GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.3 GNGTS 2024 A compact measuring system for UAV based magnetc anomalies surveys R. Carluccio 1 , I. Nicolosi 1 , F. D’Ajello Caracciolo 1 , L. Minelli 1 1 Isttuto Nazionale di Geofsica e Vulcanologia (INGV) One of the most commonly used applicatons of potental felds in geophysics is the measurement of feld anomalies in order to produce regional maps. These anomalies are in fact due to anisotropies in terrain geology and can give indirect informaton on underground layers/structures. In the magnetc feld case, anisotropies are mainly due to diferences in magnetc susceptbility and to the presence of magnetsed material (remanence) in the underlying structures. Magnetc anomaly maps are usually realised scanning the area of interest with a sensible magnetometer, usually following a parallel, equally spaced lines patern properly oriented with respect to North. Areas of interest can generally scale over orders of magnitude ranging from regional (thousands of square kms) to hundreds of square meters. Up to recent years this kind of measure has mainly been done either with airborne measuring systems, airplanes or helicopters or by walking on the ground in small areas. With the advent of UAV systems a series of intermediate targets have become possible since low alttude, square kilometres orders surveys, even on impractcable (by man) wild areas could be easily managed in a fracton of tme. In the case of UAVs, however, there are some technical aspects that arise regarding the magnetc anomaly measure. The magnetometers required for these measurements are usually protons precession or optcal pumping total feld units, which are heavy and impractcal as UAV payloads, weighing several kilograms. However, they are necessary because the anomalies being searched for can ofen be as low as a few nanotesla, which is fve orders of magnitude less than the average Earth magnetc feld. Fluxgate magnetometers are small and sensitve enough for this task, but they are difcult to use. Even if they can achieve the required sensitvity, they only measure the magnetc feld component along their symmetry axis. In a moving frame, the only way to obtain a meaningful measurement is to mount three of them in an orthogonal frame (creatng a tri-axial unit) and calculate the magnetc total feld based on those readings. However, this procedure is afected by several factors, including: 1) the calibraton of the three units in terms of their response functon to the magnetc feld and external temperature, 2) the orthogonality of their axes, and to a lesser extent, 3) the mutual interacton of the three sensors in space. It can be demonstrated that these factors can result in an error in the calculated total feld that is much larger than the precision requirements mentoned earlier, unless a thorough and challenging calibraton is performed for each individual unit. Only in recent months however a new family of optcal pumped miniaturised magnetometers have become available. They have furthermore characteristcs comparable to their big-sized relatves.