Date of this Version
Transactions of the ASABE Vol. 54(3): 757-767
Apparent soil electrical conductivity (ECa) is typically mapped to define soil spatial variability within an agricultural field. Knowledge of the vertical variability of ECa is desired to define the site‐specific behavior of the soil profile. A pneumatic angular scanning system (PASS) was developed to sense horizontal and vertical changes of ECa on‐the‐go with an electromagnetic induction (EMI) instrument using an angular scanning method. This sensor system consists of a sled with a rotating mechanism, an EMI sensor, an inclinometer, and a pneumatic actuator. The system was evaluated at the University of Nebraska‐Lincoln Agricultural Research and Development Center (ARDC) near Mead, Nebraska. The PASS was towed by an all‐terrain vehicle (ATV) and operated from a field computer with specially designed data acquisition software. Rotation of the instrument allowed continuous transition between horizontal and vertical modes of operation. Nine discrete field locations with different soil conditions were used to compare PASS estimates with measurements obtained using a manual ECa probe. With the assumption of two fixed‐depth layers, the R2 value was 0.91 for the linear regression between corresponding measured and predicted ECa values, and R2 was 0.54 for the difference between the ECa of deep and shallow soil. Unfortunately, solving the system of linear equations for a more complex model of a soil profile required inversion of an ill‐conditioned (close to singularity) matrix, which was not feasible without regularization and an inversion procedure with non‐negative constraints to be pursued in the future.