The MagArrow is a dual sensor magnetometer powered by MFAM sensors, but it is configured for use so it only has a single data output. The reason Geometrics has done this is so we could ensure the MagArrow encounters no "dead-zones". A dead-zone occurs when the orientation of a magnetometer results in the magnetometer producing poor or no measurements. The dead-zone angle depends on the location of survey.
Since we have the two MagArrow MFAM sensors in orthogonal orientations, the MagArrow Magnetometer has operability worldwide without affecting survey orientation, making it much easier to use for the customer.
Heading errors are a type of noise magnetometers can experience. They come from three sources:
Magnetic materials in the sensor itself are the primary cause of heading errors. The physics of Cesium and Potassium magnetometers can contribute small amounts to the total heading error. Magnetic contamination near the sensors, operating electronics, or operator can all contribute to heading error.
Heading errors look like herringbone patterns in survey images. Alternate lines can also be corrugated.
Dead-Zones vs Heading Errors
while these two sources of error in magnetic data are different, there is overlap between them when operating a magnetometer like the MagArrow.
Heading errors can be fixed relatively easily in software, where dead zones can be much harder to manage. If a line is completely ruined because of a dead zone then they will need to re-fly the line/mission which is time consuming. Even with advanced users, these sorts of mishaps can happen.
Additionally, the closer a mag sensor operates to a dead-zone, the larger a heading error will be measured. With compensation software and a pre-survey heading error flight, heading error can be reduced dramatically to around 1 nT for the MagArrow.
Click to view the difference between Raw and Processed MagArrow Data
The MagArrow is only outputting a single value as a means to create a “no-dead-zone” system. Obviously each sensor has a dead zone themselves, but with the sensors orientated orthogonally at least one sensor at all times will have a magnetic measurement. By combining the measurements from both sensors it is possible to generate a constant magnetic field measurement independent of orientation and location in the world. If the data from each MFAM sensor in the MagArrow was individually reported there would be gaps in the mag fields observed by either sensor as you fly, rotate, and swing.