=Paper=
{{Paper
|id=Vol-2406/paper3
|storemode=property
|title=Towards the Tunka-Rex Virtual
Observatory
|pdfUrl=https://ceur-ws.org/Vol-2406/paper3.pdf
|volume=Vol-2406
|authors=Pavel Bezyazeekov,Nikolai Budnev,Oleg Fedorov,Oleg Gress,Oleg Grishin,Andreas Haungs,Tim Huege,Yulia Kazarina,Matthias Kleifges,Dmitriy Kostunin,Elena Korosteleva,Leonid Kuzmichev,Vladimir Lenok,Nima Lubsandorzhiev,Stanislav Malakhov,Tatiana Marshalkina,Roman Monkhoev,Elena Osipova,Alexander Pakhorukov,Leonid Pankov,Vasily Prosin,Frank Gerhard Schröder,Dmitry Shipilov,Alexey Zagorodnikov
}}
==Towards the Tunka-Rex Virtual
Observatory==
https://ceur-ws.org/Vol-2406/paper3.pdf
Towards the Tunka-Rex Virtual Observatory
Pavel Bezyazeekov1 , Nikolai Budnev1 , Oleg Fedorov1 , Oleg Gress1 , Oleg
Grishin1 , Andreas Haungs2 , Tim Huege2,3 , Yulia Kazarina1 , Matthias
Kleifges4 , Dmitriy Kostunin5 , Elena Korosteleva6 , Leonid Kuzmichev6 ,
Vladimir Lenok2 , Nima Lubsandorzhiev6 , Stanislav Malakhov1 , Tatiana
Marshalkina1 , Roman Monkhoev1 , Elena Osipova6 , Alexander Pakhorukov1 ,
Leonid Pankov1 , Vasily Prosin6 , Frank Gerhard Schröder2,7 , Dmitry Shipilov1 ,
and Alexey Zagorodnikov1
1
Institute of Applied Physics ISU, Irkutsk, Russia
2
KIT, Institut für Kernphysik, Karlsruhe, Germany
3
Astrophysical Institute, Vrije Universiteit Brussel, Pleinlaan 2, Brussels, Belgium
4
Institut für Prozessdatenverarbeitung und Elektronik, KIT, Karlsruhe, Germany
5
DESY, Zeuthen, Germany
6
Skobeltsyn Institute of Nuclear Physics MSU, Moscow, Russia
7
Bartol Research Inst., Dept. of Phys. and Astron., Univ. of Delaware, Newark, USA
Abstract. The Tunka Radio Extension (Tunka-Rex) is a cosmic-ray
detector operating since 2012. The detection principle of Tunka-Rex is
based on the radio technique, which impacts data acquisition and storage.
In this paper we give a first detailed overview of the concept of the
Tunka-Rex Virtual Observatory (TRVO), a framework for open access
to the Tunka-Rex data, which currently is under active development
and testing. We describe the structure of the data, main features of the
interface and possible applications of the TRVO.
Keywords: Cosmic rays · Radio detectors · Virtual observatory · Open
data · Tunka-Rex · Tunka-Rex Virtual Observatory
1 Introduction
Following the approach chosen in the German-Russian Astroparticle Data Life
Cycle initiative (GRADLCI) [1] we are preparing to publish the data of the
Tunka Radio Extension (Tunka-Rex) experiment under a free data license.
Tunka-Rex is a digital antenna array located at the Tunka Advanced Instru-
ment for cosmic rays and Gamma Astronomy (TAIGA) observatory [2,3]. The
TAIGA setups can be divided in two main classes of installations: dedicated to
cosmic rays (Tunka-133 [4], Tunka-Rex [5] and Tunka-Grande [6]) and dedicated
to gamma rays (Tunka-HiSCORE [7] and TAIGA-IACT [8]). In Fig. 1 one can
see the layout of the facility and note that the cosmic-ray setups are grouped
in clusters: 19 clusters in a dense core and 6 satellite clusters. Each core cluster
is equipped with 3 Tunka-Rex antenna stations, while satellite clusters contain
one antenna station, each, and no Tunka-Grande scintillators.
Tunka-133
Tunka-Rex
Tunka-Grande
TAIGA-HiSCORE
TAIGA-IACT
Tunka-21cm
500 m
Fig. 1. The layout of the TAIGA setups as of 2019. The antenna stations are depicted
as crosses (the Tunka-21cm array is depicted by a single marker due to scale of the
map). The layout and hardware configuration was changes several times during the
past years. Bottom: Photo of a single cosmic-ray cluster of the TAIGA facility. Lines
mark the cable connections.
~100 events per season commission of ~1000 events per season
triggered by Tunka-133 Tunka-Grande triggered by Tunka-133 and Tunka-Grande
with
18 antennas 25 antennas 44 antennas 63 antennas open data
2012 2013 2014 2015 2016 2017 2018+
Fig. 2. The antenna array has been commissioned in 2012 with 18 antenna stations
triggered by the Tunka-133 air-Cherenkov detectors. Since the commissioning of Tunka-
Grande in 2014-2015, Tunka-Rex additionally receives a trigger from Tunka-Grande
(during daytime measurements). Starting from 2018, we are working on the public
access of Tunka-Rex software and data.
For the time being, Tunka-Rex consists of 57 antenna stations located in the
dense core of TAIGA (1 km2 ) and 6 satellite antenna stations expanding the
sensitive area of the array to 3 km2 . Tunka-Rex has been commissioned in 2012
with 18 antenna stations triggered by the air-Cherenkov array Tunka-133. In
the following years, Tunka-Rex was upgraded several times. The TAIGA facility
was enhanced by the Tunka-Grande scintillator array providing a trigger for
Tunka-Rex since 2015. One can see the timeline of the Tunka-Rex development
in Fig. 2.
Each Tunka-Rex antenna station consists of two perpendicular active Short
Aperiodic Loaded Loop Antennas (SALLA) [9] pre-amplified with a Low Noise
Amplifier (LNA). Signals from the antenna arcs are transmitted via 30 m coaxial
cables to an analog filter-amplifier, which cuts the frequency band to 30-80 MHz.
The filtered signal is then digitized by the local data acquisition system (DAQ)
with a 12 bit-sampling at a rate of 200 MHz; the data are collected in traces of
1024 samples each. Each element of this signal chain has been calibrated under
laboratory conditions, which resulted in the instrument response function (IRF)
defining the resulting digital traces recorded by the DAQ (see Fig. 3) For the
reconstruction of the original signal, the inverse IRF is convoluted with the raw
data. This convolution defines the data layers (DL) defined below.
The distinguishing feature of the broadband radio detectors is that they
can be used both for radio astronomy and astroparticle purposes (e.g. ultra-high
neutrino and cosmic-ray detection) depending on the configuration and operation
mode. For example, the core of the LOFAR antenna array has been successfully
applied for cosmic-ray detection [10]; meanwhile the proposed air-shower array
GRAND aims also at astronomy goals [11] Therefore, we will extend the concept
of KCDC [12] and implement additional features in our framework for open data,
which will result in the Tunka-Rex Virtual Observatory (TRVO).
2 Structure of the Tunka-Rex data
In this section we provide a general description of the Tunka-Rex data types,
their structure, and their connection with the hardware of the experiment and
observed phenomena.
V (ν)=H(ν)E VLNA
VOC(ν)=H(ν)E(ν) Filter V
E-FieldOC SALLA LNA ADC
Cables
Fig. 3. Scheme depicting the instrument response function (IRF). The incoming radio
signal is received by the antenna, passes through electronics and cables, and is recorded
by the ADC. For details see Ref. [5].
2.1 Antenna station data
As described above, raw Tunka-Rex data consist of traces recorded for each
antenna from the DAQ buffer after receiving an external trigger. The data on
an antenna station can be described by the following fields:
– Trace ID: unique identifier of the trace
– Antenna ID: identifier of the antenna station, enumerated with the follow-
ing convention: 1-25 (1st generation), 31-49 (2nd generation), 61-79 (3rd
generation)
– Timestamp: float number of the GPS time of the event with nanosecond
precision
– Version: the version of the data release (DR)
– Traces: serialized arrays (two channels or three electric-field components)
each with 1024 elements, either integer of float number depending on the DL
– Flags: additional flags describing the status of the antenna station, e.g.
operation, malfunction, calibration, etc.
As will be described below, DL0-2 differs only in the way of the representation
of the Traces field.
2.2 Calibration data
The calibration data defines the instrument response function and is used for sim-
ulation and for reconstruction. Moreover, it reflects the location of the antenna
station (antennas can be re-located and re-aligned) and its hardware configu-
ration, since some components were occasionally replaced due to malfunction.
Thus, each antenna station is described by the following calibration data:
– Commission: timestamp of the commission of configuration
– Decommission: timestamp of the decommission of configuration
– Antenna ID: identifier of the antenna station (identical to ID in raw data)
– LNA ID: identifier of the low noise amplifier
– Filter ID: identifier of the filter-amplifier
– X, Y, Z: coordinates of the antenna station in local coordinates
– Alignment: alignment of the antenna station with respect to the magnetic
North (the initial alignment of 45◦ slightly changed over time)
Besides these time-dependent properties of the antenna station, the calibration
is defined by the phase and gain response of the antennas and the signal chain.
2.3 Supplementary data
The supplementary data describe observation conditions, and are shared with
the other TAIGA setups. A detailed description of this type of data is given
in the same proceedings in Ref. [13]. The most important supplementary data
for Tunka-Rex are Trigger (operation mode, thresholds, online/offline clusters,
etc.) and Environment (temperature, pressure, humidity, magnetic field, etc).
2.4 Air-shower data
Since Tunka-133 and Tunka-Grande, which provide the trigger for Tunka-Rex,
feature an independent reconstruction of air-shower events, the combination of
the data from all three setups can improve the reconstruction of the primary
cosmic ray. The data structure for the particle detectors is described and im-
plemented in the frame of KCDC, and the Tunka-Grande event reconstruction
perfectly fits to this system. Because Tunka-133 and Tunka-Rex perform calori-
metric measurements, their fields differ and are described as:
– UUID: universally unique identifier1 of the event. The UUID is chosen in order
to avoid collisions during distributed data acquisition
– Timestamp: float number of the GPS time of the event with nanosecond
precision
– Theta, Phi: Arrival direction (zenith and azimuth angles)
– X, Y, Z: Coordinates of the shower core
– Energy: Energy of the primary particle
– Xmax: Depth of the shower maximum
– Particle: Type of the primary particle
Besides the reconstruction of the air-shower and primary particle properties the
signals at the individual antenna stations of Tunka-Rex and at the optical mod-
ules of Tunka-133 are described by the following fields: Timestamp, Amplitude,
SNR, Width, Power, etc.
3 Data layers
In this section we describe the naming conventions for the data layers in the
TRVO. DL0-2 are organized in the standard structure described above: Station
+ Calibration + Supplementary data, while the DL3+ can have additional entries,
e.g. cosmic-ray events, radio bursts, etc.
Data Layer 0 consists of raw traces recorded by the ADCs, i.e. arrays
containing values in the range [0;4095]. These data are intended to be used in
case of recalibration/debugging of the instrument and are not recommended for
the external application.
Data Layer 1 consists of the traces containing voltages at the antenna
stations (i.e. antenna-induced voltages) obtained after unfolding the raw traces
1
https://www.itu.int/en/ITU-T/asn1/Pages/UUID/uuids.aspx
from the hardware response of Tunka-Rex amplifiers, filters, and cables. From
these values the electrical field at the antenna station can be reconstructed using
the specific antenna pattern and direction of incoming radio wave.
Data Layer 2 consists of the traces containing voltages converted to the
values of electrical field at the antenna stations. Depending on the data release,
the electrical fields will be calculated for air-shower events (DL2-AIRSHOWER), for
astronomical objects (DL2-ASTRONOMY), or for any other kind of measurements,
e.g. background, RFI, etc (DL2-OTHER).
Data Layer 3+ will contain high-level reconstruction of radio data, i.e.
quantities obtained after sophisticated processing and analyzing of radio traces.
These data can be represented in tables, histograms, FITS files, etc.
4 Storage of the data
Since the main Tunka-Rex data are represented as a linear set, we have decided to
use a relational database based on an open engine such as MySQL or PostgreSQL.
The raw data from the single antenna station have a relatively small size (few
KiB) and can be stored entirely in a single row of the SQL table. We have
deployed several testing databases with Tunka-Rex events on the servers of the
Irkutsk State University (ISU) and the Karlsruhe Institute of Technology (KIT).
The expected number of entries in the database from several data releases is in
the order of billions which result in TiB scale of DB. Currently we are testing
the performance of the database and implementing a user interface and basic
features.
5 Access to the data
As mentioned in the previous section, for the time being we are working on the
implementation of a client for TRVO, which features basic access to the primary
data and a plugin extension for more sophisticated quality cuts. Plugins will
provide an interface to the DB and allow for end-user implemented scripts for
online data analysis, quality cuts, and other preprocessing manipulations of data.
Below we give the description of two initial plugins which will be delivered by
default.
5.1 Cosmic-ray event builder
Since the metadata of cosmic-ray events reconstructed by Tunka-Rex will be
integrated in the common GRADLCI framework, TRVO will only provide an
index of events reconstructed by Tunka-Rex (DL3) and the connection between
corresponding data layers. The query engine supports backward compatibility,
and data can either be selected by TRVO directly of via the GRADLCI metadata
engine (with support of joint analysis including third-party data).
5.2 Radio astronomy tools
Besides access to cosmic-ray events, we will provide astronomy-related tools for
the direct manipulation with radio traces: band-stop, band-pass, and median
filters, beam-former, skymap builder, and others.
5.3 Software and datasets published already
The previously published Tunka-Rex datasets and software can be found at the
following URL: http://soft.tunkarex.info; the official Mercurial repository
of the Tunka-Rex software can be found on Bitbucket: https://bitbucket.org/
tunka. We plan to use the astroparticle.online platform for future releases.
6 Application of the Tunka-Rex Virtual Observatory
Since the primary goal of Tunka-Rex is the detection of cosmic rays, the main
application of TRVO is providing access to the high-level reconstruction of air
showers (DL3+). The architecture of this part of the Virtual Observatory has
already been developed in the frame of KCDC and we do not plan to depart from
this concept significantly. Besides public access to cosmic-ray data of the TAIGA
observatory, the radio data can be used for cross-calibration of different cosmic-
ray experiments, as shown in Ref. [14]. Below we discuss unique features of the
Tunka-Rex archival data and their application to current and future research (it
is worth noting, that the Tunka-Rex trigger is tuned for cosmic-ray detection
and the selection from the archival data might be significantly biased and can
be used only for tentative studies).
– Studies of the radio background in the frequency band of 30-80 MHz. Nowa-
days there are only few radio telescopes operating in this frequency band,
moreover these telescopes operate in an interferometric mode. They correlate
the radio signal using beam-forming and record the resulting correlation,
while radio arrays aimed at cosmic-ray detection record full uncorrelated
time series. The broadband measurement of radio background in this fre-
quency band is of special interest to search for a possible cosmological signal
from neutral hydrogen. Since this signal has a signal-to-noise ratio (SNR)
of about 10−5 , understanding of systematic uncertainties is crucial for this
type of measurements. The Tunka-Rex child experiment, Tunka-21cm, tests
the possibility of application of cosmic-ray detectors for studies of this cos-
mological signal, and is a first user of DL2-BACKGROUND and DL2-ASTRONOMY.
– Searching for radio transients. Obviously archival data can be used for search-
ing for astronomical transients in this frequency band. The effective exposure
of Tunka-Rex provides only a very small probability of detection of any kind
of transients. However, the archival data can be used for the test of detection
techniques for future multi-purpose detectors.
– Training of neural networks for RFI tagging. It was shown, that deep learning
can improve the signal reconstruction of radio detectors when using an au-
toencoder architecture [15,16,17], because neural networks are able to learn
features of the background and can be used for either denoising of radio
traces or tagging of traces containing special features. It is worth noting,
that the present Tunka-Rex autoencoder is trained on a dataset containing
less than 1% of all Tunka-Rex background traces, what promises significant
improvements by using larger training samples extracted from TRVO.
– Outreach and education. Open data implies outreach and educational activ-
ities, and we support this activities. TRVO will be used as educational plat-
form in the outreach part of the GRADLCI [18] and astroparticle.online
projects. At the first stage we use the Tunka-Rex hardware, software, and
simulations for the training of students of the Physics Department of ISU.
Last but not least, the developed framework can be applied to future arrays:
GRAND [11] and radio extensions of the Pierre Auger Observatory [19] and the
Tien-Shan cosmic-ray setup [20].
7 Conclusion
The Tunka-Rex Virtual Observatory provides open access to the data of exper-
iments measuring cosmic rays with radio technique. We plan to combine both
astroparticle- and astronomy-related features in TRVO and provide fast and
user-friendly access with the possibility of custom scripting for complex pres-
election and preprocessing of the data. The first databases have already been
deployed and are now under internal testing. Besides users from the education
sector (ISU) and partner experiments (TAIGA) we have requests from the re-
cently established engineering setup Tunka-21cm aimed at astronomical goals.
Acknowledgements
This work was supported by Russian Science Foundation Grant 18-41-06003
(Section 2), Helmholtz Society Grant HRSF-0027 and by Russian Foundation
for Basic Research Grant 18-32-20220. We thank the members of KCDC and
GRADLCI for the fruitful discussions and support of the deployment of testing
databases.
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