Deutsche Forschungsanstalt Fur Luft-und Raumfahrt E.v.

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Alberto Moreira

Josef Mittermayer

Frank Blaser

For two-dimensional processing of spotlight SAR data into exact image data, the spotlight SAR raw data are divided into azimuth sub-apertures and transformed into the range-time/azimuth-frequency domain through short azimuth FFTs. The obtained data are multiplied by a frequency-scaling function H,(f,, t,; r,) and transformed into the two-dimensional frequency domain through short range FFTs, multiplied by an RV-phase-correction function H,(f,) and subsequently transformed back into the range time/azimuth-frequency domain through short range IFFTs. The data formed in this manner are multiplied by the inverse frequency-scaling function H,(f,, f,), then transformed back into the two-dimensional frequency domain, multiplied by the phase-correction function H,(f,, f,) and the azimuth-scaling function H,(f,, f,), and transformed back into the range-frequency/azimuth-time domain through short azimuth FFTS. Then the azimuth sub-apertures are re-assembled, multiplied by a de-ramping function H,(t,) and transformed into the two-dimensional frequency domain through long azimuth FFTs.

Method of processing spotlight SAR raw data

In a method for azimuth scaling of SAR data without interpolation, raw SAR data in azimuth are multiplied with a phase function H.sub.5 (f.sub.a ;r.sub.o), where f.sub.a denotes the azimuth frequency and r.sub.o denotes the range to a target point, and where a desired scaling factor is entered into the phase function. An azimuth modulation of the SAR data is subsequently adapted with the phase function H.sub.5 (f.sub.a,r.sub.o) to that of a reference range, in a manner so that the azimuth modulation no longer depends on the range. In a last step of the process, a quadratic phase modulation is performed in the azimuth so that, in order to attain an azimuth processing with a very high phase accuracy, the azimuth frequency modulation becomes exactly linear.

Method for azimuth scaling of SAR data and highly accurate processor for

In a method for compressing raw digital SAR data input data are first coded with fewer bits by means of an adaptive block quantization (BAQ) and subsequently vectors are formed from the block-quantized data. The vectors are coded by a special mapping table in order to achieve an effective data reduction. In a method for decompressing digital data, vectors are generated from the coded data by means of a code book table, from which scalar values are formed. After de-standardization of the scalar values, decoded data are obtained in that the scalar values are multiplied for the de-standardization by the standard deviation of each block already calculated during coding.

Methods for compressing and decompressing raw digital SAR data and

In connection with a method for image generation by means of two-dimensional data processing, received SAR data are multiplied by a phase correction (H.sub.mc) for a reference range (r.sub.ref) for the insertion of a motion compensation and for processing at a high drift angle, and an additional cubic phase term is inserted for compensating a range migration. The entire range migration is then eliminated by means of an additional linear frequency displacement; subsequently the SAR data are transformed back into the 'range-Doppler' domain. A remaining phase error, created by a 'chirp scaling' correction, is corrected, the SAR data are transformed back into the time domain and a phase correction as a function of the range is performed by multiplication for the exact motion compensation in the time domain. The one-dimensional reference function is performed in the frequency domain for azimuth compression, by means of which two-dimensional SAR data are obtained.

Method of image generation by means of two-dimensional data processing

In a method for digital generation of SAR images obtained by means of a coherent imaging system a signal compression in the azimuth and/or range direction is carried out with high resolution by means of a subaperture configuration. A stepwise linear approximation of a quadratic phase characteristic is performed with regard to a reference function and frequency overlapping of the subapertures is effected for optimizing the approximation of the phase characteristic. For the formation and synthesis of the subapertures complex multiplications are carried out, the signal of each subaperture thereby being shifted in the frequency. The individual subapertures are integrated twice by means of the moving average method for reducing the side lobes of the low resolution impulse response and after a time shift for equalizing the relative positioning of the subapertures and after the complex multiplications for the frequency shift the results obtained in the individual subapertures are coherently summated.

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Garching, Germany

Alberto Moreira