AMTAtmospheric Measurement TechniquesAMTAtmos. Meas. Tech.1867-8548Copernicus PublicationsGöttingen, Germany10.5194/amt-10-527-2017VHF antenna pattern characterization by the observation of meteor head echoesRenkwitzToralfrenkwitz@iap-kborn.deSchultCarstenLatteckRalphhttps://orcid.org/0000-0002-0001-7473Leibniz-Institute of Atmospheric Physics, Schloss-Str. 6, 18225 Kuehlungsborn, GermanyToralf Renkwitz (renkwitz@iap-kborn.de)14February201710252753528September20167October201613December201627December2016This work is licensed under a Creative Commons Attribution 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/This article is available from https://amt.copernicus.org/articles/10/527/2017/amt-10-527-2017.htmlThe full text article is available as a PDF file from https://amt.copernicus.org/articles/10/527/2017/amt-10-527-2017.pdf
The Middle Atmosphere Alomar Radar System (MAARSY) with its active
phased array antenna is designed and used for studies of phenomena in the
mesosphere and lower atmosphere. The flexible beam forming and steering
combined with a large aperture array allows for observations with a high temporal
and angular resolution. For both the analysis of the radar data and the
configuration of experiments, the actual radiation pattern needs to be known.
For that purpose, various simulations as well as passive and active
experiments have been conducted. Here, results of meteor head echo
observations are presented, which allow us to derive detailed information of
the actual radiation pattern for different beam-pointing positions and the
current health status of the entire radar. For MAARSY, the described method
offers robust beam pointing and width estimations for a minimum of a few days
of observations.
Introduction
The Middle Atmosphere Alomar Radar System (MAARSY) was built in 2009/2010 by
the Leibniz-Institute of Atmospheric Physics (IAP) on the northern Norwegian
island Andøya (69.3∘ N, 16.04∘ E) for improved studies of
various atmospheric heights at high spatial and temporal resolution. The main
target regions are the troposphere/lower stratosphere and the
mesosphere/lower ionosphere, typically 1–25 and 50–120 km,
respectively.
MAARSY's main active phased antenna array consists of 433 yagi antennae (see
Fig. ), which are connected to their individual transceiver
modules, allowing for independent phase and amplitude control. Such a
configuration allows for both flexible pulse-to-pulse steering and forming of
the radar beam by appropriately selecting amplitude and phase distribution
over the array elements. A detailed description of the radar and its
properties is given by , while recent geophysical investigations
with MAARSY regarding layered phenomena in the mesosphere have been presented
in and .
The knowledge of the current radiation pattern characteristics is important
for both the design of experiments, e.g. specific experimental settings, and
is even more crucial for the analysis of radar data. The most important
points to know are the beam-pointing accuracy, shape and width of the beam,
the antenna gain and the position and intensity of side lobes.
Sketch of MAARSY's main antenna array, consisting of 433 yagi
antennae. The anemone subarray groups A, C, E and M, each composed of
49 antennae, are individually colour coded, while 7 antennae form a hexagon,
e.g. D-01. Besides the total antenna array, the subarray groups marked in
grey are used for reception in the examined experiment mst006.
For the validation of MAARSY's radiation pattern, various passive and active
experiments were already conducted. In passive experiments, cosmic radio
emissions from our galaxy, as well as distinct radio sources like radio
galaxies, supernova remnants and the diffuse background, were observed.
Subsequently, the derived intensity maps covering a northern declination from
10 to 90∘ were compared to the detailed temperature Global Sky Model by , using a reference map involving
the simulated radiation pattern of MAARSY. The simulation of MAARSY's
radiation pattern considering the mechanical structure, soil properties and
antenna coupling were performed using the well-accepted Numerical
Electromagnetics Code (NEC 4.1) for different arctic weather conditions. This
enabled us to derive the pointing accuracy and beam width for different
antenna array sizes and estimated the antenna array gain by
knowing the absolute intensity flux of the observed radio sources
. Furthermore, observations of distinct radio sources
like Cassiopeia A allow absolute phase calibration for the individual
subgroups of an antenna array as described for MAARSY in .
Knowledge of the individual antenna array subgroup phases is essential for
integrating them into synthetic arrays, providing different beam shapes and
widths as well as the interferometric analysis of the data, e.g. to locate
the mean angle of arrival of the radar echo.
Additionally, active experiments were conducted in which the Earth's moon and
large artificial satellites were used as radar targets, as described in
, as well as scattering off a sounding rocket's payload
more recently. In general, these experiments have shown
a good agreement with the simulated radiation pattern, though some
discrepancies have been found in the estimated beam widths and negligible
inaccuracy of the beam pointing. The cause for the slightly increased beam
width was assumed to be a matter of the existing mixed polarization during
the system upgrade in 2012/2013, converting from linear to circular
polarization. This widening of the radiation pattern was also indicated in
thorough NEC simulations.
In this paper we present the methodology that has been used to augment our
knowledge of the actual three-dimensional radiation pattern of the MAARSY
radar by analysing meteor head echo observations. Here, the main aim is to
present a robust approach to estimate and validate the simulated radiation
pattern using the angularly resolved statistical distribution of meteor head
echo trajectories.
For specular meteor radars, the angular distribution of detected trails
allows us to map the general coverage of the used radars. This coverage
distribution can be seen in wide-beam meteor radars using, e.g. one single
beam , multiple beams like the SAAMER/DRAAMER installations
, but also in narrow-beam antenna arrays like
the MU radar . The observation of specular meteors,
however, does not allow the actual beam shape to be derived, but gives an
indication of the maximum radial coverage off the nominal pointing direction.
This is caused by the necessity of having perpendicularity between the
emitted radio wave and the meteor trajectory. With this, for specular meteors
only one single point of the plasma trail perpendicular to the radar beam is
seen for the duration of the event.
Thus, only a subset of all existing meteors are seen by a single monostatic
specular meteor radar. Furthermore, most of the specular meteors are
typically seen around 50∘ elevation angle and below due to the
increasing observation volume for the meteor ablation heights. Especially,
for the zenith-near directions, the geometry for suitable meteor trajectories
perpendicular to the radio wave is very limited. Thus, the angular
statistical appearance of specular meteors cannot be used for the beam
pattern validation.
However, the perpendicularity requirement does not hold for the observation
of meteor head echoes when the plasma around the meteor head acts as an
isotropic scatterer. This allows echoes for every single pulse to be emitted
by the radar towards the meteor head on its trajectory through the dense
ionosphere, namely the E and D regions. Therefore, meteor head echoes can be
used to map the radiation pattern by the angular distribution of detected
echoes for a certain amount of time. Meteor head echoes, however, are
severely weaker than specular meteor echoes scattering off the meteor trail
and therefore high-power large-aperture radars are needed to compensate for
the lower efficiency of this scattering process. Meteor head observations are
described for various radar systems of sufficient power-aperture products,
e.g. in , , ,
, , and
.
In the following, section meteor head echo observations with MAARSY are
briefly described, followed by the methodology of this experiment using
meteor head echo observations for radiation pattern validation. The proposed
method is shown for two case studies in which MAARSY was operational with the
entire antenna array and for a short period when about 20 % of the array
was non-functional resulting in a distorted radiation pattern. The results
underline the exceptional value of this analysis to monitor the health status
of the radar as a byproduct of routine observations. Finally, a discussion
and conclusions are given.
Meteor head echo observations with MAARSY
The MAARSY radar is one of the few radar systems that are
capable of observing meteor head echoes as has been successfully demonstrated
during the Geminids meteor shower in 2010 . Contrary to
other radars that observed meteor head echoes on a campaign basis, MAARSY
recently completed its second year of nearly continuous observations. For
example, this extraordinarily rich meteor data set allows for the generation
of radiant maps and velocity distributions but, even more interestingly, for
the estimation of dynamical meteor masses seen by the radar and thus its
potential contribution to an improved meteor input function, which is
presented in detail in . The advantage of such meteor head
echo measurements by radars is their uniqueness, as they do not depend on
weather conditions or the time of day like optical instruments. For MAARSY,
meteor head echo observations are performed with either specialized or
multi-purpose experiments. The most interesting details of the multi-purpose
experiment used during the examined period are shown in Table .
Within this experiment, the troposphere and mesosphere regions were monitored
together. The echo intensity is typically derived for the entire antenna
array, while the radial and angular position of the meteor head echo
trajectories are derived by interferometric means using smaller subarrays.
For transmission, the entire antenna array was operated at maximum output power
without employing an amplitude taper. For reception, various subarrays, hexagons
and anemones comprising of 7 and 49 antennas respectively have been used for the interferometric analysis. The benefit of
using different sizes of subarrays and the baseline between them is connected
to their individual gain and beam width as well as the resulting
interferometric unambiguous angular range. The use of closely spaced smaller
subarrays (B-06, B-08, C-02; see array sketch in Fig. ), each with
a 30∘ beam width, facilitates an unambiguous angular range of
approximately 15.6∘. In addition, widely spaced anemone subarrays (A,
C, E, M), each with an 11∘ beam width, provide more gain in the main
beam direction. Thus, the closely spaced hexagons permit the rough angular
location of the event, while using the anemones allows for the detection of
weaker events, as well as precise phase and thus position information of the
observed target with their longer baseline lengths.
Details of the monitoring experiment mst006 also used to observe
meteor head echoes, accompanied by the list of used subarray groups (see
Fig. for comparison). The antennae Y1, Y2, Y3 and ALW64 are
external antennae and are not used in this study.
Example of a long lasting and intense meteor head echo observed with
MAARSY on 18 January 2016 at 12:46 UT. (a) Detected signal-to-noise
ratio, (b) trajectory of the meteor in colour-coded altitude for
zenith angles θx and θy. Black and red circles indicate
the position of the first and second null and side lobes of the radiation
pattern. The red asterisk mark an arbitrary position of a specular meteor
event.
In Fig. is an extraordinary long lasting and intense example of
meteor head echoes observed with MAARSY. In the left panel is the
signal-to-noise ratio, while in the right panel the angularly resolved
trajectory of this meteor event with colour-coded altitude is depicted.
Additionally, the first and second null and side lobes of the MAARSY two-way
radiation pattern are marked with black and red circles. This specific meteor
event was seen from roughly 105 km down to 82 km altitude,
traversing MAARSY's first side lobe. In contrast to the meteor head echo
trajectory, a single arbitrary point was added, marked by a red asterisk,
which would be seen for a specular meteor event.
Due to the high velocity of the observed targets the received signals need to
be decoded Doppler-corrected for the individual complementary codes to ensure
proper reconstruction of the signals and thus the individual meteor
trajectory see e.g.and references
within.
The detected power of meteor head echoes for the same radar parameters vary
significantly from one event to the other due to the meteor's orientation and
entry velocity to the Earth atmosphere, its size and composition, which
therefore requires normalization of the individual data. First attempts to
use normalized meteor head echo intensities for some events observed with
MAARSY were compared to simulated radiation pattern cross sections as
described in . Here, quite good agreement for the main beam and
the first side lobe were found, both in shape and width. However, as
previously quoted, this approach was limited to the piecewise comparison of a
few individual meteor trajectories.
Methodology and experiment
The initial premise for this study was to automatically analyse the
trajectory data without additional discrimination or selection of individual
meteor head echo events and their trajectories. The detected intensities, or
better the sufficient signal-to-noise ratio, is a necessary requirement for
the calculation of the trajectory, but is not used in the subsequent analysis
described here. Contrary to the previously mentioned method of inferring the
two-dimensional radiation pattern from the detected intensities of selected
meteor trajectories, here the statistical occurrence of trajectory points per
defined angular bin is used to deduce the three-dimensional radiation
pattern.
The assumption is that, as long as the radar parameters, especially beam
pointing and width, are not changed significantly, the radiation pattern
should be reflected in the angular occurrence of the events. As previously
noted, the detectability of meteor head echoes depends on the volume
illuminated by the radar and the reception depends on the selection of
subarray groups (beam width, gain), but also on the available baselines to
recover the unambiguous position of the meteors. Thus, the angular
occurrence, or count rate, of the meteor head echo positions within the given
unambiguous angular range is only determined by the actual radiation pattern.
The data we use in this study were collected with the MAARSY radar between
1 December 2013 and 26 February 2014 with the monitoring experiment mst006
(see Table ). With this experiment radar measurements in two
distinct beam directions were performed, pointing towards zenith and
off-vertical towards ϕ=185∘, θ=12.4∘.
For the reliable reconstruction of a meteor's trajectory a minimum of 11
points are defined, but may consist of a few hundred points for larger, but
rare, examples as previously shown in Fig. . During the entire
period, the average length of derived trajectories accounts for 28 points.
For this experiment, the occurrence of all derived meteor trajectory points
are calculated for angular bins of a resolution of 0.2 × 0.2∘
resolution and ablation heights of 85 to 115 km are used. The
increasing volume for greater zenith angle off-sets is negligible for zenith
near directions, <0.1dB for 5∘, but more crucial for
θ=15∘ accounting for -0.3 dB. The resulting occurrence map
is smoothed (9-point-median) and interpolated where necessary to derive the
complete three-dimensional intensity and shape of the main beam and the first
side lobes as well as the beam width.
During the period studied here, on 31 December one of the six containers housing the radar
hardware for the anemone group F and two hexagon groups of the centre anemone
M were not operational for either reception or transmission, but operation
was restored on 7 January. This period of restricted operability is
individually investigated to underline the reliability and sensitivity of
this method.
Angular occurrence of meteor head echo trajectories for a period of 3 months
For the nearly 3 months of full functionality in total, 141 118 meteor head
echo trajectories, accounting for more than 4×106 trajectory points
for the zenith beam and the southwards tilted beam, were derived and used to
generate angular occurrence maps.
The calculated occurrence of meteor trajectories for the zenith pointing
radar beam is depicted in Fig. . The occurrence map is accompanied
by contour lines of the simulated two-way radiation pattern. While the entire
antenna array, superposed of 433 nominal antennae, are used for transmission,
the latter 49 antenna subgroups are the largest directly sampled subarrays of
MAARSY and are used on reception for the final interferometric examination of
the trajectory estimation. A very similar distribution was derived for the
tilted radar beam, pointing to ϕ=185∘, θ=12.4∘,
but it is not shown separately as no additional information is apparent.
Angular occurrence rate of meteor head echo trajectory points for
zenith beam pointing observed with MAARSY during a period of almost 3 months
and overlaid by the simulated radiation pattern.
As for MAARSY, every array element has its own transceiver module that
sensitively reacts to the adjacent antennae and their emissions. For example,
in the case of unfavourably superposed mutual coupling of the antennae
resulting in excessive reflected power, the monitoring circuitry temporarily
disables modules during the experiments. Additionally, in some cases
amplifier modules may get damaged over time, but are repaired during the next
maintenance. The health status of MAARSY's transmitter modules is stored in a
database, which for the period analysed in this paper unfortunately got lost
due to a hard disk failure. Therefore, we performed thorough simulations in
which nearly 5% of the array elements were disabled (quasi-randomly
distributed). These simulations should better match MAARSY's health status
during that period and actually also predict a better agreement with the
observations. Initial simulations incorporating all 433 antennae have shown a
lower side lobe attenuation of about 3 dB.
For both cases, the occurrences agree well to the simulated radiation pattern
for the main lobe and first side lobe, which is highlighted in
Fig. . There, the cross sections in the north–south and
east–west planes for both beam directions are shown as well as the simulated
pattern reference.
The observed beam shape and width for both pointing directions match the
simulations, while a slight broadening is seen for the tilted beam, which is
caused by a decrease in the effective antenna area. The broadening factor can
be estimated by the cosine of the off-boresight pointing, which agrees to the
observed broadening of 0.1∘. Besides this, a slight beam-pointing
error of approximately 0.1∘ towards the south-west is visible in the
figure.
Cross sections through the angular occurrence rate for both
beam-pointing directions, ϕ=0∘, θ=0∘ (blue) and
ϕ=185∘, θ=12.4∘ (black) with respect to their
nominal position, compared to the simulated radiation pattern (magenta).
A precise beam-pointing estimation was achieved by calculating the median of
all original trajectory points, before sorting the data into 0.2∘
bins. The beam-pointing positions for the entire period of proper operation
were calculated to ϕ=246.7∘, θ=0.12∘ and
ϕ=185.6∘, θ=12.47∘ for the zenith pointing and
tilted beam. The offset of the nominal beam pointing may consistently be
accounted for by setting both beam directions to 0.12∘ south-west of
the initial direction.
Estimated radiation pattern for a period of a few days
Contrary to the previous section, in which the MAARSY radar was in normal
operation nominally using the entire antenna array, here the period from 1 to
late 7 January 2014 is investigated. During that period, container F failed
and therefore 20 % of the antenna array was not available (subarray
groups F-01 to F-11; see Fig. ). This inoperability affected the
transmission and reception, in addition to the illumination of the target
volume and loss of the hexagon F-09, which is also sampled for potential
interferometric use. The latter does not affect the recovery of the meteor
trajectories as the explicit hexagon is not part of the smallest essential
baseline group (B-06, B-08, C-02).
For this period of 1 week, approximately 250 000 reliable trajectory points
for each beam-pointing direction were derived and analysed. The occurrence
map for this period for the tilted beam is shown in Fig. , while
the vertical beam is the same. As in the earlier figures, the occurrence maps
have been superimposed by the simulated radiation pattern. For a horizontal
cut through the main beam, i.e. contour line (yellow) of -13 dB,
the normally circular shape of the main beam is clearly deformed to an oval
shape due to the large proportion of inactive antennae. The longer axis of
the oval is oriented along the direction of the missing array elements,
north-west–south-east, which agrees with the inverse relationship of beam
width and maximum extent of incorporated array elements. For both beam
directions, the occurrence maps appear to be similar in terms of shape and
spread around the nominal beam-pointing direction. This underlines the proper
function of the remaining radar hardware and antenna array in use and allows
for the detailed analysis shown in Fig. . In the left panel the
south–north cross section is shown for both beam-pointing directions with
respect to their nominal beam-pointing position, while in the right panel the
south-west to north-east cross section is depicted. The latter is especially
interesting as the prominent side lobes are generated in these directions,
seen in both the observations and the simulations. For both beam-pointing
directions the simulated pattern proposes less side lobe suppression than we
actually see in this analysis, especially for the south-west–north-east
cross section, though they still agree fairly well for the south–north cross
section. It is worth noting that earlier observations of scattering off a
sounding rocket's payload , however, indicated a better
agreement of side lobes' intensity to the simulations. The position of the
first null, especially for the SW–NE cross section, seems to be slightly
shifted outwards.
Angular occurrence rate for the tilted beam (ϕ=185∘,
θ=12.4∘) overlaid by the simulated radiation pattern for
January 2014 when about 20 % of the antenna array was non-functional.
Cross sections through the angular occurrence rate for both beam
directions compared to the simulated radiation pattern for the period of
1–8 January 2014. The simulated and estimated beam widths are shown at the
bottom.
To complement the earlier findings and to underline the sensitivity of the
described method, the occurrences of meteor trajectory points for 15 December
2013 for both beam-pointing directions ϕ=0∘, θ=0∘
and ϕ=185∘, θ=12.4∘ are depicted in
Fig. . On that day, about 2850 meteor head echo trajectories,
consisting of 82 000 points, were derived in total for both beam directions.
The high number of detected trajectories and visible distinct spurs next to
the main beam positions are related to the day of these measurements around
the maximum of the Geminids meteor shower. The detected distribution already
matches the Gaussian-like shape of the radiation pattern fairly well, but for
the precise derivation of parameters like beam width a larger data set should
be used. With the assumption of pattern symmetry and referencing to the
centre of the beam, it would be possible to average the occurrences in
azimuth to overcome the low count rates. However, the median beam-pointing
direction for this single day is estimated to be about 0.17∘
south-westwards off the nominal direction, which is in good agreement with
the value estimated for the entire period of nearly 3 months.
Angular occurrence of meteor head echo trajectory points observed on
15 December 2013 for two beam-pointing directions, ϕ=0∘,
θ=0∘ and ϕ=185∘, θ=12.4∘.
Discussion
The described method seems to be suitable for deriving the actual radiation
pattern by analysing the occurrence of meteor head echo trajectory points.
For the rough estimation of the pattern, we have shown occurrences for just a
single day. Although it occurred during the maximum of the Geminids shower,
it proved the general reliability of the method. Of course, it is certainly
recommended to use as much data as is available to improve the statistics for
both the reconstruction of all individual trajectories and the parameters
derived from the total occurrences.
Altogether, the estimated beam widths for the individual periods correspond
well to the simulation, though a minor broadening can be distinguished.
Broadening can be caused by amplitude tapering (typically used to gain
additional side lobe suppression, which was not consciously applied, as well
as missing active antennae at the rim of the antenna array) or improper phase
distribution. Besides the beam width, other remarkable points in the
radiation pattern are the position and attenuation of nulls. The first null
next to the main lobe, at about 4.3∘, is clearly seen in the
simulations, but is not as pronounced in the observations for the initially
presented period of nominal functionality. A potential cause of this inferior
behaviour is assumed to be connected to random phase and amplitude variations
over the antenna array. However, the position of the first null for the
south-west–north-east cross section is well accentuated for the shown period
when container F failed and thus 20 % of the transceiver modules were
inoperable. As previously noted, at times transceiver modules and their
antennae randomly distributed over the antenna array are temporarily or
permanently disabled. As the database of transceiver modules' health status
was lost, we assumed a quasi-random distribution of nearly 5 %
non-functional array elements in the simulations. These missing array
elements modify the ideal radiation pattern, but are repaired during the next
regular maintenance of the radar. With these assumed missing elements, the
detected side lobe intensities agree better than with the radiation pattern
of the entire array of nominal functionality. For the period in which about
20 % of the antenna array were inactive, higher discrepancies are seen in
the south-west–north-east cross section, perpendicular to the orientation of
reduced array diameter. Furthermore, the detected and simulated beam widths
differ slightly during that time, which is likely caused by the comparably
small data set and uncertainties in the radar's health and thus in the
simulations.
In , the influence of malfunctioning transceiver modules,
and thus the temporary loss of antenna array elements, was examined in
addition to random amplitude and phase errors of all array elements. For the
loss of 21 randomly distributed antenna modules a beam broadening of up to
0.2∘ was seen, while the position of the side lobes were mostly
unchanged and only their absolute amplitudes varied. For random amplitude and
phase errors (±1 dB and ±10∘) a negligible beam broadening
was seen, but the intensity and positions of side lobes were significantly
modified. Therefore, the estimated minor discrepancies seem to be well in
line with the previously mentioned study.
With the unambiguous interferometric angular range of maximum 15.6∘
around the nominal beam position in this experiment, the main lobe and first
three side lobes of transmit radiation pattern should be covered. A plausible
flaw might origin from intense meteor head echoes originating from
18∘ off the main beam, corresponding to the third radiation pattern
side lobe. Such meteor head echoes are likely misplaced within the
unambiguous angular range, impairing the derived occurrence maps. However,
with the reasonably well-shaped form of the main and side lobe derived from
the occurrence rates, the meteor positions generally seem to be recovered
reliably, which is connected to correct decoding and unwrapping of observed
phases between the individual small subarrays used in the interferometric
analysis. A systematically flawed determination of the meteor trajectories
would directly result in an anomalous shape of the contour maps. However,
minor phase errors and temporary variations result in slightly wrong
localization of the echoes, which likely also spoil the nulls in the
radiation pattern.
Still, the most likely cause of the seen overestimated side lobe attenuation
is probably related to the initial detection of meteor events, which is
performed on the data of the entire antenna array. Meteor events off the
nominal beam direction are already less frequently seen within the entire
antenna array than with a smaller subarray like the anemones. The reasoning
for the initial detection of meteor events using the entire array is related
to the high likelihood of also detecting the same event in all subarrays.
Complementing the initial meteor detection by also searching in the anemone
and hexagon data might provide a higher number of meteor events off the
nominal beam position.
The beam-pointing accuracy was consistently estimated to be in the order of
0.12∘ south-westwards off the nominal beam direction for all examined
data. A potential cause might be a slightly flawed phase calibration of the
individual subarrays or the calibration of the radar containers housing the
equipment of the individual subarrays. However, the effect of this error
seems to be negligible as the nominal half-power beam width is almost 40
times larger.
Other radar experiments facilitating an equivalent quality to verify the
radiation pattern depend on either distinct scattering structures of known
properties, which are rare for the wavelength used here, or highly sensitive
receive-only observations of cosmic radio emissions and the ability to
perform angular scans. With this, the generation of meteor head echo
occurrence maps as a byproduct within standard monitoring experiments seems
to be very adjuvant, provides valuable information about the health status of
the radar and validates the radiation pattern.
Conclusions
In this paper, we presented analysis results for two periods of meteor head
echo observations. The continuous operation of MAARSY with a multi-functional
monitoring experiment also allows meteor head echoes to be extensively
observed. The observation of meteor head echoes with MAARSY is motivated by
performing the first continuous meteor head echo measurements, e.g. to derive
the climatology, radiant maps, dynamical meteor masses and to investigate
meteor showers in detail. As a byproduct of this rich data set, the deduction
of the radiation pattern was envisaged.
Earlier methods related the detected intensities of individual meteor head
echo trajectories in piecewise comparisons to cross sections of the simulated
radiation pattern. Contrary, the method described here relies only on the
derived positions of the meteor head echo trajectories, but not on the
detected intensities. The angular distribution of meteor head trajectories
and count rates for 0.2 × 0.2∘ bins are determined and
occurrence maps are generated. These occurrence maps are assumed to be highly
equivalent to the combined two-way radiation pattern.
For the cases shown in this study, a zenith beam and a 12.4∘ tilted
beam were used during normal operation of the entire array and a period when
about 20 % of the transceiver modules failed, which mainly influenced the
transmission pattern. The occurrences during these periods and the individual
beams were compared to the simulated radiation pattern, which revealed a
remarkable good agreement. Especially, for the 1-week period of restricted
functionality, the derived occurrence map matches exceptionally well to the
simulations with its deformation of the main lobe and emerging side lobes. A
minor deficiency seems to be existent in the derived absolute intensity of
the side lobes, which is most likely related to the involved meteor detection
method basing on the measurements with the entire antenna array.
Nevertheless, the obvious performance of this method makes it to a very
sensitive and reliable tool to monitor the radar system's health as a
byproduct, which was underlined by the occurrence map derived for just one
day.
Acknowledgements
The authors explicitly acknowledge the contribution of Jorge L. Chau for
adjuvant discussions and suggestions related to the interferometric analysis
in general and to meteor head echo observations as well as Svenja Sommer who
was involved in deriving absolute calibration phases for MAARSY. Furthermore,
we express our gratitude to the Andøya Space Center for their permanent
support for the operation and maintenance of the MAARSY radar. The radar
development was supported by the German grant 01 LP 0802A of
Bundesministerium für Bildung und Forschung, while the meteor head echo
observations are supported by the grant STO 1053/1-1 of the Deutsche
Forschungsgemeinschaft (DFG). We also like to thank the referees for giving
valuable comments to improve this paper.
Edited by: M. Rapp Reviewed by: two anonymous referees
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