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- W2053007876 abstract "view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Three-station radar and visual triangulation of meteors. Millman, Peter M. ; McKinley, D. W. R. Abstract This paper presents one phase of the combined Dominion Observatory-National Research Councii program for the observation of meteors. Since the summer of 1947 the following observational data have been collected: 100 meteor photographs, 5,000 visual meteor plots, 50,000 photographic recordings of Doppler meteor whistles, I ,500,0OO photographic records of meteor radar echoes. The Doppler and radar work has been carried out in the 30 megacycle band. In previously reported results we have indicated the dependence of the form of the echo on the distance of the meteor from the radiant, i.e. on the angle between the meteor path and the line of sight. We have also shown, in agreement with others, that the great majority of meteor echoes are produced in a fairly restricted region of the upper atmosphere centered somewhere between 90 and 100 km above sea level. Since the radar employed was essentially non-directional, all height data depended on a correlation of visual and radar observations. To investigate the possibility of height determination by radar alone, three stations located at Ottawa, Arnprior and Carleton Place respectively, were put into operation in August, 1948. The base lines between stations were 36, 41 and 57 km in length. Photographic, visual and radar observations were carried out at all three stations. It was found that a large percentage of the meteors producing enduring echoes were detected by all radar sets. Where visual observations were also available from two or more points this made possible the computation of heights in three ways: (a)by the use of the three radar ranges, (b)by the combination of one radar range with a visual plot, (c)by the use of two or more visual plots. To study the relation between heights determined by the three methods detailed computations have been carried out for the night of Aug. 10/Il, 1948. Since the computation of meteor heights by radar range alone becomes insensitive for objects at long ranges the most reliable results are obtained from meteors with sub- points less than 150 km distant from the ceutroid of the three observing stations. A total of 41 meteors was fO~~d which satisfied the above condition, had radar echoes from all stations lasting over one second, and were visually observed from at least one point. The values of mean radar height for each meteor varied from 79 to 112 km with an average height of 94 km. The corresponding values for the same 41 meteors determined by combining radar ranges with visual plots gave heights from 68 to 142 km with an average height of 100 km. The addition of 21 meteors of long range or with very short duration echoes did not materially alter these figures. Heights computed purely from visual plots showed a much greater spread and were not accurate enough to be of value individually. The mean height of 26 meteors computed from visual observation alone was 98 km, agreeing well with the other results. It would appear that, for the August period, the heights computed from radar alone average somewhat lower than those found from a combination of visual and radar data. This indicates that there is a tendency for the radar echo to occur near the end of the visual trail for the Perseids at least. Confirmation of this fact, and a check on the reliability of the correlation of the radar echoes with visual meteors, was found by computing from the radar ranges alone the position of each echoing source in the sky and then comparing this with the visual meteor plot. The mean angular distance on the celestial sphere of all radar points from the corresponding visual meteor plots was only 7 degrees, a good agreement since this figure includes the summed effect of at least five separate sources of error. Over twice as many radar points were plotted near the end of the visual trails as near the beginning. Additional radar heights were computed for meteors appearing on the same night but not visually observed. A compilation of all radar heights determined, corresponding to a total of 94 different meteors, gave a mean height of 95 km. The moving type of echo (b or h characteristic in our classification) was observed for 16 of these meteors. Mean height of appearance of this echo was 110 km and mean height of disappearance 95 km. It seems clear from the above results that meteors produce ionization clouds which may be satisfactorily detected on the 30 megacycle band from widely separated points on the earth's surface. Triangulation of these clouds by range measures alone is practical and yields results wbich compare favourably with those obtained by any other methods. This technique, when applied to individual meteor echoes of certain types, makes possible the accurate determination of daytime meteor paths and orbits. It may also be noted that these results confirm our earlier conclusions concerning echo heights and the relation between the echo form and distance from the radiant. Doniinion Observatory, Ottawa, Ont., and National Research Council of Canada. Publication: The Astronomical Journal Pub Date: June 1949 DOI: 10.1086/106292 Bibcode: 1949AJ.....54R.132M full text sources ADS |" @default.
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- W2053007876 title "Three-station radar and visual triangulation of meteors." @default.
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