Yi Yan

Application of phase retrieval algorithm in reflective tomography laser radar imaging

We apply phase retrieval method to align projection data for tomographic reconstruction in reflective tomography laser radar imaging. In our experiment, the target is placed on a spin table with an unknown, but fixed, axis. The oscillatory motion of the target in the incident direction of the laser pulse is added at each view to simulate the real satellites random motion. The experimental simulation results demonstrate the effectiveness of this method to improve image reconstruction quality. Future research also includes the development of projection registration based on phase retrieval for targets with more complicated structure.

Filters effects for different objects surfaces in reflective tomography laser radar

In range-resolved reflective tomography laser radar imaging system, different objects surfaces have a major impact on signals reflected, and the corresponding different filters in filtered back-projection algorithm would attenuate varying degree artifacts in the resulting images reconstructed. In this paper, light reflection from a surface is described by the Stanford-Robertson bidirectional reflectance distribution function (SR BRDF) model developed by the Air Force. Different reflective parameters in SR BRDF were assumed to simulate various surfaces with different proportion between diffuse reflection and specular reflection. The projections of objects were simulated with 1 degree view increment covering the entire angular domain. We also add the experimental imaging results to validate the effectiveness of this SR BRDF model in reflection tomography. Several filters with different parameters were applied and the quality of images reconstruction was compared, especially beam hardening artifacts and the crossed streak artifacts.

Imaging resolution analysis using Fourier-Slice theorem in reflective tomography laser radar

Reflective tomography is one of the most promising high-resolution imaging methods for the remote objects. But in practical application, because of the sampling angle error and limited view of projections in signal collecting process, anisotropic resolution is inevitable and the reconstruction image quality of reflective tomography system degrades. In this paper, the theoretical imaging resolution derived from Fourier-Slice theorem is presented, computer simulation and experimental verification are also given. Imaging analysis in this paper will make a complement and perfection of the theory in reflective tomography imaging ladar.

Angle-Doppler resolved reflective tomography imaging lidar

A system of angle-Doppler resolved reflective tomography imaging Lidar and its algorithm are given. The issue between transverse range resolution and the sampling time of single angle is solved. The condition of far-field diffraction transmission in the laboratory is designed, and the angle-Doppler reflective projections of the target are collected. Filtered back-projection algorithm is used to reconstruct the cross section of the target image. Because of the utilization of coherent detection of coaxial beams, both the imaging signal to noise ratio and the receiving sensitivity are improved. Due to the simplification in configuration and operations without involving signal phase processing, this technique has a great potential for applications in extensive imaging Lidar fields.

Modified radon-Fourier transform for reflective tomography laser radar imaging

This paper presents imaging result of computer simulation using a modified Radon-Fourier transform algorithm to reconstruct images from reflective tomography data. Since the signal returned is reflected off the illuminated outer surface of an opaque target, only information about the exterior of the target can be obtained, and the images reconstructed using reflective tomography techniques is an outline view of the target cross section. The projection p(r,φ ) and p(r,φ + 180°) contain different information about the target surface, and will lead different Fourier estimates along the same line through the origin based on the standard Fourier-Slice tomography theorem. Here, using the functional similarity between transmission tomography and reflective tomography, we add the collinear reflective projections to become corresponding transmissive projections before Fourier transform. Then the target can be reconstructed from the Fourier domain using the same operations in transmission tomography. The computer simulation result demonstrates the effectiveness of this modified algorithm to reconstruct image in reflective tomography using the diffuse reflection model (lamberts body). Future research will include the development of image reconstruction based on this modified algorithm for targets with much more complicated reflective characters.

Study on corrective algorithms for reflective tomography laser radar imaging wavefront curvature

The filtered back-projection algorithm is referenced and used for reflective tomography laser radar imaging reconstruction because of its simplicity and computational efficiency. Due to the divergence angle of the laser beam, wave front becomes fanned surface. However, direct fan-beam filtered back-projection imaging algorithm with the fan-beam reflective projection data exits huge computational complexity and long time consuming. To solve this question, the double broken lines filtered back-projection algorithm is introduced to implement the image reconstructions. Fan-beam reflective data is filtered and back-projected to the double broken lines with corresponding angles and distances. Images reconstructed by fan-beam filtered back-projection and double broken lines filtered back-projection are compared by computer simulation based on reflective projection data. The simulation results show that double broken lines filtered back-projection algorithm is effective in solving the computational complexity problem in image reconstruction without compromising the image resolution, also with the increasing distance between the detector and the target, the images reconstructed by the double broken lines filtered back-projection are increasing closely to the reference image.