By: Detlef Koschny, Andrea Toni.
The Fireball Recovery and InterPlanetary Observation Network (FRIPON) is currently operational in France and includes about 100 cameras. 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.
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: 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 I want to compute the mass (or size) of a meteoroid from the magnitude, I 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 1; the complete hardware including the computer can be seen in Figure 2. The camera itself is a Basler aca1300-30gm 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-capable router. The router connects the camera to the computer and the internet. In principle any computer can be used. We use a ‘NUC’, a ‘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 3 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 4, see also this web article). 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 correlation 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 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.
Detlef Koschny and Andrea Toni work at the Meteor Research Group of the Science Support Office of the European Space Agency, situated at its technical establishment ESTEC in Noordwijk, The Netherlands