Pi Yiming

An Approximated Analytical Solution for Two-Dimensional Spectrum of Spaceborne/Airborne Hybrid Bistatic SAR

A solution for the approximated two-dimensional spectrums analytical expression of spaceborne/airborne hybrid BSAR is presented. To overcome the difficulty of resolving analytical solution for the systems stationary phase point, the two-dimensional spectrums phase is approximated by two-order Taylor expanding around the point, which is not only in the neighborhood of the systems corresponding stationary phase point but also can be obtained analytically. Thus the spaceborne/airborne hybrid BSAR system responses approximated spectrum is pretty close to the actual one and can be expressed analytically. Taking TerraSAR-X as transmitter and PAMIR as receiver, the phase error caused by the approximation is simulated for different point targets in the image scene, and the simulated echo of point target is focused by the approximated two-dimensional spectrum. The simulation results demonstrate the validity of the proposed solution.

Multi-target Imaging Processing Algorithms of ISAR Based on Time-frequency Analysis

This paper analyzed the features of the Doppler frequency shift of multi-target of ISAR at different moving states. Based on the model of rigidity multi-target, several modified time-frequency analysis approaches were proposed to simulate ISAR imaging of multi-target. The results showed the feasibility of the ISAR imaging method and the ability of recognition for multiple targets

Azimuth space-variant properties of BiSAR with nonequal velocities*

Abstract Bistatic SAR possesses characteristic of the azimuth space-variant when the velocities of transmitter and receiver are not equal. The geometric model of BiSAR with the parallel trajectories and the nonequal platform velocities is presented. Analyzing the motion relationship of transmitter and receiver, the formula of azimuth space-variant is derived in time domain. Via Taylor polynomial expansions, the azimuth space-variant is factorized by four terms: zero-order, first-order, second-order, and third-order term. And, their impacts on impulse response are illuminated. Some characteristics about azimuth space-variant of airborne BiSAR case are exhibited by simulation experiments, and these simulated results are coincident with the formulae of azimuth space-variant.

SAR tomography imaging based on high-order spectrum analysis

This paper, the issue of achieving real 3D reconstruction of the 3D scene is discussed to avoid the height blur in the conventional 2D SAR imaging. By analyzing multiple pass (or antenna) system, the conclusion is drawn that the 3D system can be realized with two 2D imaging. The problem of aperture synthesizing in height direction is presented, while conventional SAR image can be obtained with existed methods. The second aperture is synthesized in height with SPOTSAR mode by high-order spectrum analyzing. Finally, the actual imaging of the scene reflectivity is obtained through two apertures synthesizing. To validate the methods, several experiments are carried out using simulated data sets.

SAR stereo imaging algorithm based on amplitude and phase estimation

This paper discusses the application of APES for analysis in SAR stereo imaging algorithm. Firstly, we present an adaptive FIR filtering approach, which is referred to as the amplitude and phase estimation of a sinusoid (APES), for complex spectrum estimation. We show the simulation results for comparing the methods of FFT, Capon and APES and show the simulation result for imaging.

Analysis and compensation of errors of precalculated satellite overpass time and aircraft navigation system in spaceborne/airborne hybrid bistatic SAR

The impact of errors of the precalculated satellite overpass time and aircraft navigation system on some performance parameters, i.e. the footprint overlapping time, the scene extension in azimuth, the offset of the imaging scene, in spaceborne/airborne hybrid bistatic SAR (SA-BSAR) is analyzed. Several related formulae are derived and simulations were performed using parameters of TerraSAR-X as the transmitter and PAMIR as the receiver. The results indicate that predication error of only 0.01 second for the satellite overpass time would cause the scene extension in azimuth to decrease 20 percent when the aircraft navigation system error reaches 5 seconds (the maximum possible value in normal case). Under the same prerequisite predication error of 0.28 second for the satellite overpass time would miss the chance to getting overlapped. A compensation method is proposed based on the idea that the radar satellite starts the beam steering just at the instant when it passes its ideal position rather than at the precalculated instant to begin steering. To accomplish this goal a far more precise prediction for the satellite overpass time must be made on the aircraft several seconds before the satellites arrival. The concrete requirement for the prediction accuracy is derived. The required accuracy must be guaranteed to achieve the expected scene extension in azimuth.

A new method for estimating parameters of SAR clutter

The authors analyse several typical estimators for the shape parameter of K-distributed SAR clutter, both the accuracy and reliability of the estimators are studied and compared. A new estimator is proposed which combines the normalized log and fractional moments of the data. This new estimator is found to provide a more accurate estimation of the shape parameter while having high reliability.

Analysis of range alignment in inverse synthetic aperture radar imaging

In this paper, the basic theory of range alignment in Inverse Synthetic Aperture Radar (ISAR) imaging is analyzed. Two new methods of range alignment are proposed: one is peak point alignment; another is direct range-alignment. Based on the measured radar data, the differences between the above-mentioned new methods and the amplitude correlation method are discussed, resulting in the confirmation on the superiority of the direct range-alignment method.