High Resolution Imaging Of Airborne Three Dimensional SAR

Airborne 3D SAR Imaging technique,which is aimed at obtaining three dimensional(3D) image of ground object, is realized by SAR operating mode of single-pass or multi-pass, utilizing a series of radar elements carried by aircraft. It can reconstruct 3D scene comprehensively, and has superiority in the field of shading area and fast changing terrains. In consideration of the advantages and great value in both military and civilian, this technique has been become a research focus so far.This thesis mainly studies airborne linear array 3D SAR technique, which is divided into three sections, i.e. airborne linear array 3D SAR imaging theory and array design, 3D imaging algorithm and super-resolution imaging method of cross track.Firstly, basic theory of airborne linear array 3D SAR imaging is researched. Airborne linear array 3D SAR operates in downward-looking mode generally. And it obtains resolution in height direction and along track direction by employing wideband signal and synthetic aperture respectively, while the resolution in cross track direction is obtained by applying the linear array on fuselage and wings. The imaging models of airborne linear array 3D SAR both based on mono-static and bistatic radar array are established, and the resolution formula of each direction is derived.In the second section, imaging algorithm of airborne linear array 3D SAR is researched. Space-time joint processing of the whole sampling data is key technique for airborne linear array 3D SAR imaging. Normal 3D imaging algorithms, i.e. 3D range doppler algorithm and 3D range migration algorithm are introduced and then applied to imaging of airborne linear array 3D SAR. A imaging method base on 3D spectral filling is proposed for airborne linear array 3D SAR after the 3D spectrum of airborne linear array 3D SAR is analyzed. Imaging performance of this method is discussed through analyzing the density of 3D spectral domain.In the last section, super-resolution imaging methods for airborne linear array 3D SAR are researched. As the range of linear array is limited to the length of wings and the amount of antenna is limited to the load capacity of aircraft, undesired imaging performance such as insufficient theoretical resolution and intolerable high sidelobe may arise. To solve these drawbacks, super-resolution imaging methods are employed. Super-resolution imaging methods are discussed under the condition of data complete and data sparse. Through establishing linear observation model, the imaging process in cross track direction is separated from integral 3D imaging. Specific to several typical scenes, APES method, SVD method, GAPES method and compress sensing method are introduced to realize super-resolution imaging in cross track direction.