What is it about?

Ground and low-level unmanned aerial vehicle (UAV) surveys covering 15 line kilometers, using a lightweight PicoTesla (pT) resolution 3-axis fluxgate vector magnetometer (FVM), are compared with each other, that are traversed over an urban landfill in an area with high levels of 60 Hz electromagnetic interference (EMI). The FVM data is then benchmarked by a femtoTesla (fT) resolution scalar ground magnetometer survey.

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Why is it important?

FVM have improved greatly the past few decades and are now small, lightweight and robust, and effectively omnidirectional and low noise after a simple fully spherical field calibration. Being small and lightweight they can be traversed easily on backpacks and mounted on smaller UAV such as quadcopters. The quadcopters can import high resolution LiDAR surfaces that are used as flight height control for low level surveys that approach ground survey sensor heights. The main limitation of the UAV system is the standard GNSS positioning that on the vertical Z axis is 2-3 m at best. The pT resolution FVM proved to map well, when compared with a fT resolution scalar ground magnetometer benchmark.

Perspectives

FVMs, particularly the fast-sampling (200 Hz in this case) 3-axis pT variety that can be field calibrated, proved to be a cost-effective and robust mapping solution in an EMI noisy urban landfill environment. A UAV slung sensor survey, using standard GNSS with imported LiDAR drape surface control, can be flown at near ground survey sensor levels. The average sensor height for this UAV survey was 3-4 m above ground, whereas the ground survey used a 2m high sensor. The standard GNSS X, Y and particularly Z coordinate positioning was the limiting factor on sensor positioning accuracy, as the LiDAR control at 1m resolution was higher positional accuracy than the UAV GNSS. It's posited that an improvement on the UAV results presented here might be possible with the use of a UAV with RTK GNSS or active RADAR or LiDAR flight control. Regardless, a cost effective small UAV quadcopter with standard GNSS and a pT resolution FVM produced data of a quality that was enhanced by both low pass filtering to remove 60 Hz power line noise, that was amenable to downward continuation filtering to ground survey levels to approximate a ground survey.

Ed Cunion

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This page is a summary of: Spherical calibration and quality control of ground and UAV vector magnetometer data, The Leading Edge, May 2021, Society of Exploration Geophysicists,
DOI: 10.1190/tle40050382a1.1.
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