Fig. 4. Plot of prediction root mean square error (RMSE) and mean error (ME) for the various kriging methods used to interpolate raw electromagnetic induction instrument (Type EM38) data and converted EC_e data across all eight fields. Co-K = cokriging, OK1 = ordinary kriging of raw EM_0,H data, OK2 = ordinary kriging based on EC_e estimates, RK = regression kriging, 3-DK = three-dimensional kriging