Afield mill is a specialized instrument used for measuring the strength of electric fields in the atmosphere, one of the key parameters ofatmospheric electricity. They are used in the launch criteria for rockets bound for orbit, as well as the now-retiredSpace Shuttle, to avoid lightning strikes. They are also used in outdoor laboratories for lightning protection equipment to determine favorable experiment conditions,[1] or simply to measure the atmospheric electric field away from thunderstorms.
The "mill" is a typical rotating shutter design in the instrument. It acts as aChopper, converting the tiny DC signal of ambient static electricity into a tiny AC signal that is easier to detect without the amplifier's DC bias swamping it. It can be used on the ground, or deployed airborne and flown throughanvil head clouds to make measurements.
AtKennedy Space Center (KSC) in Florida, 31 field mills are deployed around KSC and the nearbyCape Canaveral Space Force Station. Data from the field mills help forecasters determine when electric charge aloft might trigger lightning during a launch.[2]
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