Blog #3 describes how the atmospheric electric field was measured using two aircraft: 1. South Dakota School of Mines and Technology (SDSMT) armored T-28 aircraft, 2. New Mexico Institute of Mining and Technology (NMIMT) Special Purpose Test Vehicle for Airborne Research (SPTVAR). The objective was to accurately measure the electric field produced by lightning storms. Five electric field mills which were attached at specific locations on the fuselages of both aircraft. [1]
The E – 100 electric field mill is shown in the following figure:
Its specification is given in the Appendix.
In a field mill, a conducting, grounded, rotating shutter alternately shields and exposes electrodes from the electric field to be measured. The charge induced on the electrodes, which is periodic, passes through an amplifier. After amplification, the signal is demodulated and filtered to produce a voltage that is proportional to the electric field.
Since the aircraft fuselage is also charged, it produces an electric field of its own that must be subtracted from the data through a calibration procedure. To calibrate the five field mills, self-test calibration flights was made which the roll, pitch and yaw of the aircraft were varied through most angles sensed by each electric field mill, and regression analysis was used to process the data. The placement of the mills is shown in the following figures:
In addition, for calibration purposes, intercomparison flights were made with both aircraft.
A typical result is shown in the next figure [1]
The top three plots are the heading, roll and pitch of the two aircraft, while the bottom three plots compare the electric field outputs of the two aircraft (kV/M) which are very close to one another.
References
1. Rand E. Feind, Qixu Mo, and Andrew G. Detwiler, REPORT ON T-28 ELECTRIC FIELD MEASUREMENTS AND THEIR CALIBRATION, Division of Atmospheric Sciences, National Science Foundation, Institute of Atmospheric Sciences, South Dakota School of Mines and Technology, September 1998 http://www.eol.ucar.edu/projects/t28/publications/reports/R98-01.pdf
Appendix
MODEL E-100 DC ELECTRIC FIELD METER
SPECIFICATIONS