Soil salinity mapping with electromagnetic induction and satellite-based navigation methods

Abstract

This project was undertaken to develop a system to map salinity with a towed electromagnetic induction meter (EM) and to position the meter with the Global Positioning System (GPS). The characteristics of the GPS are reviewed and the differential GPS (DGPS) mode of positioning, as applied to the EM meter positioning case, is explained. An EM38 salinity meter was time synchronized to GPS through a field portable personal computer (PC) and mounted on a non-magnetic toboggan for this purpose. The PC was also used to record all data for post-processing and analysis. The system was towed at velocities of up to 25 km h−1 during the field measurements. Continuous positioning of the system was achieved with an accuracy of 1–3 m. Salinity and GPS measurements were integrated and recorded on a field portable PC laptop. The results from a 30-ha site near Brooks are presented as well as those from a 100-ha site near Stettler, AB, which was surveyed in 3 h yielding 6000 salinity measurements. In order to test the repeatable accuracy of the system, the survey at Stettler was repeated the following day. The agreement is of the order of 1 dS m−1 which is satisfactory for most applications. The effect of measurement spacing on accuracy is also analysed using various scenarios. Key words: Soil electrical conductivity, salinity, satellite navigation, Global Positioning System, positioning, precision farming