Engineering topics
Publications and source records attributed to Thomson, E. M..
The specific problem objective was to locate the sources of radiated electric field from lightning using an overdetermined set of measurements of time-of-arrival. A similar problem exists for epicentral sources in earthquake location, acoustic sources of thunder, and terrestrial navigation using LORAN and GPS.
A system has been developed to measure wideband electic field derivatives (dE/dt) at five ground stations in a 15 km x 15 km network at Kennedy Space Center. Individual station responses are normalized using digital filters. Pulse-timing resolution is improved to much less than 50-ns sample interval by interpolation using packing in the frequency domain. A time tag for each pulse is defined as the mean of the times of the rising-edge half peak, peak, and falling-edge half peak. The standard deviation in these times defines the timing error and is shown to be a function of noise and bandwidth rather than digitization rate. Each of the four unknowns for a pulse source location (x,y,z) and time of occurrence (t) is found from the five time-tag measurements using different weightings for all five combinations of the four-station hyperbolic equations. Weighting factors and errors in x,y,z and t are estimated using error propagation techniques.
An experiment to measure simultaneously the wideband horizontal and vertical electric fields from lightning return strokes is described. Typical wave shapes of the measured horizontal and vertical fields are presented, and the horizontal fields are characterized. The measured horizontal fields are compared with calculated horizontal fields obtained by applying the wavetilt formula to the vertical fields. The limitations and sources of error in the measurement technique are discussed.
The expression for the radiation electric field from a current pulse propagating along a channel of arbitrary orientation is derived. Representative radiation fields indicate that approximately 1-msec duration pulses occur at rates of up to 1/msec in intracloud flashes, thereby furnishing a valuable tool for the tracking of streamer development. Attention is given to the errors which arise when radiation pulse measurements are inverted, in order to determine the pulse's current-waveshape, channel-orientation, and current-speed product properties.