Complex photographic and radar meteor observations have been carried out since 1957. Using the available observational data, the density of incident flux of meteoroids was estimated over a wide mass range of 0.001 to 100 g. To avoid the influence of apparatus selectivity a special technique was applied. The application of this technique to the radar shower data analysis is discussed in detail

Simek, M.

English

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288 
N88-  1 4 5 4 1  
A METHOD OF LONG-TERM RADAR SHOWER DATA ANALYSIS 
M. Simek 
Astronomical Institute of the Czechoslovak Academy of Sciences 
Ondrejov, Czechoslovakia 
Long-term radar observations of any meteor shower yield good data for 
a study of the features of its cross-section structure in detail. The 
hourly rates of meteor echoes represent usually the basic data from which 
shower characteristics are derived. Unfortunately, the hourly rate does 
not depend only on the activity of the shower in question but also on the 
position of the shower radiant (i.e., its zenith distance), on the mutual 
radiant-antenna position and, on the parameters of the radar system. We 
know that the knowledge of the response function of the radar is necessary 
for good interpretation of the hourly echo counts. 
The response function introduced by MCINTOSH (1966) corresponds to the 
radar sensitivity for different radiant zenith distances. It varies with 
meteor mass, slightly with the population exponents and with the meteor 
velocity. In most cases we do not know the response function well enough 
and, therefore, many authors use, for shower activity analysis, daily rates 
(or a fraction of a day, say 6, 8, 10 or any other number of hours of 
observation which repeats every day). Then a knowledge of the response 
function is irrelevant, but, every day of observation is t'lem represented 
by only one value on the activity curve. The fine structure of the shower 
activity is then lost. 
The basic idea for using the hourly echo counts without knowing the 
response of the radar is based on the fact that the same diurnal variation 
of geometrical observational conditions repeat every day. We are 
neglecting here the daily motion of the radiant and the four minutes a day 
difference between siderival and standard time. Let us suppose that the 
cross-section patterns of the shower do not change drastically from 
year-to-year except for the activity level. This is the case for the 
Geminids, Perseids, Quadrantids and other meteor streams. 
Previous studies by severai authors covered often only one or at best 
a few years of observation from one station only; these results do not 
yield a homogenious view an the stream and its structure. Radar 
observations and their lack of dependency on weather conditions enables 
complete analysis when satisfactorily long time series of data are 
available. We must also not forget that the shower radiant will not be 
above the observer's horizon for the whole 24 hours period, and that the 
antenna characteristics will permit observations only for some fraction of 
the day. It is very worthwhile to supplement the data set, using the 
results of other radars situated on different geographical longitudes. 
When dealing with overdense echoes the condition of identical 
transmitting powers for the radars is not very serious. The wavelength 
should not be very different, within, say, some 202, which is satisfied by 
most meteor radars operating in the wavelength range of 8 - 10m. 
https://ntrs.nasa.gov/search.jsp?R=19880005159 2020-03-20T09:11:07+00:00Z
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Particular difficulties, however, arise when combining the data from radars 
with different antenna characteristics. 
We start the analysis using a preliminary model of the cross-section 
patterns of the shower. The model is usually just a rough estimation of 
the behavior of the activity within at least 48 hours of the shower 
observation. After subtraction of the sporadic background, the data are 
organized as a series of sets for each individual year. One set of data in 
a particular year is represented by measured hourly echo shower rates with 
respective solar longitude for say 8 - 9 hours through all days of shower 
observation. One set must necessarily contain at least two members. 
Similarly, we have another set for 9 - 10 hours and so on. In this way the 
shower rates for every single year are organized. The same equinox must be 
used. Each set is then normalized to the sum of the model data at the 
appropriate solar longitudes. We then obtain a new model of the shower 
pattern. This process is repeated for a sufficient number of times until 
the last resulting model is identical with the previous one. The 
convergence usually occurs after 4 to 6 iterations. As a by-product of 
this method we also obtain the response function of the radar system 
without a knowledge of its antenna characteristics. The method is 
described in more detail in SIMEK (1985). 
This whole procedure has been applied to the Swedish Perseid 
observations from 1953 to 1978, and published by LINDBLAD and SIMEK (1985). 
The data was first divided into two parts: daytime observations and 
night-time observations (see LINDBLAD and SIMEK, 1983). Results were, in 
general almost identical. The cross-section patterns for combined day and 
night observations for echo durations 2 1s are presented in Fig. 1. The 
scale is here normalized to 100 at the maximum. 
Canadian Perseid observations were carried out in the period 1958 to 
1974. The same method was applied and the resulting cross-section patterns 
for echo durations 2 1s are presented in Fig. 2 .  Detailed analysis is 
presented by SIMEK and MCINTOSH (1986). 
The Czechoslovak meteor radar program covered the Perseid activity for 
11 years between 1958 and 1984. As with recent Swedish and Canadian data 
analysis, we concentrated our interest on the 2 1s echo duration group. 
The Swedish, Canadian and Czechoslovak data all show very similar 
features for the fine mean structure of the Perseid meteor stream activity. 
When combining all three resulting patterns together, each individual point 
at a particular solar longitude was averaged using a weight inversely 
proportional to its standard deviation. The observed shower data base 
contains some 300000 meteor echoes with durations 2 1s. The position of 
peak activity was found at a solar longitude of 139.20" 0.02" (equinox 
1950.0). It should be understood that the stream shows slj.ghtly different 
features in the cross-sectional patterns from year to year. Therefore, the 
histogram in Fig. 3 describes the most probable pattern of the stream along 
the Earth's path. The peak is less pronounced than for a single year's 
observation, and is slightly flatter. Note that, because of the 6 hour 
shift per year in the diurnal cycle, peak activity cannot be observed from 
one station in those years when it appears around the time of the radiant 
culmination. 
290 
. . 
0. . 
0 .  . 
0. 
. 
0 .. . . 
0 .  . 0% .. 
Fig. 1 Relative Perseid meteor flux producing meteor echoes having 
durations 2 Is as a function of solar longitude L (epoch 1950.0). 
Swedish observations. 
291 
Fig. 2 Relative Perseid meteor flux producing meteor echoes having 
durations 2 1s. Canadian observations. 
2 9 2  
Fig. 3 Relative Perseid meteor flux producing meteor echoes having 
durations 2 Is. Resulting histogram of Swedish, Canadian and 
Czechoslovak observations. 
293 
One would expect that the activity patterns should reach zero level on 
both wings of the histogram. This is contrary to our result in Fig. 3 .  
Residual shower activity before and after the central part of the histogram 
result from one sided normalization of the data when negative shower rates 
were discarded. 
In addition to the response function of each radar, the variation of 
shower activity from year-to-year was determined. Long series of 
observations of the sporadic meteor complex yield very good data for the 
analysis of solar activity cycle and its influence on upper atmosphere 
phenomena. 
Final detailed conclusions concerning the complete set of long-term 
Perseid radar observations from different stations require further 
analysis, which will be published later. Colleagues who are interested in 
contributing their own data from Perseid radar observations are invited to 
participate in this project. We plan to concentrate our interest in the 
future also on other meteor streams such as the Quadrantids and the 
Geminids. 
References 
Lindblad B. A. and M. Simek, 1983, in Asteroids, Comets, Meteors, ed. C.-I. 
Lagerkvist and H. Rickman, p. 431. 
Lindblad B. A. and M. Simek, 1985, in Asteroids, Comets, Meteors 11, 
Uppsala symposium (in print). 
McIntosh B. A., 1966. Can. J. Phys. 44, p. 2729. 
Simek M., 1985, Bull. Astron Inst. Czechosl. 36 (in print). 
Simek M. and B.A. McIntosh, 1986, Bull. Astron. Inst. Czechosl. 37 (in 
print). 


A method of long-term radar shower data analysis

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