No abstract

No abstract

High-resolution airborne synthetic aperture radar (SAR) imaging requires long synthetic aperture time (LSAT). However, the LSAT invalidates the Fresnel approximation in the traditional autofocusing method, leaving a residual signal phase in the motion error. To solve the problem, a signal-reconstructionbased phase gradient autofocus (SR-PGA) and a sub-image resampling (SIR) methods are proposed. They are developed on the hyperbolic model. First, a sub-aperture division strategy divides the full-aperture high-order error into multiple low-order sub-aperture errors. Then, the SR-PGA is developed to estimate the sub-aperture error (SPE), in which the precise deramping is reconstructed to eliminate the residual signal phase in the SPE. Third, the SIR is proposed to eliminate residual Doppler-variant shift of the adjacent sub-images, improving the accuracy of the SPE combination. Finally, simulation and actual data processing verify the effectiveness and validity of the algorithm.

For applications such as high-precision current velocity field monitoring, Ka-band SAR has an important advantage in baseline configuration, which can be configured with dual antennas or more effective phase centers for a single satellite, forming omnidirectional current field measurement capabilities. However, the normalized radar cross section of the sea surface will decay rapidly with the larger incident angle, and it is difficult to obtain a high echo signal-to-noise ratio by active radiating method. Considering that the digital beamforming (DBF) scan on receive at a small incident angle will cause gain loss and phase error due to echo pulse extension and reduce the interferometric accuracy, this article proposes a dual-beam along-track interferometry (ATI) implementation architecture combined with pulse compression and channel forming, which has the advantages of bidirectional current velocity measurement capacity and compact hardware structure. Under a set of parameters, verified by simulation, it could be demonstrated that the proposed method has good robustness, can extract the velocity of the wide-swath current, and complete the extraction of the nongeotropic components. Moreover, the concept of DBF ATI-SAR was validated with airborne data.

No abstract