Introduction to Miriad for CARMA users

A new miriad data-reduction carma-specific cookbook is now available: (as draft)

Usage Setup

From the Unix point of view MIRIAD is a set of programs that you can execute from the command line. So your Unix search path needs to be modified for this. For most situations something like

	source /usr/local/miriad/miriad_start.csh

will do, but check your local variations on the path name. For example, Maryland uses a method referred to as astroload. At CARMA, depending if you are in the Owens Valley or at Cedar Flat, you would use /sw/miriad/cvs/ or /array/miriad/cvs/ resp.

Keywords

All MIRIAD programs need a supply of "keyword=value" pairs on the command line. Often many take up a reasonable default, but keywords such as the input file and the plotting device often do not have a default.

vis=: The name of the visibility dataset. MIRIAD datasets are always directories, in which various files live (in MIRIAD often referred to as items)
in=: A more generic name for an input dataset. Most image analysis programs use this.
select=: Select certain visibilities for processing. It is a list of comma separated actions, each of which is logically AND-ed. Example:
select=vis(20,30) would select visibilities 20 through 30.
select=ant(1)(3) would select baselines with only baseline 1-3.
select=ant(1,3) would select baselines with antennea 1 or 3.
line=: Select how to re-sample the line channel data (this includes wideband). Examples:
line=channel,10,5,3,2 would select the 10 channels, starting at channel 5, in steps of 3, with width 2.
line=velocity,20,-100,10,20 would select 20 channels, starting at -100 km/s, in steps of 10, width 20 (km/s).
region=: Selects a certain region (in ra-dec-vel) space to be used for image analyis. Example:
region=box(20,20,30,30)(4,10) would select a region from pixel (20,20) to (30,30) and planes 4 through 10.
device=: the pgplot plotting device. Commonly used are device=filename/ps for postscript, and device=1/xs, device=2/xs for examples of persistent X-windows

The "miriad" shell

Some users, particularly if unfamiliar with a program's inputs, prefer using MIRIAD via an AIPS-like shell called "miriad". This is where you can select a task to run, inspect and set its parameters, and run the task. Start the miriad shell by typing "miriad". Then you can list a program's keywords and any values that are set by typing e.g. "inp uvplt". You can assign values to the keywords with "keyword=value" (e.g. vis=myfile.vis), check its inputs again by just typing "inp", see explanations of the program and its keywords by typeing "help", and then running it with "go". Keyword values are saved until overwritten or explicitly unset. The command "mirhelp miriad" gives some more details.

Help!

The commands "doc" and "mirhelp" .... they explain all the keywords, their meaning and defaults.

Visibility Data Inspection

The data at CARMA are written in MIRIAD visibility format. Here are some frequently used programs to inspect, visualize and calibrate these data.

listobs: Makes a summary of a set of observations.
varlist: List all uv variables in dataset
uvlist: Print data, variables and statistics from uv dataset
uvindex: Scan a uvdata file, and note when uvvariables change.
uvplt: Make plots from a UV-data base on a PGPLOT device.
varplt: Plot and list variables.
uvspec: Plot averaged spectra of a visibility dataset.

Data Calibration and Manipulation

gpplt: Plot and list gain and polarization correction terms.
selfcal: Determine self-calibration of calibration gains.
mfcal: Multifrequency antenna and passband calibration.
uvcat: Catenate and copy uv datasets; Apply gains file, Select windows.
uvcal: Apply special processing options to uv-data.
uvaver: Copy and average a uv dataset.

Mapping

Once calibrated, conversion to an image (the FFT stage) and deconvolution can be done with the following programs:

invert: Transform multi-pointing visibility data into a map
clean: Apply Hogbom, Clark or Steer CLEAN algorithm to a map
mossdi: Apply Hogbom, Clark or Steer CLEAN algorithm to a map (mosaic'd version)
restor: Restore clean components to make the CLEAN map
maxen: Maximum Entropy deconvolution
mosmem: Maximum Entropy deconvolution (mosaic'd version)

Image Data

Images (and cubes) can be inspected and visualized with the following tools:

imhead: List items and pixel values from an image.
histo: Find statistics of image and plot simple histogram
cgdisp: displays and overlays images on a PGPLOT device
imlist: List items and pixel values from an image
imspec: calculate and plot map statistics

Starting with no data

If you have no data yet, and would still like to get started, two programs, depending on what flavor of data you want to use, are useful:

uvgen: Visibility Data

This program needs a few small text files for the description of the source and the antenna configuration. There are examples and templates in the $MIRCAT directory. Here is an example for continuum data:

  % uvgen out=vis1 source=$MIRCAT/point.source ant=$MIRCAT/carma_de.04oct.ant telescop=carma

imgen: Image Data

This program creates maps or cubes, and is very easy to use. Example:

  % imgen out=map1 object=gaussian spar=10,0,0,20,10,30

Installing

Some readers really want to know this ..... but installing MIRIAD on your own machine is actually easy, assuming you have all the right tools, compilers etc. installed. It is known to work out of the box on most Linux and MacOSX machines.. On the simplest level it can be done with the following two commands:

  curl ftp://ftp.astro.umd.edu/progs/bima/miriad.tar.gz | tar zxf -
  miriad/install/install.miriad

after which you can do

  source miriad/miriad_start.csh

If that doesn't work, please refer to the MIRIAD installation guidelines.

Page last modified: Wednesday, 11-Jun-2008 12:50:34 EDT by PJT.