Astronomy and Telescopes
FRIPON: A new ground-based All-Sky Meteor Network
On February 15, 2013, the world awoke to dramatic news as an asteroid roughly 20 meters across exploded over Chelyabinsk, Russia. The asteroid approached Earth unannounced from a sunward direction, and weeks went by before researchers could analyze all the dash-cam footage, determine the rock's trajectory, and recover debris from the surviving meteorite. 1)
Now, imagine a network of all-sky observing sentinels that speeds this whole process up to just days or even hours.
That's the goal of FRIPON (Fireball Recovery and InterPlanetary Observation Network). A collaboration between the Observatory of Paris, the National Center of Scientific Research (CNRS), the University of Paris-South, the French National Museum of Natural History, and the Aix-Marseille University, this network of 100 cameras and 25 radio receivers provides continuous all-sky coverage over all of France. Catching a meteorite's fall from various angles from known coordinates enables researchers to quickly and accurately determine the location of a possible strewn field for an organized search campaign.
"If tomorrow a meteorite falls in France, we will be able to know where it comes from and roughly where it landed," says Jérémie Vaubaillon (Paris Observatory) in a recent Nature.com article. 2)
Scientists in France have launched an unprecedented campaign to catch shooting stars, an effort that will rely on thousands of volunteers to comb the ground for bits of space rock.
The program already includes 68 cameras that scan the skies for meteors, which are seen when bits of asteroid, comet or other planetary material streak through Earth's atmosphere. By the end of this year, some 100 cameras will blanket France, organizers say. That would make it one of the biggest and densest meteor-spotting networks in the world.
"If tomorrow a meteorite falls in France, we will be able to know where it comes from and roughly where it has landed," says Jérémie Vaubaillon, an astronomer at the Paris Observatory and one of organizers of the system. Dubbed the FRIPON (Fireball Recovery and InterPlanetary Observation Network), it was officially inaugurated on 28 May 2016.
Meteorites — chunks of stone that have fallen from space and reached Earth's surface — provide valuable insights into everything from the history of the Solar System to the identity of asteroids that could potentially collide with Earth. Snagging such objects is "the one chance you get to see Solar System material in your hands", says David Clark, who studies meteors at the University of Western Ontario in London, Canada. "We simply don't have enough of this stuff."
Especially prized are meteorites that were tracked on their inward journey. Scientists can use data on the journey to reconstruct the object's trajectory and reveal where in the Solar System it came from. People manage to scoop up only one to three meteorites each year with known trajectories, says Peter Jenniskens, an astronomer at the SETI Institute in Mountain View, California.
Fire in the sky
FRIPON's organizers dream of collecting one tracked meteorite per year from the French landscape. By comparison, researchers with the Spanish Meteor Network — another large and dense network — have scored 2 meteorites in the past 12 years.
The French network's cameras are very densely and evenly spaced, sitting roughly 70–80 km apart at laboratories, science museums and other buildings. That is close enough together to yield good information about where meteorites land. "That increases your chance of finding something," says Jenniskens.
FRIPON is also the first fully connected and automated network, says principal investigator François Colas, of the Paris Observatory. When a camera detects a meteor, it sends a message to a central computer in Paris. If two or more cameras spot the fireball, FRIPON scientists receive an e-mail describing where it was seen. Eventually, the e-mail will include automatically generated information about the object's probable landing zone, pinpointing it to an area roughly 1 km x 10 km.
The researchers will then face the arduous job of searching this area to find the object. At first, scientists will conduct the ground searches. But in the next few years, FRIPON organizers plan to train an army of citizen scientists to walk the French landscape looking for bits of meteorite — and to hand over any finds.
Perhaps one in 1,000 volunteers will actually turn up for a search, estimates Brigitte Zanda, a meteorite specialist at the National Museum of Natural History in Paris, who heads the volunteer effort. Organizers hope to field a search team of 30 people in every part of France, so they will have to recruit hundreds of thousands of people, she says. "It's ambitious." But hundreds of people have already signed up, even though the official recruitment drive is just getting underway.
Northern France's extensive forests could also make meteorite recovery challenging, says Josep Trigo-Rodríguez, an astrophysicist at the Institute of Space Sciences in Barcelona, Spain, and a co-founder of the Spanish Meteor Network. Still, he thinks that FRIPON could help investigators to find more meteorites. An average of just one meteorite was recovered per decade in France in the twentieth century, down from one every other year in the previous 100 years.
French FRIPON Network
FRIPON is a French program planning to use a network of 100 video cameras and 25 radio receivers running 24/24 7/7 to observe fireballs and to determine their trajectories and their eventual strewnfields. 4) 5)
The official launch of FRIPON started on 31 May 2016 with a unique interconnected network to search for meteorites. Eventually comprising 100 cameras spread out all over France, FRIPON introduces a night and day 360° watch of the sky. Born from the joint scientific expertise of Observatoire de Paris, of Muséum national d'Histoire naturelle, of Université Paris-Sud, of Université Aix-Marseille and of CNRS, this network aims to detect meteorite falls, measure their trajectories and estimate their strewnfields so that field search campaigns can be organized. 6)
General principles of the FRIPON radio network
FRIPON uses cameras to compute the trajectories of the fireballs, and a radio set-up allows to obtain accurate target velocity measurement.
The radio set-up is based on a multistatic radar configuration and consists in:
• One VHF HPLA (High Power Large Aperture) transmitter scanning a large volume of sky
• Twenty five SDR (software defined radios) located with some of the 100 video cameras
The Doppler Fizeau frequency shift affecting a meteor radio echo is presently used to compute the velocity of this meteor.
FRIPON in The Netherlands
Based on the French FRIPON system, a new fireball camera network is currently being extended to the Netherlands, offering new opportunities for scientific research, fireball detections and even meteorite recovery. 7)
FRIPON is an all-sky camera network with the aim of detecting fireballs and computing their trajectories. By computing the ‘dark flight' of surviving pieces of the meteoroid, the location (strewn field) of meteorites from the fireball can be predicted. This is the ultimate goal of the project, funded by the French National Research Agency (CNRS): to find meteorites on the ground and link them, via the orbit determined from the observation of the fireball, to its parent object. The IMCCE (Institut de Mécanique Céleste et de Calcul des Éphémérides) in Paris has developed and commercialized the camera hardware, installed a central server, and designed the detection and data processing software. Almost 100 cameras are operational in France, and the data processing part is in the final stages of implementation.
The Meteor Research Group at ESA's Science Support Office is currently operating a double-station meteor camera system on the Canary Islands called CILBO (Canary Islands Long-Baseline Observatory). It records meteors down to fainter than magnitude 5. It will saturate for meteors brighter than magnitude 0. To extend our observations to larger objects, or brighter magnitudes, we decided to get started with all-sky fireball cameras. Rather than developing our own system we decided to use something which already exists. Due to existing contacts to the IMCCE, we decided that we would expand the FRIPON system to the Netherlands.
The initial science rationale of FRIPON was to increase the number of meteorites found in France and to link them to their parent bodies. This can be done by observing fireballs – propagating their trajectory backwards will allow to determine their orbits in the Solar System; extrapolating the flight path forward, taking into account wind direction and speed, allows the prediction of the location of any meteorites from the fireball.
For us the science rational for using a FRIPON-based system differs. At the Meteor Research Group of ESA, we have been working on the flux density of meteoroids, i.e. how many meteoroids enter the Earth's atmosphere per area and time. We did this by using data from our double-station meteor video camera system on the Canary Islands (CILBO). For meteors brighter than about magnitude 0 this system will go in saturation. Depending on the material and the velocity of the object, this corresponds to meteoroid diameters of about 2 mm to about 3 cm. With the data from FRIPON, the flux densities of larger objects can be determined.
Another important potential science result will be to compute the luminous efficiency. This is the percentage of kinetic energy of the meteoroid which is converted to light. I.e., if we want to compute the mass (or size) of a meteoroid from the magnitude, we need to know this number. With just the brightness curve of a meteor, this value cannot be determined. For our CILBO setup, we have used values obtained by simultaneous observations with video and radar systems performed in Canada. Another determination method is to take the deceleration of the meteor into account. The deceleration is best seen for objects larger than what we can detect with CILBO. FRIPON regularly observes this deceleration and allows the determination of the luminous efficiency without requiring another detection technique.
The camera hardware
The FRIPON camera currently installed on top of ESA/ESTEC in Noordwijk is shown in Figure 7; the complete hardware including the computer can be seen in Figure 4. The camera itself is a Basler aca1300-30 gram digital camera (older systems have a DMK23g445) operated at 25 frames per second. It is installed in a protective housing with an optical quality transparent dome on top. The camera housing is less than 10 cm in diameter and about 15 cm in height. It is manufactured by the company Shelyak, it costs about 1200 Euro. The included mounting hardware allows it to be installed either on a flat surface or attached to a pole not more than 5 cm in diameter. It has a short Ethernet pigtail cable for connection to the computer.
The power is provided via the same cable. This requires a ‘Power-over-Ethernet' capable router when connecting the camera. If needed, the camera cable can be extended via a ‘Cat-6' Ethernet cable to connect to a PoE (Power over Ethernet)-capable router. The router connects the camera to the computer and the internet. In principle any computer can be used. We use a NUC (Next Unit of Computing) machine, a very compact computer only about 10 x 10 x 5 cm in size. When purchased with the correct solid state harddisk, the complete software system can be installed via a disk image.
The system does not have a keyboard or monitor – it connects to a server in France and is only accessible remotely via the French computer. If we want to see our own computer, we have to log into the server in France, only from there we can access it. The reason is explained in the section on data processing.
The NUC reads the image data coming from the camera in real time. Detection software identifies events – it searches for bright objects which move in a straight line. It has some filters, e.g. to reject objects which move too slow. Still, it may detect not only fireballs, but also airplanes or other things. All detections – typically a few per night – are directly sent to a server in Paris, France. There the data from all French, Belgian, and German cameras is collected. An ‘event' is generated when 3 or more cameras have detections at the same time.
The direct connection to Paris is the reason that the computer cannot be accessed directly – this would violate the security rules, as it might allow hackers to enter the French network. The system sends out email messages once per day, summarizing all events which have been created in the last night. It should also compute the trajectory relative to the ground, the orbit, and potential locations for meteorites. This last part, however, is not yet fully operational.
Status in the Netherlands
To get acquainted with the FRIPON system, we installed a camera on top of ESA's technology center ESTEC, in Noordwijk, Zuid-Holland. The already mentioned software security regulations exist also at ESA. Therefore, we initially had issues to connect to the Paris network. We finally installed the router in a ‘de-militarized zone' in our science network. Private networks seem to have no problem – we managed to install and connect the second camera in Oostkapelle within a few hours in an afternoon in November 2017.
These are the two cameras currently in operation in the Netherlands. Figure 5 shows the location of the two stations in green. In addition to Klaas Jobse, who hosts the station in Oostkapelle, we have agreements with Felix Bettonvil (Dwingeloo), Jos Nijlands (Benningbroek), Arnold Tukkers (Lattrop) and Sebastiaan de Vet (Tilburg) to host additional cameras. One camera, funded by the University of Oldenburg, Germany, has been set up in Groningen. We are still looking for hosts for a few more stations. From an internal ESA grant, we have received funding to purchase a few more cameras and additional hosts are still needed. If somebody is interested in Gelderland, contact me! After this initial expansion, we would like to add additional cameras roughly at the transparent-yellow locations on the map.
The first large fireball which we have recorded happened just before my presentation of the camera at last year's International Meteor Conference, on 21 September 2017 (Figure 6). Before that, we had seen three faint events, always together with the camera in Brussels and one or two other stations in Belgium. However, for a fireball to be observable from both Brussels and Noordwijk it has to be about half way between the two stations and will be low on the horizon from both. Oostkapelle is in a much better distance of about 100 km and we now expect typically one to two fireballs per month.
The cameras are operated in a ‘hands-off' manner, i.e. the host doesn't really need to do anything. All the detection and event correlations are done automatically. Still, typically the hosts – like the authors – are interested in accessing the data of their camera directly. Sometimes people ask ‘did you see anything at time xx:xx' and it would be nice to quickly check the data. While this is possible, logging in via the French server and transferring data is tedious. We are currently setting up a system where all data of the Dutch stations is pushed to an ftp-server hosted at ESA. We are in the process of testing the system, but it is not yet operational.
As mentioned before, the more detailed parts of the software, e.g. the computation of the orbit or prediction of potential meteorite fall areas are not yet final and not yet easily accessible. Together with two Ph.D. students working at the University of Oldenburg, we are involved in the data processing and preparing scientific data analysis routines. In particular we are interested in being quickly informed in a fireball before we read about it in the news.
FRIPON-NL (Netherlands) is in the process of being set up. Currently, two cameras are operational, with 3 more where hosts have been identified. Funding for more cameras is available. Once installed, the network will link together the French and Belgium cameras with those in northern Germany.
The cameras have demonstrated that they can detect fireball events. The data processing – computing the trajectory relative to the Earth, orbits, and possible meteorite fall locations – still needs to be finalized by our French colleagues. ESA is involved from a scientific point of view and to be able to get fast alerts after a fireball has happened.
The cameras have shown to be robust and reliable, and we expect to be able to cover the complete Netherlands by 2019. The network is very complementary to e.g. the CAMS system, which is optimized for fainter meteors, or the three cameras of the German ‘EN' network which give better positional accuracy but no time information.
We are looking for a few more hosts for cameras, so if you are interested in providing scientifically useful data, please contact the authors.
FRIPON camera atop ESTEC
Asteroid researcher Kristiane Schmidt and ESA data technician Andrea Toni inspect a camera fixed to the five-storey-high rooftop of ESA's technical heart in the Netherlands, keeping a constant watch for fireballs – very bright meteors burning up in the atmosphere. This small fisheye camera atop the ESTEC technical center in Noordwijk on the North Sea coast is one of a network of cameras stretching across Europe, called the Fireball Recovery and Planetary Inter Observation Network, FRIPON. 8)
FRIPON cameras work together to plot the course of meteorites entering Europe's skies, supporting efforts to retrieve fresh-fallen meteorites for study.
Figure 8: Mounted at the highest point of ESA's ESTEC technical center in the Netherlands, a fisheye camera keeps a constant watch on the sky, looking out for bright fireballs – very bright meteors burning up in the atmosphere. This is one of a network of more than a hundred specially-designed cameras stretching across Europe, called the Fireball Recovery and Planetary Inter Observation Network, FRIPON. This network gives scientists the ability to determine the trajectory of fireballs and calculate where they fall to guide recovery of any surviving debris (video credit: ESA, Published on Sep 5, 2018)
1) David Dickinson, "FRIPON: A New All-Sky Meteor Network," Sky and Telescope, 21 June 2016, URL: https://www.skyandtelescope.com/astronomy-news/
2) Traci Watson, "France launches massive meteor-spotting network," Nature News, 10 June 2016, URL: https://www.nature.com/news/france-launches-
3) Francois Colas and the Fripon Team, "FRIPON, the French Fireball Network," June 2016, URL: https://www.cosmos.esa.int/documents/653713/1049689/10_Colas-F
4) Jean-Louis Rault, "FRIPON radio," 14 October 2017, URL: http://brams.aeronomie.be/files/BRAMS_
5) Jean-Louis Rault, Mirel Birlan, Cyril Blanpain, Sylvain Bouley, Stéphane Caminade, François Colas, Jérôme Gattacceca, Simon Jeanne, Julien Lecubin, Adrien Malgoyre, Chiara Marmo, Jérémie Vaubaillon, Pierre Vernazza, Brigitte Zanda, "Fine-scale observations of the Doppler frequency shifts affecting meteor head radio echoes," Proceedings of the IMO (International Meteor Organization), 14 April 2018, URL: https://arxiv.org/ftp/arxiv/papers/1804/1804.05203.pdf
6) "Official launching of FRIPON," MeteorNews, 30 June 2016, URL: https://www.meteornews.net/2016/06/30/official-launching-fripon/
7) Detlef Koschny, Andrea Toni, "FRIPON-NL: Extending the French all-sky fireball camera network to The Netherlands," 2 July 2018, URL: https://werkgroepmeteoren.nl/fripon-extended-to-the-netherlands/
8) "FRIPON camera atop ESTEC," ESA, 01 May 2019, URL: https://www.esa.int/spaceinimages/Images/2019
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: "Observation of the Earth and Its Environment: Survey of Missions and Sensors" (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates (firstname.lastname@example.org).