Three different systems capture lightning discharges over a range of different frequencies, which correspond to the energies being produced.
"The higher the frequency you go to, the smaller the object you get to image," Cummins said.
Very high frequency (VHF) arrays, collections of sensors that measure electromagnetic radiation, capture images of the fine branching structures of a lightning strike. VHF sensors operate in the range of 10 to 100 megahertz and are spaced close togetherAbout a dozen VHF arrays exist nationwide, including at the University of Alabama in Huntsville, New Mexico Tech, and the Kennedy Space Center in Florida.
By contrast, low frequency (LF) arrays image larger-scale lightning activity, such as the long channels of electricity in cloud-to-ground and inter-cloud flashes. These provide information about the energy released in the form of electrical current in channels to ground. Lightning also produces energy in the form of light, heat and atomic energy such as X-rays and gamma rays — by a strike. These arrays operate in the range of hundreds of kilohertz to a few megahertz. The National Lightning Detection Network (NLDN), a network of more than 100 low-frequency sensing stations around the United States, is widely used by researchers and provides vital monitoring for predicting severe weather.
At the broadest scale, very low frequency (VLF) arrays measure electromagnetic signals not just along the Earth's surface, but between the Earth and the ionosphere, the upper layer of the atmosphere that is electrically charged by solar radiation. These operate in the 5-to-30 kilohertz range, and are spaced thousands of kilometers apart. VLF arrays can detect lightning over land and oceans, where hurricanes and other storms develop. (Electric Earth: Stunning Images of Lightning)
Bitzer and his colleagues at the University of Alabama in Huntsville have developed a sensor that operates in the LF/VLF range and measures the change in electric field from a lightning discharge and converts it into a voltage. They protect the sensor from rain using an inverted metal dish. "It's literally a salad bowl — we got it from Target," Bitzer said.
These sensors give scientists a pretty good view of lightning on the ground, but to get a global view, why not observe it from space?
The University of Alabama scientists have also developed a satellite-based sensor that counts photons from low-Earth orbit. The satellite makes a lap around the planet every 90 minutes, giving scientists a picture of the amount and distribution of lightning worldwide.
The National Oceanic and Atmospheric Administration (NOAA) and NASA are building a geostationary lightning mapper, or GLM, to fly aboard the GOES-R satellite set to launch in 2015.