The local calibration of the previous section enables the determination of the electric field at the instrument. This electric field, however, will be distorted if the conducting surface below and around the instrument is not planar. An uneven conducting ground can either amplify or reduce the measured electric field relative to that which would exist above a planar surface. The charge moment calculations based on the vertical static electric field (Section 3.5) and vertical ELF electric field (Section 4.1) assume that the field is measured above a flat surface. Thus, the amplification factor due to local topography must be calculated and removed before the charge moment can be calculated.