DroneSOM success story 12/2024
In the DroneSOM project, Radai Ltd is developing a novel drone-based electromagnetic (EM) system called Louhi. In the semi-airborne version of the Louhi system, the transmitter is a current carrying loop (100 x 100 m2) laid out on the ground surface and a 3-component EM receiver is towed in the neighborhood of the transmitter with the help of a VTOL (Vertical Take-Off and Landing) type of drone. The EM system operates at three frequencies (2.3, 4.6, 9.2 kHz) and the response is provided as the in-phase and quadrature component of the magnetic flux density (B-field, pT) in north, east, and down (NED) direction.
In August 2024, Radai made the first commercial drone-EM survey with the Louhi system. The survey was commissioned by an international mineral exploration company over an active prospect area in eastern Finland. The size of the survey area was 3 km2, the line separation was 50 m, and the total length of the planned flight lines was about 70 km. The survey, conducted by a three-person field crew, was completed in four days. The survey utilized five different loop locations distributed inside the survey area and around the expected target(s). In semi-airborne surveys, it is necessary to use multiple loop locations to “illuminate” the conductive targets from different directions, and thus, provide better data for data interpretation. For each loop, two ca. 60 km long survey flights were made. The total number of survey flights was 13 as some loops were measured multiple times.
Initially, the data quality was found to be good. Closer inspection showed, however, that the time synchronization between the transmitter current and receiver signal was astray. Some novel data processing techniques were implemented in Radai’s EM processing and inversion software, Lempo3D, to enable numerical inversion. At the time of writing this story, the software development and data interpretation are still going on. The initial inversion results, however, reveal weak conductivity anomalies where the fieldwork can be focused.
Figure caption: The 3-component Louhi EM-receiver “birdie” towed by a Coot VTOL drone. The length of the tow line is about 20 m. (Photo by M.Pirttijärvi)
