SOIL-SALINITY MAPPING WITH ELECTROMAGNETIC INDUCTION AND SATELLITE-BASED NAVIGATION METHODS

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 G PS are reviewed and the differential GPS (DGPS) mode of positioning, a s applied to the EM meter positioning case, is explained. An EM38 sali nity meter was time synchronized to GPS through a field portable perso nal computer (PC) and mounted on a non-magnetic toboggan for this purp ose. The PC was also used to record all data for post-processing and a nalysis. The system was towed at velocities of up to 25 km h-1 during the field measurements. Continuous positioning of the system was achie ved with an accuracy of 1-3 m. Salinity and GPS measurements were inte grated 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 si te 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 application s. The effect of measurement spacing on accuracy is also analysed usin g various scenarios.