Fig. 6

Boxplots of the log ratio of σ _b /σ (y-axis) versus the target altitude (x-axis) for the four different frequencies based on apparent resistivity (R) values. Higher values (above zero) indicate that the variability between replicates (σ _b ) was greater than that of the internal variability (σ). The majority of values appear to be concentrated around zero, indicating approximate equality. However, at 12 Khz the variability between runs appears in general higher than that of the internal variability