May 17, 2022 8:16 am

Looking for lightning, finding fireballs

Francis Martin Leon 8 min
Distribution of more than 3,000 fireballs detected by GLMs aboard GOES-16 and GOES-17 between July 2017 and January 2022. See text for details

The new year started off strong in Pittsburgh, Pennsylvania. At the start of New Year’s Day, many local residents heard a loud bang and felt the ground shake, prompting calls to 911. Allegheny County was quick to acknowledge the event, noting it was not an earthquake or thunder, and admitting that ” We have no explanation for the reports.”

The culprit was later confirmed by the NASA Meteor Watch: it was about a bolide, a very large and bright ball of fire (a meteor brighter than Venus). The meteorite was estimated to weigh half a tonne, be 0.9m wide and was traveling at about 72,420km/h. When it exploded in the atmosphere, it released the energy equivalent of a 30-ton TNT blast that was recorded by detectors at an infrasound station near Pittsburgh.

Although there are some Programs of fireball detection worldwide, most are ground-based, including NASA’s Meteorite Tracking and Recovery Network and NASA’s All-Sky Fireball Network. But nevertheless, most fireballs enter the atmosphere in the 70 percent of Earth that is covered by ocean.

Fireballs are rare, and due to the limited viewing areas of ground systems, very few fireballs are detected from the ground, perhaps only a couple a year“said Jeffrey C. Smith, a data scientist at the SETI Institute and the principal investigator on a cooperative project with the Asteroid Threat Assessment Project at NASA Ames Research Center.”Fireball explosions are also very fast, usually lasting only a fraction of a second, so very fast detectors are needed”.

detection from space

Scientists recently discovered that they have such a detector, although it was not designed to detect space rocks hurtling through the atmosphere. In 2018, astronomer Peter Jenniskens (also of SETI and NASA Ames) and colleagues showed that the detector Lightning Mapper Geostationary (GLM) aboard NOAA’s GOES-16 weather satellite could be used to observe the fleeting flashes of fireballs. The GLM samples the transient light at a rate of 500 frames per second. It can detect fireballs from about 1 decimeter to about 3 meters wide.

Two years ago, Smith and his colleagues began develop and train a machine learning algorithm for computers to automatically detect fireballs in GLM data. Their goal was to build a publicly available database of fireball events and their light curves: the paths and intensity of the light rays they left behind in the sky. Smith and his team described their work in the magazine Icarus in November 2021.

The map above shows the distribution of more than 3,000 fireballs detected by GLMs aboard GOES-16 and GOES-17 between July 2017 and January 2022. Blue dots are fireballs detected by GOES-16; GOES-17 detected pink dots. GOES-17 detected the only pink dot over the Atlantic Ocean during its start-up phase before it moved into its operational orbit over the West Coast.

Fireballs observed by GOES-16 and -17 are recorded in stereo. On the map, the slight offset between the stereoscopic detections is due to the different perspectives from which they were seen by each satellite. Stereo detection allows researchers to reconstruct the paths of fireballs through the atmosphere. These data, along with light curves, are useful for modeling how asteroids enter the atmosphere, break up, and impact Earth. Such data can also inform models that assess the risk of larger meteorite impacts, while aiding asteroid population studies that improve our understanding of the evolution of the Solar System.

No humans observed the New Year’s Day fireball over Pittsburgh, where the sky was cloudy, but the GLM detected four bright flashes of light.. It wasn’t a particularly bright fireball or even the brightest on record that day, Smith said. The others were right over the ocean or in rural areas, where they were less likely to be seen.

This is one of the best things about using a geostationary satellite: we can detect events in very remote areas that are missed by ground observers.Smith said. The geostationary orbits of GOES satellites allow them to monitor the Western Hemisphere from 55 degrees north latitude to 55 degrees south latitude. While the coverage is not global, it allows scientists to capture an unprecedented number of meteors in publicly accessible data.. “At this time, GLM is the only accessible tool available to obtain wide hemispheric coverage to search for fireballs.“.

Currently, events identified by the computer algorithm are reviewed by humans before being added to the database. After several iterations of the program, the computer is getting pretty good at correctly identifying fireballs. “Four out of five detections we make are legitimateSmith said. “A very small amount of manual investigation is now needed to eliminate false positives“.

The team’s goal is to improve detection accuracy enough that humans aren’t required in the process, Smith said. “Then we can automatically publish our fire detections very soon after the events occur, maybe within a minute”.

Picture of NASA Earth Observatory by Joshua Stevens, using NASA Bolides data courtesy of Jeffrey Smith/SETI. Text by Sara E. Pratt.

NASA Earth Observatory

This entry was posted in Reports on 27 Jan 2022 by Francisco Martín León

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