Abstract
This work presents an enhanced autonomous airborne Synthetic Aperture Radar (SAR) imaging system able to provide full 3D radar images from the subsurface. The proposed prototype and methodology allow the safe detection of both metallic and non-metallic buried targets even in difficult-to-access scenarios without interacting with the ground. Thus, they are particularly suitable for detecting dangerous targets, such as landmines and Improvised Explosive Devices (IEDs). The prototype is mainly composed by an Ultra-Wide-Band (UWB) radar module working from Ultra-High-Frequency (UHF) band and a high accuracy dual-band Real Time Kinematic (RTK) positioning system mounted on board an Unmanned Aerial Vehicle (UAV). The UAV autonomously flies over the region of interest, gathering radar measurements. These measurements are accurately geo-referred so as to enable their coherent combination to obtain a well-focused SAR image. Improvements in the processing chain are also presented in order to deal with some issues associated to UAV-based measurements (such as non-uniform acquisition grids) as well as to enhance the resolution and the signal to clutter ratio of the image. Both the prototype and the methodology were validated with measurements, showing their capability to provide high-resolution 3D SAR images.
Highlights
In the last years, there has been a massive development of new applications using Unmanned Aerial Vehicles (UAVs) [1,2,3,4]
For the results shown in this contribution, the investigation plane is obtained by shrinking the rectangle with the scale factors s ft = 0.95 and s fct = 0.85 and sampling it every δt = δct = λmin/4 = 0.025 m
To facilitate the comparison of the results shown both flights were rotated according to the same cog and the same investigation domain was used (x ∈ [−0.4, 0.6] m, y ∈ [1, 5] m and z ∈ [−0.6, 0.4] m)
Summary
There has been a massive development of new applications using Unmanned Aerial Vehicles (UAVs) [1,2,3,4]. A considerable amount of these applications is based on integrating electromagnetic sensors on board the UAVs (e.g., power detectors for antenna measurement [5], or radars for earth observation [6] and subsurface sensing [7]). Several Non-Destructive Testing (NDT) techniques have been employed for subsurface sensing applications, since they allow extracting information of the subsurface and detecting possible buried targets without interacting with them. GPR has been found to be a useful strategy for this application since it is able to provide high resolution images from the subsurface and, as a result, it makes possible the detection of both metallic and dielectric buried targets [9,10]. GPR capabilities are considerably affected by the soil heterogeneity, the roughness of the air–soil interface and the possible low signal to clutter ratio (especially for non-metallic targets) [11]
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