Photographic meteor observation has a long tradition among both professional and amateur
astronomers. One reason for that is the ability to determine most precise positions of meteor trails
from photographs. Main limitation is the low sensitivity resulting in a very small number of meteor
records compared with other observing techniques. Especially all-sky cameras as used in fireball
networks can only detect the brightest meteors (i.e. fireballs) caused by very large meteoroids
colliding with the Earth.
Those cameras, however, can monitor the whole sky at once. If a fireball is recorded from two or more stations, the true path of the meteoroid through the atmosphere as well as its heliocentric orbits before the encounter with Earth can be calculated. For meteorite candidates (fireballs that may have deposited material on the ground) the impact area can be determined, where a possibly surviving meteorite should be found. Fireball camera networks provide fundamental data for the computation of the mass flux near Earth and the probability of collisions with larger bodies. They close the observational gap between millimeter and centimeter large meteoroids observed as shooting stars every day by amateur astronomers, and larger bodies of some ten to hundred meters diameter found routinely by the Space Watch Telescope.
1959, after the fall of the Pribram meteorite in Czechoslovakia, the first network of fireball
cameras ever was initiated in Europe . Some years later it was expanded by installation of new
stations in Southern Germany. Together they were called the European Fireball Network (EN).
In the sixties and seventies two more networks were installed in the United States (Prairie Network, 1965)  and Canada (MORP, 1971) . However, both networks had to shut down after a few years of operation (1974 and 1985, respectively), whereas the EN is still monitoring the sky each night. Today, it covers an area of approximately 10^6 square kilometers with 34 camera stations in Germany, the Czech and Slovak Republics, Belgium, Austria and Switzerland (Figure 1). It is completed by associated camera stations of the Arbeitskreis Meteore (AKM) in Germany and the Dutch Meteor Society (DMS) in the Netherlands.
Since their foundation, the (currently) 22 stations that belong to the German part of the network have been equipped with all-sky mirror cameras (Figure 2). The heart of such a system is a 36 cm parabolic mirror, above which the camera is mounted. The camera contains a shutter rotating with a frequency of 12.5 Hz. This allows the computation of the fireball's apparent angular velocity as well as the geocentric entry velocity and the deceleration of the meteoroid in the atmosphere. The exposure time is controlled by a digital clock.
Figure 3 shows a typical fireball photograph, obtained at Wendelstein Observatory (EN #88) on November 9, 1995.
Contrary to this, the (currently) 12 Czech stations have been upgraded several times. Today, they
are equipped with Zeiss Distagon fish-eye lenses. Together with a larger film format this results in
more precise fireball trajectories and a better limiting magnitude. Three guided fish-eye cameras
are operated additionally. They allow the determination of fireball appearance times from pairs of
guided/unguided exposures, whereas the timing of fireballs for most of the German part of the
network relies on casual visual observations.
At each German EN station one exposure per night is obtained regardless of the weather, whereas the Czech stations are only operated when clear sky is expected. Due to daylight, clouds and moonlight, the effective monitor time is limited to about 3 hours per day on average.
Most German EN camera stations are maintained by amateur astronomers and weather stations.
After their exposure, the films are developed and sent to the network coordinator. He inspects the
photographs and selects successful fireball recordings.
The measurement of the negatives and calculation of orbital elements is a complex and time consuming task. The recordings of the Czech EN stations have been measured manually at Ondrejov Observatory for years. For the analysis of a single fireball which is recorded from several stations, a single persons needs approximately one week! Due to the enormous amount of work only a part of all recorded fireballs can be analyzed in detail. For the German stations there is currently no detailed fireball analysis at all. Especially spectacular events are measured at Ondrejov Observatory, too. However, most of the photographs are waiting in the fireball archive for their processing.
To improve the situation, it was decided to automate the measurement using computers. In the frame of his graduate work, the author developed a comfortable measurement software package at the German Aerospace Research Establishment (DLR) . In the future, fireball negatives will be scanned using a Polaroid slide scanner with a resolution of 2,700 dpi. The images are then measured digitally on a UNIX workstation (Figure 4). The program creates a data file that can later be processed with the existing Czech Firbal software package to compute atmospheric trajectories and heliocentric orbits.
Today, the EN obtains approximately 100 photographs of 50 different fireballs each year. In 1996
it has been especially successful recording 71 fireballs (156 photographs). One of the most
spectacular events happened in the evening hours of August 18, 1996. 15 fireball cameras and
several visual observers reported a -10 mag kappa-Cygnid that entered the atmosphere near
Göttingen (Germany) and evaporated completely.
Since 1959 a number of meteorite candidates have been observed and successive ground searches were carried out (table 1).
date time location impact point terminal mass [UT] (computed) (computed) (computed) longitude latitude [kg] 07.04.1959 19:30:21 ± 1s Pribram (+) 14° 11' E* 49° 40' N* 50 15.10.1968 19:53:30 ± 30s Cechtice (+) 15° 03' E 49° 37' N 0.15 10.04.1969 21:44:30 ± 90s Otterskirchen (+) 13° 20' E 48° 39' N 5 24.11.1970 01:47:00 ± 1m Mt. Riffler 10° 21' E 47° 08' N 0.9 30.08.1974 01:25:00 ± 5m Leutkirch (+) 09° 54' E 47° 51' N 9.6 02.05.1976 19:12:00 ± 20s Kamyk (+) 14° 19' E 49° 39' N 0.07 01.06.1977 21:46:00 ± 2m Freising 11° 39' E 48° 28' N 0.7 12.06.1977 23:03:00 ± 2m the Alps 06° 29' E 46° 06' N 30 27.05.1979 20:38:50 ± 50s Zvolen (+) 19° 08' E 48° 34' N 1.2 09.10.1983 18:55:21 ± 43s Zdar (+) 15° 55' E 49° 36' N 1.5 04.12.1983 17:09:48 ± 5s Neuberg I 15° 32' E 47° 43' N 4 03.08.1984 21:05:53 ± 12s Valec (+) 16° 43' E 49° 09' N 16 13.08.1985 23:32:00 ± 5s Valmez (-) 17° 56' E 49° 25' N 2.1 04.10.1987 02:57:00 ± 1m Janov (-) 17° 28' E 50° 15' N 75 24.12.1987 02:25:23 ± 56s Freiberg 13° 27' E 50° 52' N 10 14.05.1988 23:15:50 ± 5s Brdy 14° 06' E 49° 47' N 1 07.05.1991 23:03:53 ± 3s Benesov (+) 14° 37' E 49° 47' N 3 22.09.1991 16:48:00 ± 30s Dobris (#,-) 14° 15' E 49° 43' N 100 09.05.1992 04:06:00 ± 30s Neuberg III 15° 36' E 47° 39' N 10 22.02.1993 22:12:45 ± 2s Meuse 04° 48' E 49° 25' N 2.7 07.08.1993 21:08:15 ± 15s Polna 15° 55' E 49° 32' N 0.2 25.10.1995 02:25:53 ± 1s Tizsa 20° 47' E 47° 48' N 2.6 23.11.1995 01:29:00 ± 1m Jindrichuv Hradec (-) 15° 02' E 49° 08' N 2.0 * coordinates of the largest recovered fragment "Luhy" (5.6 kg) + systematic ground search in the predicted area - only non-systemantic attempt to recover the meteorite: people in the area were informed by radio, local newspapers and postings # daylight fireball: all data rely on approximately 200 visual observations
Despite the large number of meteorite candidates only one fireball could be recorded, from which the meteorite was recovered afterwards. The other ground searches failed for various reasons, and reported meteorite falls in the last 38 years (table 2) occured either in daytime or under unfavourable weather conditions.
date time location longitude latitude mass type [UT] [kg] 07.04.1959 19:30 Pribram* 14° 02' E 49° 40' N 5.600 stone 26.04.1962 11:45 Kiel 10° 09' E 54° 24' N 0.738 stone 12.06.1963 12:58 Usti nad Orlici 16° 23' E 49° 59' N 1.260 stone 16.09.1969 07:15 Police nad Metuji 16° 01' E 50° 31' N 0.840 stone 14.11.1985 18:17 Salzwedel ** 11° 12' E 52° 48' N 0.043 stone 01.03.1988 12:30 Trebbin 13° 10' E 53° 13' N 1.250 stone 04.07.1990 18:33 Glanerbrug 06° 57' E 52° 13' N 0.855 stone * first photographed meteorite fall in the history of meteor science ** photographed by one German EN station
The two other camera networks had been successful only once in that respect, too. The American Prairie-Network recorded the fall of the Lost City meteorite , and the Canadian MORP captured the Innisfree meteorite fall . In addition, the fireball caused by the Peekskill meteorite was recorded by chance with several video systems in 1992 .
The EN detection rate of meteorite candidates  is in good agreement with predictions based on
previous studies of MORP fireball data . According to them, about 15% of the meteorite
encounters taking place in the EN area are photographically recorded (Figure 5). This coincides
with the estimate, that the EN enjoys clear sky conditions of only 3 hours per day, on average.
Furthermore, the records of meteorite falls and recoveries suggest, that 1% or less of all meteoritical material of the considered mass range deposited on the ground is actually recovered. Therefore it can be estimated, that the joint probability of recording a fireball photographically and recovering the meteorite is only about 0.0015. Given the MORP flux rate, a meteorite of 100 g or 1 kg mass would be recorded and recovered in the European Fireball Network area only every 20 or 100 years, respectively. This conservative estimate, however, does not account for the possibility, that a fireball photograph makes the recovery of meteorite actually feasible.
The European Fireball Network has been recording several hundred fireballs since operation was
initiated in 1963. Even though only one meteorite fall could actually be photographed so far, it
provided a wealth of information on the population of meteoroids in near-Earth space.
We hope that with the digital analysis of fireball photographs more data of the orbits and properties of meteoritic material will be gained from the network.
The German part of the European Fireball Network is funded by the DLR Institute of Planetary Exploration. The Czech camera stations are maintained by Ondrejov Observatory and funded by the Academy of Sciences of the Czech Republic.