Synthetic aperture radar (SAR) imaging systems are becoming increasingly useful in military and civilian surveillance applications. Installation of a SAR system on a miniature unmanned aerial vehicle (mini UAV) enables high resolution terrain imaging in adverse observational conditions, e.g. at night, in fog or in smoke, where classical or infrared cameras would be useless. Use of a small and relatively low-cost radar platform allows for reduction of the mission costs and reduces the risk of detection and destruction of the carrier by the enemy's air defence. The paper presents a concept, a structure, and the most important elements of the UAV-based SAR terrain imaging system, currently developed in a project WATSAR, jointly realized by the Institute of Radioelectronics of the Faculty of Electronics, Military University of Technology, Warsaw, Poland and a Polish private company WB Electronics S.A., under a grant financed by the National Centre for Research and Development. It is assumed that the system will provide high resolution radar images, comparable with aerial photographs, which will be used for tactical scale military reconnaissance. The SAR images from the developed system can also augment multisensory data processed in Battlefield Management Systems (BMS), supporting decision processes on contemporary battlefield and increasing situational awareness of individual soldiers.

The article presents a navigation system used to improve the quality of terrain images obtained from a Synthetic Aperture Radar (SAR) installed on a miniature unmanned aerial vehicle. An inertial navigation system is used to determine the flight path deviations from an assumed straight line. Calculated position corrections are used to correct the phase of the received echo signal in order to get a focused SAR image. The paper describes chosen results of in-flight experiments, presenting the influence of navigation correction on SAR images.

The paper describes a Synthetic Aperture Radar system currently developed by the Military University of Technology and a Polish private company WB Electronics S.A. in a frame of a project under acronym WATSAR. The project is aimed at designing, development and testing of a terrain imaging radar system operating from a miniature UAV. The paper presents structure and way of operation of the system and its current state of development. The main focus of the paper is directed onto presentation of radar images obtained during two flight campaigns realized in May and July 2015. The paper addresses also the algorithms used for SAR processing and the adopted methodology of in-flight experiments.

In order to obtain good quality radar terrain images using an aerial-based synthetic aperture radar, a motion compensation procedure must be applied. This procedure can use a precise navigation system in order to determine the aircraft’s position and velocity. A major challenge is to design a motion compensation procedure that can operate in real time, which is crucial to ensure convenient data for a human analyst. The article discusses a possibility of Inertial Measurement System (INS)/Global Positioning System (GPS) navigation system usage in such a radar imaging system. A Kalman filter algorithm designed for this system is described herein, and its modifications introduced by the authors allow the use of navigational data not aligned in time and captured with different frequencies. The presented navigation system was tested using measured data. Radar images obtained with the INS/GPS-based motion compensation system were compared to the INS-only results and images obtained without navigation corrections. The evaluation results presented in the paper show that the INS/GPS system allows for better reduction of geometric distortions in images compared to the INS-based approach, which makes it more suitable for typical applications.