Inversion of Geo-Magnetic SQUID Gradiometer Prospection Data Using Polyhedral Model Interpretation of Elongated Anomalies

Abstract

This paper is based on data sets acquired by a fast and efficient ground-based measurement system, which is based on superconducting quantum interference device technology and ensures geo-magnetic mapping of large areas. The local variations (gradients) of the Earth's magnetic field are represented in so-called magnetograms, which typically include a large number of magnetic anomalies with different appearance and shape. Here, elongated anomalies are investigated, which are explainable by a polyhedral source body. These underground structures can be represented by a cross section that is approximately uniform along the main strike extent of the source. After introducing the measurement system, a source description model is developed theoretically and in the following adapted to practical problems. In order to illustrate the utility of this kind of minimization-based inversion and to validate the produced results, an example of archaeological measurements in Mongolia is shown. Results of the field measurements are used for inversion toward a description of possible subsoil situation. Finally, an excavation shows the accuracy of the results.

Mapping Karakorum, the capital of the Mongol Empire

“…The complex setup of the SQUID sensors further enables the calculation of object depths and the modelling of 3D shapes (Schneider et al 2014), but due to the high density of magnetic signatures-especially within the city centre-thousands of individual features need to be calculated and classified.…”

Proto-Urban Establishments in Inner Asia: Surveys of an Iron Age Walled Site in Eastern Mongolia

“…In the course of our field expedition, we used the magnetic measurements from fluxgate gradiometers to produce a site plan of KHB-2 subsurface anomalies, and sought to clarify some of these features through test excavations. However, it is often also useful to perform non-invasive investigations of these features by modeling the anomalies, or, in other words, trying to find a model of the subsurface that explains the measured anomalies (Schneider et al 2014). The problem with this procedure is that it is non-unique: the measured magnetic anomaly could be approximated by several different models.…”

What over 100 drillings tell us: a new method for determining the Koenigsberger ratio of soils from magnetic mapping and susceptibility logging

“…Case studies often approach a quantitative interpretation of magnetic anomalies using the assumptions of a simplified source geometry and induced‐only magnetization. To explain the observed data, the susceptibility contrast between the source and the surrounding subsurface matrix is then determined for this geometry by linear inversion (Miller et al, 2019; Schneider et al, 2014; Wilken, Wunderlich, Majchczack, Andersen, & Rabbel, 2015).…”