Ascertaining mean Doppler frequency of SAR system in real=time - reading complex data in memory module as range lines and reading out as azimuth LINES

摘要

A transposition of the data matrix in a buffer memory module (3) is connected on the input side to a digital low-pass filter (1) and to a data reduction process (2) for the compressed digital signals. The complex data are read in as ranges and read out as azimuth values. These are multiplied by a number corresp to the antenna integration time (TA), of reference function values produced in the generator (4) and, when the FM rate, with the frequency shift of the radar signal, and the linear FM reference signal have opposite signs and the same magnitude, there results for a pin-point target, an approximately mono-frequency compound product which can be filterd out by a narrow-band low-pass filter (5). By averaging a number of times and squaring and adding real and imaginary parts the variation in time of the energy signals received by a detector (6) is obtained and this corresponds to the SAR (synthetic aperture radar) antenna characteristic in squared form. The phase is determined by a max detector (8). ADVANTAGE - Reduction is time between successive estimates of average Doppler frequency.