Review of airborne downward looking 3D imaging systems and algorithms

Conventional 2D SAR operates in either side-looking or squint-looking modes, where the shadow effect caused by object obstruction is significant, preventing the detection of details on the back of buildings. By arranging MIMO arrays along the wings in the cross-track direction and operating the beams in a forward-looking down mode, three-dimensional imaging can be achieved in the elevation, track, and cross-track directions, effectively overcoming the shadow effect issue. This paper reviews the development history of downward-looking 3D imaging, summarizes the current research status across four key technologies: array design, orthogonal waveforms, imaging algorithms, and motion compensation. It analyzes the strengths and weaknesses of the system and finally explores its potential applications.