Hongtu Xie

Fast Time-Domain Imaging in Elliptical Polar Coordinate for General Bistatic VHF/UHF Ultra-Wideband SAR With Arbitrary Motion

In this paper, a fast time-domain imaging algorithm called bistatic fast factorized back projection algorithm (BFFBPA) is proposed for the general bistatic VHF/UHF ultra-wideband synthetic aperture radar. It cannot only accurately dispose the large spatial variant range cell migrations, serious range-azimuth coupling and complicated motion error, but also achieve the imaging efficiency similar to frequency-domain algorithms. It represents subimages in elliptical polar coordinate to reduce the computational load. The imaging geometry with arbitrary motion in this coordinate system is provided, and the bistatic back projection algorithm (BPA) is derived to provide a basis for the proposed BFFBPA. Considering motion errors, the more accurate sampling requirements for elliptical subimages is deduced to offer the near-optimum tradeoff between the imaging quality and efficiency, and the constraint of motion errors for acceptable sampling requirements is discussed. Based on this sampling requirement, the advantage of using elliptical subimage grids for this BFFBPA is analyzed. A phase error correction is performed to reduce the impact of phase errors caused by interpolations in the BFFBPA. The speed-up factor of this BFFBPA with respect to the bistatic BPA is derived. Simulation results and evaluations are given to prove the correctness of the theory analysis and validity of the proposed method.

Research on Spatial Resolution of One-Stationary Bistatic Ultrahigh Frequency Ultrawidebeam–Ultrawideband SAR Based on Scattering Target Wavenumber Domain Support

Compared with the traditional one-stationary bistatic narrowbeam-narrowband (NB) synthetic aperture radar (SAR), the coupling between the azimuth and range wavenumbers for the one-stationary bistatic ultrahigh frequency (UHF) ultrawidebeam-ultrawideband (UWB) SAR is much larger due to the large fractional signal bandwidth and wide antenna beamwidth, which may affect the behavior of spatial resolutions. Considering the wavenumber coupling, the more accurate spatial resolutions for the one-stationary bistatic UHF UWB SAR are proposed based on the wavenumber domain support of the scattering target in this paper. First, the one-stationary bistatic SAR imaging geometry is provided, and then the spatial wavenumber of the scattering target for the one-stationary bistatic UHF UWB SAR is analyzed. Second, based on the spatial wavenumber spectrum, spatial resolutions of the one-stationary bistatic UHF UWB SAR are derived in detail. In addition, the squint angles of radars are considered in the derivation of the spatial resolutions. Besides, the narrowing/broadening factors defined as the ratio of the proposed spatial resolutions to traditional spatial resolutions are presented, which describe the effects of the fractional bandwidth and associated integration angle on the spatial resolutions. Finally, simulation results are given to prove the correctness and validity of the proposed resolutions.

Fast Factorized Backprojection Algorithm for One-Stationary Bistatic Spotlight Circular SAR Image Formation

In this paper, a fast factorized backprojection (FFBP) algorithm is proposed for the one-stationary bistatic spotlight circular synthetic aperture radar (OS-BSCSAR) data processing. This method represents the subimages on polar grids in the slant-range plane instead of the ground plane, which can be accurately referenced to the tracks of both transmitter and receiver. It can not only accurately accommodate the complicated circular track including the motion error, scene topographic information, large spatial variances and significant range-azimuth coupling of the echo data, but also improve the imaging efficiency compared with the backprojection (BP) algorithm. First, OS-BSCSAR imaging geometry is provided, and then the bistatic BP algorithm for the OS-BSCSAR imaging is derived to provide a basis for the proposed FFBP algorithm. Second, based on the subaperture imaging model, the polar grids for calculating the subimages are defined, and the sampling requirements for the polar grids are derived from the viewpoint of the bandwidth, which can offer the near-optimum tradeoff between the imaging quality and the imaging efficiency. Finally, implementation and computational burden of the proposed FFBP algorithm is discussed, and then the speed-up factor of the proposed FFBP algorithm with respect to the bistatic BP algorithm is derived. Experiment results are given to prove the correctness of the theory analysis and validity of the proposed FFBP algorithm.

A fast back-projection algorithm for bistatic forward-looking low frequency UWB SAR imaging

Bistatic forward-looking low frequency ultrawideband synthetic aperture radar (UWB SAR) has the complicated range-azimuth coupling, which limits the application of frequency-domain algorithms. In this paper, an extended fast back-projection algorithm is presented to focus the bistatic forward-looking low frequency UWB SAR data. First, the imaging geometry and signal model are established. Then, the phase error of the fast back-projection (FBP) algorithm for processing the bistatic forward-looking SAR (BFSAR) is analyzed, and the implementation of the FBP algorithm is given. Finally, the simulation experiment is carried out to prove the validity of the proposed approach.

Spatial resolution analysis of low frequency ultrawidebeam–ultrawideband synthetic aperture radar based on wavenumber domain support of echo data

Abstract. Compared with the traditional narrowbeam–narrowband (NB) synthetic aperture radar (SAR), the large fractional signal bandwidth and wide azimuth beamwidth of the low frequency (LF) ultrawidebeam–ultrawideband (UWB) SAR induce serious coupling between the azimuth and range wave numbers of the echo data, which might influence the behavior of the spatial resolution in the SAR imaging. The spatial resolution considering the system wave number coupling and radar squint angle for the LF UWB SAR system is proposed based on the wave number domain support (WDS) of the echo data. First, the SAR imaging geometry is built and then the spatial wave number of the echo data for the LF UWB SAR is analyzed. Second, based on the WDS of the echo data, the spatial resolution of the LF UWB SAR is derived. Moreover, the narrowing/broadening factor defined as the ratio of the proposed spatial resolution to the traditional spatial resolution is presented, which indicates the effects of the fractional bandwidth and associated integration angle as well as the squint angle on the spatial resolution. Finally, simulation results are given to prove the correctness of the theory analysis and validity of the proposed spatial resolution.

Focusing one-stationary bistatic circular SAR data using fast backprojection algorithm

This study presents a fast backprojection algorithm (FBPA) for one-stationary bistatic circular synthetic aperture radar (OS-BCSAR) imaging. This method reconstructs an illuminated SAR scene in a ground plane instead of a slant-range plane. First, the imaging geometry of the OS-BCSAR is given. Then, based on the subaperture imaging model, the sampling requirements of the subimage polar grid are derived from the bandwidth angle. Finally, the implementation of the proposed FBPA is discussed. Simulation results are shown to demonstrate its validity.

Spatial resolution analysis of low frequency UWB SAR

In this study, the more accurate spatial resolution for the low frequency (LF) UWB SAR is analyzed considering the wavenumber coupling. First, the SAR imaging geometry is provided, and then the spatial wavenumber of the LF UWB SAR echo data is analyzed. Second, the spatial resolution of the LF UWB SAR is derived based on the spatial wavenumber domain support. Besides, the squint angle is also considered in the spatial resolution derivation. Finally, simulation results are given to prove the validity.

Processing bistatic forward-looking spotlight SAR data using fast backprojection algorithm

This study presents a fast backprojection algorithm (FBPA) for bistatic forward-looking spotlight synthetic aperture radar (BFSSAR) imaging. It represents the subimages on the polar grids to reduce the computational burden. First, the backprojection algorithm for the BFSSAR imaging is introduced. Then, FBPA for the BFSSAR imaging based on the subaperture processing is provided, and the sampling requirements for the polar grids of subimages are derived from the bandwidth angle. Simulation results are shown to demonstrate its validity.

Spatial resolution analysis of low frequency UWB one-stationary bistatic SAR

This study analyses the spatial resolution for the low frequency (LF) ultra-wideband (UWB) one-stationary bistatic synthetic aperture radar (OSBSAR) system. It considers the wavenumber coupling and radar squint angle to derive the finest possible spatial resolution. First, the spatial wavenumber of the LF UWB OSBSAR echo data of the target is analyzed. Then, its spatial resolution is derived based on the spatial wavenumber domain support. Simulation results are given to prove its validity.

Fast time-domain focussing for general bistatic low frequency ultra wide band SAR in elliptical polar coordinate

A novel fast time-domain approach called bistatic fast factorized backprojection algorithm (FFBPA) for general bistatic low frequency ultra wide band (UWB) synthetic aperture radar (SAR) imaging is proposed. This method is able to accurately dispose the azimuth-variance of range cell migrations and motion errors in general bistatic SAR imaging and achieve the imaging efficiency in parity with frequency-domain methods. It represents subimages in elliptical polar coordinates to reduce the number of operations. Taking into account motion errors, the sampling requirements of the elliptical subimages is deduced by analyzing the bistatic range error. The implementation and computational load of the bistatic FFBPA (BFFBPA) are discussed. Simulation results are shown to demonstrate the correctness of the theory analysis and the validity of the proposed method.