Reducing ACSIS data

A quick guide – for all details see the Cookbook .


JCMT continuum data obtained with ACSIS are written to disk and available at the JCMT or via CADC.


For information on downloading and installing Starlink suite of data reduction and analysis software click here.

Raw Data

Raw JCMT heterodyne data obtained with ACSIS data files follow a fixed naming convention. For instance, within the file name “a20070420_00014_01_0001.sdf“, the sub-sections have the following meaning:

  1. “a”: indicates data has been obtained by ACSIS.
  2. “20070420”: Indicates the UT date on which the observation was take.
  3. 00014″: An index that uniquely identifies the observation within the night in question. So for instance, this file holds data for the 14th observation taken on the 20th April 2007.
  4. “01”: for files with multiple sub-systems this number identifies the sub-system.
  5. 0001“: The sub scan index i.e. if the are too much data to fit into one raw file.
  6. .sdf”: Indicates the file holds data in the STARLINK NDF format.

Quick Reduction

To invoke the ORAC-DR software:


This sets up ORAC-DR to run in your current working directory. You will also need to specify where your raw data is stored. For tcsh users we do:

setenv ORAC_DATA_IN folder/

or for bash:

 export ORAC_DATA_IN=folder/

For help with ORAC-DR simply do:

oracdr -help

To reduce your raw Heterodyne  data using the ORAC-DR software run:

 oracdr -loop file -file mylist.lis

where mylist.lis is a list of raw files (either for a specific wavelength, single/multiple observations/sub arrays) that should be located in the “folder” directory as specified by ORAC_DATA_IN. the raw data will be automatically reduced using a per-defined reduction recipe.

oracdr -loop file -file mylist.lis -nodisplay -log sf

The above is another way of running the ORAC-DR pipeline. In the above example the output will be written to screen and logged in a .oracdr_* file (as specified by -log sf s = screen f = file) and not displayed in an xwindow (as specified -nodisplay).

To really understand what is happening to your data it is advised to also (for the first few times/reductions) run with -verbose. This will print messages from the Starlink engines (rather than just ORAC-DR messages):

oracdr -loop file -file mylist.lis -nodisplay -log sf -verbose

If you have HARP data and one or two receptors are bad it is possible to exclude them (i.e H02 and H08 in this example) from a reduction by using a bad receptors mask by running:

oracdr -loop file -file mylist.lis -nodisplay -log sf -verbose -calib bad_receptors=\"H02:H08\" 

Please note sometimes this will mean you are required to update the default Quality Assurance parameters as fewer pixels will remain in your map.


Data Products

Data that have been reduced by the pipeline have Tsys and RMS for all receptors calculated, the pipeline also find and fits baselines, locates regions of emission using Clumpfind, creates moments maps, velocity maps and integrated intensity images. The output of the pipeline includes the following:

  1. .oracdr_*.log – The ORAC-DR log file
  2. – The files contributing to each group
  3. a20140103_00043_01_cube001.sdf – baselined cube
  4. a20140103_00043_01_integ.sdf – Integrated intensity image
  5. a20140103_00043_01_rimg*.sdf – Representative image (same as integ file), used to form rimg PNG
  6. a20140103_00043_01_sp001.sdf – Spectrum taken from position of peak intensity in the integ file
  7. a20140103_00043_01_rsp*.sdf – Representative spectrum (same as sp001), used to form rsp PNG
  8. a20140103_00043_01_iwc.sdf – Intensity weighted co-ordinate image
  9. a20140103_00043_01_noise.sdf – Noise map
  10. a20140103_00043_01_reduced001.sdf – Final trimmed, baselined cube of the 1st (of n) file.
  11. a20140103_00043_01_rmslo.sdf – Low-frequency noise
  12. a20140103_00043_01_rmshi.sdf – High-frequency noise
  13. – Quality assurance reports
  14. log.noisestats – Noise statistics for each observation and group

Files beginning with prefix a are individual reductions of raw observations, the a simply identifies the data as being an ACSIS obervation. Files beginning  with the prefix ga are coadded reductions of a number of observation (as determined by the files included in mylist.lis). The group files produced are as outlined above with the difference of the ga prefix and the omission of leading zero’s.

  1. ga20140103_43_1_reduced001.sdf – Combined baselined cube
  2. ga20140103_43_1_integ.sdf – Combined integrated intensity image

For larger cubes the reduced file is split into several subcubes with the numbers 001, 002, …, which can be combined using the KAPPA command PASTE.

paste g*.sdf out=fullmap

or then they can be combined into a single co-added map with the PICARD recipe MOSAIC_JCMT_IMAGES:

picard -log sf MOSAIC_JCMT_IMAGES *files.sdf

Visualising Data

Images can be viewed using  GAIA (cubes; GAIA-3D)– in interactive image and cube visualisation tool created by the STARLINK project for viewing NDFs and FITS files.

gaia ga20140103_00043_01_integ.sdf

For greater versatility, the STARLINK KAPPA package contains many commands for visualising images in many different ways, including displaying multiple pictures in a grid, overlaying masks and contours, scatter plots, histograms, etc, etc.

Data can also be viewed in SPLAT (single spectra):

splat a20140103_00043_01_sp001.sdf

Configuration files

ORAC-DR is a pipeline that calls several STARLINK commands in order to reduce your data. the precise behavior of the pipeline is governed by the recipe file.  You can find out which recipe is set in the data header via the FITS header RECIPE keyword in any of your raw files. For example both of these options will return the same result:

>> kappa

>> fitsval ga20140103_43_1_reduced001.sdf RECIPE

>> fitslist ga20140103_43_1_reduced001.sdf | grep RECIPE

It is possible to run with a different recipe (i.e. REDUCE_SCIENCE_GRADIENT). Links to specific reductions can be found in Appendix B – Main Recipes and are executed by entering the following:

>> oracdr -loop file -files myfiles.list REDUCE_SCIENCE_GRADIENT

You can tailor the recipe parameters by supplying a .ini file (called myparams.ini in the following example). This file contains the recipe name (which must match the one assigned to your data, whether from the header or any different one specified on the command line) followed by the options you wish to specify in the following format:

PIXEL_SCALE = 6.0,10.0

For more information about running ORAC-DR click here.

Combining Images

If you have reduced several Heterodyne files that you wish to combine into a single co-added map, this can be done with the PICARD recipe MOSAIC_JCMT_IMAGES:

picard -recpars mypar.lis MOSAIC_JCMT_IMAGES *files.sdf

where the “parameter file” mypar.lis looks like the following, with a mosaic method specified (in this example makemos):

MOSAIC_TASK = makemos

Other useful commands

Header information can be checked with

fitslist a20070420_00014_01_0001.sdf

Fitslist is a powerful tool and with it you can check particular attributes: Dates of observations

fitslist file | grep DATE-OBS
fitslist file | grep DATE-END

Observing conditions:

fitslist file | grep TAU225ST TAU225EN
fitslist file | grep WVMTAUST WVMTAUEN

System temperatures:

gettsys -statistics myfile
hdstrace a20090718_00024_01_0001.more.tsys nlines=all
fitslist file | grep MEDTSYS

Tracking receptor (HARP only):

fitslist file | grep INSTAP

Observing mode

fitslist file | grep SAM_MODE
fitslist file | grep SW_MODE
fitslist file | grep CHOP_FRQ CHOP_PA CHOP_THR

Bandwidth and resolution

fitslist file | grep BWMODE
fitslist file | grep SUBBANDS
fitslist file | grep NCHNSUBS

reference position

fitslist file | grep SKYREFX
fitslist file | grep SKYREFY

Instrument calibration

fitslist file | grep SW_MODE
fitslist file | grep CHOP_FRQ CHOP_PA CHOP_THR

Integration time

fitslist file | grep INT_TIME

Reduction history

hislist out


fitslist file | grep BACKEND

The positional information can be found with (add fullframe for even more info) ndftrace which displays the attributes of the data structure. This will tell you the units of the data, pixel bounds, dimensions and axis assignations.

ndftrace a20070420_00014_01_0001.sdf
ndftrace file fullframe fullwcs

other information in fits extensions can be accessed with

hdstrace a20070420_00014_01_0001.sdf

or in more detail for e.g. Trx with

hdstrace a20070420_00014_01_0001.more.acsis.acsis.trx nlines=all

Files contributing to a coadd can be examined via:

provshow out

Conversion to CLASS format

It is possible to convert the spectra to CLASS format, or the cubes to GDF files, readable by the IRAM GILDAS software package, see here.

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