Dick Spalding’s all-sky-all-the-time camera setup

A paper published in the Nov. 21 issue of the journal Nature makes a compelling case that multimegaton-sized asteroid and comet impacts with Earth aren’t as common as had previously been thought.

The paper by University of Western Ontario meteor expert Peter Brown and four coauthors including Sandian Dick Spalding (5740) presents data indicating that impacts of the scale of the 10-megaton Tunguska event in Siberia in 1908 occur on average just once every 1,000 years. Previous best estimates put the frequency at closer to 200 to 300 years.

The new estimate is based on a sophisticated analysis of data from DoD and DOE satellites that monitor the planet for unusually brilliant flashes of light — flashes that might be signatures of a rogue nuclear test.

Dick Spalding’s involvement in the paper is based in part on his work as one of Sandia’s resident experts on the satellite data cited in the study, but his interest in the field goes beyond that. The lights in the nighttime sky have long fascinated him, and he’s convinced that if he were just able to watch the skies more closely, more completely, he’d see important phenomena that have never been credibly documented before.

In his quest not to miss a thing, he conceived of a way to watch the entire sky — the whole sky — all at once, all the time, 24/7.

Through his work with proliferation-monitoring systems, Dick knew that satellites not infrequently saw large inexplicable flashes of light, flashes that weren’t necessarily being recorded from the ground. (It was this kind of data that formed the basis of the Nature paper).

Dick figured that if he could get "ground truth" — a simultaneous recording of an event from the ground and from a satellite — the resulting data could tell a lot more about the phenomenon than could satellite data alone.

The satellite typically records just the flash; a ground-based recorder — or better, a series of ground-based stations — could record direction, velocity, and trajectory data. That’s the kind of information that could help a researcher figure out where in the solar system a fireball’s object might have originated.

Pure science and ground truth

"A lot is known about the regular meteor showers, the Leonids, the Perseids," Dick says. "Less is known about the sporadics — the occasional fireballs that don’t show up here on any predictable schedule. It seems that the larger [fireball] events fall into the ‘sporadics’ category. Few systems out there capture this kind of [trajectory/velocity] data on sporadics; certainly, none of the imaging satellites do."

Dick’s interest in this was pure science — to know more than we do now about our cosmos. Additionally, "ground truth" can help analysts better understand and interpret the data collected by space-based imaging and sensor technology.

During the mid-1990s, there seemed to be a spate of fireball/meteor activity; Dick recalls an especially bright fireball in Colorado Springs that a private citizen caught on videotape in a most peculiar way.

"This was unusual," Dick says, "in that the individual just happened to have a security camera mounted under the eaves, pointing down toward his car in the driveway in front of his house. The fireball’s reflection in the car’s windshield was captured on videotape. We decided a domed mirror would do the job better. We even initially experimented with chrome hubcaps!"

There were similar large fireball events around the same time, notably the Oct. 9 El Paso and Dec. 9 Greenland fireballs, both in 1997.

"Although these large events were being seen by satellite, they weren’t being recorded from the ground, so we weren’t getting the kind of data that could tell us about their orbits. We began to realize that what we really needed to do was watch the whole sky — all the time."

But how to do that? There were all-sky cameras available, but they were expensive dedicated high-end setups. Their cost made widespread deployment unfeasible — and widespread deployment was central to the vision of real-time monitoring of as much of the sky as possible.

Off-the-shelf equipment

Being a Sandian, Dick is nothing if not resourceful: "Using a hemispheric security mirror and off-the-shelf video equipment — a black-and-white video camera and some VCRs — we were able to put together a prototype system; it was a cheap system, but it got the job done."

The setup was simple: aim the mirror at the sky, point the camera at the mirror, program the three VCRs to begin recording at eight-hour intervals and get 24-hour coverage.

Dick placed one of the first-generation all-sky cameras on the roof of Bldg. 890 and began looking for places to set up some others. Canada, it turns out, is a center of meteor science, probably because the ancient Canadian Shield geologic formation — one of the oldest surface features on the planet — contains a lot of meteorite impact craters. As a result, there is a concentration of meteor professionals in Canada. Dick was able to enlist a couple of his northern colleagues to take on the job of hosting all-sky camera systems.

Sandia researcher Mark Boslough (9216) learned about Dick’s all-sky camera concept and thought it added a valuable dimension to an LDRD project he was involved in to study so-called near-Earth objects, those little-understood fellow travelers whose orbits intersect Earth’s own track. Mark was one-half of the celebrated Boslough-Crawford team that did the computer model that predicted with startling accuracy the observable effects of the Shoemaker-Levy comet during its descent into Jupiter in 1994.

Genesis of sporadics not always clear

Mark says satellite data were indicating a lot of meteor events in the upper atmosphere, but adds that "there are a lot of these events whose genesis isn’t completely clear. We were relying on serendipity, and that was kind of frustrating. We needed to get more systematic."

With better data, Mark knew, it would be possible not only to learn more about where fireballs originate, it might help pinpoint where they end up. In other words, with trajectory data, you have a lot better chance of pinpointing where to look for meteorites, whose composition can also tell a lot about the origin of the fireball — and perhaps even of the solar system itself.

Big-name events

Mark remembered the famous Peekskill Fireball event. (Meteor researchers recall and refer to major events by name, the way a hurricane scientist might recall Camille or Agnes.)

The Peekskill event happened on a Friday night in October 1992, first appearing in the sky over West Virginia. Most high schools play their football games on Friday nights; there were plenty of parents and coaches with camcorders in the stands that night to capture the action on the playing fields. When the fireball streaked overhead, 16 different video cameras from West Virginia to Peekskill captured some part of the flight on tape. The data gave researchers enough information to calculate the original orbit of the fireball. One large piece smashed into the trunk of a 1981 Chevy Malibu in Peekskill, N.Y.

Mark saw right away that Dick’s all-sky camera concept offered a way to replicate the Peekskill-level coverage on a full-time basis. He brought Dick into the LDRD, under the title "Collection and Data Synthesis of Atmospheric Explosion Ground Truth for Global Monitoring Systems."

With LDRD support, Dick was able to extend the network of cameras. There are now operating systems at Vancouver Island, Seattle, Edmonton, Calgary, Regina, Albuquerque, Los Alamos, Las Cruces, and El Paso.

The pieces of Dick’s concept, then, were beginning to come together. Obviously, the network would need to be extended and the sky coverage expanded. More important, a way would have to be found to streamline the monitoring process. In its original bare-bones configuration, the all-sky camera recorded everything on videotape. Someone then had to scan the tape every day to look for the bright flashes that might indicate an atmospheric event. After a while, that task could be a big-time demotivator, even for a volunteer camera "owner" committed to the mission.

Joe’s thesis project

Enter Joe Chavez (5733), a Sandian who was going for his CS masters at New Mexico Tech. Solving Dick’s all-sky camera monitoring challenge offered a perfect thesis project. Joe conceived of and designed a low-cost computer-based system that tied into the all-sky camera rig. Joe’s system included hardware and software that together could automatically detect, recognize, and save to a file the bright flashes and tracks in the sky that merited further investigation. The software saves the interesting parts as movie files.

"Each morning, as we scan through the collection of movies recorded throughout the night, Joe says, "we can usually easily tell if we have recorded a meteor or (more likely) just an airplane taking off from the airport."

As components get better — and more available — Dick hopes to see the all-sky network expand. In his most optimistic and imaginative moments, he envisions an all-sky meteor-watching network similar to the network of amateur weather stations that together provide comprehensive coverage of the US, all of their data available via the World Wide Web.

In the meantime, even though, as the Nature paper suggests, the big Tunguska-scale events may happen only once in a thousand years, Dick will be scanning the skies, watching.