Lightweight TEM and VLF systems for low-altitude UAV-based geophysical

Summary To create a complete set of UAV-based aerogeophysical methods, two lightweight UAV-electromagnetic systems were developed. The first one (VLF-type) is designed to first-stage geophysical mapping over large areas; it can be performed simultaneously with magnetic and gamma surveys on one UAV. In this case, the receiver with mutually orthogonal ferrite antennas provides measurement of the vertical and horizontal components of the electromagnetic field in the audio frequency range (10 – 48 kHz), at the far field region of the electromagnetic field of navigation radio stations. The second variant is the UAV-TEM, where the time-domain transmitter located on the ground and connected to a galvanically grounded line several kilometers long, and the receiver with coil is towed by the multirotor UAV. From one line placement, it is possible to perform surveys in areas up to several square kilometers. This variant is optimal for detailed electromagnetic soundings in local sites identified at the previous stage of geophysical mapping, it provides the possibility of data inversion to a depth more than 300 meters. Together with UAV-magnetic prospecting and gamma-spectrometry, the created systems provides a solution to a wide range of geological tasks in any complexity of landscape conditions.