CASA VLBI Workshop 2023

5 Jun 2023, 09:00 → 9 Jun 2023, 18:00 Europe/Amsterdam

JIVE

In the late spring of 2023, from 5-9 June, JIVE will be hosting the third edition of the CASA VLBI workshop. The aim of this workshop is to train participants on data processing and imaging of VLBI observations with the CASA package. Though the focus will be on continuum astronomical experiments, other applications of VLBI will be discussed. Participants are expected to have a basic understanding of radio interferometry, but do not need to be experts. Introductory lectures on VLBI and CASA will be part of the programme.
 

The programme will consist of lectures and hands-on work, in a roughly 50/50 division. The lecture topics include basic VLBI calibration, imaging and self-calibration, as well as more advanced topics like polarization calibration, spectral line and wide-field experiments.

 

For the practical work we expect the participants to bring their own laptop with a working version of CASA 6 and, optionally, their own data. Support for EVN, e-MERLIN and LOFAR data will be available on site, but participants are welcome to bring any VLBI dataset of their choice. 
 

This 2023 workshop edition will be in hybrid format. All lectures will be live-streamed and recorded. A messaging service will be available for all participants for discussions and questions. However, the hands-on data processing will only be done in-person. Registration is mandatory for both in-person and online participants. Please note that there is a cap of 50 participants for in-person participation.

 

The event is over.

 

Useful mailing lists

 

• CASA information lists: casa-announce, casa-news 
• EVN News and announcements: evntech mailing list
• Subscribe to the eMERLIN mailing list here
• The VLBI list at NRAO for any NRAO based news related to VLBI
• The NRAO-eNews list to receive the NRAO call for proposals
• The LOFAR mailing list for any news related to LOFAR 

 

Getting more help

 

Here are some standard places to look for answers:

• Questions about the EVN proposals: evnpc@jive.eu
• Questions about EVN data processing: usersupport@jive.eu
• The DARA tutorial pages for ERIS2022
• The CASA Docs page is the main go-to for information about tasks, task parameters, examples
• The CASA Guides contain several examples but can be out-dated in some places
• CASA Knowledge base contains tips and tricks from users and CASA developers
• CASA Memo series has more in-depth articles about the CASA workings
• Questions and feedback for the CASA development team can be sent to casa-feedback@nrao.edu
• You can file a report at the NRAO Helpdesk for bugs, feature requests, or other problems you encounter.
• To stay up to date about CASA you can subscribe to the CASA Newsletter through this link

 

 

     

This event has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101004719.

Monday 5 June

11:30 Registration Open

12:30 Lunch

1 Start: welcome

Welcome address.mp4

2 Lecture 1 Introduction to interferometry & calibration

Speaker: George Moellenbrock

Lecture 1 .mp4

3 Lecture 2 Introduction to CASA

Speaker: Bjorn Emonts

Lecture 2.mp4

15:45 Break

4 Lecture 3 Introduction to CARTA

CARTA, Cube Analysis and Rendering Tool for Astronomy, is a new image visualization and analysis tool designed for ALMA, VLA, and SKA pathfinders. Its focus is the support of large image cubes (several hundred GB to a few TB). In this tutorial, we will provide some basic information about the CARTA development project, as well as basic usages of CARTA for continuum, spectral line, and polarization images. Lecture slides and image data for hands-on exercise will be provided.

Speaker: Kuo-Song Wang

Lecture 3.mp4

Tuesday 6 June

5 Lecture 4 VLBI instruments and data access

• 9:00 - 9:15 EVN -- Zsolt Paragi
• 9:15 - 9:30 VLBA -- George Moellenbrock
• 9:30 - 9:45 e-MERLIN -- David Williams
• 9:45 - 10:00 LOFAR -- Emanuela Orru'

Lecture 4.mp4

6 Lecture 5 Amplitude calibration in CASA

One of the major differences between calibration of connected-element
interferometry data (VLA, ALMA) and calibration of VLBI data is how
amplitude calibration is done. This lecture will discuss how
amplitude calibration works for VLBI, how to obtain the relevant
metadata in a form that can be used with CASA and the CASA tasks
involved in creating and applying the amplitude calibration for VLBI data.

Speaker: Mark Kettenis

AmplitudeCalibration.pdf

Lecture 5.mp4

11:00 Break

7 Lecture 6 Fringe fitting and other VLBI specifics in CASA

When combining signals from separate antennas to do interferometry, we focus our observation on a phase centre by applying appropriate delays based on a geometric and atmospheric model. However, the atmosphere isn't perfectly predictable, and signal chains may also introduce delays. In order to be able to average down data for imaging and other analysis we need to calibrate out residual delays by fringe fitting. Building on the Radio Interferometry Measurement Equation, this lecture will explain the theory and the practice of fringefitting in CASA.

Speaker: Des Small

Lecture 6.mp4

12:45 Lunch

8 Data processing A : Introduction to EVN Jupyter-CASA notebooks

Speaker: Ilse van Bemmel

15:30 Break

9 Data processing B

Wednesday 7 June

10 Lecture 7 Imaging

The laborious task of “imaging” consists in the process of transforming the interferometer natural measurements (visibilities) into images. This tutorial will cover the basic concepts, and how to use CASA for imaging radio interferometric data and calculate statistics on them.

Speaker: Cristiana Spingola

Lecture 7.mp4

11 Lecture 8 Self-calibration

Self-calibration is a powerful but delicate technique in interferometry used to improve the calibration of a data set when a moderately bright source is present in the target field, which can boost the dynamic range of target images. It consists of refining the phases and amplitudes of visibilities using a model of the same field we aim to image. We will see why this technique is needed and when it is feasible, and we will explain how to use CASA to obtain and apply self-calibration to VLBI data.

Speaker: Javier Moldon

Lecture 8.mp4

11:00 Break

12 Lecture 9 Spectral line processing

Spectral line data reduction largely follows the logic and steps of continuum data reduction. However, there are a few specific deviations that need to be taken into account. For instance, narrow and bright maser lines could be flagged out, and broad absorption lines could affect bandpass calibration if not taken special care of. More dos and don'ts of spectral line processing in this lecture

Speaker: Olga Bayandina

Lecture 9.mp4

12:45 Lunch & Group picture

13 Data processing C

15:30 Break

14 Data processing D

18:00 Social Event

Thursday 8 June

15 Lecture 10 Polarization calibration

We will review the basic concepts of polarimetry, as well as the astrophysical exploitation of polarization observations, with emphasis in the radio/mm window and VLBI. Then, we will study how polarization is observed and calibrated in radio astronomical interferometry, with emphasis on the peculiarities of VLBI. Finally, we will learn the use, tips and tricks, of VLBI polarimetry calibration software based on CASA.

Speaker: Ivan Marti-Vidal

Lecture 10.mp4

16 Lecture 11 Wide-field data processing

Surveys using the whole field-of-view of VLBI arrays are now possible, permitting sensitive investigations of multiple sources within a single observation. This mode has already borne fruit, with investigations into many different phenomena such as active galactic nuclei, supernovae, and gravitational lenses, across degrees of the sky.

In this lecture I shall outline the differences between standard VLBI observing and wide-field VLBI. I will focus on how we deal with the multiple phase centres, and the extra direction-dependent effects, such as the atmosphere and primary beams. I will conclude by presenting the VLBI Pipeline (VPIPE), a CASA-based, highly parallelised, pipeline that can automatically process wide-field VLBI in a fraction of the observing time.

Speaker: Jack Radcliffe

Lecture 11.mp4

11:00 Break

17 Lecture 12 rPicard and mm-VLBI

High-frequency VLBI instruments, such as the EHT and GMVA, offer the highest angular resolution observations from the ground. To measure the short millimeter wavelengths, excellent weather conditions and telescopes with superb surface accuracies are needed. Hence, mm VLBI observations are typically made with sparse arrays consisting of dishes with small collecting areas. Additionally, short atmospheric coherence times can limit the sensitivity substantially.

In this lecture, I will describe how to deal with these difficulties and properly calibrate mm VLBI data, following the steps of the rPICARD pipeline (https://bitbucket.org/M_Janssen/picard). rPICARD is a generic open-source tool, which allows the VLBI community to obtain reproducible results. Next to mm VLBI data sets, rPICARD can also be applied to cm VLBI data, as well as phase-referencing and spectral line experiments.

Speaker: Michael Janssen

Lecture 12.mp4

12:45 Lunch

18 Data processing E

polarization_tutorial.mp4

15:30 Break

19 Data processing F

Friday 9 June

20 Data processing G

10:15 Break

21 Wrap-up lecture

22 Final remark

12:30 Lunch