Testing an airborne TEM system in Denmark using a heavy-lift drone

Introduction

Time domain electromagnetics (TEM) is a well-established geophysical method commonly applied from ground-, helicopter- and fixed-wing platforms. Hybrid ground transmitter/drone receiver TEM systems are occasionally in use. However, the inherent size and weight of an active TEM system have been limiting factors for a true drone-based TEM system. Here we describe the successful process of developing a fully airborne TEM drone system. Earlier stages of development of this project have been published by e.g. Panzner et al. (2022) and Nyboe and Mohr (2023). A fundamental design philosophy of the project has been the early field testing of prototype hardware and software solutions designed for the fully airborne TEM drone system. These tests have been mainly performed using a helicopter-born scaled-down frame flown at low speed and low altitude to simulate a drone operation. Using this setup we have been able to proceed significantly in our developments without the added complexity of ensuring that drone providers and legislation align with our testing objectives. However, this approach can only take us so far. Thus, we organized a heavy-lift drone to be available for testing in Denmark in the summer of 2023. Regulatory authorization for performing drone TEM surveys at the designated test sites required prior procedure validation demonstrations in a controlled airspace. For this reason, testing was initiated at the UAS Test Centre Denmark near Odense in June 2023. In this paper, we present the test sites we have flown with the drone setup, and we discuss the regulatory circumstances and their implications for the operations. We describe practical aspects of the field operations, including features of the transmitter frame designed for improved flight stability and maneoeuvability. We finally present data examples and inverted sections as well as discuss future plans.

Conclusions

We have described significant elements in our process of developing and testing a fully airborne TEMdrone system. Specifically, a Danish field test campaign has been detailed involving both SORA procedure validation, high-altitude flights for system characterization, data acquisition, processing, and in version. A comparison to inversion results from state-of-the-art high-resolution ground-basedTEM system data shows favorable properties of the drone TEM system. Testing is planned to continue using a new carrier drone, promising more data to show later in 2024.

Acknowledgements

We would like to thank Eureka/Eurostars for the financial support of this research and development project (nr. E114169). We would also like to thank the collaboration partners within this project, the Norwegian Geotechnical Institute (NGI) and the University of Southern Denmark (SDU) for fruitful discussions and valuable contributions to this project. We are grateful that ACC Innovation has enabled us to perform the airborne tests of our drone TEM system in Denmark.

Final praise goes to the development and manufacturing teams at SkyTEM Surveys, who have been innovative, flexible, and persistent in their efforts to make the fully airborne drone system a reality.