機載合成孔徑雷達訊號之運動補償

Abstract

合成孔徑雷達系統為一不受晝夜及天候影響之主動式微波影像偵測系統，已廣泛應用在軍事或民事上來遙測地表資訊。由於機載合成孔徑雷達在天空中合成陣列天線時，受到飛機載具不預期的偏航或大氣亂流的干擾以及飛機本身結構的振動等，造成雷達掃瞄軌跡的偏移，使得高解析度的影像被模糊化。為解決此問題，雷達系統必須適時補償飛機之運動變化，穩定雷達天線，並改變參考訊號，消除相位誤差，使回波之雷達訊號能被正確的量得。本論文之主旨將闡述合成孔徑雷達系統成像原理、軟硬體架構及運動補償功能。在成像處理流程中，將以感測器為基礎，整合飛機之慣性導航系統，產生參考相位來修正微波訊號，並提出追蹤控制法則來穩定雷達天線。另一方面，利用相位梯度自動聚焦演算法來估測相位誤差，以接收訊號為基礎做訊號之運動補償。藉此，機載之孔徑雷達解決了影像的失焦，並確定掃瞄目標位置的準確性，防止解析度的降低以確保微波影像的品質。

Synthetic Aperture Radar (SAR) is the active microwave remote sensing image system immune to the night and adverse weather and applied on the military and civil affairs to obtain terrain information widely. The antenna mounted on the aircraft deviates from its predicted trajectory by pilot-induced maneuvers, atmospheric gusts disturbance and structural vibrations, and will smear the high-resolution images. To gain correct echo pulses from array antenna synthesized on air, the system must be compensated the motion uncertainty of aircraft by correcting the motion deviation of radar properly, stabilizing the antenna, updating the phase of reference signal and eliminating phase error. This study proposes to describe architecture and signal processing of a SAR system and generalized approach to motion compensation. In the image formatting procedure, radar will integrate into the airplane’s inertial navigation system to generate the sensor-based reference function and use the tracking control to stabilize the antenna gimbals. On the other way, the signal-based motion compensation uses the phase gradient autofocus algorithm to estimate the phase error of receiving microwave signal. Then, both of the positioning accuracy and the image quality will be guaranteed.