Quantitative detection of water content in soil using drone-based digital radar

• Applicant: Professor Dr.-Ing. Christian Waldschmidt
• Subject Area: Communication Technology and Networks, High-Frequency Technology and Photonic Systems, Signal Processing and Machine Learning for Information Technology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541018053

The recording of soil water content is an important metrological task, especially for climate and weather modeling as well as for agriculture and ecosystem research. Currently, local measurement of soil water content is done by taking soil samples or invasive measurement systems. Both result in a high time expenditure. Alternatively, radar sensors on satellites are used. However, these remote sensing methods are less accurate and allow only sporadic measurements, as they depend on satellite overpasses. However, to gain comprehensive knowledge from soil moisture measurements, a frequent, fast, large-scale, and accurate detection of the soils water content is required. Drone-based ground penetration radar (GPR) offers the ideal combination of flexibility and cost and time efficiency in this regard. Combined with measurement evaluation leading to direct determination of soil moisture as a relevant measurand, there is great potential for drone-based soil moisture measurements in ecology and agriculture. In this context, the quantification of the measurement error is also crucial in order to be able to interpret the measurement data in a meaningful way. In the proposed project, a completely new measurement principle is developed. The water content in the soil will be measured point by point using a drone-based GPR. A model will be researched to determine soil moisture from the radar data via the dielectric properties of the soil. Using signal processing approaches for synthetic aperture radars, these point measurements can be applied to larger areas. The focus is furthermore on evaluating the measurement accuracy of the new measurement principle as a function of resources such as flight time and drone weight. The project consists of four main objectives. Objective 1 is to explore a new measurement principle for detecting soil water content using drones. This includes the use of a suitable radar signal modulation and the development of a tomographic SAR method suitable for the application. The latter will be evaluated via the ratio of measurement accuracy to resource expenditure in terms of flight duration. Objective 2 is to research a new radar sensor including broadband antennas with low weight and low wind load. Exploration of signal processing approaches for soil water content measurement is objective 3. This objective will be achieved by modeling the effects of soil moisture on radar data. Objective 4 is the analysis of error influences as well as a comprehensive measurement accuracy determination according to GUM. Extensive measurements are planned to verify the signal processing approach and to analyze the errors. The existing infrastructure will be used optimally to perform measurements under laboratory conditions over a sandy soil as well as an extensive open field measurement campaign on an existing test field.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2433: Metrology on flying platforms