Geophysical Correlation: Global Versus Local Perspectives
Channel: Recording Archaeology
Date: 2019-11-23

Correlational studies at the regional level and theory suggest the near-independence of many geophysical data sets acquired by different survey modalities (e.g., GPR, magnetic gradiometry, electrical resistivity). Nevertheless, robust anomalies that point to the same buried features frequently occur in diverse data sets, creating a paradox because parallel anomalies suggest that robust correlations should exist. Relationships between corresponding anomalies traditionally have been noted subjectively, through visual comparisons of mappings of geophysical results. Through application of local Pearson’s r in small neighborhoods, with radii from 0.71-1.6m, a means is offered for the quantification and mapping of local correlations between two geophysical data sets. A case study examines relationships between a GPR depth-slice, apparent electrical resistivity, and magnetic susceptibility data acquired at Army City, a Great War troop support town in Kansas, now obliterated except for subsurface remains. Intricate spatial patterns of positive and negative correlation between these modalities are illustrated that vary in complexity with neighborhood size. Moderately sized neighborhoods are preferred because the spatial patterning of correlations best corresponds with anomaly forms and is enhanced through moderate smoothing. Overlays of high correlation correspond well with robust anomalies observed in each data set and offer objective criteria for assessments of correlation. However, the occurrence of mutually robust anomalies does not necessary imply correlation. Methods of data integration generally capitalize on composite relationships. Methods offered here offer a means to place integration studies on a firmer footing and may also improve understanding of complex geophysical relationships.

(Kenneth L Kvamme)