Conclusions drawn from test of a radar sensor mounted on a small UAV

This report presents results and conclusions from FOI's continued work involving the use of a small radar sensor mounted on a small UAV (max payload of about 0.5 kg) for SAR2 measurements. This work has been funded by the Swedish Armed Forces R&D programme for Sensors and low observables (FoT SoS, AT.9220419). This report describes how a previously developed system [1], been improved by integration of a position sensor with a position accuracy of about one centimeter. This gives us the possibility to generate SAR images using data collected from curved trajectories (compared to the earlier limitation to straight trajectories only), either unintentionally curved (because of e.g. wind gusts etc), or intentionally to realise other SAR modes (such as e.g. Interferometric SAR). The report also describes how we successfully focused radar data from a small UAV with the help of logged position data collected along a curved trajectory with nonconstant speed. Objectives with the presented work are:  Build competence to perform radar measurements from small flying platforms for later specification and assembly of a multi-channel flying measurement system, e g for 3D-SAR  To obtain knowledge on the usage of a radar sensor in measurements from a small UAV  To collect measurement data for use in evaluation and further development of signal processing methods for radar and data fusion in multi-sensor systems  To enable the use of radar data from arbitrary flight trajectories for SAR  To build a working SAR system using inexpensive COTS in order to be able to have multiple sensors for less vulnerability Initial measurements and development work were carried out using a rail mounted wagon available on a rooftop lab at FOI, Linköping. Airborne measurements and final tests were carried out at the FOI test site Lilla Gåra using the small UAV. Measured scenes for both sites contained buildings, vehicles etc and including corner reflectors deployed as reference targets. A general conclusion from the measurement results is that the quality of the generated SAR images is good (considering the simple type of low-cost equipment used). This applies to both straight trajectories with constant speed without position sensor data and to curved trajectories and/or non-constant speed using position sensor data. Further improvements have previously been shown achievable using autofocus techniques.