Interferometric Techniques for Impulsive Signals at
Radio/Microwave Frequencies
Interferometry in UHE particle
astrophysics
Andres Romero-Wolf
Jet Propulsion Laboratory,
California Institute of Technology
April 22, 2012
April 22, 2013 A. Romero-Wolf
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Interferometric Techniques for Impulsive Signals at
Radio/Microwave Frequencies
Interferometry in UHE particle
astrophysics
Andres Romero-Wolf
Jet Propulsion Laboratory,
California Institute of Technology
April 22, 2012
April 22, 2013 A. Romero-Wolf
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Motivation
• First detection of ultra-high energy neutrinos are
expected to lie close to the detector threshold.
• Increased demands for higher sensitivity
techniques to reduce the detection threshold.
• Interferometric techniques have been applied for
decades to detect weak signals.
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Radio Interferometry Applied to
Imaging and Astrometry
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Imaging
VLA
VLBA
M87
Image credit: http://www.nrao.edu/images/M87_trifold.jpg
Image Credit: http://www.vlba.nrao.edu/sites/
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Astrometry
Very Long Baseline
Interferometry
applied to identifying
a source location.
Image Credit: O. Sovers, J. Fanselow, and C.S. Jacobs, Reviews of Modern Physics, Vol. 70, No. 4, October 1998
200 µas
(1 nanoradian)
resolution.
Applied to
spacecraft
navigation
catalogues,
measuring Earth
motion parameters,
plate tectonics, etc.
Delay and delay rate are
partial derivatives of the
phase.
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Astrometry
Astrometric Density
Astrometric
time-series
display
typical source
location
variations of
200 µas for
the most
compact
sources.
Image Credit: http://astrogeo.org/images/J2236+2828/J2236+2828_X_2003_05_07_pus_map.ps
Image Credit: C.M. King, JPL / UH Manoa
Image Credit: C.M. King, JPL / UH Manoa
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Ultra-high Energy Particle
Astrophysics
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Ultra-high Energy Cosmic Rays
Charged
particles of
cosmic origin
constantly
bombard the
Earth’s
atmosphere.
Protons and
nucleons are
observed with
the energy of
a well thrown
fastball.
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1 per 1000 km2 per year
1 per 10 km2 per year
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What are the
sources of the
highest energy
particles observed
in the Universe?
Particles with
energies > 1020 eV
require very
powerful and
efficient
accelerators.
Magnetic Field Amplitude, Gauss
What Are The Sources of the Highest
Energy Particles in the Universe?
Active Galactic Nucleus
Gamma Ray Bursts
Supernova Remnants
Inter-galactic magnetic shocks
Size, cm
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Extended Air Showers
Ultra-high energy
cosmic rays interact
with the Earth’s
atmosphere to
produce showers of
secondary particles.
These extended air
showers are
observed with
particle counters on
the ground and by
UV fluorescence.
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Geosynchrotron Radiation
• The extended air
shower contains a
significant quantity of
positrons and
electrons moving at
nearly the speed of
light.
• The Earth’s
geomagnetic field
separates the
charges producing
coherent synchrotron
radiation
April 22, 2013 A. Romero-Wolf
ve-
Transverse current
gives polarization
vector.
v
q
q
q=-|e|
ve+
q=+|e|
y
B Magnetic field
Shower Axis
z
x
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Radio Detection of Extended Air Showers
• First observed in the
1960’s by Jelley.
• Active field during
the 1960’s and
1970’s.
• The technique has
been revived in the
last decade with
modern radio
detection
techniques.
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Radio image produced by cosmic
ray impulse data from the LOPES
detector.
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Cosmic Rays and Neutrinos
• Cosmic photon
backgrounds attenuate
UHECR energy
• Interaction threshold at
4x1019 eV
• UHECRs observed
with E>4x1019 eV must
be within 100 MPc
Cosmic Distance Scales
Milkyway: 30 kpc
Andromeda: 800 kpc away.
Cen A: 4Mpc
Virgo Cluster: 17 Mpc
Coma Cluster: 90 Mpc
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Neutrino Radio Detection
Antenna
Detector
Outside of
Target
Target
SALSA
Antennas in
salt domes
Dense and
RF
Transparent
Cosmic
Neutrino
Particle
shower
20% charge
excess
L<l
Interaction
point
Radio Emission
Coherent
Cherenkov
Radiation Cone
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RICE
Dipole
antennas in
South Pole
ice.
Antenna
Detector
in Target
ARA
Large
detector
antenna
network in
South Pole
GLUE
Lunar
regolith
target with
DSN
antenna.
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The ANITA Ultra-high Energy
Particle Telescope
• Synoptic horn antenna
array (200-1200 MHz)
• Circumpolar trajectory
on a balloon.
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Neutrino Limits with ANITA
ANITA provides the
strongest limits to
ultra-high energy
neutrino fluxes to
date.
Several models of
ultra-high energy
neutrino production
have been ruled out.
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Geosynchrotron Radiation
Detected with ANITA.
Radar
backscatter
amplitude
• Detected with ANITA in UHF band (200-1200 MHz).
• ANITA-3 (2013) will be tuned to detect hundreds.
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Interferometry in Ultra-high Energy
Particle Astrophysics
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Impulse response
Or Effective Height
Voltage
Electric
Field
Impulse Response
Time
Frequency
v=E★ h
Voltage
Electric
Field
Time
Frequency
ANITA horn antenna
effective height
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Geometric Delay
• Beam forming
combines the
signals from
multiple
antennas.
• The geometric
delay is the basic
quantity that
connects multiple
observations of
the same signal.
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The ANITA Array
•
•
•
ANITA antenna array observes the same impulse with multiple channels.
The array is unusual in that the antennas are not all pointed in the same direction.
The arrangement is designed for full azimuthal coverage.
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Beam-forming
The signals from the
previous slide are
aligned in time
according to the true
geometric delay of
the signal.
The directional
response of the
antennas does not
affect the phase of
the signal and it can
be added coherently.
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Coherently Summed Waveform Power
Global image of the
coherently summed
power for each
assumed direction of
the incident radiation.
The direction of true
incidence presents
itself as a sharp
peak.
The diametrically
opposed direction
sees the thermal
noise background.
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Beam-forming with Cross-correlations
Cross-correlations of
an impulsive signal
event.
The time-domain
cross-correlation is
mapped to incident
direction via the
geometric delay
relation.
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Beam-forming with Cross-correlations
Example of a global
coherence map
derived from the sum
of cross-correlations.
The true direction of
the signal presents
itself as a sharp
peak.
The map is
analogous to the dirty
map of radio
interferometry.
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Beam-forming with Cross-correlations
Examples of
signals and
background
s detected
with ANITA.
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Angular Error
ANITA-I
The ANITA array
has < 1-degree
angular errors.
This is due to the
ultra-wideband
signals used in
the correlation.
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Angular Error
ANITA-II
The ANITA array
has < 1-degree
angular errors.
This is due to the
ultra-wideband
signals used in
the correlation.
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Summed Waveforms vs. Cross-Correlations
The relation
between the
summed
waveform signal
to noise ratio
and crosscorrelation
coefficient
reveals features
that are specific
to each kind of
signal and
background.
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Thermal Noise Rejection
A discriminant
formed by the
linear
combination of
the cross
correlation
coefficient and
the peak of the
summed
waveform
provides a highly
efficient filter.
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Discrimination Techniques
Thermal noise
and carrier wave
signal
backgrounds
both have
comparable peak
and secondary
lobes.
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Signal Strength
The peak of the
coherent
waveform sum
provides
additional
efficient
discrimination
between signals
of interest and
thermal noise.
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Imaging the Sun
Averaging events in a
sun-centered coordinate
system reveals a radio
image of the sun along
with its reflection on the
ice.
These images can be
used to measure the
surface roughness of the
ice.
See talk by J. Stockham.
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Imaging Anthropogenic Backgrounds
Clusters of
events that pass
all cuts provide
locations of
anthropogenic
backgrounds.
Not all clusters
originate from
identified field
camps.
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Imaging Anthropogenic Backgrounds
Average
Correlation
Coefficient
Imaging of all
data, including
thermal noise,
provides a
complementary
view of the
Antarctic noise
sources.
ANITA-1
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Imaging Anthropogenic Backgrounds
Average
Correlation
Coefficient
ANITA-2
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Conclusions
Pulse-phase interferometry offers highly sensitive
techniques for analysis of ultra-high energy particle
transients.
Implementation of this technique into a real-time
digitization and triggering scheme can yield improvements
in detection sensitivity.
Research described herein done under contract with NASA.
Copyright ©2013 Jet Propulsion Laboratory, California Institute of Technology.
Government sponsorship acknowledged.
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