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I recently downloaded some data from the NRAO archive.

It came as a file in the "VLA export format" with the extension .xp1. From what I gather I can open this using some software called CASA or a Python library called casatools using the importvla command.

The trouble is that I can't seem to find any way to install CASA on Windows 10. Infact as far as I can tell CASA isn't supported at all for Windows.

How do I open this file on Windows? I just want a big matrix of data that I can process with my own tools and astropy. Is there some reason that the NRAO distributes data using this (as far as I can tell) arcane and undocumented (I couldn't find any documentation after about 1/2 an hour of looking) file format instead of something like NetCDF or hdf5?

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The VLA data downloaded from the archive is raw data. It contains the output of the correlator in its own format, data on weather, water vapor in atmosphere, turnings of the antennas, wellbeing of each antenna, all calibrators, information which part of the data might not be healthy and why, comments by staff, if any, who examined the data, etc.

CASA allows the user to run the data through the data reduction pipeline, which is designed to process these outputs and deliver “the product”, i.e. calibrated data.

The product is a large file containing the UV data (Fourier transform data) on calibrators and targets. To get images this data has to be imaged and cleaned. Imaging implies doing the inverse Fourier transform. Cleaning implies application of CLEAN algorithm which takes care of the fact that the telescope beam has non-trivial shape.

Unless one knows everything about the telescope hardware and software, it is impossible to make any use of the raw data from the archive. The purpose of CASA is to eliminate necessity of the telescope’s inner working knowledge as well as necessity to write ones own imaging code.

CASA is essential tool. Try NRAO’s Helpdesk. They might know a workaround the Windows issue.

If you are determined to play with data yourself, ask Helpdesk to point you to the documentation about VLA’s correlator and its output format.

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  • $\begingroup$ This is a really good answer, thank you. I'm just interested in getting the raw in phase and quadrature time series, not making images. But now it occurs to that almost all astronomical objects are incoherent sources so this kind of data is going to be hard to come by... It's all going to be squashed by the correlator I imagine. $\endgroup$
    – alessandro
    Commented Mar 8, 2021 at 13:50
  • $\begingroup$ You still need to calibrate to get meaningful data. Here is an idea, if you ask the NRAO people really really nicely, they might process the data through the pipeline themselves and give you the product. $\endgroup$
    – MeL
    Commented Mar 8, 2021 at 20:44
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Have you tried using windows subsystem for linux? That gives you a linux environment inside Windows from which you can install the linux version of casatools.

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    $\begingroup$ That's a good idea, but the problem there is that I'm running Windows 10 LTSB which does not support that feature. I will probably just use a virtual machine based on MeL's answer, but it's kind of inconvenient. $\endgroup$
    – alessandro
    Commented Mar 8, 2021 at 17:17

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