Starlink Project
Starlink Cookbook 22

H. A. L. Parsons, D. S. Berry, M. G. Rawlings, and S. F. Graves

2021 July 15

Copyright © 2021 East Asian Observatory

The POL-2 Data Reduction Cookbook



This cookbook provides an introduction to POL-2 data reduction, using the Starlink facilities Smurf(the Sub-Millimetre User Reduction Facility) and in particular its command pol2map. This cookbook illustrates the various steps required to reduce the data, including an overview of the method. It also describes how to calibrate and display the data as images or vector maps.


1 Introduction
 1.1 This cookbook
 1.2 Before you start: computing resources
 1.3 Before you start: software
  1.3.1 Data formats
  1.3.2 Initialising Starlink
  1.3.3 KAPPA and SMURF for data processing
  1.3.4 GAIA for viewing your images and vector maps
  1.3.5 How to get help
2 POL-2 Overview
 2.1 The instrument
 2.2 Instrumental Polarisation
 2.3 Observing mode
 2.4 The raw data
3 POL-2 Data Reduction – The Theory
 3.1 The data flow
 3.5 PCA
 3.6 Masking
 3.7 Tailoring a reduction
4 POL-2 Data Reduction – Running pol2map
 4.1 How to use pol2map
 4.2 pol2map – producing the initial I map
 4.3 pol2map – producing the I, V, U maps and catalogue
 4.4 Output vectors from pol2map
 4.5 POL-2 FCFs
 4.6 Changing pixel size in pol2map
5 POL-2 Image Display
 5.1 GAIA
  5.2.1 Example 1 – a vector map with no background
  5.2.2 Example 2 – a vector map over a contour map
  5.2.3 Example 3 – a vector map over an image
6 POL-2 – Advanced Data Reduction
 6.1 Adding new observations
 6.2 Experimenting with pixel sizes
 6.3 Investigating systematic error in IP
 6.4 Adding WCS information back into a vector catalogue
 6.5 Re-modelling the error estimates in a POL-2 vector catalogue
 6.6 Changing the de-biasing in a POL-2 vector catalogue
 6.7 Smoothing 450-µm POL-2 maps to 850-µm-map resolution
 6.8 Controlling the masks used by pol2map
 6.9 Checking for convergence in pol2map log files
 6.10 Combining multiple POL-2 fields
A PCA on SCUBA-2 data


CADC Canadian Astronomy Data Centre
FCF Flux Conversion Factor
FITS Flexible Image Transport System
GAIA Graphical Astronomy and Image Analysis tool
HWP Half-Wave Plate
ITC Integration Time Calculator
I Total intensity
IP Instrumental Polarisation
JCMT James Clerk Maxwell Telescope
NDF Extensible N-Dimensional Data Format
P Percentage polarisation
PCA Principal Component Analysis
Ip Polarised intensity
SCUBA-2 Submillimetre Common User Bolometer Array-2
SMURF Sub-Millimetre User Reduction Facility
SNR Signal-to-noise ratio
SUN Starlink User Note
WCS World Coordinate System


[1]   Archibald, E. N., et al, 2002, On the atmospheric limitations of ground-based submillimetre astronomy using array receivers, MNRAS, 336, 1-13 (DOI:10.1046/j.1365-8711.2002.05582.x)

[2]   Bastien, P.,et al., 2011, POL-2: The SCUBA-2 Polarimeter ASP, 449, 68B

[3]   Berry D. S., 2015, FellWalker - a Clump Identification Algorithm, Ast. & Comp., 10, 22-31 (DOI:10.1016/j.ascom.2014.11.004)

[4]   Berry D. S, Gledhill T. M, 2015, POLPACK – An Imaging Polarimetry Reduction Package, Starlink User Note 223

[5]   Cavanagh B., Jenness T., Economou F., Currie M. J., 2008, The ORAC-DR data reduction pipeline, Astron. Nactr., 329, 295 (DOI:10.1002/asna.200710944)

[6]   Chapin E. L., et al., 2013, SMURF – Sub-Millimetre User Reduction Facility, Starlink User Note 258

[7]   Chapin E. L., et al., 2013, SCUBA-2: iterative map-making with the Sub-Millimetre User Reduction Facility, MNRAS, 430, 2545 (DOI:10.1093/mnras/stt052)

[8]   Currie M. J., Wallace P. T., Warren-Smith R. F., 1989, Starlink Standard Data Structures, Starlink General Paper 38.2

[9]   Currie M. J., Berry D. S, 2013, KAPPA – Kernel Application Package, Starlink User Note 95

[10]   Dempsey J. T. et al., 2013, SCUBA-2: on-sky calibration using submillimetre standard sources, MNRAS, 430, 2534 (DOI:10.1093/mnras/stt090)

[11]   Dempsey J. T., Friberg P., Jenness T., Bintley D., Holland W. S., 2010 Extinction correction and on-sky calibration of SCUBA-2, Proc. SPIE, 7741 (DOI:10.1117/12.856476)

[12]   Draper P. W., Gray N., Berry D. S., Taylor M., 2012, GAIA – Graphical Astronomy and Image Analysis Tool, Starlink User Note 214

[13]   Friberg, P., et al, 2016, POL-2: a polarimeter for the James-Clerk-Maxwell telescope, SPIE, Volume 9914, id. 991403 (DOI: 10.1117/12.2231943)

[14]   Gibb A. G., Jenness T., Economou F., 2012, PICARD — a PIpeline for Combining and Analyzing Reduced Data Starlink User Note 265

[15]   Holland, W. S., et al, 2013, SCUBA-2: The 10,000 pixel bolometer camera on the James Clerk Maxwell Telescope, MNRAS, 430, 2513 (DOI:10.1093/mnras/sts612)

[16]   Jenness T., et al, 2002, Towards the automated reduction and calibration of SCUBA data from the James Clerk Maxwell Telescope, MNRAS, 336, 14-21 (DOI:10.1046/j.1365-8711.2002.05604.x)

[17]   Jenness T., et al, 2014, Learning from 25 years of the extensible N-Dimensional Data Format, Ast. & Comp., 12, 146, (DOI:10.1016/j.ascom.2014.11.001)

[18]   Savini, G., et al. 2009, Recovering the frequency dependent modulation function of the achromatic half-wave plate for POL-2: the SCUBA-2 polarimeter, Applied Optics, 48, 2006 (DOI: 10.1364/AO.48.002006)

[19]   Scott D., Van Engelen A., 2005, Scan Mode Strategies for SCUBA-2, SCUBA-2 Data Reduction document SC2/ANA/S210/005