Design of a Novel Scalable Multi-Channel GPR System for High-Resolution High-Speed Tomography of Soil Columns

Ground penetrating radar (GPR) offers the great potential to non-invasively monitor soil and root conditions in agricultural environments. A novel experiment in Jülich aims at analysing the interactions between soil, plants and atmosphere under controlled laboratory conditions with as realistic as possible soil and atmosphere composition and temperature. In order to monitor the distribution of water and nutrition as well as the growth of roots and the flow processes in the soil, a 3D GPR tomography system with a spatial resolution of up to 5 cm and a temporal resolution of about 10 s was designed. The novel system consists of 39 multi-antenna tiles (MAT), each holding 64 antennas that can be used as transmitters and receivers. A MAT can be connected to the main module (MAM) in a star-shaped topology or to another MAT in a chain. In both configurations, the tiles are synchronized with an accuracy of about 25 ps. By this approach, the system is very versatile in terms of adjusting the amount and distribution of modules. Each tile contains its own data acquisition (DAQ) module, which is based on a RF-system-on-module (RFSoM). Each RFSoM includes DACs, ADCs, FPGA and CPU, such that the system internal analog path in between of the data generation, the antennas and the digitization is no longer than one meter. The antennas need to have a wide bandwidth for the use of Ricker pulses with a center frequency of 900 MHz and need to be optimized for our specific setup that includes a large amount of very close antennas. Therefore, we designed two-dimensional antennas with a shape we refer to as “circular bow-tie” and a size of 3 cm × 6 cm. Here, we present the system requirements and our derived system concept. The system is scalable in terms of reducing/extending the amount of antenna channels and DAQ modules. Due to the versatile DAQ hardware, the system also offers great flexibility in terms of adjusting the generated transmitter waveform and the signal processing.