ATA: The Allen Telescope Array

Link to ATA Web site

I. General project/facility description

1. Overview of the facility/project
   The Allen Telescope Array (ATA) will consist of 350 6.1-meter dishes arrayed together at the Hat Creek Radio Observatory. The range of baselines is from about 9.8-meters to about 800-meters. The project is proceeding in phases delineated by the number of antennas available for use as an array. The initial phase will yield 32 dishes by Spring of 2005 and is called the ATA-32. The second phase (ATA-206) will yield 206 dishes expected by Winter of 2006. The third phase (ATA-350) will yield 350 dishes projected to be available by the end of 2008. Additional phases yielding more telescopes are possible in future years.

2. Managing institution and organization
   The Allen Telescope Array is a joint project between the University of California Berkeley, Radio Astronomy Laboratory and the SETI Institute. The array is operated by the Allen Telescope Array Consortium established in a Memorandum of Understanding between the Regents of the University of California, Berkeley and the SETI Institute.

3. Funding source(s)
   Funds for the technology development and construction of the Allen Telescope Array have been raised by the SETI Institute primarily from a variety of individual and corporate philanthropic sources. Additional salary and operations support has been contributed by the state of California, through its ongoing support of the UC Berkeley Radio Astronomy Laboratory, an Organized Research Unit at UCB. Additional funds for acquisition of antennas have come from the USNO.
   It is the expectation that NSF funds will become available to operate the ATA once it comes on line. If the NSF funding materializes, the ATA will become open for proposals from the scientific community.

4. Construction history and cost
   Dollar amounts are in actual year dollars through 2004, and constant 2004 dollars thereafter. The ATA project was initiated in 1999 with a MOU signed between UC Berkeley Radio Astronomy Laboratory and the SETI Institute to cooperate on design and implementation of an innovative telescope with 10⁴ square meters of collecting area, suitable for full-time, simultaneous radio astronomy and SETI observations, over a very large bandwidth. Significant funding was obtained in 2000, and a 3 element Production Test Array was installed at Hat Creek Observatory in Jan 2003. Current plans are for:
   • Spring 2005: ATA-32 begins operation
   • Winter 2006: ATA-206 construction complete
   • Winter 2007: ATA 350 element array complete.
   The ATA-32 is fully funded and the other phases will proceed as funds become available.

5. Operational history and cost
   Future facility.
   It is expected that the annual operating costs of the ATA will be $2M. These funds will be requested from the NSF program for University Radio Observatories. In addition, the SETI Institute and UC Berkeley will attempt to raise from other sources an additional $1M annually for continual upgrades of the digital IF and back-end processors (the Moore's Law components) to maximize the capability of the array throughout its life cycle.

II. Technical details

1. Specifics of telescope/instrument
   The Allen Telescope Array, née the 1 Hectare Telescope, is an array of 350 antennas of 6.1 m diameter with an overall collecting area of 10,000 m². The receiver input band covers the whole range of 500 MHz to 11.5 GHz all at once. This is enabled by dual wide band, low noise input amplifiers (LNAs) connected to a wide band, dual linearly-polarized, log-periodic feed followed by a dual fiber optic transmission system of 12 GHz bandwidth. The LNAs are located in a vacuum dewar cooled by a refrigerator to 50 K to achieve a system temperature of about 40 K at all wavelengths. The fiber optic system carries the analog signals from the antenna to the processing laboratory. The antenna reflector system is an offset Gregorian with a 2.4 m secondary to enable the wide bandwidth, and there is a metal shroud around the bottom part of the feed to insure low ground noise and RFI pick-up. The effective areas of the antennas are approximately frequency independent.
   Four bands of 100 MHz each anywhere in the 0.5 - 11.5 GHz range can be selected for simultaneous processing. Four separate summed beams can be formed in each band within the primary beam (a total of 16 dual-polarization phased array beams). Output from each of these beams can be routed to different phased array backends (PABEs) such as SETI detectors, pulsar machines, or general purpose spectrometers. Two of the 100 MHz bands can be sent to two 1024 spectral channel cross-correlators for imaging of the primary field of view. The FX correlators are configured to output all four stokes parameters. The array is distributed over a region of about 800 m diameter and provides a resolution of about one arc minute over the 2.5 degree primary field of view at 1.42 GHz. That corresponds to about 15,000 independent pixels over the primary field. The 350 antennas are arranged in such a way that the distributions of baseline pairs is close to a two dimensional Gaussian. This results in a synthesized snap-shot beam which has peak near-in sidelobes (over the primary beam) that are less than one percent.
   In addition, the dishes may be used as many independent sub-arrays, where the number of antennas per sub-array may range from 1 to 350.
   The ATA resources available to users are then:
   • pointing of the dishes in a sub-array (usually the full 350-dish complement)
   • four independent frequency tunings
   • four independent phased-array, dual-polarization beams per tuning
   • "resourced" phased-array back-ends (i.e. existing PABE's made available by the provider for use by others, for example a general-purpose astronomical spectrometer, or special-purpose back-ends furnished by the proposer). Note: during most observations, specialized SETI signal processing equipment will be operating as PABE's on three or more (out of a total of 16) of the available dual-polarization beams.
   • imaging correlator (on two of the independent tunings)

2. New capabilities anticipated/planned in next 5-10 years
   Future facility. Future upgrades may include:
   
   • The Hat Creek site can accommodate as many as 700 dishes. Doubling the array collecting area is a possible future option.

   • Initial radio astronomy observations will commence with single correlator on one tuning with 100 MHz of bandwidth. This will be replicated on a second tuning as soon as funding is available. Thereafter further generations of correlators will be designed and built with increased bandwidth per tuning, with a goal of 1 GHz within 10 years. Early PABEs for radio astronomy will be a pulsar timing machine and a generalized astronomical software detector in a server cluster.

   • Initial SETI signal detectors will provide ~20 MHz of dual-polarization bandwidth on each of 3 phased-array beams (Prelude system), evolving into 100 MHz of bandwidth on 4 phased-array beams (SonATA). Within 10 years, the goal is to have ~1 GHz of bandwidth on each of eight phased array beams.

III. User profile

1. % of "open skies" time
   The Telescope Utilization Plan for the ATA anticipates support from the NSF for annual operating expenses, therefore up to 20% of the observing time on the ATA-32 and up to 33% of the observing time on the 350 element ATA will be allocated to external observers. Formal proposals for observing time will be evaluated by a time allocation committee, three times per year.

2. Institutional affiliations of users
   Scientists affiliated with the UC Berkeley Radio Astronomy Lab and the SETI Institute will have guaranteed-time on the ATA.

3. Student access, involvement, usage
   The Allen Telescope Array is intended to remain within the NSF-defined category of a University Radio Observatory rather than becoming a national observatory facility. This means that the user will retain a larger degree of involvement in, and responsibility for, the success of the observing process (there will be fewer available service-mode observations). Furthermore, training of the next generation of researchers will be emphasized. Students will be particularly encouraged to submit observing proposals, and participate in the ongoing technical enhancements of the array. Students proposing to use the ATA as part of their thesis work may also designate their proposal as a Thesis Proposal, which allows them extra flexibility and guarantees of array usage.

IV. Science Overview

1. Current forefront scientific programs
   Future facility: NA

2. Major discoveries (through 1999)
   Future facility: NA

3. Science highlights of last 5 years
   Future facility: NA

4. Main future science questions to be addressed
   
   • Radio Astronomy:
     • All sky survey of HI in galaxies out to z ~ 0.17 (40,000 km/s)
       • Study dark matter distribution in galaxies
       • Search for dark galaxies
     • Observe HI in absorption against AGNs for z < 2
     • Study dense ISM and star formation within the Galaxy
       • Map dark (molecular) clouds in emission from complex and long chain molecules [utilizing full receiver coverage from 0.5 - 11.2 GHz] with good angular resolution
       • Measure all 4 Stokes parameters to use the Zeeman effect in HI and CCS to study the large scale magnetic fields in the Milky Way and M31, in the regions of field transition, and in dense molecular clouds
     • Map HI at high spatial resolution (~1 arc min) over very large fields
     • Characterize the radio transient sky: survey 10⁴ square degrees at 500 MHz, to 50 µJy or 10 square degrees at 5 GHz to 85 µJy in 12 hours
       • Flares from black holes
       • Supernovae
       • 1-100 Gamma Ray Bursters (per 12 hours at 5 GHz)
     • Pulsar searches and monitoring
       • Pulsars in close binaries
       • Old, low duty cycle pulsars
       • Large time commitment to pulsar timing program
     • Gravitational wave detection: monitoring millisecond pulsars in the Pulsar Timing Array with 100 nanosecond precision can sample strain amplitudes of 10^-14 and periods of one year.

   • The Search for Extraterrestrial Intelligence (SETI) on the ATA:
     Based on a plan for signal processing development, and the phased construction of the ATA, SETI observations will first take advantage of the larger size of the ATA-32 phased beams to conduct a survey of the inner galactic plane, and later use the ATA for a sensitive targeted search.
     
     • SETI - survey of inner galactic plane with ATA-32 and Prelude signal processing equipment (2005 Q1 - 2006 Q4)
       • +/-1° of galactic latitude, from galactic longitude 0° to 90°.
       • 2-beams scanning in constant galactic latitude, 28 MHz bandwidth per beam
       • near-real-time searches for CW and pulsed signals
       • 10 hours per day (exclusive control of array, not commensal modality)
       • 80,000 pointings at 10 seconds per point
       • Detection limit ~5 × 10^-24 Wm^-2 (3 x 10¹⁸ W EIRP at 25,000 ly)
     • SETI - targeted search of between 10⁵ and 10⁶ solar-type stars using SonATA signal processing equipment (2007 Q1 - 2016 Q4).
       • 1 - 10 GHz frequency range
       • 300 seconds per beam per frequency × 2 or 3 lookbacks
       • Initial observations will use 4 phased array beams with 100 MHz each
       • Evolve to using 8 phased array beams with perhaps 1 GHz of bandwidth each.
       • Near-real-time searches for CW and pulsed signals, expanding over time to include more complex and noise-like classes of signal
       • Near-continuous commensal observations
       • Detection limit ~1 × 10^-25 Wm^-2 (10¹⁴ W EIRP at 1000 ly)

5. Synergies with other major forefront facilities
   
   • Down link for bistatic radar from Arecibo or Goldstone.
   • VLBI station in conjunction with VLBA, HSA, etc.
   • Rapid response to GRB or other transient phenomena (no feed change required 0.5 - 11.2 GHz, fully steerable horion to horizon with slew rate < 4°/sec, dual-polarization).

6. Unique contributions
   
   • 22 to 1 bandwidth, simultaneous access to 0.5-11.2 GHz
   • fast survey speed (wide primary field of view and 15,000 pixel imaging resolution with 1024 channels per pixel from correlator),
   • excellent transient detector,
   • simultaneous ability to image primary field of view and position up to 16 dual-polarization phased array beams,
   • ability to form wide bandwidth and wide angle nulls anywhere on sky,
   • excellent psf for correlator and phased beam with < 1% near-in sidelobes,
   • excellent snapshot images (61075 baselines),
   • ability to image below 1 GHz (HI to z=2),
   • supports multiple scientific users simultaneously.

V. Education/Outreach activities

1. Visitor facility
   Hat Creek Observatory currently hosts nearly 1000 visitors each year, even though it does not yet have a formal visitor center. These visitors are primarily school classes during the academic year, and families on vacation during the summer. With the start of construction of the ATA, there is increasing public interest in the facility and plans have been drawn up to convert an old laboratory building close to the site access road into a temporary visitor and information center. The EP/O office at the SETI Institute has begun discussions with the Turtle Bay Exploration Park located in Redding, CA about one hour from the site. During the construction of the ATA, exhibits will be developed for use at Turtle Bay and a formal program of guided tours to the site will be established. In conjunction with the staff at Turtle Bay, a formal proposal will be developed for submission to the McConnell Foundation (whose philanthropy is targeted at Shasta and Lassen counties in Northern CA) and the NSF for the construction and operation of an ATA visitor center that involves people of all ages and abilities with the observatory and its scientific programs, without exposing the site to the interference produced by people with digital electronics and automobiles.

2. Student programs
   Following the very successful practice of the BIMA facility at the Hat Creek Radio Observatory, the ATA will continue to host an intensive, week-long, residential Summer School at the array for interested students, post-docs and researchers during the summer months (historically in June). This Summer School will train new users about the use of interferometers in general, and the ATA in particular. It will involve actual observations taken and analyzed by each participant during the course of the Summer School. Staff from the University of California, the SETI Institute and other qualified staff will provide the presentations and oversight to effect this Summer School. In partial compensation for this training, participants will be requested to return to Hat Creek for one week during the next year to serve as an observer in residence, whose general duties are to maximize the scientific output of the scheduled observations. Opportunities for participation in the Summer School will be widely advertised, and will be open to all applicants subject only to restrictions on the number of individuals that can be accommodated by the on-site residence facilities.

VI. Documentation/website URLs

1. URL of facility website
   
2. URL of EPO website
   
3. URL(s) of any brief overviews of project/facility
   http://astron.berkeley.edu/ral/home.html
4. http://www.kintera.org/site/pp.asp?c=ktJ2J9MMIsE&b=179290

5. URL(s) of miscellaneous documentation
   http://intranet.seti.org/docs/ata/ Note: this is not a public website.