FM256 Dual Gradiometer System
The dual gradiometer system uses two instruments carried together either to double the speed at which a survey can be made or to increase the sampling density of a survey. Basing the system on two individual gradiometers gives optimum flexibility since they can also be used separately at different sites when required.
A three sided carrying frame, CF6, supports the two gradiometers. One FM256 acts as a master sample trigger which controls a second slave gradiometer - this can be either another FM256 or an FM18/36. Once data sets have been collected in the two gradiometers they are downloaded, and assembled into two individual composites as normal. The two data sets are then easily merged together to form the final composite - Geoplot provides for this in one simple operation.
The system can be used in either parallel or zig-zag survey mode. When used in zig-zag mode the operator, not the frame, turns around at the end of a traverse, thereby avoiding the introduction of direction dependent heading errors (see movie clip below). Since there is no need for restrictive harnesses, turnaround is very rapid. The start/stop sample trigger button on the FM256 is replicated twice on the frame to cater for operator orientation during zig-zag surveying. Logging is simply performed by pressing the start/stop button. The four legs allow the system to be rested on the ground anywhere during survey - no need to return to a centralised support tripod. The frame is designed to support just one gradiometer at a time when resting on the ground, allowing each gradiometer to be aligned individually. The frame can also be used with the legs removed for operation over very overgrown areas.
Variations in angular orientation can introduce heading errors into the data collected. Using a handheld frame, in contrast to other instrument support systems, provides the user with greater awareness and control of angular variations which significantly improves the quality of the data collected. The sturdy frame is well balanced and easy to use even in long undergrowth, and can be lifted easily over other obstacles. The frame is very lightweight, packs flat and is easy to assemble and transport.