Catching Lightning With Phantom Cameras

Gamma-ray emissions — a form of high-energy electromagnetic radiation — are typically observed either as radioactive nuclei or high-energy bursts traveling through space. In 1992, however, a new kind of gamma-ray source was discovered on Earth.

Found in high-altitude storm clouds, terrestrial gamma-ray flashes (TGF) occur unpredictably, have energies up to 20 million electron volts and last less than a thousandth of a second. Exactly how TGFs generate and propagate remains under investigation, due to their elusive, short-lived nature. Today, researchers are looking to advance their understanding of how TGFs work.

Astroparticle Physicist Dr. Rasha Abbasi, an Assistant Professor in the Department of Physics at Loyola University Chicago, works with the Telescope Array project. Located west of Delta, Utah, the project is an international collaboration between universities to observe high-energy cosmic rays. Abbasi and her team study how TGFs originate from the Earth’s atmosphere and propagate. In particular, the team hopes to answer key questions, such as:

Which part of the lightning flash do TGFs originate from?
When do TGFs occur during the lifespan of a lightning flash?
What is the overall behavior of TGFs — from generation to termination?

As part of their work, the researchers pair their electromagnetic radiation data with observations of the lightning’s optical emissions. In order to slow down the lightning, they use a high-speed imaging system to record the lightning flashes at very high frame rates while other instruments track other metrics.

Casting a Large Net

High-speed still images of a TGF-producing lightning flash. The green square is the area monitored for variations in luminosity. (Image: Phantom)

Capturing TGF data requires a large, continuously running experiment. The southwestern Utah desert provides enough land and open sky for successful upper atmosphere research, and this is where the Telescope Array project positions its ground array.

The array consists of 500 scintillator detectors covering over 300 square miles. Each detector is housed within a metal container roughly the size of a ping-pong table. Within the container are several layers of acrylic material infused with molecules that interact with charged particles. When high-energy particles interact with the acrylic material, these molecules are excited and emit ultraviolet (UV) light. Optical fibers gather the UV light and direct it to a photomultiplier tube that converts the light into an electrical signal. This signal is received, stored and analyzed by a central computer. While the detectors were originally designed to analyze high-energy particles from space, the equipment can detect and analyze gamma-ray flashes originating from Earth’s atmosphere.

The Phantom camera that was used in this research to capture high-speed still images of a TGF-producing lightning flash. (Image: Phantom)

In addition to the detectors, this experiment relies on atmospheric instruments including a lightning mapping array (LMA), a fast electric field change antenna (FA) and a broadband very high frequency (VHF) interferometer (INTF) which were installed by New Mexico Institute of Mining and Technology collaborators Paul Krehbiel, William Rison, Daniel Rodeheffer and Mark Stanley. The instruments allow the researchers to study the complete anatomy of lightning and provide valuable information, including the lightning’s direction, speed, height, relation to the cloud base and radio emissions. The team’s goal is to observe how a lighting flash’s optical and radio wave emissions relate to the TGF it generates.

In order to record their findings and obtain visual observations of the lightning, Dr. Abbasi and her team use a Phantom v2012 camera. A Phantom v2012 was selected for this lightning-fast experiment due to its high frame rate and workflow capability. Some of the notable features on the v2012 that are also featured on other Phantom high-speed cameras include the options for 64, 128 or 256 GB RAM. There are also on-camera controls for field use, interchangeable lens mount options and optional compatibility with CineMag. Two different versions of the camera include the standard 1 μs minimum exposure capability and the export-controlled 190 ns with FAST option. Exposure in saturated areas of an image can also be automatically adjusted using the camera’s extreme dynamic range (EDR).

The featured next-generation camera for this application is the Phantom T2410, incorporating back side illuminated (BSI) sensor technology for improved low-light performance in an updated compact platform. The Phantom T2410 features a custom Forza^® 12-bit BSI CMOS sensor with a quantum efficiency rating of 80.3 percent mono at 532 nanometers (EMVA 1288), providing improved response for highly detailed images in challenging conditions like lightning flashes. Sustained 24 Gpx/s throughput and binned mode result in greater pixel resolution and aspect-ratio flexibility at the frame rates required to capture the event. 10 GB Ethernet ensures data is saved as fast as possible, and when combined with multi-cine and continuous recording in PCC software, the image capture workflow can run continuously without interruption.

Positioned in a warehouse window, this advanced high-speed imaging tool faces the 700 square-kilometer array, which includes several lightning rods. The researchers have optimized the camera’s 84-degree field of view to capture a span of 20 kilometers. When lightning flashes, the changes in luminosity trigger the camera, which records the phenomena at 40,000 frames per second (fps) at 1,280 × 448 pixel resolution. Camera data is saved to an on-site computer and then analyzed later. Using the elevation angle from the camera in conjunction with information from the LMA allowed the researchers to calculate the altitude of the TGF sources.

Thunderous Results

A high-speed still image of a TGF-producing lightning flash. (Image: Phantom)

The Phantom v2012 provides Dr. Abassi and her team with an up-close look at the lightning, allowing them to match the readings from the instruments with what they observe in the high-speed videos. Prior to the camera’s use, TGF research such as this had traditionally been performed with satellite imaging that uses special lenses and filters.

Thanks to the Phantom v2012’s high resolutions and frame rates, the researchers have gained new insights into TGFs while confirming satellite-based measurements recorded by the Atmosphere-Space Interactions Monitor (ASIM) aboard the International Space Station (ISS). One notable discovery resulting from this experiment was the first recorded instance of a downward-directed TGF occurring at the same time as an optical emission. The high-speed camera and suite of instruments additionally allowed the team to observe the stage in the lightning flash event that is associated with the observed TGFs, as well as the lightning’s height, speed, footprint and energy output.

A TGF flash event using the INTF and the Telescope Array Surface Detector (TASD) (left) and the Phantom v2012 in addition to the INTF (right). (Image: Phantom)

Going forward, Dr. Abbasi’s team will continue to compare optical signatures of TGF emissions using new onsite photometers with better wavelength timing resolution. These photometers were developed and tested through the collaborative efforts of Dr. Abbasi’s team, Marcelo Saba of the National Institute of Space Research (INPE), and Miguel Guimaraes and Litz Arujo of the National Institute of Space Research and the Federal Center of Technological Education (CEFET) in Minas Gerais, Brazil.

The new photometers will detect both 337 and 777 nanometer wavelengths. They will share the same field of view as the Phantom camera, and together will help to directly compare both upward and downward TGFs.

The collection of data has been ongoing since the installation of the new photometers in April 2023, further supporting the team’s continued research of TGFs and other upper atmospheric events. They will be bringing along their Phantom high-speed camera to capture the lightshow.

This article was written by Dr. Rasha Abbasi, Assistant Professor in the Department of Physics at Loyola University Chicago (Chicago, IL). For more information, visit here .