Abstract
Quadrature-polarimetric synthetic aperture radar (quad-pol SAR) has extensive applications, including climate zones classification, extraction of surface roughness, soil moisture mapping, moving target indication, and rice mapping. Hybrid quad-pol SAR ameliorates the range ambiguity performance of conventional quad-pol SAR. However, the azimuth ambiguity of its cross-polarized (cross-pol) echo signals is serious, limiting the swath width of SAR. Therefore, this paper proposes a spaceborne weighted amplitude modulation (WAM) full-polarimetric (full-pol) SAR system, and it can suppress the azimuth ambiguity of hybrid quad-pol SAR. The performance boost of the azimuth ambiguity by the two imaging modes of the proposed SAR system is detailed and evaluated with the L-band system parameters. Moreover, the chirp scaling algorithm (CSA) is adopted to execute scene simulations for the two imaging modes. The results indicate that the proposed SAR system can effectively suppress the azimuth ambiguity of hybrid quad-pol SAR and verify the theoretical analysis.
Highlights
Quadrature-polarimetric synthetic aperture radar (SAR) has a dual-polarized antenna with twice as many degrees of freedom as a similar antenna with only one polarization channel [1,2,3]
0 ( η ) is the backscatecho and n ∈ {1, 2, . . . , N }, N is the number of ambiguity regions, σpq tering coefficient of the pq polarization, p, q ∈ { H, V }, Q( f ) is the weighting of Doppler spectrum in data processing, G2 (θ, f ) is the two-way antenna pattern, f is the Doppler frequency, B p is the Doppler bandwidth, Rmain and Rn are the distances from the antenna phase center to targets and the center of the nth ambiguity region respectively
The results are shown in Figure 1. (a) is the range ambiguity-to-signal ratio (RASR) of hybrid quad-pol SAR, which is smaller than −20 dB within the preset observation range, meeting the design requirements of spaceborne SAR, and (b) is its azimuth ambiguity-to-signal ratio (AASR) varying with incidence angle
Summary
Quadrature-polarimetric (quad-pol) synthetic aperture radar (SAR) has a dual-polarized antenna with twice as many degrees of freedom as a similar antenna with only one polarization channel [1,2,3]. The range ambiguity of the cross-polarized (cross-pol) echo signals of conventional quad-pol SAR is serious [18], and the ionosphere produces a Faraday rotation effect on radar signals [19]. A hybrid quad-pol SAR is proposed to eliminate the effect of Faraday rotation and reduce the range ambiguity of conventional quad-pol SAR by alternately emitting leftand right-circular polarization pulses [17]. The azimuth ambiguity of the crosspol echoes of hybrid quad-pol SAR is bad, which reduces the system performance of Remote Sens. A spaceborne weighted amplitude modulation (WAM) full-pol SAR system is proposed to suppress the azimuth ambiguity of hybrid quad-pol SAR.
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