Dr. Nigel Crook carries the EM-31 instrument to map a landfill along coastal California. The sensor is walked in parallel lines with about 10 to 20 feet spacing in between and has a depth of investigation of approximately 20 feet (6 meters).

In this image HGI Project manager Dr. Nigel Crook field survey using an EM-31 instrument. The instrument consists of a large sensor that is walked over the area of interest and is coupled with a GPS system for measurement locations – Image by Shawn Calendine