The scientific and technical foundations for satellite-based VHF global lightning detection and storm mapping from GPS orbit will be presented. Lightning data collected by experimental VHF receivers currently in orbit aboard two GPS satellites (SVN 54 and SVN 56) will be used to demonstrate and explore the potential use of GPS-based VHF receivers for such purposes. Ground-truthing for the GPS-detected events is provided by the Los Alamos Sferic Array (LASA) for lightning activity in the Florida area and by the World Wide Lightning Location Network (WWLL) for storm activity in the central and western Pacific Ocean. Analysis of GPS/LASA correlated events indicates that the majority of GPS-detected VHF emissions (about 80%) are associated with positive-polarity narrow bipolar events (NBEs). NBEs are a ubiquitous type of in-cloud lightning found in most thunderstorms, are associated with deep convective processes, and their occurrence rates are excellent statistical indicators of thunderstorm convective strength. The remaining 20% of the GPS events are due to intense VHF return stroke attachment transients occurring primarily over sea water. The detectability of each emission type from GPS orbit is a function of the receiver sensitivity, the source strength and the source radiation pattern (the statistical VHF radiation pattern associated with NBE activity is shown to peak at an angle of about 40 degrees from the horizontal).
Two-satellite observations of lightning/storm activity, ground-truthed with the WWLL network, demonstrate the ability of GPS-based VHF receivers to routinely identify, locate and track generic storm activity. GPS storm detection and tracking statistics will be presented from a 3-month study of storm activity in the central and western Pacific Ocean. We conclude that GPS-based VHF lightning detection presents a viable means of monitoring global severe weather from space.