Science Highlight




ALMA Primer Instructional Videos

Radio interferometry, including with ALMA, is a complex and often non-intuitive field.  Like the ALMA introductory document, Observing with ALMA - A Primer, the brief (5-15 minutes) videos presented here are designed to provide a basic introduction to radio interferometry, calibration, imaging, and other topics.  These videos are works in progress;  new ones are added periodically. You can find the ALMA Primer Instructional Video Series at https://www.youtube.com/channel/UCwTfiIlYuUQr4sRc5iSJaRg

If you have a suggestion for a video, please email naasc-videos(at)nrao.edu.


Concepts of Radio Interferometry

  • An Introduction to Radio Interferometry (Legacy OVRO Video)
    • A brief and entertaining introduction to radio interferometry by Dr. Dale Gray. The video was produced in 1991 to explain how the Owens Valley Radio Observatory solar array worked. The explanation of interferometry remains timeless and can easily be applied to modern interferometers such as ALMA and the Jansky Very Large Array. A must-watch for novices and experts!
    • Length 15m44s
    • Keywords:Fourier transform pairs; uv plane; image plane; visibilities; aperture synthesis; baselines; uv coverage; sidelobes; rotational synthesis; frequency synthesis
  • Largest Angular Scale and Maximum Recoverable Scale
    • With any interferometer, the angular resolution you can achieve depends on distance between the furthest apart antennas, but the antennas which are closest together will limit how large an object you can detect.This video will explain why.
    • Length 4m30s
    • Keywords: Largest angular scale; maximum recoverable scale; angular resolution; missing flux; baselines; zero spacings
  • Estimating ALMA Sensitivities using single dish data
    • This video explains how you can use single dish data (like from the JCMT, APEX, IRAM, etc.) to estimate the sensitivity you'll need when writing an ALMA proposal.It also tells you roughly how to convert between antenna temperatures and flux densities.
    • Length 7m06s
    • Keywords:Jansky; Antenna temperature; flux density; beam; aperture efficiency; beam filling
  • What are sidebands? (planned)
    • heterodyne, sidebands, basebands
  • Double sidebands receivers (planned)
    • Walsh switching, noise, etc.



  • An introduction to Calibration
    • In this video we explore the fundamentals of calibrating interferometric data:why calibration data are needed, how they are obtained, and how they are used to calibrate your data.
    • Length 9m47s
    • Keywords:phase calibration; flux calibration; bandpass calibration water vapour; system temperature
  • An introduction to Self-Calibration 
    • Self-calibration is a powerful tool that can greatly improve the S/N and quality of your image.  Here we explore how it works, why it works, and its limitations.
    • Length 8m17s
    • Keywords:  Phase calibration; Self-calibration



  • An introduction to CLEAN
    • In this video, we take a look at why interferometric images need to be deconvolved, and focus on the CLEAN algorithm and how it works.
    • Length 8m14s
    • Keywords:dirty beam; fourier plane; image plane; clean component; major cycles; minor cycles; residual image
  • Weighting in Imaging
    • We discuss how the issue of weighting arises when imaging your data, various types of weighting, and how to choose the best type/value to use to address your science.
    • Length 6m57s
    • Keywords: uniform weighting; natural weighting; Briggs weighting; robust
    • Video extract shorts:
      • A short, 54s video illustrating how the choice of weighting affects an image; suitable for use in presentations or for a demonstration, can be found here
  • Image Size and Cell Size
    • In this installment, we tackle image and cell size; two of the most important parameters when imaging. We talk about field of view, the relationships between image and U-V plane parameters, and show some of the consequences of poor choices, such as aliasing
    • Length 14m10s
    • Keywords:field-of-view; primary beam; mosaic; image plane; uv plane; resolution
    • Video extract shorts:
      • A short, 59s video illustrating how the image and cell size are interrelated;suitable for use in presentations or for a demonstration, can be found here
      • A short, 58s video illustrating aliasing in imaging; suitable for use in presentations or for a demonstration, can be here here
  • Intro to CLEAN masking
    • We tackle the topic of Clean masking, where we restrict the areas in a dirty image or residual where the CLEAN algorithm can assign components.
    • Length 5m53s
    • Keywords:clean bias; clean components; clean mask; auto-multithresh
  • Multi-Scale CLEANing
    • By default, CLEAN uses delta functions to model the image, but this may not be appropriate for extended emission.In multi-scale cleaning, we supplement the delta function components with wider components that better model extended emission.  This video shows why and how this works.
    • Length 5m59s
    • Keywords: multi-scale; clean components
  • Combining Single Dish Data with Interferometry Data (future?)
    • By combining


ALMA I-Train

These topics, and many more, are covered in much more detail in a series of videos accessible from https://almascience.org/tools/eu-arc-network/i-train