Abstract
The two-step approach (TSA) is an efficient full-aperture method to solve the Doppler spectrum aliasing when processing data acquired by a synthetic aperture radar (SAR) system operating in beam steering mode. This simple approach solves the spectral aliasing by implementing an azimuth convolution between the raw data and a chirp signal, thus avoiding complex subaperture division and recombination of subaperture approaches. However, as aliasing reoccurs in the slow time-domain after the convolution, the estimation and compensation for residual motion error by autofocus cannot be performed immediately, which is crucial for airborne and high-resolution spaceborne SAR processing. The extended TSA solves this problem by implementing full-aperture azimuth scaling, but it is inefficient when the scaling factor deviates from unity severely, which is common in the data acquisition geometry of an airborne SAR. Aiming at addressing the existing shortcomings, this article combines the TSA with autofocus by the time-domain dealiasing and provides an efficient full-aperture processing framework of airborne spotlight SAR data. Simulated and experimental airborne spotlight SAR data with the transmission signal bandwidth of 1.2 GHz and a coherent integration angle of 15<inline-formula><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> are processed by the proposed algorithm and the clarity of the processed results shows its effectiveness.
Highlights
A NTENNA beam steering mode synthetic aperture radar (SAR), such as staring spotlight [1] and sliding spotlight SAR [2]–[4], can overcome the azimuth resolution limitation of a strip-map SAR by extending the coherent integration angle
Aiming at addressing the shortcomings of the existing approaches above, this paper proposes an efficient approach for airborne spotlight SAR processing, which combines the two-step approach (TSA) and autofocus
After the second de-aliasing in the Doppler domain, the azimuth compression is carried out to obtain a focused image
Summary
A NTENNA beam steering mode synthetic aperture radar (SAR), such as staring spotlight [1] and sliding spotlight SAR [2]–[4], can overcome the azimuth resolution limitation of a strip-map SAR by extending the coherent integration angle. The main advantage of these approaches is that they can work with the autofocus algorithms [12], [13], which is vital for airborne and very high-resolution spaceborne SAR data processing [14]. Their disadvantages are complex sub-apertures division and recombination, which can degrade the image quality when the number of sub-apertures is large enough [5]. The second category includes the full-aperture approaches, such as the so-called two-step approach (TSA) [2], [15] and its extended versions [5], [16], which address the spectral aliasing by implementing azimuth convolution between the raw data and a chirp signal.
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