Two-dimensional variability in porosity, density, and electrical resistivity of Eckernfِrde Bay sediment

Image-based analysis techniques are employed to compare sediment density heterogeneity as interpreted from X-radiography and electrical resistivity measurements. Assessments of sediment heterogeneity in two dimensions through the use of the two methods, with some exceptions, yield similar results. Autocorrelation functions estimated from density fluctuations reveal an anisotropy between vertical and horizontal sediment structure indicated by horizontal correlation lengths being greater than vertical correlation lengths. In addition to the anisotropy, discrepancies between values of correlation lengths calculated from two statistical methods are indicative of the scale-dependent nature of the sediment structure. This scale dependence is also exemplified by the differences between the images of X-radiography and electrical resistivity. The unequal volume of sediment over which the respective methods are integrated produces results differing by the amount and type of information included in each image. Electrical microresistivity is more sensitive than X-radiography to many smaller-scale variations in sediment density. Combining the results from X-radiography and microresistivity imaging allows the calculation of Archie’s m parameter, an extremely sensitive indicator of sediment microstructure. In addition, electrical microresistivity gives a measurement of sediment tortuosity coincident with sediment porosity and density.