RESUMEN
Doppler tomography is an important means to obtain two-dimensional (2-D) images of remote targets. It is especially suitable for imaging spinning targets such as space debris, warheads, and aircraft blades. However, related research is mostly focused on the microwave band rather than the laser. Higher resolution can be achieved by implementing Doppler tomography in the laser band compared to the existing Doppler tomography in the microwave. Moreover, existing imaging methods are mostly directed at point targets. When these methods deal with extended target echoes, the image quality is unsatisfactory. These problems severely limit the application of Doppler tomography. Here, a novel laser Doppler tomography method has been proposed. The method is based on a single-frequency laser radar (LADAR) that does not require any form of wideband modulation of the transmitted signal. The imaging process is based on the precise relationship between the scattering coefficient of the target and the statistical characteristics of the Doppler spectrum and finds the maximum a posteriori (MAP) estimate of the scattering coefficient distribution. The imaging resolution depends on the Doppler frequency resolution, which exceeds the diffraction limit and is independent of the imaging distance. A laser Doppler tomography experimental system was established. With this system, high-quality laser Doppler tomograms of extended targets were obtained for the first time. In the experiment, the targets have different rotational speeds from 100 to 1000 r/min. The images of these targets with a resolution of 0.4 mm are obtained at a distance of 5 m indoors. In these images, the target details such as textures on the surfaces can be rendered. The quality of these images is greatly improved compared to existing processing methods. The experimental results confirm the effectiveness of the proposed laser Doppler tomography method.
RESUMEN
We present a three-dimensional (3D) imaging method for long-range spinning targets. This method acquires multi-angle two-dimensional (2D) images of spinning targets by the inverse synthetic aperture lidar (ISAL) imaging technique. The 3D distribution of the scattering coefficients of a target has a mapping relationship with the series of 2D images. This mapping is analyzed, and a 3D Hough transform is used to implement inverse mapping. The parameter space of the Hough transform is the estimation of the 3D distribution of the scattering coefficients. The 3D point spread function obtained by the method has narrow main lobe widths and sufficiently low side lobes to achieve high image quality, which is verified by computer simulations. In the simulations, the main lobe widths in the three dimensions are 0.29 cm, 0.29 cm, and 3.48 cm, respectively. In outdoor experiments, 3D images of targets at 1 km away from the lidar were obtained. The images clearly show the 3D shape of targets.
RESUMEN
The magnitude error and phase error (MEPE) in the transfer function of a stepped-frequency synthetic aperture radar (SAR) system results in a periodic MEPE in the synthesized wideband waveform (SWW), which induces the grating lobes in the high-resolution range profile (HRRP). In this paper, a robust data-driven grating lobe suppression (GLS) method is proposed. Based on a contrast-based error estimation method and the grating lobes of the brightest scatterers in the SAR image, the periodic MEPE can be robustly estimated using the proposed method. By compensating the estimated periodic MEPE, the range grating lobes can be suppressed to the background level of the SAR image. Simulation results and real data processing have demonstrated the superiority of the proposed method.