Algorithm of Synthesizing Radar Scene Images in Passive SAR being the Part of Airborne Bi-static Radar System of General Configuration
The paper is devoted to the problem of radar image synthesis in the airborne bi-static look, in which the carriers (planes) of bi-static pair have arbitrary different constant velocity vectors and fly on constant heights. The bistatic analog of Spotlight Mode is considered - the rays of active SAR-1 and passive SAR-2 are being directed into the same ground-based point (scene center). The hologram is being formed in passive SAR-2 (it is being compressed by range). The following two topics are considered in the paper: 1) The a-prior formation of secondary data arrays, necessary for image synthesis, based on primary navigation data and on data about demanded geometric resolution. 2) The image synthesizing algorithm, for which both the general structure with all appropriate formulae and detailed step-by-step illustration are considered. In frames of the first topic (a-prior processing) the following problems are solved: a) Dependence of bi-static pair resolution abilities from the target position was explored and time interval of synthesizing, providing the demanded resolution, was calculated. c) The bi-static look is reduced to side quasi-mono-static look using compensation of linear part of summary slant range migration {SAR-1 - target - SAR-2} for scene center. d) Inverse geo-coding law, mapping scene coordinates into range-way coordinates and taking place in formula of transforming the hologram into the image, is obtained. e) Legendre Transform (as a Taylor series by radial velocity) of migration law and its variations (by scene coordinates) up to second order is calculated. By usage of this result, coefficients defining the set of spectral-domain references for synthesizing image array being written in scene coordinates, are calculated. In frames of the second topic (synthesizing algorithm) the following problems are solved: a) Formulae of spectral variables transform (Stolt Transform generalization, GST) reducing («modulo» second-degree variations of reference phases by scene coordinates) the synthesizing operator to the simple form of twodimensional Inverse Fourier Transform were obtained. The step-by-step representation of GST by limited number of one-dimensional operators of scaling and shift was obtained. b) The problem of influence second order variations (by scene coordinates) of reference phases is solved by means of Inverse Fourier transformation of the special binary series. The correctness and exactness of the all described algorithms was proved by means of step-by-step modeling.