Hunt H.G.P., K.J. Nixona, I.R. Jandrella, W. Schulz:
Can we model the statistical distribution of lightning location system errors better?

Electric Power Systems Research (EPSR), Volume 178, 106042, 2020

Lightning location systems geolocate lightning strokes. Given assumptions made in the geolocation models, errors in the reported locations can occur. Modelling these errors as a bivariate Gaussian distribution of historic stroke detections has found success in the form of confidence ellipses. However, the presence of outliers - strokes with large location errors - indicate that there is a better model for these errors. The Students’ t-distribution is a “heavier” tailed distribution. This paper investigates whether the bivariate Students’ t-distribution is a better model for such errors. A methodology for modelling and evaluating the distribution of location errors using maximum likelihood estimation, expectation-maximization and a Mahalanobis distance quality-of-fit test is described. This method is applied to stroke reports from the South African Lightning Detection Network and the Austrian Lightning Detection and Information System time-correlated with photographed lightning events to the Brixton Tower, South Africa and current measurements to the Gaisberg Tower, Austria respectively. In both cases, we find outliers in the distribution of location errors - even as the performance of the networks increase. Using the Mahalanobis test, we find the bivariate Students’ t-distribution to be a better statistical model for both the South African and the Austrian events.

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Schwalt L., St. Pack; W. Schulz:
Ground Truth Data of Atmospheric Discharges in Correlation with LLS Detections

Electric Power Systems Research (EPSR), Manuscript Number: EPSR-D-19-00476, 2019

This paper presents recent ground truth data analyses in the Austrian Alps run by Graz University of Technology in cooperation with Austrian Lightning Detection and Information System (ALDIS). The project "Lightning Observation in the Alps - LiOn" was established in 2017 at the Institute of High Voltage Engineering and System Performance at Graz University of Technology. Atmospheric discharges are observed at different measurement locations in Austria by using a Video and Field Recording System (VFRS). This system consists of a high speed video camera (2000 frames per second) and a flat plate antenna to measure the electric field. The recorded data can be used to better understand the atmospheric discharges, especially in the alpine area. For the present analysis a data set of the measurement periods 2015, 2017 and 2018 was used for validation of the Lightning Location System (LLS) data of ALDIS. In total 463 negative cloud-to-ground (CG) flashes and 1527 negative CG strokes were recorded in Austria during 51 days. The LLS performance parameter, location accuracy and detection efficiency and further the flash multiplicity and peak currents have been analyzed for these three years. Values for location accuracy are in the range of 90 m to 130 m. Flash detection efficiencies in the range from 96.08 % to 98.62 % and for the stroke detection efficiencies in the range from 76.36 %to 85.60 % have been determined. Mean multiplicity values determined with the VFRS data are comparable to the results of previous analyses in the Austrian Alps. The median values of negative stroke peak currents are around 10 % to 30 % lower for 2015, 2017 and 2018, than for detections of older VFRS measurements in the Alps.

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