Processing of multiple-receiver spaceborne arrays for wide-area SAR

Abstract

Abstract-The instantaneous area illuminated by a single-aperture synthetic aperture radar (SAR) is fundamentally limited by the minimum SAR antenna area constraint. This limitation is due to the fact that the number of illuminated resolution cells cannot exceed the number of collected data samples. However, if spatial sampling is added through the use of multiple-receiver arrays, then the maximum unambiguous illumination area is increased because multiple beams can be formed to reject range-Doppler ambiguities. Furthermore, the maximum unambiguous illumination area increases with the number of receivers in the array.One spaceborne implementation of multiple-aperture SAR that has been proposed is a constellation of formation-flying satellites. In this implementation, several satellites fly in a cluster and work together as a single coherent system. There are many advantages to the constellation implementation including cost benefits, graceful performance degradation, and the possibility of performing in multiple modes. The disadvantage is that the spatial samples provided by such a constellation will be sparse and irregularly spaced; consequently, traditional matched filtering produces unsatisfactory results.We investigate SAR performance and processing of sparse, multiple-aperture arrays. Three filters are evaluated: the matched filter, maximum-likelihood filter, and minimum mean-squared error filter. It is shown that the maximum-likelihood and minimum mean-squared error filters can provide quality SAR images when operating on data obtained from sparse satellite constellations. We also investigate the performance of the three filters versus system parameters such as SNR, the number of receivers in the constellation, and satellite positioning error.

System Error Analysis and Calibration Methods for Multi-Channel Sar

“…After the above simplification, now we only need to estimate two errors: the gain-phase error (i.e., g m e jζm ) and the position error along the track. As mentioned in Section 2, the spectra of all ground stationary reflecting cells are superimposed in the space-time plane after performing the azimuth FFT transformation, as formulated by (7). Due to Doppler aliasing, for each range-Doppler bin there are three spectrum components with different spatial angles.…”

“…To overcome the minimum antenna area constraint, multi-channel SAR system [7][8][9][10][11][12] has been developed which employ multiple receive-apertures to obtain additional information along the flying track In this system, small transmitaperture is implemented to illuminate wide area with high resolution, and the receiving antenna is split into multiple sub-apertures with independent receiver channels. Since each individual antenna does not meet the minimum antenna area constraint, range and/or Doppler ambiguities will be inevitably induced into the echoes.…”

“…The maximumlikelihood (ML) filter and the minimum mean-squared error (MMSE) filter have been used to resolve the range-Doppler ambiguities [7]. A reconstruction algorithm based on the sampling theorem has been investigated to recover the unambiguous Doppler spectrum [8].…”

Self-calibration method without joint iteration for distributed small satellite SAR systems

“…In the conventional spaceborne SAR systems, large antennas are required due to the minimum antenna area constraint [5]. However, it leads to the failure for the systems to obtain an image of wide area since the illumination area is inversely related to the aperture size of the antennas [6]. Distributed small satellite synthetic aperture radar (DSS-SAR) systems [6][7][8][9][10][11][12] were developed to deal with the problem and have received considerable attention in recent years.…”

“…However, it leads to the failure for the systems to obtain an image of wide area since the illumination area is inversely related to the aperture size of the antennas [6]. Distributed small satellite synthetic aperture radar (DSS-SAR) systems [6][7][8][9][10][11][12] were developed to deal with the problem and have received considerable attention in recent years. In DSS-SAR systems, several small satellites move in a special orbital configuration and function as a single "virtual satellite".…”