SAG: Stars and Galaxies Vol. 4, id. 1, 2021 December 28
c 2021. Center for Astronomy, University of Hyogo.
⃝

A new simple method to observe Doppler shift of the meteor head echo using
low-cost and low-power ham radio devices and free FFT software
Kazuhiro SUZUKI 1, 2 and Yasuo KATOH 3
1

Seijoh High School, Sakae-cho, Toyoake, Aichi, 470-1161, Japan
Toyohashi High School of Technology, Kusama-cho, Toyohashi, Aichi, 441-8141, Japan
3
Institute for Space-Earth Environmental Research, Nagoya University, Honohara, Toyokawa, Aichi, 442-0061, Japansuzuki kazehiro@yahoo.co.jp
2(Received 2021 October 30; accepted 2021 November 20)

Abstract
A meteor is a phenomenon in which extraterrestrial material, generally known as a meteoroid, enters the Earth’s
atmosphere, ionizing the surrounding components and/or emitting light. The surface of a meteoroid moving athigh speed reﬂects very high frequency (VHF) radio waves by melting itself and ionizing the components of thesurrounding atmosphere. The radio wave reﬂected from the head of a meteor is called a meteor head echo andresults in a Doppler shift.
Since the early 2000s, some researchers have made multi-static measurements of head echoes using high-powerlarge-aperture pulse radars. Meanwhile, the authors have attempted to observe meteor head echoes with Doppler
shifts using traditional low-cost and low-power ham radio devices for over a year. Moreover, by setting the transmitter and the receiver in close proximity, it became clear that the Doppler shift shows a value that follows the meteor
velocity component in the line-of-sight direction. This implies that any observer who is involved in amateur radio
operations can make observations similar to those obtained from a large-scale pulse meteor radar.
Using this technique, the authors recorded two remarkable Eta Aquarids meteor head echoes in a location very
close to the transmitting station, in May 2021. The Doppler shift calculated from the meteor head echo agreed wellwith the data obtained from the position of the meteor’s actual path using the known physical parameters of the Eta
Aquarids meteors. We propose that this method facilitates the observation of meteor head echoes at multiple points
simultaneously, enabling the estimation of the position and ground velocity of a meteor. This system will help us
ﬁnd the path of a meteorite during daytime hours or on cloudy days.
Key words: meteor head echo — Doppler shift: ham radio devices — Eta Aquarids meteor

1. Introduction
When an extraterrestrial dust particle distributed around theorbit of the Earth is caught by the gravity of the Earth, it enters
the Earth’s atmosphere and melts and evaporates owing to its
own kinetic energy. Subsequently, the dust particles and thesurrounding atmospheric components become ionized and/or
they start emitting light. In general, this ionization and lightemission phenomenon is called a meteor. The body of a meteor
is called a meteoroid and is composed of ﬁne dust of extraterrestrial origin, in particular comet or asteroid origin. The ionization takes place approximately in the E region of the ionosphere (80–140 km height). The E region ionized by meteors
can be divided into an ionized trail and a localized ionized region surrounding the meteoroid (Kaiser 1953). The ionizedtrail of a meteor is cylindrical in shape, with dimensions ofkilometers in length and meters in diameter. The duration ofa meteor trail varies from less than 1 second to several minutes (Sugar 1964). Meteor trails are mostly stationary, except
for motion due to atmospheric winds. Appleton and Barnett(1925) discovered that ionized meteor trails reﬂect less thanvery high frequency (VHF) radio waves (30–300 MHz) due tothe increase in the density of free electrons.
Following this discovery, the study of meteors using the radio method was developed before and after the Second WorldWar (Millman & McKinley 1949). In recent years, meteor
trails observed in the E region of the ionosphere have been analyzed in detail, and research on the upper atmosphere has been
conducted (Nakamura et al. 1991). In the 1970s, radio observations of meteors using FM broadcasting radio waves in the
76–90MHz frequency band was initiated in Japan (Suzuki et al.
1976). Subsequently, radio observations of meteors using beacon waves in the VHF (ham radio) band have been conducted(Maegawa 1999). Amateur radio meteor observations using
beacon waves have been conducted throughout Japan, and it
has become possible to detect the diurnal and annual variationsof meteor echoes (Okamoto & Maegawa 2008).
It has been shown that not only the meteor trail but also
the meteoroid itself, which enters the Earth’s atmosphere athigh speed, is heated through collisions with the Earth’s atmospheric components. During melting and evaporation, the components of the meteoroid head are converted into plasma and2

K. Suzuki and Y. Katoh

begin to reﬂect VHF radio waves (Pellinen-Wannberg 2005).
VHF radio waves reﬂected from a localized ionized region surrounding the meteoroid are called the head echo of a meteor,
as opposed to the trail echo that originates from the ionizationof the upper atmospheric components (Close & Hunt 2000).
Because the ionized material surrounding a meteoroid moves athigh speed, the reﬂected radio wave of a meteor head exhibits a
Doppler effect owing to the velocity of the moving meteoroid.
The Doppler shift is higher than the original frequency of awave source when the source approaches an observer and lower
when the source moves far away. The same is true when a moving body reﬂects radio waves. The frequency of radio waves
impinging on an approaching object increases, and when theobject moves away, the frequency decreases. If a VHF radio
wave is directed at a meteoroid that has entered the upper atmosphere at high speed, the ionized components and free electrons become enhanced near the meteoroid. Therefore, due tothe Doppler effect, the frequency of the reﬂected radio wave
becomes higher or lower depending on the transmitted radio
wave.
Since the early 2000s, some researchers have made multistatic measurements of head echoes using high-power largeaperture pulse radar. There are a number of published studies describing the method of measuring head echoes, as reported by Kero et al. (2008). However, although many meteor
observers have detected meteor echoes by using VHF beaconwaves as well as broadcast radio waves, it has been impossible
to observe detailed Doppler shifts from the head echoes of meteors. Under such circumstances, the authors have tried to detect meteor head echoes with Doppler shifts by setting in close
proximity a traditional low-cost and low-power transmitter andreceiver (which can be obtained by anyone) and observing theresults for more than a year. Consequently, we were able to perform a detailed analysis of the Doppler shift for the ﬁrst time,
which was previously considered impossible. This means thatany observer who has been involved in amateur radio operations can make observations similar to those obtained with alarge-scale pulse meteor radar.
The Eta Aquarids is a meteor stream of the parent comet,
Halley (1P/Halley). It reaches its maximum activity on May
5 and 6, almost every year. The right ascension and declination of the radiant are 337.◦ 5 and –1.◦ 1, respectively. In Japan,
twilight occurs only for a short duration when the radiant rises
above the horizon; therefore, optical observations are difﬁcult.
A meteor belonging to the Eta Aquarids meteor stream has anextremely high ground velocity, at 65.5 km s−1 (Koseki 2021).
Multiple comprehensive studies of the Eta Aquarids shower
have been conducted using head echo observations (Chau &Galindo 2008; Schult et al., 2018).
In the present study, we report in detail the Doppler shift of
the two meteor head echoes observed in May 2021. Our observations are in agreement with the known physical parametersof the Eta Aquarids meteors.
2. Observation
2.1. Transmitting station
Table 1, Fig. 1 (c), and Fig. 2 (a, b) show the transmitting station of the VHF beacon radio wave and some param-Vol. 4,

Fig. 1. Locations of the transmitting stations and the two receiving
stations. The transmitting station is Hanakikou Observatory (TX),
and the receiving stations are Soyogonomori Observatory (RX(1)) andTsukude Observatory (RX(2)), similar to that presented in (c). (a)a map of central Japan, (b) a map of Tokai region in Honshu, central Japan, and (c) a topographic map of Aichi prefecture including
TX and RX(1), RX(2). These maps are published by the Geospatial
Information Authority of Japan (GSI).

eters of the transmitting devices used for this radio observation. The transmitter (TX) was located at Hanakikou observatory (HK; call sign: JA2SDA; location: 34.◦ 819 N, 137.◦ 344
E; Fig. 1 (c)). In Japan, the radio band is assigned to hamfrom 50.0MHz to 54.0MHz. In this experiment, a transmitting
frequency of 53.100000 MHz was used, and the output power
was 5.0W continuous wave. This VHF beacon radio wave wastransmitted for 9 min and then stopped for 1 min owing to radio regulations. Subsequently, the call sign was sent out by the
Morse signal at the ﬁrst part of the stopping time of the radio
wave. Yaesu FT991AM (Table 1, Fig. 2 (b)), manufactured by
Yaesu Radio, was used as the transmitter. The VHF radio wave
was transmitted using a 2-element Yagi antenna directed to thezenith (Fig. 2 (a)).
2.2. Receiving stations
Two receiving stations were set up for the experiments. One
receiver (RX(1)) was located at Soyogonomori observatory(SG; location: 34.◦ 838 N, 137.◦ 291 E; straight line distanceto the transmitting station is 4.53 km; Fig. 1 (c)) and another (RX(2)) at Tsukude Observatory (TK; location: 35.◦ 001
N, 137.◦ 453 E; straight line distance to transmitting station
is 22.4 km and Mt. Hongu (height: 789 m) is situated between TX and RX(2); Fig. 1 (c)). The receiving antenna at
Soyogonomori observatory (SG) was a 2-element Yagi antenna(Comet CA-52HB), which was directed to the zenith (Fig. 2(c)). IC-PCR1000 was used as the receiver (Fig. 2 (d)), which
is manufactured by ICOM. Similarly, the receiving antenna at
Tsukude observatory (TK) was also a 2-element Yagi antenna(Comet CA-52HB), which was directed to the zenith (Fig. 2

id. 1A new simple method to observe Doppler shift of the meteor head echo

3

Table 1. Parameters of the radio observations of the meteor head echoes analyzed in this study.

Transmitting(TX)
Observatory

stationHanakikou (HK)◦◦

Receiving station (1)(RX(1))

Receiving station (2)(RX(2))

Soyogonomori (SG)Tsukude (TK)◦◦

Location

34 .819 N, 137 .344 E

34 .838 N, 137 .291 E

35◦ .001 N, 137◦ .453 E

Transmitter (Output)

Yaesu FT991AM(5 W)**********************************

Receiver*****************ICOM IC-PCR1000

ICOM IC-R7000

Antenna (Elements)

Comet CA-52HB(2-ele.)Comet CA-52HB(2-ele.)Comet CA-52HB(2-ele.)Transmitted or received frequency(Radio wave type)53.100 MHz

53.099 MHz(USB)

53.099 MHz(USB)

PCM recorder(Format, Sampling freq.)*****************TEAC LX-110(16 bits, 48.0 kHz)

Tascam DR-600MK(16 bits, 44.1 kHz)(e)), and the receiver used was IC-R7000 (Fig. 2 (f)) manufactured by ICOM.
The description provided in this paragraph is common forboth the receiving stations. The received wave was a beacon VHF radio wave transmitted from Hanakikou observatory (HK), and USB was the type of received radio wave
used. When the frequency of the receiver is synchronized
to 53.099000 MHz and the transmitted VHF radio wave of
53.100000 MHz is received by the radio wave type USB,
the transmitted signal can be heard as a sound of 1000 Hz.
If the Doppler effect of the head echo caused by the meteor velocity component in the line-of-sight direction is obtained, sound with frequency higher than 1000 Hz should bereceived when a meteor approaches a receiver. In contrast,sound with frequency lower than 1000 Hz should be received
when it moves far away. The sound representing VHF radio wave received by the USB radio type was recorded on
an IC recorder (Soyogonomori observatory: TEAC LX-110(16bits, 48.0kHz); Tsukude observatory: Tascam DR-60DMK
II (16 bits, 44.1 kHz)). After the observation period, theDoppler effect associated with the head echo of a meteor was
veriﬁed using frequency analysis with freely available FFT
software, Audacity (https://www.audacityteam.org/).
The radio data were recorded for 6hr a day from 05:00 AM,
LT (when the altitude of the radiant of Eta Aquarids is about40◦ ) to 11:00 AM (the altitude, about 30◦ ) for 5 days fromMay 3 to 7, 2021.
Fig. 2. Images of the observational devices for receiving meteor headechoes in this study. (a): Transmitting 2-elements Yagi antenna (Comet
CA-52HB) at TX, HK. (b) Transmitter (Yaesu FT991AM; lower left inphoto (b)) at TX, HK. (c): Receiving 2-elements Yagi antenna (Comet
CA-52HB) at RX(1) ,SG. (d): Receiver (IC- PCR1000) at RX(1) ,SG.
(e): Receiving 2-elements Yagi antenna (Comet CA-52HB) at RX(2),TK. (f): Receiver (IC-R7000) at RX(2) , TK.

3. Observational results
Two meteor head echoes with remarkable Doppler shifts
were obtained during the 30-hr observation period. Althoughhead echoes of more than 10 meteors were obtained in ﬁve
days, this study is limited to two typical head echoes in which
the Doppler shifts could be reliably observed. The ﬁrst meteor
head echo was obtained at TK at 06:18:00 (LT; LT=UT+9h) on
May 4, 2021 (Fig. 3; Fig. 4), and the second was obtainedat SG at 08:51:25 LT on May 5, 2021 (Fig. 5). To determine
the Doppler effect caused by the head echo, the transmitter and4

K. Suzuki and Y. Katoh

Vol. 4,

Fig. 5.
Frequency
analysis
imagesby
Audacity(https://www.audacityteam.org/) of the meteor echo received at
08:51:25 LT on May 5, 2021 observed at SG. (a) is the image of thehead echo portion. (b) is a copy of the head echo portion of (a), which
was used for the calculation of the Doppler shift.
Fig. 3. Frequency analysis images of the total reception of the meteor
echoes received at 06:18:00 LT on May 4, 2021 observed at TK by
Audacity (https://www.audacityteam.org/).

Fig. 4. (a) Frequency analysis image by Audacity, in which the headecho portion of Fig. 3 is enlarged and (b) is a copy of the head echo
portion of (a), which is used for the calculation of the Doppler shift.

receiver should be assumed to be at the same location for convenience.
In Figure 3, we show the frequency analysis images acquired
continuously by Audacity from the start to the end of reception of the meteor echo received at 06:18:00 LT on May 4,
2021, at TK. The duration of the trail echo from this meteor
was approximately 23 s. The (*) symbol in Figure 3 is thetransmitted direct wave line of 53.100000 MHz, which showsa slight reception. The distance between the transmitter andreceiver is 22.4 km, and Mt. Hongu is situated between them(Fig. 1(c)). Therefore, direct waves are not always received.
The dark line extending horizontally from the symbol (**) in
Figure 3 is the echo signal from the meteor trail. For the meteor
trail echo, the transmitting VHF radio wave is reﬂected by theionized column formed along the meteor path. Given that theionized components in the E region of the ionosphere move at
a rate of approximately 10–100 m s−1 (Bourdillon et al. 2005),
the Doppler shift should correspond to the velocity of ionizedcomponents. However, in such an echo case, the difference infrequency from the direct radio wave is negligible. Therefore,both the signal line indicating the reception of the direct radio
wave and the reception of the trail echo almost overlap eachother. In the last diagram of Figure 3, it can be seen that theecho signal, after repeatedly rising and falling, eventually disappears.
As shown by the symbol (***) in Figure 3, a pulse (presentedas ”Head echo”) that intersects the head of the trail echo withthe tilt orthogonal to the 53.100000MHz signal line was found.
which is a meteor-head echo. In Figure 4 (a) we present the frequency analysis image acquired by Audacity, in which the headecho portion of Figure 3 has been enlarged. As the authors usedbackscattered meteor radio observations, the highest reception
efﬁciency of the reﬂected wave occurred at the point where themeteor path (meteor trail) is orthogonal to the reﬂected radio
wave (f0 point, Fig. 6) (McKinley 1961). In accordance with
the Doppler effect, the frequency of the meteor head echo increased compared to the transmitted frequency when the meteor approached the f0 point, and it decreased when the meteor
moved away. With this particular meteor head echo, the largest
Doppler shift was 1.25 kHz before 0.0862 s from the f0 point,where the meteor velocity component in the line-of-sight direction was zero (Fig. 4 (b)).
The frequency analysis images acquired by Audacity of themeteor echo that was received at 08:51:25 LT on May 5, 2021,
at SG are shown in Figure 5 (a, b). The distance between theHK (transmitter) and SG (receiver) is only 4.53 km, and thetransmitted direct radio wave is always received at SG. Because
the frequency of the meteor trail echo is almost the same as thatof the transmitted direct radio wave, it is difﬁcult to distinguishthem. However, a pulse (presented as ”Head echo” in Fig. 5

id. 1A new simple method to observe Doppler shift of the meteor head echo

54, 2021 had a Doppler frequency of 1.25 kHz at 0.0862 s before reaching the f0 point, where the signal line of the transmitted frequency exists (Fig. 4 (b)). If this head echo corresponds to that of the Eta Aquarids meteor, its ground velocity
is 65.5 km s−1 , and the meteor moves 5.65 km in 0.0862 s to
the f0 point. The altitude of the radiant of Eta Aquarids meteor
is 49.◦ 8 at the received time (06:18:00 LT). Assuming that theheight of the f0 point is 93 km, which is the ordinary heightof the meteor echoes (McKinley 1961), θ in Eq. (1) was calculated to be 87.◦ 75 (Fig. 6 (a)). If these numbers are substituted
into Eq. (1),fd = 2 v cos θft /c= 2 × 6.55 × 104 × cos 87.◦ 75
× 5.31 × 107 / (3.00 × 108 )= 9.10 × 102 (Hz).

(2)

This Doppler frequency (9.10 × 10 Hz; Eq. (2)) agrees withthe experimental result (1.25 × 103 Hz) obtained from the frequency analysis with 73% accuracy. This result suggests thatthe received signal is the head echo of the Eta Aquarids meteor. It should also be noted that if the height of the f0 point is
90km, the Doppler frequency is calculated as 9.71 × 102 (Hz),and 100km, 8.50 × 102 (Hz). The experimental and geometricvalues were more consistent when the height was assumed to
be 90 km.
Similarly, the head echo of the meteor received at 08:51:25
LT on May 5, 2021, had a Doppler frequency of 1.31 kHz at
0.121 s before reaching the f0 point (Fig. 5 (b)). If this headecho corresponds to the Eta Aquarids meteor, its ground velocity is 65.5 km s−1 , which is similar to the former case. It
was calculated that the meteor moves 7.93 km in 0.121 s to the
f0 point. The altitude of the radiant of the Eta Aquarids meteor
was 49.◦ 4 at the received time (08:51:25 LT), and assuming thatthe height of the f0 point is 93 km, θ in Eq. (1) was calculated
to be 86.◦ 82 (Fig. 6 (b)). If these numbers are substituted into
Eq. (1),
2

Fig. 6. Relation between the real paths and the Doppler frequencies of
two Eta Aquarids meteors whose head echoes were observed. Eachvalue was calculated assuming that both the meteors belong to Eta
Aquarids (radiant: right ascension is 337.◦ 5, and declination is −1.◦ 1;
ground velocity: 65.5 km s−1 ) (a) is the meteor echo received at
06:18:00 LT on May 4, 2021. (Fig. 3, Fig. 4) (b) is the meteor echo
received at 08:51:25 LT on May 5, 2021. (Fig. 5)(a)) that intersects the head of the trail echo with a tilt orthogonally close to the 53.100000 MHz signal line (similar to Fig.
3 and Fig. 4) was detected, which is also a meteor head echo.
With respect to this meteor head echo, the largest Doppler shift
was 1.31 kHz before 0.121 s from the f0 point (Fig. 5 (b)).
4. Discussion
In the present study, a continuous wave was transmitted to
the zenith to receive a meteor head echo. Assuming that boththe transmitter and receiver are located at the same point, theDoppler shift due to moving a meteoroid can be expressed by
Eq. (1) (Merrill 2002). If the Doppler frequency fd is observed, the meteor velocity component in the line-of-sight direction v cos θ can be estimated. Furthermore, if the angle θ
between the direction of the meteor’s movement (meteor path)and the line-of-sight direction of the meteor can be determined,
the ground velocity v of the meteor can be determined.
fd = 2 v cos θft /c,(1)where fd is the Doppler frequency (Hz), v is the ground velocity (m s−1 ) of the meteor, θ is the angle between the directionof the meteor’s movement and the direction of the line of sightof the meteor (degree), ft is the transmitted frequency (Hz),and c is the velocity of light (m s−1 ).
The ground velocity of the Eta Aquarids meteor is v =6.55 × 104 m s−1 , the transmitted frequency is ft = 5.31 ×
107 Hz, and the velocity of light is c = 3.00 × 108 m s−1 .
The head echo of the meteor received at 06:18:00 LT on May

fd = 2 v cos θft /c= 2 × 6.55 × 104 × cos 86.◦ 82
× 5.31 × 107 / (3.00 × 108 )= 1.29 × 103 (Hz).

(3)

This Doppler frequency (1.29 × 10 Hz; Eq. (3)) agrees wellwith the experimental result (1.31 × 103 Hz) obtained fromthe frequency analysis with 98% accuracy. The result strongly
suggests that the received signal is the head echo of the Eta
Aquarids meteor. Similarly, on this meteor, if the height of
the f0 point is 90 km, the Doppler frequency is calculated as
1.33 × 103 Hz, and 100 km, 1.17 × 103 Hz. The experimental
and geometric values were the most consistent when the height
was assumed to be 90–93 km.
35. Conclusions
By utilizing continuous VHF radio waves (ham radio), twohead echoes from the Eta Aquarids meteors were detected at
a location in close proximity to the transmitter, Japan, in May
2021. The Doppler shifts of the moving head echoes of the me-6

K. Suzuki and Y. Katohteors were determined using freely available frequency analysis
software. The Doppler shift calculated from the meteor headecho agreed well with the data obtained from the position of
the meteor’s actual path using the known physical parametersof the Eta Aquarids meteors.
To our knowledge, this is the ﬁrst detailed report of a
Doppler shift of a meteor’s head echo using ordinary low-costand low-power ham radio devices. Our results suggest that it
may be possible to estimate some physical parameters of themeteor. Assuming that meteor head echoes can be observed at
multiple points simultaneously using this new simple method,
the position and ground velocity of a meteor can be estimated.
This system will help us ﬁnd the path of a meteorite during
daytime or on cloudy days.
6. Acknowledgements
The authors would like to thank Dr. T. Watanabe for his
advice and suggestions regarding the physics and radio astronomy of meteors. The authors are also grateful to Mr. S.
Okamoto, Ms. M. Kobayashi, and several members of Tsukude
Observatory for their help and encouragement in this study.
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