High-resolution Inverse Synthetic Aperture Research Articles

Two-dimensional Hermite S-method for high-resolution inverse synthetic aperture radar imaging applications

The two-dimensional multiwindow S-method for radar imaging applications is proposed. It represents a combined technique that uses the standard S-method and the multiple windows approach based on the two-dimensional Hermite functions. The proposed method provides significant improvement of radar image concentration in comparison with the standard S-method. Also, it does not require an additional post-processing algorithm. The efficiency of the proposed method is demonstrated through various examples.

Achieving Higher Resolution ISAR Imaging With Limited Pulses via Compressed Sampling

Recent theory of compressed sampling (CS) suggests that exact recovery of an unknown sparse signal with overwhelming probability can be achieved from very limited number of samples. In this letter, we adapt this idea and present a framework of high-resolution inverse synthetic aperture radar imaging with limited measured data. During the framework, we mathematically convert the imaging into a problem of signal reconstruction with orthogonal basis; hence, a conceptive upper bound of the cross-range resolution is presented based on the CS theory. Real data results show that the CS imaging approach outperforms the conventional range-Doppler one in resolution.

Inverse synthetic aperture radar imaging of ship target with complex motion

High-resolution inverse synthetic aperture radar (ISAR) imaging and recognition of ship target is very important for many applications. Although the principle of ISAR imaging of ship target on the sea is the same as that of flying target in the sky, the former usually has more complex motion (fluctuation with the oceanic waves) than the latter, which makes the motion compensation very difficult. However, the change in phase chirp rate caused by the complex motion of ships will deteriorate the azimuth focusing quality. In this paper, we first model the complex motion of ship target with cubic phase terms (parameterised on chirp rate and its change rate), then a new ISAR imaging method, referred to as TC-DechirpClean, is proposed, which estimates the chirp rate and the change rate of chirp rate of all scatters in the time-chirp distribution plane. Both numerical and experimental results are provided to demonstrate the performance of the proposed method.

High-resolution ISAR imaging of maneuvering targets by means of the range instantaneous Doppler technique: modeling and performance analysis

Very high resolution inverse synthetic aperture radar (ISAR) imaging of maneuvering targets is a complicated task. In fact, the conventional range Doppler (RD) ISAR technique does not work properly when target motions generate terms higher than the first order in the phase of the received signal relative to each scatterer. This effect typically happens when at least one of these situations occur: (1) very high resolution images are required; (2) the target maneuvers; and (3) the target undergoes significant angular motions (roll, pitch, and yaw). A novel ISAR technique, named range instantaneous Doppler (RID), has been proposed for the reconstruction of very high resolution images of maneuvering targets. In this paper, we analytically show that the RID technique works properly when high-resolution ISAR images are required of maneuvering and/or rolling, pitching, and yawing targets; we also quantify the performance improvement of the RID technique with respect to the RD technique. The problem is tackled from an analytical point of view. First, we define a new model of the ISAR received signal that is valid for maneuvering targets, then we derive and compare the analytical expression of the point spread function (PSF) for the two techniques. Furthermore, we perform a statistical analysis to evaluate the improvement of the RID technique versus the RD technique in terms of spatial resolution. Finally, we prove the effectiveness of the RID technique by simulating the imaging process for two different targets: (1) a ship that undergoes roll, pitch and yaw motions and (2) a fast maneuvering airplane.

High-resolution radar imagery of the Mirage III aircraft

High-resolution radar imagery has attracted increasing interest in recent years. As more radars are endowed with a high-resolution capability, target classification will become a regular system function. In order to classify an aircraft using radar, one must have an understanding of how the radar imagery relates to the physical aircraft. This paper illustrates the more important radar backscattering features on a typical fighter aircraft. Radar backscatter from an aircraft can occur through a variety of mechanisms. Although direct specular and diffractive mechanisms usually account for the majority of the scattering, indirect phenomena such as cavity scattering and creeping wave scattering are significant. This investigation finds that scattering from engine cavities is a particularly important radar backscatter mechanism for a fighter aircraft. Radar data of an actual Mirage aircraft is collected from a target turntable facility. This data is processed to obtain high-resolution range profiles (HRRP) and inverse synthetic aperture radar (ISAR) images, which indicate the prominent radar scatterers on the aircraft. The imagery is qualitatively examined, and its suitability for target classification is discussed. >