| Summary: | 碩士 === 國立中央大學 === 遙測科技碩士學位學程 === 99 === Synthetic aperture radar (Synthetic Aperture Radar, SAR) is an all-weather active microwave imaging radar. It transmits microwave signals toward the target on a moving platform and records the returned signals. Conceptually, the resolution along the transmission path is determined by the echo path delay time while the resolution along the moving track is resolved by the Doppler effect between SAR platform and the target objects.
Compared to pulse wave radar, LFM-CW (Linear Frequency Modulation Continuous Wave) radar has advantages of compact size, light weight, and low energy transfer, among others, which are suitable for ground and unmanned platforms requirements..
Ideal imaging algorithm assumes the vehicle is moving at a constant speed and along a straight line. In practice the platform movement is subject to turbulence that causes vibration and perturbation in speed and attitude, in turn. resulting undesired phase noise in the returning signals and thus degrading the image quality. Hence, to achieve good quality of SAR image, the phase changes, due to system motion must be properly compensated.
In this study, an IMU (Inertial Measurement Unit), consisting of a three-axis rate gyroscope, linear accelerometer, magnetic tap, and A/D converter, was installed at the phase center of the antenna to record the trajectory of the platform. By measuring the linear and angular acceleration and attitudes, a motion compensated LFM-CW SAR imaging algorithm was developed to produce high quality SAR image. Simulations and experiments at both C and K bands ground demonstrator are used to verify and validate the algorithm.
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