Abstract: The study region is near the TERENO (TERrestrial ENvironmental Observatories) site Selhausen, and spans across a rectangular area with the southwest corner at (50º51’43”N 6º23’18”E) and the northeast corner at (50º53’02”N 6º27’10”E). The climate is characterized by an average annual precipitation of 715 mm and a mean annual temperature of 10.2 °C. All soils are developed in Quaternary sediments. EMI measurements were performed on this field. This field is selected because of different spatial patterns visible in satellite images, and its accessibility (i.e., no crops in the field) at the time when the measurements were conducted.
Measurements of apparent electrical conductivity (ECa) were performed using the CMD-MiniExplorer and the CMD-SeptialEdition (GFinstruments, Brno, Czech Republic). The MiniExplorer (ME) consists of three receiver coils separated by 32, 71 and 118 cm from the transmitter coil, whereas the SeptialEdition (SE) has six coil configurations with separation distances of 35, 49, 71, 97, 135, 180 cm from the transmitter coil to the receiver coils. The ME is set at the vertical coplanar (VCP) mode and SE is set at the horizontal coplanar (HCP) mode. Two differential global positioning system (DGPS) modules are mounted on the EMI measuring systems. The entire EMI measurement system is pulled by an all-terrain vehicle. Coordinates and corresponding ECa are recorded at the frequency 5Hz and the dragging speed is around 7.0 km/h. The raw data was filtered so that outliers were deleted and calibrated using the approach as described in Lavoué et al. (2010) and von Hebel et al. (2014).