Inter-Comparison of Space- and Ground-Based Observations of Lightning

Abstract

Lightning observation from space provides a unique way to study the optical properties of lightning flashes. The satellite-based sensors including the Lightning Imaging Sensors (LISs) and Geostationary Lightning Mappers (GLMs) detect optical emissions that are associated with transfer of electrical charge due to lightning, and clusters them into flashes. This work provides an overview of lightning detection from ground- and space-based systems, and presents three research efforts focused on system validation. The first study addressed the performance characteristics of the LIS that was onboard the Tropical Rainfall Measuring Mission (TRMM) satellite. Four different quadrant thresholds in the LIS pixel array caused an approximate 20% variation in the number of detected emissions and the mean energy density. Sensitivity decreased more rapidly along the off-boresight angle than was measured in the pre-launch laboratory calibration. A 5 km periodical location offset in the LIS group centroid is caused by the TRMM yaw maneuvers. In addition, LIS groups/flashes with a temporally and spatially corresponding report by the U.S. National Lightning Detection Network (NLDN) tended to be spatially larger and last longer. Two GLM sensors are deployed on the new GOES East and West satellites. The second study focuses on the performance of these sensors, as part of a NOAA funded validation effort by the GLM Science Team. One of the GLM detection behaviors is difficulty in detecting short and/or small flashes. LIS data with finer resolution and a statistical model were used to investigate possible explanations. The results show that more than half of the light sources were relatively smaller than a GLM pixel size. Short flashes do not have enough time to propagate and develop spatial area large enough or a channel long enough to be detected by GLM. Lightning locating systems (LLSs) inter-comparisons are complicated because the various measurements operate in different frequency ranges, and thus, detect different portions of lightning processes or flashes. The final study compares the LIS with the ground-based U.S. National Lightning Detection Network. Our conventional inter-comparison employed individual reports provided by each LLS, with results that were consistent with previous studies. Future work will include a more-general way to make inter-comparisons based on the physical processes within flashes.