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e-VLBI in the U.S.: Planning for the future

NRAO/Haystack Planning group - Draft 4

2007 March 9

What is VLBI and why is it important?

Very-Long-Baseline Interferometry (VLBI) is used by radio astronomers as
the most powerful technique: for studying objects in the universe at
ultra-high resolution, for measuring earth motions in space with ultra-
high accuracy, and for providing precise sky-position navigation of deep-
space explorers:

For astronomical studies: VLBI allows images of distant radio sources to
be made with angular resolution of tens of microarcseconds, far better
than any optical images. As such, the structure and dynamical evolution
of some of the most distant objects in the Universe can be studied in
unprecedented detail.

For Earth science studies: VLBI provides direct measurements of the
Earth's dynamic orientation in space in the near-inertial reference frame
provided by distant quasars, which in turn provides information ranging
from plate tectonic motion to mass interactions at the core-mantle
boundary, as well as earth-rotation measurements critical to civilian and
military navigation.

For deep-space navigation: U.S., European, and Japanese space programs
all use VLBI in various ways for high-precision navigation of deep-space
craft on the 2-dimensional plane of the sky. Fast turnaround is often
required to make critical decisions regarding course-correction
maneuvers.

VLBI combines data simultaneously acquired from a global array of 20 or
more radio telescopes to create a single coherent instrument, as
illustrated at right for a simple 2-element VLBI array. Traditionally,
VLBI data are collected on magnetic media (magnetic disks) which are
shipped to a central site for correlation processing. This laborious and
expensive data-collection and transport process, requiring a multi-
Petabyte (Petabtye = 1015 bytes) global media pool, now has the
possibility of being replaced by modern global high-speed networks
(dubbed 'e-VLBI'), opening important new capabilities, potential
scientific returns, and lower costs.

Why is e-VLBI important?


The advantages for scientific productivity and technical operations of e-
VLBI over traditional VLBI are:

1. Higher sensitivity: For the majority of VLBI observations, sensitivity
increases as the square root of the recorded data rate. Typical
recorded VLBI data rates today are 1 gigabit/sec/station
(Gbps/station). Short periods of observations at several Gbps are
possible but, due to media costs, are uneconomical for extended
periods or for extension to many Gbps. The potential to extend e-VLBI
to many-Gbps data rates in the future will allow an increase in
observation sensitivity well beyond what is possible today.
Furthermore, such high data rates will be sustainable for long periods
of time. The only alternatives to higher data rates for increased
sensitivity are larger antennas and/or quieter receivers. Larger
antennas are, of course, hugely expensive; while many receivers are
already very close to theoretical noise limits. For astronomical
observations, the benefits of higher sensitivity are obvious. For
geodetic observations, the number and distribution of reference
sources improves dramatically as sensitivity improves. For spacecraft
navigation, which is based on phase referencing with respect to nearby
calibrators, systematic errors can often be reduced by being able to
select a calibration source near to the spacecraft.
For radio astronomy, the recently formed High-Sensitivity Array
(HSA), consisting of the VLBA + phased-VLA + GBT + Arecibo, is among
the most sensitive VLBI arrays in the world. (Further information
about the component instruments is presented in a later section.) A
major increase of data rates for the HSA, to 10Gbps or more, enabled
by high-speed networks would open an entirely new class of accessible
observations.
2. Targets of opportunity: For a full-time astronomical VLBI instrument,
targets of opportunity, which arise primarily from transient
astronomical events, present a major opportunity for unique scientific
discovery. As the only dedicated VLBI observing instrument in the
world, the VLBA (described in a later section) has a strong
competitive advantage through a quick, flexible response to targets of
opportunity. However, without rapid access to at least preliminary
results from such observations, the opportunity to refine or re-direct
observing configurations for increased scientific payback is
impossible. Using e-VLBI can reduce the time to obtain results from
weeks to hours or even, potentially, to minutes, giving scientists
rapid feedback. This is especially important for rapidly evolving
events, such as extragalactic supernova, gamma-ray-burst events, and
other transient phenomena increasingly being observed in the Universe.
3. Lower costs: Ultimately, e-VLBI will eliminate the need for a multi-
million-dollar multi-Petabyte global pool of magnetic media. With
expeditious planning and implementation of a full-time e-VLBI network,
we believe that the benefit-to-cost ratio will be quite high.
4. Quick diagnostics and tests: The verification of the proper operation
of VLBI equipment at part-time observing stations is notoriously
difficult since correlation must be done before results can be
obtained. Unfortunately, this characteristic has too often led to bad
or poor observations and the waste of expensive telescope time. With
e-VLBI, proper operation of the entire telescope array can be verified
in a matter of minutes to hours. This is particularly important when
new equipment is brought on-line, or when equipment that has been
repaired needs to be re-verified for service.

Examples of e-VLBI success

The feasibility of real-time global e-VLBI has now been demonstrated many
times using national and international research networks. The work at
Haystack Observatory, supported initially by DARPA in 2001-2 and most
recently by NSF (ANI-0230759 and ANI-0335266), has been at the forefront
of high-speed global e-VLBI development. For example, at the Super
Computer 2005 meeting in November 2005, data from three telescopes in the
U.S. and Europe were streamed at 512Mbps in real-time to the Mark 4 VLBI
Correlator at Haystack Observatory and the results displayed in real-time
on the conference floor. Also demonstrated at the same time were
national and international dynamically switched optical paths in
collaboration with the NSF/EIN-supported DRAGON project (ANI-0335266) and
the Internet2 HOPI project.

With support from NSF, NRAO has established an 80-km experimental fiber
connection to allow the VLBA station at Pie Town, NM, to be used as an
extension of the VLA for certain observations.

As a reflection of e-VLBI success and future promise, e-VLBI was recently
honored with an Internet2 IDEA award, which recognizes applied advanced
networking at its best and hold the promise to increase the impact of
next-generation networks around the world. The award was received
jointly by Alan Whitney of MIT Haystack Observatory, Arpad Szomoru of
JIVE, The Netherlands, Yasuhiro Koyama of NICT, Japan, and Hisao Uose of
NTT Laboratories, Japan, on behalf of their institutions.

The success of several high-profile demonstrations, plus an increasing
level of routine global near-real-time e-VLBI data transfers, provides
evidence of both the utility and promise of a fully developed global e-
VLBI system.

International e-VLBI activities

Almost by definition, e-VLBI is a strongly international activity, and
development work is international in scope. Japan has been active in e-
VLBI development over dedicated networks since the mid-1990s and now
participates very actively in global e-VLBI development. The Joint
Institute for VLBI in Europe (JIVE) has recently received a 3-yr ~$20M
grant from the EC Research Infrastructure Grid Program to connect 16
telescopes in Europe for real-time e-VLBI observations at 1Gbps using a
dedicated optical wavelength to each telescope to bring data back to a
correlator in Dwingeloo, The Netherlands. In addition, JIVE has also
recently received a ~$5M grant from the EC for development of Grid
technologies for e-VLBI, including distributed software correlator
development. The Australians have recently announced support for
connecting all of the country's major radio telescopes with 10Gbps
connections. And the Chinese are aggressively connecting their
telescopes to high-speed global networks. Within about three years, most
of the major radio telescopes outside the U.S. are expected to be
connected to the global grid of high-speed R&E networks at speeds of at
least 1 Gbps.

e-VLBI development collaborations with the networking community

By nature, e-VLBI lends itself to collaborative developments with
networking research and applications, and such collaborations have
already allowed significant development work on the e-VLBI technique. e-
VLBI development work at Haystack was first supported in 2001-2 by DARPA,
followed by NSF support[1] for development of protocol and transmission
techniques specifically tailored for e-VLBI. A prime example of active
collaboration with the networking development community is the DRAGON
('Dynamic Resource Allocation via GMPLS Optical Networks') project[2],
also working with the Internet2 HOPI project, to develop dynamically-
switched on-demand dedicated light paths for high-speed data streams.

Broad international e-VLBI collaborations have been established between
the U.S., Europe, Japan and Australia both for demonstrations and for on-
going routine data transfers between connected telescopes and
correlators. Many TeraBits/month of data are successfully transferred in
this fashion. For telescopes outside the U.S., this activity is
increasing dramatically. Within the U.S. it is severely limited by lack
of high-speed connectivity to major radio telescopes.

In 2002, Haystack Observatory hosted the first international e-VLBI
conference, which was attended by 80 VLBI and network practitioners from
around the world, and which formed the basis for an annual e-VLBI
conference circulating among the U.S., Europe, Japan and Australia. In
fall 2006 Haystack Observatory again hosted this international meeting.
These meetings have been an important forum for bringing together
scientists and network specialists to discuss techniques, applications
and tests.

NRAO is currently developing two major interferometer systems, the
Atacama Large Millimeter Array (ALMA) in Chile, and the Expanded Very
Large Array (EVLA). Although in both cases, the baselines are
substantially shorter (~20Km) than what is usually considered "e-VLBI",
the techniques used are similar. The EVLA instrument is already
transferring data at 120Gbps from individual antennas to a central
correlator. The expertise gained by NRAO in these developments is almost
all transferable to the development and implementation of high-speed e-
VLBI network.

The current e-VLBI situation in the U.S.

The U.S. hosts approximately 15 radio telescopes that are regularly used
for VLBI. Ten of these, spread over US territory from St. Croix to
Hawaii, form the Very Long Baseline Array (VLBA), operated by the
National Radio Astronomy Observatory (NRAO). The VLBA is the only
dedicated VLBI observing instrument in the world and has a rich history
of scientific discoveries. A dedicated correlator, located at the NRAO
Array Operations Center (AOC) in Socorro, NM, is also part of the VLBA.
Plans for replacing t VLBA's digital data path by new, significantly
wider-band equipment, including an e-VLBI-ready correlator, are under
development.

Although not dedicated to VLBI, several other U.S. radio telescopes are
included regularly: the 300m diameter Arecibo telescope in Puerto Rico;
the 100m diameter Green Bank Telescope (GBT) in Green Bank, WV; and the
Very Large Array (VLA; a 27-antenna interferometer with effective single-
dish diameter 135m, currently being upgraded to the EVLA described above)
west of Socorro, NM. Millimeter-wavelength antennas in Hawaii and
Arizona have been used for high-frequency VLBI observations, with the
expected addition of the CARMA facility in California in the near future.
The 18m Westford radio telescope at Haystack Observatory in
Massachusetts and the 20m telescope at Kokee Park, Hawaii, are used
regularly for geodetic VLBI observations supported by NASA. All of these
telescopes are good candidates for an e-VLBI network.

Currently the Westford telescope and a small experimental telescope at
NASA/GSFC in Maryland are the only telescopes connected to the
national/international networks at Gbps speeds. These two telescopes
currently form the primary e-VLBI testbed in the U.S and are connected at
2Gbps to the global high-speed network. The VLA is connected to the NRAO
AOC in Socorro, NM, via an OC-3 link, which is in turn connected to
Internet2 via an OC-3 link shared with New Mexico Tech. On Hawaii, the
telescopes at the Mauna Kea summit share a 1Gbps link, and Arecibo
maintains a connection limited to ~20Mbps, which is only marginally
useful for e-VLBI.

What needs to be done to keep the U.S. competitive in the e-VLBI arena?

While Europe, Japan, China and Australia are moving aggressively towards
extensive national and global e-VLBI capability, the U.S. is nearly
stalled. Leadership in e-VLBI is in imminent danger of being ceded by
default to the rest of the world. To correct this imbalance, the U.S.
must also make a commitment to a healthy and aggressive e-VLBI
development program if it is to remain a viable partner in this global
scientific enterprise.

We suggest the follows steps as guidelines to developing a healthy and
robust e-VLBI capability within the U.S.:

Continue e-VLBI development and testing

e-VLBI has already benefited greatly from significant development work
funded by NSF, as earlier indicated. However, still more optimization
and improved efficiency are needed to keep up with both with higher data
rates as well as changing and improving network technology. New
capabilities built into network technology are often only accessible by
development efforts designed specifically to support them; the dynamic
optical switching capabilities developed collaboratively with the NSF-
supported DRAGON program are a prime example. Additionally, e-VLBI data
occupies a special niche in high-speed networking as it is somewhat loss
tolerant and can therefore sometimes use network bandwidth that is less
than optimum, as demonstrated by the EGAE development program at Haystack
Observatory.

Further software research and development strategies for e-VLBI include
integration of other emerging network services such as: 1) national
storage depots (REDDNET program) and networking software tools to aid in
the identification of inter-domain networking problems, 2) aggressive
transport protocols for end-to-end dedicated light paths that take into
consideration special VLBI data characteristics, and 3) investigation of
multi-cast techniques for possible use with distributed correlation
systems of the future.

In order for this research and development to proceed, work in both
laboratory settings and in actual e-VLBI test experiments are necessary.
For the most part, networks made up of a small array of working VLBI
stations will be sufficient, operating on a non-interfering basis with
normal VLBI usage of stations. Of course, collaborative testing on a
national and global scale with institutions such as NRAO, NAIC, EVN/JIVE,
Japan and Australia is critical to ensure proper behavior across a wide
range of network topologies and scales.

Estimated costs: ~0.5 FTE/yr plus ~$30K/yr materials & services

Begin real-time e-VLBI testing using VLA Telescope

The existing connection of the VLA to Internet2 is an OC-3 (~150Mbps)
link shared with New Mexico Tech. This connection is sufficient to begin
e-VLBI testing using the VLA (or a single antenna of the VLA) and the
Westford antenna in Massachusetts for real-time transfer of data to the
Mark 4 correlator at Haystack Observatory. The first tests will be at
32Mbps/station and then up to a probable maximum of ~64Mbps/station.
These first steps would establish the feasibility of real-time e-VLBI
with an NRAO antenna and establish a baseline from which to proceed in
the future.

Estimated costs: ~4 person-months plus ~$20K network charges

Investigate and connect VLBA AOC to high-speed network

Establishing a high-speed network connection from the NRAO Array
Operations Center (AOC) in Socorro, NM, to a national high-speed R&E
connection point is essential in order to bring data from VLBA stations,
as well as potentially from other U.S. and international sites, into the
AOC for processing. The most likely connection point is Albuquerque as
Internet2 maintains a 10Gbps connection point in Albuquerque. National
Lambda Rail (NLR) also has a presence in Albuquerque which might be
similarly utilized. Collaboration with both Internet2 and NLR should be
initiated to determine the most cost-effective way to connect the AOC to
the high-speed national network grid.

Ultimately, as the data rate from each of the VLBA stations increases to
~10Gbps or higher, the connection to the AOC correlator must be capable
of supporting this data-transfer rate from at least the 10 stations.

Estimated costs:

Investigation: ~2 person-months

Actual connection costs: Will be determined by the study

Investigate and connect 6 western continental VLBA sites to high-speed
networks

The six western continental VLBA sites (Fort Davis, Los Alamos, Pie Town,
Kitt Peak, Owens Valley, Brewster) are of interest to NASA for near-real-
time deep-space navigation and form a good core group of stations for
initial high-speed network connection. Cooperation by both NASA and
NSF/AST in making these connections could benefit both. In particular,
the resources of Internet2 expertise should be tapped to identify the
most cost-effective method of connection to the VLBA correlator, which
might be located at the AOC, at the VLA site, or elsewhere. The
Internet2 organization maintains an extensive database of fiber routes
and connections that could prove invaluable in ascertaining the most
effective connections. NASA has a division which could interact with the
fiber owners once this information is known. Another option would be to
involve a subsidiary of Internet2, called WaveCo, which has been actively
procuring low-cost long-term access to dark fiber all across the U.S.,
with the expectation that such access will help to minimize costs for
future connections. Of course, there will be inevitable costs of
providing 'last mile' access to each station, but the one-time 'last
mile' costs, must be viewed in the perspective of the potential ultimate
benefits. Close cooperation between NRAO and NASA should help to
minimize costs for both institutions. A carefully conducted costing
study involving networking experts such as Internet2 and others should be
conducted as a first step. Some preliminary information regarding
possible fiber connections at the VLBA sites was gathered by Craig Walker
a couple of years ago
(http://www.aoc.nrao.edu/~cwalker/VLBA_fiber/fiber.html) which forms a
initial reference, but clearly much further investigation is warranted.

NASA's use of this VLBA subarray for spacecraft navigation would be
sporadic according to their specific requirements, but typically would
occupy only a few hours per track at ~50% duty cycle at ~512Mbps or
greater bandwidth. Access to this capability during other times would
allow the 6-element VLBA subarray to operate continuously at or beyond
512Mbps without the purchase of additional disk drives, which would
otherwise have to be used to support these observations.

When developing connections to these sites, careful consideration should
be given to economical upgradeability to 10Gbps or more over the course
of a few years, as e-VLBI data rates quickly climb towards these levels.

Estimated costs:

Investigation: ~4 person-months

Actual connection costs: Will be determined by the study

Investigate and connect the GBT to high-speed network

The GBT, certainly one of the premier radio telescopes of the world, is
in high demand for high-sensitivity VLBI observations. As a high-
sensitivity add-on to the VLBA, the GBT brings much value and would lay
the groundwork for ultra-high data-rate e-VLBI observations that simply
are impractical with record-and-ship VLBI. Furthermore, the GBT is
desirable for inclusion in high-sensitivity EVN observations, due both to
its location and sensitivity. Ultra-high-bandwidth observations
including the GBT with the EVN would benefit all international observers,
including U.S. scientists. An initial connection at 1Gbps would lay the
groundwork for eventually extending to much higher data rates. Data
could be brought to either a European correlator or an American
correlator for processing.

NRAO is currently discussing the possibility of collaboration with West
Virginia University in Morgantown, WV in developing a high-speed
connection to the GBT; such a collaboration could be mutually beneficial
and should be pursued.

Estimated costs:

Investigation: ~2 person-months

Actual connection costs: Will be determined by the study

Investigate and connect Arecibo to high-speed network

The Arecibo Observatory, with its vast collecting area, is another
obvious choice for ultra-sensitive very-high-bandwidth observations, both
with the High Sensitivity Array and as a member of the European VLBI
Network (EVN). Currently, Arecibo shares with the Univ. of Puerto Rico a
commercial OC-3 (~150Mbps) link to the U.S. mainland with the support of
the Americans Pathways (AMPATH) network. However, due to traffic demands
of the university, Arecibo is currently limited to a data rate of ~20Mbps
across this expensive commercial link. Puerto Rico is just one of the
islands in the Caribbean that currently lack high-speed connectivity.
Several initiatives are currently underway within the R&E Internet
community to dramatically improve this situation, including extensions
and augmentations of the AMPATH and/or CLARA (Latin American Cooperation
of Advanced Networks) networks (including to St. Croix, site of one of
the VLBA stations). Arecibo and the U.S. astronomy community must work
together with the networking community to help facilitate a cost-
effective high-speed network connection to Arecibo. There is no lack of
interest in the networking community, and collaboration of the U.S.
astronomy community will be warmly welcomed.

Interestingly, other non-VLBI applications are demanding increasing data
rates from Arecibo. In particular, on-going pulsar projects and SETI
observations at Arecibo are consuming increasing amounts of network
bandwidth to bring data back to U.S. mainland investigators. These
projects would benefit equally from a network-bandwidth upgrade to
Arecibo.

Estimated costs:

Investigations: ~3 person -months

Actual connection costs: Will be determined by the study

Development Schedule

We suggest that the program described above be carried out in a phased
timeline spanning three years, though the actual timeline will most
likely be influenced by potential budget constraints. Figure 1Figure 1
shows a strawman timeline for these activities over a 3-year period.

[pic]

Figure 1: Straw man timeline for proposed e-VLBI activities


Comments

Due to the rapidly changing environment of high-speed networking and the
need to implement e-VLBI solutions that promote scientific progress most
effectively at any given time, we believe that e-VLBI development and
testing should be a continuing activity. Initial real-time experiments
using VLA and the Westford antenna should be initiated at the outset to
provide initial experience for NRAO as well as a foundation from which to
proceed. When the connections of the VLA and AOC to a high-speed network
are completed, the data rates of these experiments may be increased.

As indicated above, connection of six western VLBA sites to high-speed
Internet is of interest to NASA for precision spacecraft tracking. NRAO
should work closely with NASA to maximize the usefulness of such a
network for non-NASA observations; scheduling and cost-sharing agreements
should, of course, be carefully worked out.

Since the GBT is well suited for wider participation in national and
international VLBI scientific investigations, we suggest that
investigation and connection of the GBT should proceed somewhat ahead of
Arecibo. In addition, the connection to Arecibo may benefit greater from
the evolving efforts of the R&E community to bring the Caribbean Islands,
including Puerto Rico, into the R&E networking mainstream.

Summary

e-VLBI is an important international activity that is being developed
very actively by Europe, Japan, China and Australia, but is currently
stalled in the U.S. This potentially puts the U.S. at a serious
disadvantage as these groups develop high-speed e-VLBI capabilities that
improve sensitivities beyond those possible with traditional recording
techniques, as well as offer rapid turnaround of processed data to aid in
follow-on observations and quicker production of science results. We
suggest a program of action that will remedy this situation and allow the
U.S. to participate with the rest of the world in creating the important
science that we believe will inevitably result.


-----------------------
[1] NSF/STI, ANI-0230759, 2004-2006, Haystack Observatory PI
[2] NSF/EIN, ANI-0335266, 2004-2007, U. of MD, PI; Haystack Observatory,
collaborator