Fig. 4

Boxplots of the estimated signal to noise ratio (y-axis) versus the target altitude (x-axis) for the four different frequencies based on apparent resistivity (R) values. These are created from the output of the Weiner Process model detailed in Section (“Approach 1 - Weiner process”). Higher values indicate that there is better preservation of signal. For both the 900 Hz frequency and 25 KHz frequency flying at lower altitudes seem strongly desirable. This is less clear however at frequencies 3 and 12 KHz