Hirofumi Sugimoto (The Nippon Meteor Society)

It has been very difficult to estimate Zenithal Hourly Rate in the case of Radio Meteor Observations, although it is very useful method for catching all meteor activities even if in bad weather or daytime. This research tries to estimate Zenithal Hourly Rate using Radio Meteor Observations.

1. Introduction

As a known method for combining all radio meteor observations, H. Ogawa et al.(2001) published a new index that was “Activity Level” Index. Although this index is very useful for catching meteor activity profiles (period, level etc.), it is impossible to compare with visual observations.
This research tried to estimate Zenithal Hourly Rate using radio meteor observations. By using this estimated ZHR, it becomes possible to discuss on the same table as visual observations.

2. Method

An estimated ZHR is led by steps as following.
(1) correcting machine feature such as antenna, receiver, receiving level, etc. and removing sporadic meteors
(2) correcting limiting magnitude
(3) correcting radian elevation
(4) combining all calculated data

2.1. correction machine features

This step adopts previous method by H. Ogawa et al.(2001). First step means as same as leading to Activity Level index. Activity level is led by as following formula.
A(t) = [ N_obs(t) – N_ave(t) ] / D_ave
where, N_obs is the hourly rate of observed meteor echoes. N_ave is the background level past two weeks. N_ave, therefore, stands for sporadic meteor activities. D_ave is the average meteor echoes for a day past two weeks. A(t) means the activity level at time t.

2.2. correcting limiting magnitude

Corrected Hourly Rate was led by following formula.
CHR = A(t) * S_bas
where, A(t) is Activity Level led by previous section. S_bas is the number of daily sporadic meteors under Limiting Magnituide = 6.5. The number of sporadic meteors shows a change for a year. Shigeo Uchiyama provides a result of visual observations. S_bas led by comparing radio observed data to visual observed data (Figure 1). Radio Meteor Obervations data were provided by about 800 months. This formula translate radio results as activity level to visual results as CHR (Figure 2 and 3).

Figure 1

Figure 1 – the relationship between S_bas, Visual results and Radio results.

Figure 1

Figure 2 – Results of Hourly Rate.

Figure 1

Figure 3 – Results of CHR.

2.3. correcting radiant elevations

This research basically use only radiant elevation over 20 degree. ZHR is led by as following formula.
ZHR = CHR * sin(h)
where, CHR is led by previous section. h is a radiant elevation (Figure 4).

2.4. combining all calculated data.

Calculations until previous sections is each observing station. It therefore needs to combine all observing stations data. Final step calculates an average all observing stations at time t.
(Figure 4 : bold line as worldwide average)

Figure 1

Figure 4 – Results of estimated ZHR using worldwide data.

3. More corrections

3.1. removing a unusual data

Radio Meteor Observations sometimes have unusual observed data except for meteor activities. This is caused by noise, sporadic-E, receiving conditions etc.
These clear error data are removed in this research.

3.2. removing meteor showers activity in D_ave

D_ave sometimes include some meteor shower activities. This is because D_ave is led by observed data in past two weeks. If one meteor shower has a long period activity, D_ave is influenced by this meteor showers. This research tries to remove this influenced when correction of radiant elevation.

4. Results

This research succeeded to estimate Zenithal Hourly Rate using Radio Meteor Observations, and they are similar results as visual observations.
It therefore becomes possible to catch Zenithal Hourly Rate even if in bad weather or full-moon nights. Of course, it becomes possible to catch daytime meteor showers.
This methodology has already used at many meteor showers results (see my website). It sometimes succeeded to detect predicted outburst activities.

5. Acknowledgement

We wish to thank all radio meteor observers, in the world, Mr. Shigeo Uchiyama for providing visual data, Mr. Masayoshi Ueda for advice to this research and transmitting stations.

6. References.

[1] Ogawa H., Toyomasu S., Ohnishi K. and Maegawa K., 2001: The Global Monitor of Meteor Streams by Radio Meteor Observation all over the world. Proceeding of the Meteoroids 2001 Conference, 189-191.
[2] The International Project for Radio Meteor Observations : http://www.amro-net.jp
[3] Radio Meteor Observation Bulletin : http://www.rmob.org/
[4] Hirofumi Sugimoto web site : http://www5f.biglobe.ne.jp/~hro/Flash-e/index.html