Data rate improvements

1
e-VLBI real-time radio astronomy how a network
becomes a telescope
Arpad Szomoru, JIVE
2
Outline

• Radio Astronomy and VLBI
• principles, techniques
• e-VLBI and networks
• a real-time telescope of intercontinental size
• Motivation, results
• the transient universe
• Reaching beyond current technology
• the future of VLBI, SKA pathfinders and the SKA

3
Acronyms / organisations involved

• VLBI Very Long Baseline Interferometry
• A radio-astronomical technique to obtain high
  resolution
• EVN European VLBI Network
• Consortium of (European) Telescopes
• Arecibo (Puerto Rico), Cambridge (UK), Effelsberg
  (D), Hartebeesthoek (S-Africa), Jodrell Bank
  (UK), Medicina (I), Metsahovi (FI), Noto (I),
  Onsala (S), Robledo (ES), Shanghai (CN), Torun
  (PL), Urumqi (CN), Westerbork (NL), Wettzell (D),
  Yebes (ES)
• Joint Institute for VLBI in Europe
• Institute established in Dwingeloo, the
  Netherlands
• Funded by NWO (NL), ASTRON (NL), STFC (UK), INAF
  (I), ICN-IG (ES), OSO (S), CAS (CN), CNRS (F),
  MPG (D)
• EXPReS EXpress PRoduction e-VLBI Service
• EC-funded project, started in 2006
• Partners most radio-telescopes in Europe, some
  outside
• DANTE and a number of NRENs, SURFNet, AARNET,
  PSNC

4
Todays demo

• 6 European radio telescopes
• Streaming data in real-time to correlator in the
  Netherlands
• Westerbork (NL)
• Torun (PL)
• Onsala (SW)
• Jodrell Bank (UK)
• Medicina (IT)
• 512 Mbps each, maybe more

5
Radio vs. Optical Astronomy

• Radio waves with ? of 0.7mm to 90cm
• Compared to optical light 400 700 nm
• Can be detected and amplified with antenna

6
And more wavelengths
7
A bit of early history

• Radiation from Galaxy discovered in 1931, by
  Jansky
• result largely ignored
• Grote Reber started pioneering radio-astronomy in
  1937

8
Radio Astronomy and VLBI

• Radio emission from astrophysical sources can be
  detected against the sky with telescopes larger
  than a few meters
• Resolution scales with size
• Solution build larger telescopes!
• Only goes so far....

• Or combine series of telescopes into
  radio-interferometer
• Even longer baselines are needed to see astronomy
  in motion

9
Principles of VLBI aperture synthesis

• Correlator also registers signals with different
  phase information
• Builds up Fourier components of sky image as the
  earth turns

• Electronic equipment brings signal to focus in
  phase
• Similar to properties of parabola
• Usually only room for single pixel detector

10
Principles of VLBI

• Record same frequency band simultaneously at N
  telescopes
• Use best possible local clocks and frequency
  standard
• Sample and digitize and record (on magnetic
  medium)
• Find all ½N(N-1) correlation coefficients at
  correlator
• Compute back image from thousands of these
  measurements

11
(No Transcript)
12
(No Transcript)
13
Nearby mass-loss around an old star
14
Further exploding stars in other galaxies
supernova in M81 (1993)
15
And quasars at the edge of the universe

• A resolution which is high enough to see things
  move at cosmological distances

16
VLBI digital processing

• To reach the faint end of the universe
• Need many big telescopes
• And as much frequency space as you can get
• Bandwidth!
• Typical VLBI uses 64 MHz bandwidth in 2 pols
• Nyquist sampling
• 2 x 2pol x 32 MHz 128 M samples/s
• Noisy data 2 bits/sample recover 86 SNR
• 256 Mb/s, more is preferred
• Bits are not sacred
• Some losses are tolerable

radio sources in the Hubble deep field require
several days of integration (Garrett et al., 2000)
17

• Recording on Linux PC platform
• Harddisk recorder based system
• Parallel writing on 8 disk system

• Sending hard-drives around the world
• Typically have a few thousand going around

18
Now turn to e-VLBI!

• PC based recording
• Also allows Internet transmission
• Upgrade EVN to e-EVN
• Started with a pilot in 2003
• And was boosted with EXPReS
• Retrofit correlator to work real-time
• Help solve last mile problem at telescopes
• Work closely with NRENs on robust connectivity
• Push to 1024 Mb/s limit
• Bring in the big telescopes
• And start the revolution in radio-astronomy
  culture

Express Production Real-time e-VLBI Service
19

• Establish connectivity through Europe on GÉANT2
• Greatly catalyzed by having EC funded project

• All come together on the Dutch SURFnet6
• Large bundle from Amsterdam to Dwingeloo

20
EXPReS network upgrade
21
Remarkable progress

• 7-8 telescopes regularly on line, interesting for
  science
• Correlator operations optimal for direct results
  and feedback
• Connectivity reached impressive reliability
• Started with TCP, but obviously not well-suited
  for e-VLBI
• Now dedicated light-paths to many telescopes
• UDP protocol implemented for optimal throughput

Size of balloon set by number of telescopes
participating, height by station sustained
bit-rate
22
Insert demo here....

• 5 European radio telescopes
• Streaming data in real-time to correlator in the
  Netherlands
• Westerbork (NL)
• Torun (PL)
• Onsala (SW)
• Jodrell Bank (UK)
• Medicina (IT)
• 512 Mbps each, maybe more

23
Lots of connectivity
24

• Major changes to real-time and embedded
  correlator software
• New tools for public status, rapid feedback,
  streamlined processing, adaptive observing

25
(No Transcript)
26
more telescopes

• Effelsberg on-line since April 2008
• Yebes first e-light later this year
• Extremely important for science impact
• Important boost to the sensitivity of the e-VLBI
  array

27
Miyun 50m
Irbene 32m
Sardinia 64m
Kunming 40m
28
EXPReS connectivity progress

• Long-haul high-bandwidth data transport
• TCP on old Linux kernels clearly inadequate
• Circuit TCP performs well (TCP with UDP-like
  behaviour, without congestion control)
• UDP better, but needs modification of Mark5A
  control code
• And can be hostile to other users on open network
• Stability of original code a serious issue
• Has led to complete re-write of subset of Mark5
  control code

29
Connectivity progress towards 1Gbps

• Gbps connectivity
• All data transport via UDP
• Using various techniques to optimize use of
  bandwidth
• Channel dropping, packet dropping, mixed
  configurations
• Improved robustness
• 6 x 512 Mbps
• gt 12h uninterrupted
• One-person operation

30
EVN Reliability Index
31
Beyond 1 Gbps
32
(No Transcript)
33
Why e-VLBI is exciting for science

• Rapid response for rapid variability
• Fast response to requests
• Immediate analysis of data, flexible observing
• Coordination with current and future
  observatories
• Immediate feedback
• Increased robustness
• Fewer consumables, logistics
• Constantly available VLBI network
• Monitoring for example astrometry
• Spacecraft tracking (landing of the Huygens
  probe on Titan)
• Growth path for more bandwidth
• Increased sensitivity

34
Radical shortening of timeline

• Test case black holes in outburst
• Data processing took 1-2 weeks with first images
  within 48 hours
• Publication took less than 2 months

35
Rapid response science
36
2007 connecting China and Australia

• The APAN demo (XiAn)
• Opened up Siberia connection
• Excellent PR
• Longest (e) baseline ever

37
First global high-bandwidth data transport

• EXPRES-OZ demo
• Three Australian telescopes (Mopra, ATCA, Parkes)
• 12 hours at 512 Mbps without a hitch
• Beautiful detection of SN1987a

38
2008 Africa and the Americas
39

• Demo in 2008 at TERENA
• Arecibo, Puerto Rico
• TIGO Chile
• Hartebeesthoek, South Africa
• 4-continent e-VLBI
• 4-continent fringes!

40
Many providers...

• To connect telescopes in 4 continents
• Europe Westerbork (NL), Effelsberg (DE), Onsala
  (SE), Medicina (IT)
• MPG, DFN, SUNET, NORDUnet, GARR, GÉANT2, SURFNet
• North America Arecibo, Puerto Rico
• Centennial, AMPATH, AtlanticWave, NGIX,
  Internet2, StarLight, GÉANT2, SURFNet
• Africa Hartebeesthoek, South Africa
• Internet Solutions, TENET/SANReN, GÉANT2, SURFNet
• South America TIGO, Chile
• Transportable Integrated Geodetic Observatory
• Reuna, RedCLARA, GÉANT2, SURFNet

41
The next challenge

• Real-time demo during opening ceremony of IYA,
  15-16 January 2009 in Paris
• 24 hours real-time tracking of one source
• 6-continent e-VLBI
• Although we may have to cheat a little
• Will involve telescopes in Europe, China, Japan,
  Australia, USA, Puerto Rico, Chile and
  South-Africa
• Will feature real-time build-up of image
• And educational items like an interactive program
  to show different results with different
  telescope configurations
• Remote control of Oz telescopes...

42
Further in the future more spacecraft tracking

• LAPLACE and TANDEM
• accepted by ESA for study for 2015-2025
• Earlier projects may include Bepi-Colombo

• LAPLACE a mission to Jupiter and Europa
• VLBI on Europa landers/orbiter
• Radio astronomy experiments Jovian orbiter

• TANDEM Titan and Enceladus mission
• VLBI on Titan probes/balloons
• Radio astronomy exps Enceladus orbiter

43
Roadmap for future radio telescopes
Part of Future Infrastructure Roadmap of ESFRI
SKA and SKA pathfinders
44
The future of the e-EVN

• Currently the EVN is at the forefront of
  technological developments
• Distributed correlation, use of GRID
• Long-haul, high-bandwidth data transport
• Use of (dynamic) lightpaths
• 4 Gbps systems currently under consideration
• (barely) doable using magnetic media
• But easily accommodated on 10 Gbps networking
  architecture
• Upgrade of EVN correlator, receiver systems will
  lead to a massive increase of bandwidth and
  sensitivity
• Will keep EVN competitive and complementary in
  the era of SKA
• Providing global baselines
• Located predominantly in Northern hemisphere
• Upgrade will lead to 100 Gbps data streams from
  telescopes
• Maps perfectly onto emerging networking
  technologies

45
(No Transcript)