Time Delay Correction for the MARCOS Lightning VHF Mapping Array System

In practical applications, system time delay (STD) of a VHF lightning mapping system, resulting from system manufacturing, installation, site differences, and signal channel inconsistency etc., is unavoidable and will affect the localization accuracy of the direction finding algorithm. In this article, a multiantenna VHF radiation continuous observation system (MARCOS) consisting of 7 channels is used as an example to make a quantitative analysis for the relationship between STD and localization error. The array is in an “L” shape, with a 9 m baseline. And its STD is obtained through actual measurement, using sweep-frequency method. The analysis results show that STD reduces the localization accuracy significantly. Especially, emissions with lower elevation are more vulnerable to STD. In order to correct localization error caused by STD, we utilize the actual measured STD of MARCOS to correct the error during the implementation of the algorithm. Field experiments are designed to verify the effectiveness of this correction method, with an unmanned aerial vehicle (UAV) and a portable radiation source. For MARCOS used in this article, the UAV experimental results show that the error caused by STD exceeds at least 2°, and even worse for the low elevation. However, after the STD is compensated, the localization error is alleviated within 1°. Finally, STD correction is applied to a triggered lightning data. Comparisons and analyses of the results are presented before and after STD compensation.