Abstract
Hybrid and ±π/4 quadrature-polarimetric (quad-pol) synthetic aperture radar (SAR) systems operating from space can obtain all polarimetric components simultaneously but suffer from severe azimuth ambiguities in the cross-polarized (cross-pol) measurement channels. In this paper, the hybrid and ±π/4 quad-pol SAR systems with multiple receive channels in azimuth are widely investigated to suppress the azimuth ambiguities of the cross-pol components. We first provide a more thorough analysis of the multichannel hybrid and ±π/4 quad-pol SAR systems. Then, the multichannel signal processing is briefly discussed for the reconstruction of the quad-pol SAR signal from the aliased signals, in which the conventional reconstruction algorithm causes extremely severe azimuth ambiguities. To this end, an improved reconstruction method is proposed based on a joint optimization, which allows for the minimization of ambiguities from the desired polarization and the simultaneous power of undesired polarized signal. This method can largely suppress azimuth ambiguities compared with the conventional reconstruction algorithm. Finally, to verify the advantages and effectiveness of the proposed approach, the azimuth ambiguity-to-signal ratio (AASR), the range ambiguity-to-signal ratio (RASR) and signal-to-noise ratio (SNR) of all polarizations, as well as a set of imaging simulation results, are given to describe the effects of reconstruction on the multichannel hybrid and ±π/4 quad-pol SAR systems.
Highlights
Quadrature polarimetric synthetic aperture radar (SAR) systems play an important role in remote sensing
Hybrid or ±π/4 quad-pol SAR operates with the interleaved transmission of the alternate left (L)- and right (R)-circular polarizations or alternate +π/4 (H+V) and −π/4 (H-V) polarized pulses, receiving horizontal (H)- and vertical (V)- polarizations simultaneously after each transmission to build up a measurement of the complex scattering matrix formulated in a different polarimetric basis for each scattering target on the ground [5,6,7]
Method [10], to retrieve the polarized signals. This method leads to extremely severe azimuth ambiguities for all polarizations, in which these azimuth ambiguities consist of two parts: one is from the azimuth ambiguity of the desired signal that can be ignored, and the other is induced by undesired polarizations, which is the main contribution of the azimuth ambiguities [19]
Summary
Quadrature polarimetric (quad-pol) synthetic aperture radar (SAR) systems play an important role in remote sensing. Hybrid or ±π/4 quad-pol SAR operates with the interleaved transmission of the alternate left (L)- and right (R)-circular polarizations or alternate +π/4 (H+V) and −π/4 (H-V) polarized pulses, receiving horizontal (H)- and vertical (V)- polarizations simultaneously after each transmission to build up a measurement of the complex scattering matrix formulated in a different polarimetric basis for each scattering target on the ground [5,6,7]. The hybrid or ±π/4 quad-pol architecture leads to hardware that is more readily calibrated compared with the conventional quad-pol SAR system, because neither receiving channel is cross-polarized with respect to the transmitted polarization. ±π/4 quad-pol architecture can significantly reduce the problem of rang ambiguities of cross-polarized (cross-pol) channels in a conventional quad-pol SAR system [7,8]. The hybrid or ±π/4 quad-pol SAR has very promising advantages in the measurement of all polarizations
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