Research On Principles And Imaging Techniques Of Bistatic SAR & LASAR

With the ability of all-day and all-climate observation, synthetic aperture radar (SAR) plays an important role in earth observation, environment monitor and reconnaissance fields. To improve its capability and application fields, research on the novel SAR systems has been carried out in the radar field. Bistatic SAR is a kind of synthetic aperture radar whose transmitter and receiver are mounted on difference platforms. Compared with monostatic SAR, bistatic SAR can obtain the target's non-backscattering feature, make the design of the transmitter and receiver more flexible and is beneficial for the receiver platform's stealth design. LASAR is a kind of synthetic aperture radar that synthesizes a 2-D virtual array by mounting a linear antenna array on a moving platform to obtain the 3-D RCS distribution of the observation scene by combining with the pulse compression technique. Compared with traditional SAR, LASAR can obtain the observation scene's 3-D image, and overcome the shadow-effect of traditional SAR, which is good at observing the steep area. Thus, bistatic SAR and LASAR could widely be used in both military and civilian fields.Sponsored by the National Natural Science Foundation of China and the 863 national projects, this dissertation researches the principles and imaging techniques of the bistatic SAR and LASAR.In the aspect of principle, this dissertation builds the mapping between the 3-D observation scene and 2-D image space using the concept "equiv-range-history set", "circle-projection", "ellipse-projection ", "perspective line", "ambiguity function" and "ambiguity region", reveals the essence of synthetic aperture radar, and discusses the space-variant feature of bistatic SAR. Then, the ambiguity function of full-element LASAR is analyzed to explain the reason that it can produce 3-D resolution. To overcome the disadvantages of full-element LASAR, such as, high cost and complex system architecture, the concept of "one-active" LASAR is proposed. By analyzing the spatial feature of "one-active" LASAR echo, the reason that "one-active" LASAR can produce 3-D resolution is explained; then based on the discussion on the ambiguity function of "one-active" LASAR, the main factors affecting its system performance have been found, i.e., length of the linear array and the switch mode of the antenna phase centre. Then the switch mode is optimized by the Lagrange multiplier method under the minimum variance criterion, and we find that when the switch mode obeys the parabolic distribution, the cross-range 2-D AF is optimal.In the aspect of imaging technique, the time-domain imaging method of bistatic SAR is researched and employed in bistatic SAR experiment data processing, and the imaging results of bistiatic SAR are obtained. Then the motion measure errors of bistatic SAR are discussed, and the main errors cause bistatic SAR defocus have been found, which is important for the design of bistatic SAR motion error estimation method. To eliminate the space-variant feature of bistatic SAR. the scaled IFFT Range-Doppler method is presented in the dissertation, which provides a new idea for the design of transitional-variant bistatic SAR imaging method. The time-domain imaging method of LASAR is researched and employed in "one-active" LASAR experiment data processing; and the 3-D RCS distribution of observation scene has been obtained, which demonstrates the feasibility of "one-active" LASAR. Based on the assumption that the illuminated scatterers combine a surface in the imaging space, the surface-tracing-based LASAR 3-D imaging technique has been proposed, which can reduce the computational cost greatly. Finally, based on the matrix expression of discrete signal, a radix-N multi-resolution approximation method has been proposed, and is used in "one-active" LASAR resolution fusion. The radix-N resolution fusion method proposed in this dissertation provides a new way to improve cross-track resolution of LASAR.In a word, this dissertation builds the principles of bistatic SAR and LASAR, proposes their imaging methods and resolution fusion method for LASAR. The research results are useful for the design of bistatic SAR and LASAR system and imaging algorithms.