Advantages to using the pseudogravity transformation to aid edge detection of total field archaeomagnetic datasets

摘要

Magnetic surveys are becoming increasingly common on archaeological sites due to the amount of data that can be collected rapidly in a non-invasive manner. Owing to their relatively low cost compared with excavation they commonly provide the only dataset that covers an entire archaeological site, which can then be used to target other surveys and excavations to areas of interest. Typically interpretation is done visually using optimized images of the raw data, which when dealing with large datasets can be time-consuming and subjective. Various derivative based methods have been developed recently to aid the interpretation of magnetic data. A particular use for these techniques is to locate the edges of subsurface magnetic bodies, and their use is gaining popularity in aeromagnetic regional and mineral exploration surveys. Despite this they are rarely used in archaeological survey interpretation. This probably is due to the particular challenges posed as a result of the low amplitude and high-wavenumber content of archaeomagnetic surveys, where features of interest are often only slightly above the noise level. Here, it is demonstrated that when derivative-based methods are applied directly to total-field data, the high-wavenumber components of the data are amplified, making datasets difficult to interpret and often proving less useful than the total-field dataset alone. The pseudogravity transformation is a readily available tool for suppressing this bias to the high-wavenumber features and providing derivative-based results with a power spectrum comparable to the original total-field response, but with all the qualities to enhance interpretation that are obtained from using the derivative methods.