| This thesis is part of the 863-2 project 揔ey Technology of Spaceborne Three Dimentional Imaging Altimeter (CIALT: China Imaging Altimeter)? CIALT system is to be used for both ocean and land imaging. It is different from traditional altimeters because it gets height information by the interference of two complex-value images in two channels and it can get high-resolution 2-D images by synthetic aperture technology. In this thesis, the imaging (both 2-D and 3-D) methods are described at first. Then the research work is stated in two aspects. The first one is about the computer simulation of CIALT imaging, which includes the simulation of getting raw data; 2-D imaging; analysis of the influence to output images caused by CHIRP signal抯 bandwidth, windowing functions, focus depth, noises and range curvature; and 3-D imaging. By using IDL (Interactive Design Language), we can design a software platforrii to perform the demonstration of CIALT system, which can change system parameters and conditions flexibly and can be used for both research and teaching purpose. The other aspect of this thesis is about the hardware/software design of the digital control system of dALI. The design of high-speed AID sampling and real-time data storage, which is a creative work, is the key point to realize imaging correctly for CIALT system. On the other hand, to control the transmitter, receiver and A/D sampling, we need a series of periodical pulses for triggering, with the time resolution of at least 1 us. An ISA card is designed for this purpose and the key part is 82C54 chips. All the program for digital control is integrated into one software platform, which can change the parameters conveniently and can realize such real-time calculations as height tracking, AGC control, calculation of echo signal抯 delay time. Another merit of this software platform is its expansibility. The outcomes of the works above are now used in the experiment of CIALT system successfully. |
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