
Results Application of the proposed method to ALOS-1 full-polarization SAR images with descending and ascending orbits over the region of Alaska shows that, for Experiment 1 with ascending orbit, SAR-derived VTEC is consistent with GPS-derived VTEC and the difference between them is about 3.1 TECU (total electron content unit). For Experiment 2 with descending orbit, the difference between SAR-derived VTEC and incoherent scattering radar (ISR) VTEC is only 0.2 TECU.When comparing with the electron density derived from ISR, the standard deviations has decreased by 33.57% for the proposed method, and the standard deviations has decreased by 47.98% at the attitude over 133 km.
Conclusions It can be concluded that it is capable to estimate high-spatial-resolution VTEC and 3D electron density from full-polarization SAR images. These products can help us better understand the characteristics of ionospheric variation in space.