HR: 1340h
AN: AE23A-0838    [Abstracts]
TI: A Comparison of Charge Retrievals using Standard One- and Two-Charge Source Models and the Dimensional Reduction Method
AU: * Murray, N D
EM: murray@atmo.arizona.edu
AF: Institute of Atmospheric Physics, University of Arizona 1118 E. 4th Street Room 542, Tucson, AZ 85721 United States
AU: Koshak, W J
EM: william.koshak@nasa.gov
AF: Earth Science Department, NASA Marshall Space Flight Center, Huntsville, AL 35805 United States
AU: Krider, E P
EM: krider@atmo.arizona.edu
AF: Institute of Atmospheric Physics, University of Arizona 1118 E. 4th Street Room 542, Tucson, AZ 85721 United States
AB: Lightning poses a frequent threat to US space vehicle operations in Florida. In response to this threat, the Launch Pad Lightning Warning System (LPLWS) was developed in the early 1970s. Today, it consists in part of a network of 31 electric field mills situated over Kennedy Space Center (KSC) and Cape Canaveral Air Force Station (CCAFS) in east central Florida. When a lightning flash occurs in the vicinity of the LPLWS, several or all of the mills will record a change in electric field. Provided the flash is not too distant and/or too complex, the set of field changes can be analyzed to reasonably retrieve the locations and magnitudes of charges deposited by the flash. This work assesses retrieval accuracy for flashes that occur in the vicinity of the LPLWS and that are not overly complex. Two optimization methods have been used to analyze simulated electric field change data produced from computer-generated charge sources. The first method, a standard least-squares optimization procedure using the Levenberg-Marquardt algorithm, has been used to find the eight unknown parameters in a general two-charge model. The second, a Dimensional Reduction (DR) technique described by Koshak (this session), reduces the eight parameters to four by analyzing residual measurements. The simulated field change data wereas generated using known charge sources and a forward law (i.e., Coulomb's law of electrostatics with the assumptions that the Earth is an infinite plane conductor and the atmosphere a perfect vacuum). To determine the typical retrieval error of a particular source situated at a particular location relative to the LPLWS, the source was analyzed 100 times (each time the simulated field change measurement error was defined by selecting it from a random distribution). Hence, statistically significant retrieval errors were obtained for the given source location. The process was repeated for many other source locations, both over and outside the LPLWS, so that a color-coded "retrieval error map" could be obtained for each retrieved model parameter. The process was completed for three different source types (monopole, vertical 2-charge, slanted 2-charge), and the results are inter-compared and summarized.
DE: 3324 Lightning
SC: Atmospheric and Space Electricity [AE]
MN: 2004 AGU Fall Meeting