Nrao vla archive survey
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National Radio Astronomy Observatory. Jared Crossley Loránt Sjouwerman Edward Fomalont Nicole Radziwill. 2008-06-25 SPIE: Observatory Operations: Strategies, Processes, and Systems. NRAO VLA Archive Survey. (NVAS)

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NRAO VLA Archive Survey

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Nrao vla archive survey

National Radio Astronomy Observatory

Jared Crossley

Loránt Sjouwerman

Edward Fomalont

Nicole Radziwill

2008-06-25 SPIE: Observatory Operations: Strategies, Processes, and Systems

NRAO VLA Archive Survey


Nrao vla archive survey1

  • (NVAS)

  • Survey of the VLA Archive generated by an automated data pipeline.

  • Under development since 2006.

  • Data products include: images, calibrated data, diagnostics, logs, …

  • Project ongoing, but data is already available on the Web.

  • http://archive.nrao.edu/

NRAO VLA Archive Survey


Very large array

Very Large Array

  • Synthesis array of 27 antennas

  • Located in New Mexico, USA

  • Operational for 28+ years

  • Maximum baseline: 0.3 to 35 km

  • Frequencies: 0.07 to 50 GHz

  • Produces over 150 papers per year

  • Outputs “visibility” measurements


Typical vla data reduction

“Typical” VLA Data Reduction

  • Project scientists are responsible for all parts of the data reduction process.

  • Download VLA raw data from the VLA Archive.

  • Making images requires:

    • Careful editing and calibration

    • Fast Fourier transform processing

    • Deconvolution methods

  • To make data more easily accessible we have created the VLA Archive Survey


Present state of survey

Present State of Survey


Nrao vla archive survey

Sky Coverage


Nvas pipeline system

1.

Acquire

2.

Process

3.

Archive

4.

Validate

NVAS Pipeline System

  • Makes use of preexisting components:

    • Raw data archive and interface

    • AIPS synthesis imaging software package

  • Perl and shell scripts connect components to form the pipeline.

  • NVAS data is incorporated in the raw data archive. One interface provides access to raw and processed data.


Acquire data

NVAS Pipeline Stages

Acquire Data

1.

Acquire

  • Perl script automates communication with Archive server by HTTP requests.

  • Input start and stop dates for processing

    • Script queries the server

    • Algorithm selects one or more data files

    • Download to local disk

    • Data is loaded into AIPS, split by frequency, and prepared for processing


Data processing

NVAS Pipeline Stages

Data Processing

1.

Acquire

  • AIPS “runfile” (script) performs standard synthesis imaging steps

    (VLARUN)

  • Output data products:

    • Images

    • Calibrated data

    • Diagnostic plots

    • Log files

    • Metadata for Web interface

2.

Process


Nrao vla archive survey

Example image and diagnostic plots:

Crab Nebula at 5 GHz


Archiving

NVAS Pipeline Stages

Archiving

1.

Acquire

  • Shell and Perl scripts

  • Move data products to archive server

  • Generate HTML for survey Web interface

2.

Process

3.

Archive


Validation

NVAS Pipeline Stages

Validation

1.

Acquire

  • Human-interactive process

  • A private Web interface is used to remove low quality data.

  • All NVAS data is reviewed by a human.

  • Less than 5% of images have been removed during data validation.

2.

Process

3.

Archive

4.

Validate


Pipeline system performance

Pipeline System Performance

  • Only data validation requires human interaction.

  • All other pipeline stages are limited by computer and network data rates.

    • Data processing requires the most time; high-resolution imaging may take many hours

  • Survey data is 1.4 TB and growing


Nrao vla archive survey

Data Vault:

7019-47

Access the survey from http://archive.nrao.edu/


Future development

Future Development

  • Finish imaging of VLA continuum data

    At the same time, continue algorithm upgrades:

    • Self-calibration

    • Better data editing

    • Mosaic imaging

    • Composite imaging of long-timescale projects

  • Apply new algorithms to all survey data

  • Process spectral line data

    Expect to finish these stages end of 2010.


Summary

NRAO VLA Archive Survey is…

Summary

  • Automated survey of the full VLA archive

  • Makes VLA data more accessible to all astronomers

  • Provides reference images, calibrated data, diagnostics, logs, …

  • Ongoing survey, expected completion in 2010

  • Currently available at:

    http://archive.nrao.edu/


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