Figure 8

Histograms of natural log of percentage error of thickness measurements determined using cluster analysis (top left), as deviation from expected thickness decay (middle and right hand panels) as a function of distance from source and using field measurements (shown in red). Cluster and exponential error is calculated as the percentage difference between measured thickness and either the average cluster value, or the value predicted by exponential regression. Natural variance and measurement uncertainties calculated as in Figure 7. For most cases these results correspond to lognormal distributions, however there are clear differences in range and mean error for each dataset.