Theory and Application of Motion Compensation for LFM-CW SAR

Abstract

Abstract-Small low-cost high-resolution synthetic aperture radar (SAR) systems are made possible by using a linear frequency-modulated continuous-wave (LFM-CW) signal. SAR processing assumes that the sensor is moving in a straight line at a constant speed, but in actuality, an unmanned aerial vehicle (UAV) or airplane will often significantly deviate from this ideal. This nonideal motion can seriously degrade the SAR image quality. In a continuous-wave system, this motion happens during the radar pulse, which means that existing motion compensation techniques that approximate the position as constant over a pulse are limited for LFM-CW SAR. Small aircraft and UAVs are particularly susceptible to atmospheric turbulence, making the need for motion compensation even greater for SARs operating on these platforms. In this paper, the LFM-CW SAR signal model is presented, and processing algorithms are discussed. The effects of nonideal motion on the SAR signal are derived, and new methods for motion correction are developed, which correct for motion during the pulse. These new motion correction algorithms are verified with simulated data and with actual data collected using the Brigham Young University μSAR system.

Study on the improvements for the high‐resolution frequency modulated continuous wave synthetic aperture radar imaging

“…For the MOCO procedures, the two-step MOCO method [14,15] is widely and successfully used, thus the two-step MOCO strategy is also adopted here to focus FMCW SAR data. The bulk RRCMC operation should be coupled with the first-order MOCO step [14,15] and the compensation …”

“…The bulk RRCMC operation should be coupled with the first-order MOCO step [14,15] and the compensation …”

“…8, the sub-images from left to right in every row correspond to target 1, target 2 and target 3, respectively. The FS algorithm with two-step MOCO procedures (presented in [15]) is used to focus the SAR data, whereas the imaging results processed without and with the bulk RRCMC operation are generated, respectively. The sub-images listed at the top row are obtained without the bulk RRCMC operation.…”

Analysis and compensation for motion errors in FMCW SAR data

“…Therefore, we disregard the deviation in the X-direction in this study. Since the data rate of motion measurement system (GPS/INS) is generally lower than the SAR data rate, motion data must be interpolated and synchronized so that every sample of SAR data is correctly related to the real position information [6]. Thus the real echo delay can be formulated as In the following, the motion compensation strategy will be described.…”

Estimation of Flight Path Deviations for SAR Radar Installed on UAV

“…The corrections estimated by the navigation system can then be used to determine the slant range between the UAV COG and the target which enables to calculate the proper phase of the echo signal. Uncorrected deviations from the assumed trajectory exceeding 0.1 λ introduce significant phase errors and deteriorate the quality of SAR images [2]. In some authors' opinion the fully focused SAR imaging requires the positioning accuracy better than 0.25 λ [3].…”