Advances in Reconstructing Archaeological Magnetic Signals; an Algorithm for Filtering Noise due to the Ploughing Effect

Abstract

Archaeological remains are very often buried under uneven soil of agricultural fields crossed by rather parallel furrows and ridges. Consequently, ploughing in a magnetic survey might produce a repetitive, quite regular, linear noise in the data, which could impede optimal recovery of the archaeological magnetic anomalies; depending on the acquisition line orientation, this noise may show as an oblique, vertical or horizontal pattern in the magnetic maps. Several studies have tested and verified methods for oblique ploughing minimization, but, to our knowledge, no procedures regarding the vertical and horizontal types of noise have been published. The present research proposes a procedure to filter each type of ploughing effect through an algorithm working in the wavenumber domain. The procedure produces images with a considerable reduction of the noise in any direction, resulting in enhanced visibility and readability of the archaeological anomalies. Figure 6. Masks for cases of (a) horizontal ploughing; (b) vertical ploughing; (c) oblique ploughing; (d) combination of cases (a) and (b); (e) combination of cases (b) and (c). [Colour figure can be viewed at wileyonlinelibrary.com]

Dreaming of Perfect Data: Characterizing Noise in Archaeo-Geophysical Measurements

“…Low-pass filtering is similar to local averaging and can, therefore, reduce random noise if data are sampled at a sufficiently high resolution (see Section 3.2.1). Filters tuned to noise with specific periodicity and direction (e.g., related to an operator's gait or to plow lines [96], see Section 3.2.3) can suppress the unwanted effects, if they are sufficiently consistent. As these filters alter the data's spatial characteristics, they should only be applied after all processing and modeling steps have been applied.…”

Rotational speed measurement of ring spinning based on magnetic sensor

“…In contrast to the abovementioned methods, a magnetic sensor based on magnetic anomaly detection is introduced in this study to measure the rotational speed. Magnetic anomaly caused by ferrous/magnetic object motion can be used to locate or identify the targets that have been extensively applied in the fields of traffic surveillance [12,13], banknote validation [14,15], archeological artifacts [16], and hidden ordnance [17,18]. The anomalous magnetic signal can be detected by field-sensitive magnetoresistance devices, including anisotropic magnetoresistance [19], giant magnetoresistance [20,21], and tunnel magnetoresistance (TMR) [22].…”