from: "WGN - Journal of the International Meteor Organization" 25-1 (1997), p.15

Video Observations of Meteors: History, Current Status and Future Prospects

S. Molau, M. Nitschke, M. de Lignie, R. L. Hawkes, J. Rendtel

Video meteor observations have been performed by amateur astronomers for more than ten years. They enjoy a rapidly increasing interest in the meteor community and will evolve into a powerful tool for amateur observers in the near future. Video meteor observation is the key to a fundamental increase of our knowledge about meteoroid populations and their interaction with the Earth's atmosphere.
In this paper we want to summarize the history of video meteor observation and describe the current state of affairs. We discuss problems and limitations and propose future projects. The paper is intended to serve as basis for the foundation of appropriate organizational structures within the International Meteor Organziation.

History and Current Status

Professional astronomers started to use image intensified systems in connection with film equipment already in the sixties and seventies of our century [Hawkes 1993]. Among amateurs, Japanese (1986) and Dutch (1987) observers have been the first using low-light-level video systems [de Lignie & Jobse 1989, Fujiwara 1993].
At the beginning, there were only XT personal computer and rudimentary frame grabber cards available. Thus, most of the video tape analysis had to be done manually. The main advantage compared to visual observations was the increase in positional accuracy by orders of magnitude. In addition, video systems where much more efficient than photocameras, since they could record meteors down to magnitude +6 and fainter.
In the beginning of the nineties, new amateur groups started indepently to use that technology in several European countries like Austria, Germany and the United Kingdom. Thanks to the increasing power of computer hardware, more and more problems could be solved computer aided. First attemps for the automatic video tape inspection were reported in 1993, and the analysis software for video meteors became much more efficient. However, the major breakthrough did not happen before 1995/96, when image intensifiers became cheap enough to be efforded by a larger group of amateurs [Molau & Nitschke 1996].
Scientific results of video observations from several observer groups were published in different journals. So far, video systems have been used for the determination of meteoroid stream orbits, shower radiants, calibration of visual observations, cluster analysis, recording of spectra and many more research projects. A major event was the 1995 outburst of the alpha- Monocerotids, which has been completely recorded by two video teams [Rendtel et al. 1996, Jenniskens et al. 1997]. It was for the first time, that such an outburst was observed with an appropriate method.
Currently, there are about fourty video systems operated by amateur astronomers around the world. At least fifteen systems are in operation in Japan. We know of approximately ten video systems in Germany and nearly five in the Netherlands. Video meteor observations are carried out in the United Kingdom, the United States and Austria. Beside that, professionals in Canada, the Czech Republic and Tadjikistan do use this technology.
There are at least three groups who deal with computer-aided meteor detection on video tapes. One of those systems has already proved to work in practice [Molau and Nitschke 1996].
Several software packages exist for the digital measurement of recorded video meteors [de Lignie & Jobse 1989, Hawkes 1993, Molau 1995]. In the near future it is intended to provide a standard software package containing solutions for all tasks of video observers.

Why do video observations?

Video systems combine the advantages of visual and photographic meteor observation and can even compete with telescopic observers.
Current systems allow positional accuracies down to one arc minute. Thus, they are more accurate than visual meteor plottings. When used with wide angle objective lenses they can have a field of view of more than 100 degrees in diameter, which is almost comparable to all-sky photography. The limiting magnitude depends strongly on the field of view of the camera, the focal ratio of the lens and the intensifier's gain. However, modern video systems record on average more meteors in the same time than visual observers. They obtain by some orders of magnitude more meteor recordings than photographic systems.
Video systems achieve a high time resolution (25 or 30 images per second depending on the video standard used) and record the evolution of a meteor directly. All events can easily be timed down to an accuracy of less than one second. The angular speed of meteors can be determined accurately without mechanic shutters due to the short exposure times for each video frame. The brightness of video meteors varies from bright fireballs down to the level of telescopic meteors. Thus, such systems can provide uniform data over a much larger spectrum of meteoroid sizes than any other method. In addition, video systems record the light curve of a meteor, leading to important results about the properties of meteoroids and their interaction with the Earth's atmosphere.
A major disadvantage are the costs, that are still relatively high compared to photographic or visual equipment. In addition, video systems depend on the availability of electrical power.


A real limitation for video systems is the amount of time needed for data processing compared to the number of events that can be recorded. Currently, the video tapes are inspected visually and meteor positions are then measured with the help of a computer. A working solution for automated meteor search is only a question of time. However, fully autonomous analysis systems seem impossible from the current state of affairs. With the help of specialized computer software the measurement of meteors can be accelerated, but in practice it still requires five to ten minutes for each meteor to be analysed. Thus, it is impossible to analyse all meteors in detail, that can be recorded by video systems. Depending on the actual aim of investigation, one either has to restrict the amount of information to be derived, or the meteors to be analysed have to be selected.
Video systems are not as portable as photographic equipment. Even though newer cameras are more robust than earlier systems, they still are highly integrated electronic devices with some limits. Most systems are not meant to operate at temperatures far below the freezing point or when dew turns up. This, together with their power dependency, makes them only partly useful under expedition environments.

Components and Classification of Video Systems

In general, all video meteor systems consist of a fast lens, an image intensifier and a video camera.
It could be shown, that image intensifiers are absolutely neccessary for recording faint meteors. Considering the number of photons reaching the photocathode, a charge coupled device (CCD) alone may in theory be sensitive enough to detect faint objects. However, when operated at video frame rates of 25 or 30 Hz, the readout noise by far overwhelms the number of electrons generated by the meteor's light.
The least requirement is a first generation image intensifier with multiple amplification stages. The gain should be >1.000, and the diameter of the photocathode needs to be larger than 15 mm. First generation intensifiers with three sequential amplification stages can reach a higher gain than other intensifier generations, but suffer significantly from strong image distortion, a variable sensitivity within the field of view and strong noise. This is why future automatic meteor detection systems will probably not work for those cameras.
Second generation image intensifiers (micro channel plates - MCPs) do usually contain a single amplification stage. Therefore they do not reach as a high gain as first generation devices. However, they are prefered for meteor observation because of their high quality image with less noise, distortion and sensitivity variations. New MCP devices fulfiling military specifications are still very expensive (above US$ 2000), but nowadays second hand MCPs are also available at reasonable prices (below US$ 500) from several dealers around the world.
Third generation image intensifiers are not especially useful for meteor observations, since they reach their maximum sensitivity in the infrared.

Different video cameras are used to record the intensifier's phosphorous screen: A camcorder has the advantage, that it is usually able to automatically record the time. Other systems involve cheaper video cameras. They either mark the time with audio signals or insert it electronically into the video signal. In the analysis process, the video tapes need to be digitized by frame grabbers. Currently those are available at prices between US$ 200 and US$ 4000. The use of conventional CCD cameras as used for astronomical imaging has been discussed. However, major disadvantages like the loss of the high time resolution have prevented observers so far from using this technology.
In the future, the data stream may be stored digitally. With currently expensive hardware it is possible, to digitize the enormous data amount of a video signal (>9 MByte/second or >33 GByte/hour) in real time and save it on a computer's hard disc. This requires good data compression, which is possible for video meteor observations with almost no changes from one video frame to the next. The technology will become cheaper with further technological progress and is an alternative to the use of VCRs and the loss of information caused by that. Also digital camcorders may help to improve the quality of data storage and transfer in the future.
Today's high end system do not involve any signal conversion between digital image aquisition and storage. They also contain sensors with much higer resolution.

The lens is most important for the recording properties of a video system. Generally it should be as fast as possible (low f ratio) to get best limiting magnitudes. According to the focal length we can distinguish between three types of video cameras:

All image intensified video meteor detection systems are technically limited in one of three ways (see Hawkes and Jones [1986] for a more detailed treatment of this topic):

Video Observation Projects

From the described properties of video systems we would like to derive the following three key projects:

Beside those key projects, we suggest a number of other observations to be carried out with video meteor cameras:

Conclusions and Outlook

We have presented a list of projects that can be work on with video systems. This list is certainly not inclusive of all possible projects. We would like to invite other observers to join a discussion about the future of video meteor observation and the focus of our work. We want to call for participation in the projects mentioned above, which will certainly improve our knowledge about small particles in the solar system and their interaction with Earth fundamentally.
We feel, that the importantance of this observing technique, which will be the key for new investigations in the future, should be reflected by an own commission within IMO. The main aim of an video commission should be the coordination of activities and the encouragement of further observers to apply this still rarely used observation method. The key to success for many of the proposed projects lies in the coordination between video observers and fruitful cooperation with other techniques like photographic, visual and telescopic observation. An commission should provide general information on the how and why of video observations, technical hints and construction plans for video cameras, suggestions for observation targets and support for the data analysis. Forums like WGN and the WWW homepage of IMO could be employed for that function. In addition, the maintenance of a video database and the provision of free access to the stored meteor data should be realized.
Last but not least, a video commission could serve as a contact address for everybody who has specific questions or problems. With joint efforts of the currently mostly uncoordinated working video groups, we may approach our scientific tasks more efficient than ever.

Literature References

Borovicka, J. and Bocek, J. (1995): "Television spectra of meteors", Earth, Moon, and Planets 71, p.237

de Lignie, M. and Jobse, K. (1989): "Accurate radiant determination from TV meteors", Proceedings of the IMC 1989, p.41

de Lignie, M. and Jobse, K. (1996): "Double station video observations of the 1995 Quadrantids", WGN 24, p.20

Fleming, D. E. B., Hawkes, R. L. and Jones, J. (1993): "Light curves of faint television meteors", In: Stohl J. and Williams, I.P., (eds.), Meteoroids and their parent bodies, Smolenice, Slovakia, p.261

Fujiwara, Y. (1993): "Television observations of meteors in Japan", In: Stohl J. and Williams, I.P., (eds.), Meteoroids and their parent bodies, Smolenice, Slovakia, p.265

Hawkes, R. L. and Jones, J. (1986): "Electro-optical meteor observation techniques and results", Quart. J. of the R.A.S. 26, p.569

Hawkes, R. L. (1993): "Television meteors", In: Stohl J. and Williams, I.P., (eds.), Meteoroids and their parent bodies, Smolenice, Slovakia, p.227

Hawkes, R. L., Mason K. I., Fleming D. E. B. and Stultz, C. T. (1993): "Analysis Procedures for Two Station Television Meteors", Proceedings of the IMC 1992, p.28

Jenniskens, P., Betlem, H., de Lignie, M. and Langbroek, M. (1997): "The detection of a dust trail in the orbit of an Earth threatening long period comet", Astrophy. J., scheduled for February 1997

Millman, P. M., Cook, A. F., Hemenway, C. L. (1971): "Spectroscopy of Perseid meteors with an image orthicon", Can. J. Phys. 49, p.1366

Molau, S. (1995): "MOVIE - Analysis of Video Meteors", Proceedings of the IMC 1994, p.51

Molau, S. and Nitschke, M. (1996): "Computer based meteor search - a new dimension in video meteor observation", WGN 24, p.119

Molau, S. and Arlt, R.(1997): "Meteor shower radiant positions and structures as determined from single station video observations", Planetary and Space Science, scheduled for 1997

Rendtel, J., Brown, P. and Molau, S. (1996), "The 1995 outburst and possible origin of the alpha-Monocerotid meteoroid shower", Month. Not. of the R.A.S. 279, p.L31

Robertson, M. C. and Hawkes, R. L. (1992): "Wake in faint meteors", In: Harris A. and Bowell T. (eds.), Asteroids, Comets, Meteors, p.517

Sarma, T. and Jones, J. (1985): "Double-station observations of 454 TV meteors", Bull. Astron. Inst. Czech. 36, p.103, 585

Ueda, M and Fujiwara, Y. (1995): "Television meteor radiant mapping", Earth, Moon & Planets 68, p.585

Sirko Molau; last change: January 11, 1997