Abstract
This paper describes a pair of compact CW/FM airborne SAR systems for small UAV-based operation (wingspan of 3.5 m) for low-cost testing of innovative SAR concepts. Two different SAR instruments, using the C and X bands, have been developed in the context of the ARBRES project, each of them achieving a payload weight below 5 Kg and a volume of 13.5 dm3 (sensor and controller). Every system has a dual receiving channel which allows operation in interferometric or polarimetric modes. Planar printed array antennas are used in both sensors for easy system integration and better isolation between transmitter and receiver subsystems. First experimental tests on board a 3.2 m wingspan commercial radio-controlled aircraft are presented. The SAR images of a field close to an urban area have been focused using a back-projection algorithm. Using the dual channel capability, a single pass interferogram and Digital Elevation Model (DEM) has been obtained which agrees with the scene topography. A simple Motion Compensation (MoCo) module, based on the information from an Inertial+GPS unit, has been included to compensate platform motion errors with respect to the nominal straight trajectory.
Highlights
Different geophysical and biophysical parameters can be monitored with Synthetic Aperture Radar (SAR) sensors in applications such as earthquake damage assessment, subsidence mapping, harvest monitoring, deforestation and fire impact assessment, Digital Elevation Model (DEM) production and oil spill monitoring [1,2,3,4,5].In contrast to orbital platforms with rigid revisit times, airborne SAR provides the observation flexibility required in time-critical or fast dynamic applications
In the presented case we show that multichannel operation in several bands can be achieved with small Unmanned Aerial Vehicles (UAVs) platforms, which is interesting for experimental evaluation of SAR interferometric and polarimetric applications
Different measurement campaigns have been done in order to validate the correct performance of the two systems, all of them at Real AeroClub Barcelona-Sabadell (RACBSA) Radio Control Airfield (Ripollet, Barcelona, Spain)
Summary
Different geophysical and biophysical parameters can be monitored with Synthetic Aperture Radar (SAR) sensors in applications such as earthquake damage assessment, subsidence mapping, harvest monitoring, deforestation and fire impact assessment, DEM production and oil spill monitoring [1,2,3,4,5]. On the other hand energy availability, flight regulations and safety concerns limit the spatial coverage of UAV-SAR missions For these reasons the development of SAR for UAVs is interesting for low-cost testing of innovative SAR concepts, based on new instrument architectures or requiring access to raw-data databases of different scenarios, which are increasingly difficult to obtain. The design and development of a SAR sensor to be fitted to a UAV platform imposes strong constraints in compactness, weight, power consumption, and robustness. Their radar architecture is based on the previously developed Ground Based-SAR [7,8] with Commercially available Off-The-Shelf (COTS). Components in the RF, IF, control and data storage sections (Figure 1) In this case the emphasis has been placed on weight and volume reduction without loss of the radar performance. This project is affordable for an unsophisticated laboratory with basic microwave instrumentation, because it uses simple RF and microwave circuitry based on microstrip technology
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