Download What is Radio Astronomy?

Linux, SETI, and Radio Astronomy
Marcus Leech
Radio Science Laboratories
http://www.radio-science-labs.com
Image appears courtesy NRAO/AUI
What is Radio Astronomy?
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Astronomy at wavelengths from a few mm to tens
of meters
Visible light has wavelengths in the region of
500nm, that is, 5.0x10-7 meters
From a physics standpoint, there's no difference
between visible light, and microwave/radio-wave
“light”.
Living things have receptors for only a tiny part of
the EM spectrum
Optical vs Radio Astronomy
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Ability to resolve fine detail highly dependent on
wavelength
A 10cm optical telescope can resolve details that
would require a radio telescope over 42km in
diameter at 21cm wavelength!
Sensitivity, however, is proportional to collecting
area of the reflector, regardless of wavelength
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Both use parabolic reflectors
Both must have a surface that is within 1/10th of
wavelength of perfect for maximum efficiency.
History of Radio Astronomy
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Like much in science, it was discovered
accidentally
Karl Jansky, 1933, working on sources of static on
international radio-telephone circuits at
wavelengths of 10-20M.
Discovered that static rose and fell with a period of
23 hours, 56 minutes.
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Must be of celestial origin
The Genesis of Radio Astronomy
Science
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Jansky was re-assigned to other projects after his
work on radio-telephone “hiss”.
Several years went by with nobody understanding
the significance of his discovery
Grote Reber picked up on Janskys work in 1937,
building a 30ft dish in his back yard.
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Eventually mapped entire Milky Way emission at
160Mhz (1.8M wavelength)
Published in Astrophysical Journal in 1944
Radio Astronomy now taken seriously
Grote Rebers Dish
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Now preserved as
historical artefact at
NRAO, Green Bank,
West Virginia
Radio Astronomy Today
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Radio Astronomy at the cutting-edge of astrophysical
research
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Big projects all over the world
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Roughly 70% of what we know today about the universe
and its dynamics is due to radio astronomy observations,
rather than optical observations
VLA, New Mexico
Arecibo, Puerto Rico
GBT, Green Bank, West Virginia
Westerbork, Jodrell Bank, ALMA, Hat Creek, SKA, etc
Scientists named the basic flux unit after Karl Jansky
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1 Jansky == 10-26 watts/hz/meter2
SETI
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Drake equation:
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N = R* x Fp * Ne x Fl x Fi x Fc x L
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N number of potential ET civilizations
R* rate of star formation
Fraction of stellar systems with planets
Ne fraction planets that can support life
Fl fraction that actually produce life
Fi Fraction that develop intelligent life
Fc fraction that develop detectable technologies (radio, etc)
L length of time such civilizations emit (lifetime)
SETI contd
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Many observing programs over the years
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Harvard: META and BETA
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SERENDIP I/II
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NASA: HRMS
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Cancelled after only 1 year by senator Richard Bryan
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“This hopefully will be the end of Martian hunting season at
taxpayers expense”
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Was a comparatively-small NASA program
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Personnel went on to form the SETI Institute
SETI@Home -- using data gathered mostly at Arecibo
SETI Science/Engineering
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Look for narrowband (~1Hz wide) signals coming from “out there”.
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Eliminate terrestrial sources (interference, etc)
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See if signals have appropriate doppler drift (chirp)
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Do they fit the profile of the antenna pattern?
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Need for wideband, high-resolution spectrometers
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Usually done in ASIC implementing high-speed FFT
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SDR can play a role
Gnu Radio, SDR, Linux
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SDR Software Defined Radio
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Software to replace traditional hardware functions
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FAST A/D and D/A hardware
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REALLY FAST compute platforms
GNU Radio
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Open Source toolkit for SDR
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Cost-effective (like, free) solution for experimental
RF/Microwave work.
SDR Hardware
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Provides basic RF interface
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High-speed A/D and D/A
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down/upconversion to/from baseband signals
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Some digital filtering
Many hardware platforms
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USRP Universal Software Radio Peripheral
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http://www.ettus.com
Beefy gamers-class PC platform: Q6600 3.5GHz, 8GB memory
SDR RA/SETI Software
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Developed gr-radio-astronomy subtree of Gnu Radio
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Provides basic RA and SETI tools
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Open Source
New IRA software:
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Fully integrated RA/SETI receive chain
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SETI up to 16Million 1Hz channels
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Pulsar, Total Power, Spectral, Transients
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http://www.science-radio-labs.com
GNU Radio Development Tools
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Python and C++ can be used to assemble so-called
flow graphs.
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Signal processing chain
GRC
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Graphical tool to generate flow-graphs, using
MATLAB/LabView like interface.
Example GRC flow graph
Flowgraphs and GUIs
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Lots of different applications built with GNU
Radio and various GUI toolkits.
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All-mode HF transceiver
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RADAR
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GPS
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Radio Astronomy
Gnu Radio Application example
IRA Software
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RA/SETI all-mode receiver
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Based on XFORMs toolkit
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Talks to flowgraph through FIFOs
IRA Main Panel
IRA SETI Waterfall
IRA Spectral
IRA Pulsar
IRA Continuum
IRA Interferometer
Typical Total-Power observation
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Sagittarius A in Total Power
Combined multi-day observations
An exciting new project
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18M dish at Shirleys Bay
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Needs lots of work
SBRAC consortium formed to
renovate/operate for amateur RA
and SETI
Further reading
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Society of Amateur Radio Astronomers
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“Radio Astronomy Projects, 3rd ed”, William Lonc
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http://www.radio-astronomy.org
http://www.radiosky.com
National Radio Astronomy Observatory
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http://www.nrao.edu
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http://www.cv.nrao.edu/course/astr534/ERA.shtml
Radio Jove Project
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http://radiojove.gsfc.nasa.gov