Transionospheric Synthetic Aperture Radar Observation: A comprehensive review

The ionosphere is the Earth's upper atmosphere with sufficiently charged particles that influence the electromagnetic wave propagation, thereby impeding spaceborne synthetic aperture radar (SAR) observations. High precision imaging and the measurements of geographic and geophysical processes using interferometric SAR (InSAR) and polarimetric SAR (Pol-SAR) are hampered. This study presents a detailed and comprehensive review of the research on ionospheric effects on SAR, InSAR, and Pol-SAR, their correction approaches, and reverse guidance for ionospheric sounding. The prospect is raised at the end of the paper, and the ionosphere will continue to be a research hotspot in the remote sensing community due to the development of low-frequency SAR satellites. In addition, applying spaceborne SAR to ionospheric sounding is a promising issue for space weather and geospace physics due to high spatiotemporal resolution and abundant parameter information.