Comparison of Airborne Magnetic and Ground Magnetic for Identification of Sub-surface Condition Study Case Sand Caldera of Bromo-Tengger Volcanic Complex : Preliminary Study

Abstract

The Bromo-Tengger Volcano Complex is a popular geotourism destination characterized by volcanic activity also unique geological and geomorphology settings. However, limited geophysical investigations have been conducted in this area, particularly using magnetic methods, to understand the subsurface conditions. Thus, this study aims to compare geophysical methods which are airborne and ground magnetic survey methods to identify the sub-surface conditions of Bromo-Tengger Volcano Complex. Airborne magnetic measurements were conducted using a Geotron Proton Precision Magnetometer G5 as the base and a Sensys Magdrone R3 with a DJI M600 drone as the rover with 5 ms of spacing, providing rapid coverage of large areas and minimizing interference. Ground magnetic measurements were taken using only a Geotron Proton Precision Magnetometer G5 for base and rover with 200 meters of spacing. Ground magnetic measurements serve as a comparison to assess resolution and potential data loss caused by factors such as flight altitude and data sampling rate. Combining both magnetic survey measurements enables a comprehensive understanding of the magnetic properties of the surveyed area. The airborne magnetic survey produced 2,097,134 data points in just two days, while the ground magnetic survey produced only 174 points in ten days. Although the airborne magnetic survey is less detailed, it can effectively interpret the subsurface conditions. On the other hand, the ground magnetic survey provides high-resolution results but is affected by local noise and temporal changes. Both surveys identified high anomalies in the southern and northeastern regions, which were interpreted as basalt lava flows. Medium anomalies are believed to be early pyroclastic fall deposits, while low anomalies indicate subsurface volcanic activity. Overall, the results of the airborne magnetic survey correlate well with the ground magnetic survey, making it a viable and time-saving alternative to large-scale magnetic measurements.