Retrieving the Fraction of Ground Flashes from Satellite Lightning Imager Data Using CONUS-Based Optical Statistics

Abstract

retrieval method is introduced for estimating the fraction of ground flashes in a set of N flashes observed from either a low earth-orbiting or geostationary satellite lightning imager. The methodology exploits the fact that mean optical characteristics of ground and cloud flashes differ, and hence a properly posed equation set for mean conditions of a set of N observed flashes can be mathematically inverted to estimate the ground flash fraction (and hence the cloud flash-to-ground flash ratio). Explicit analytic expressions for the retrieval errors are derived, and numerical tests of the retrieval method are provided to quantify retrieval accuracy. It has been found that the retrieval method works best when only one optimum optical parameter is used (the single-characteristic solution approach) rather than a mixture of optical parameters (the multiple-characteristic solution approach); that is, the suboptimum optical parameters in the mix degrade retrieval accuracy. Since the retrieval method uses conterminous United States (CONUS)-averaged values of the lightning optical measurements, retrieval errors tend to be smallest in geographical regions whose specific mean lightning optical measurements are closest to the CONUS mean values. The rms ground flash fraction retrieval errors for 52 widely distributed regions across CONUS ranged from as low as 0.061 to 0.111, depending on the true ground flash fraction sought.