A Comparison of Space Based Optical Measurements and Ground Based VLF Measurements

Research has shown trends in total lightning (both intracloud and cloud to ground) can help improve severe weather warning times (forecast). This application of lightning data has been demonstrated with short range VHF systems. The limited range of these systems has lead to a need to provide total lightning data over large spatial domains, something VHF is unable to do.

Optical measurements from space are able to detect total lightning; the current standard for such measurements is the Lightning Imaging Sensor (LIS). However, LIS is in low earth orbit, so storms can only be monitored for a limited time.

To improve the temporal detection of lightning using space based measurements, the Geostationary Lightning Mapper (GLM) is scheduled for launch on board GOES-R in 2015. GLM will be able to detect total lightning with unprecedented temporal and spatial coverage.

In order to prepare forecasters for GLM data, several long range VLF systems have emerged to provide early estimates of total lightning, in particular the Earth Networks Total Lightning Network (ENTLN). Unfortunately, the performance of these systems have yet to be quantified relative to space based observations.

GLM is largely based on LIS; hence, LIS data provides a good proxy for future GLM measurements. In order to understand future GLM measurements, a proper understanding of the relationship of current VLF systems and optical space based measurements is useful.

We use current optical measurements from space using LIS data to compare with ENTLN data. Currently, comparison of the similarities and differences between the lightning detection systems rely on flashes, which is an intrinsically subjectively-derived data set. Since the base detecting unit of both VLF and optical measurements roughly correspond to a stroke, we use this as the basis for comparison between the two systems. Specifically, we compare LIS groups and ENTLN pulses.

We explore the differences in these measurements and the effect on the use of lightning data in severe weather forecasting.