Imaging Analysis Of Fourier Telescope

Fourier Telescopy is an active synthetic-aperture high-resolution imaging technique.Researching into and realizing the technique with great potentiality in space objectidentification can improve national defense and space power.The main steps in Fourier Telescopy are as follows: Illuminating an object bymultiple laser beams with frequency differences, collecting the reflected light fromthe object with large-area receivers which transform the light energy to electricityenergy, sampling the electricity and recording the data in an computer or other digitalequipment, reconstructing the object image by computational algorithms. This workfocuses on the image reconstruction and other closely relative problems.As many science subjects are involved in the technique, together with hardware andsoftware complexity, the perfective system is not realized yet and the technique isstill on research by simulation and laboratory or field experiment. Thus, whilefocusing on the ongoing simulation or experiment, we also do some exploratoryresearch. The main work and specific contribution include:(1) The signification and background of Fourier Telescopy is introduced, and thedevelopment of the technique is reviewed briefly.(2) Physical process in Fourier telescope is analyzed under Fourier analysis frame.In order to acquire spectral components of the object image in the recorded data,the demodulation, phase closure, and ratios product is introduced in detail.(3) The image reconstruction algorithm using spectral components is deducedrigorously. A restriction is proposed on the size of the reconstruction imagematrix, which keeps the image away from profile distortion. The restriction isvery important in attitude measurement strategies based on it. Strehl ratiomeasures the performance of the telescope. We propose formulae to fix the sizeof the reconstructed image matrix in simulation and experiment, which keepsthe strehl ratio working efficiently. The formula can also be used inversely todetermine the geometrical information of an unknown object.(4) The relations are induced among beam frequency difference, sampling period and sampling point number, and formulae are proposed based on the relations asa guarantee of the demodulation’s efficiency. A five-beam design is proposedbased on T-alignment transmitters. And the requisite amount of data array isreduced, imaging speed improved compared with three-beam design.(5) Computation simulation programs are written, and laboratory and fieldexperiment are performed, where the deduced conclusions and proposedmethods are proved.(6) A method to get feedback signal of the beam location in field experiment isproposed, which can adjust the location in real time and save time precision aswell as improving measurement precision.(7) The principle of the technique is reconsidered based on theoretical knowledgeand experiment data. The limitation is revealed, and methods to breakthrough itis proposed.