SAR System for UAV Operation with Motion Error Compensation beyond the Resolution Cell

Abstract

This paper presents an experimental Synthetic Aperture Radar (SAR) system that is under development in the Universidad Politécnica de Madrid. The system uses Linear Frequency Modulated Continuous Wave (LFM-CW) radar with a two antenna configuration for transmission and reception. The radar operates in the millimeter-wave band with a maximum transmitted bandwidth of 2 GHz. The proposed system is being developed for Unmanned Aerial Vehicle (UAV) operation. Motion errors in UAV operation can be critical. Therefore, this paper proposes a method for focusing SAR images with movement errors larger than the resolution cell. Typically, this problem is solved using two processing steps: first, coarse motion compensation based on the information provided by an Inertial Measuring Unit (IMU); and second, fine motion compensation for the residual errors within the resolution cell based on the received raw data. The proposed technique tries to focus the image without using data of an IMU. The method is based on a combination of the well known Phase Gradient Autofocus (PGA) for SAR imagery and typical algorithms for translational motion compensation on Inverse SAR (ISAR). This paper shows the first real experiments for obtaining high resolution SAR images using a car as a mobile platform for our radar.

Improved Motion Compensation for Wide-Beam Wide-Swath Airborne Sar

“…Although the sub-aperture MoCo has good accuracy at the swath centre, it is difficult to gain consistent focusing quality for the targets all over the swath. This is because the residual motion errors after first-order and sub-aperture MoCo, being zero at the reference range and increasing towards the two edges of the swath, will reduce the range cell migration correction (RCMC) accuracy by range profile shifts and phase modulation errors [4]. The uncorrected RCM error will then cause degradation of the final focusing quality after azimuth compression (AC).…”

A Minimum-Entropy Based Residual Range Cell Migration Correction for Bistatic Forward-Looking SAR

“…Using the Doppler centroid estimation method in [18], range walk migratio n be estimated. After range compression and range walk compensation, a coarse rang cusing signal s Assume that Linear Frequency Modulated (LFM) pulses are transmitted by the radar.…”

“…The residual RCM correction method proposed in [18] is based on the image quality metrics in [19]. The residual RCM of the echoes is modeled as a polynomial, and the coefficients of this polynomial are chosen to optimize a global quantity by minimizing the image entropy or maximizing the image contrast.…”

Drone-Based Micro-SAR Imaging System and Performance Analysis through Error Corrections

“…소형 드론에 탑재되는 FMCW SAR 시스템의 경우, 펄스 시스템에서 적용되는 'Stop and Go' 가정이 불가능하므로 플랫폼의 요동이 발생되면 영상의 품질 저하가 발생할 가능성이 높아진다. 소형 드론은 위 성 및 항공기와는 달리, 기상 조건과 같은 외부환경에 의 해 불안정한 플랫폼으로 운용될 가능성이 높으므로 이에 대한 대응책이 필요하다 [5] . 향후 드론 SAR 영상이 다양한 분야에 활용되기 위해서는 고품질의 영상 확보가 선행되 어야 하며, 이를 위해 기존 시스템보다 더욱 정교한 품질 보상 기술이 요구될 것이다 [6], [7] .…”