Time delay estimation of UAV-mounted UWB SAR

In high resolution Synthetic Aperture Radar (SAR) imaging, the problem of time delay estimation emerges. Generally, the time delays can be divided into system delay and time delays between the sensor data and SAR echo. The sensors include Real Time Kinematic Global Position System (RTK GPS) and Inertial Navigation System (INS). It is computationally very expensive to search for the optimum solution in three dimensions. In this paper, the authors find out that the INS delay is less affected and can be neglected in practice, and the system delay and RTK GPS delay are relatively independent. System delay will only lead to the shift of targets' position along range direction and RTK GPS delay will usually lead to the shifted position along cross-range direction and tiny shift along range direction. Based on the above conclusions, the complicated problem of three-dimensional search is simplified to be two one-dimensional searches. An off-line delay-estimated approach based on the prepared point targets is proposed, in which we search for the time delays by aligning the position of targets in SAR image with the real position of targets measured by RTK GPS. The experimental results demonstrate the effectiveness of the proposed approach.