
	      *** CRUSH User's Manual Extension for GISMO ***

			      Attila Kovacs
			<kovacs[AT]astro.umn.edu>

			Last updated: 10 Aug 2010



Table of Contents
=================

1. Introduction
2. Locating Scans
  2.1 By file names
  2.2 By scan numbers 
3. Extinction Correction
4. GISMO-specific pixel divisions
5. Runs 1 & 2 Peculiarities
6. Glossary of GISMO-specific options






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1. Introduction
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This document contains information specific to using CRUSH-2 to reduce GISMO 
data. It is assumed that you are already familiar with the contents of the main 
CRUSH-2 README (inside the distribution directory), especially its Section 1 
(Getting Started). 

If you run into difficulty understanding the concepts in this document, you
will probably find it useful to study the main README document a little longer.





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2. Locating Scans
#####################################################################


GISMO scans are typically stored in a filing hierarchy, organized by source 
name, then an IRAM scan ID (itself composed of a UT calendar date and a scan
number).

For example, files for scan 79 taken on 2010-04-12 (of Mars) are stored under 

    <datapath>/Mars/2010-04-12.79/ 

relative to the main GISMO data directory <datapath>. Inside the scan 
directory, you will find several files. The ones ending with

    [...]-GISMO-IRAM-condensed.fits

contain the merged data, which can be reduced by CRUSH. 

You can instruct CRUSH several ways how to locate your data. Your main options 
are either by their file names, or via a combination of 'object' name, 'date' 
and scan number. The latter approach is especially useful for specifying 
multiple scans taken on the same object, and over a handful of days, since it 
allows you to list scan numbers and ranges for convenience.

You can find a more detailed explanation below.



2.1 By file names
=================    

   For single scans, it may be the simplest to specify the file name itself
   (especially if your OS or shell supports autocompletion). Simply 
   give the file name, either as a fully qualified path name, or relative
   to the 'datapath' setting. Thus,

       > crush gismo /data/Mars/2010-04-12.79/[...]-GISMO-IRAM-condensed.fits
       
   and

       > crush gismo -datapath=/data Mars/2010-04-12.79/[...]-GISMO-IRAM-cond \
         ensed.fits
   
   are equivalent.



2.2 By scan numbers
===================

   When reducing several scans together (which is the recommended way to deal
   with datasets), it may be more convenient to use a combination of
   'datapath', 'object', 'date' and the scan numbers, and let crush find the
   desired data files based on these. E.g.:
   
       > crush gismo -datapath=/data -object=NGC3627 \
                     -date=2010-11-08 32-39 43 \
                     -date=2011-02-13 15 19-22 33

   Of course, for each scan, or set of scans, you may add additional options
   such as pointing corrections (via 'pointing') or in-band opacities (via
   'tau'), or calibration corrections (via 'scale') etc.




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3. Extinction Correction
#####################################################################

GISMO, being a 2-mm camera, typically operates with low atmospheric extinction.
Nonetheless, properly accounting for the extinction is important for getting 
the calibration right. By default, CRUSH will reduce the data with a 
guesstimate of the in-band tau value, based on the last IRAM 225GHz radiometer 
measurement before the scan. The scaling of the 225GHz value to 2-mm passband 
is approximate, and is based on the CSO atmospheric transmission model of Juan 
Pardo.

You can also set an in-band zenith tau value based on your estimate directly, 
using the 'tau' option (see the GLOSSARY).




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4. GISMO-specific pixel divisions
#####################################################################

For a general overview of channel divisions, please consult Section 3.
(Correlated Signals) in the main README document.

   mux		A grouping of pixels based on their SQUID multiplexing scheme
		Each 4x8 pixel quadrant of the array is read out through the
		same SQUID amplifier. Therefore, it is not suprizing that 
		correlated signals are present on these quadrants. The
		decorrelating on 'mux' groups is default in GISMO reductions

   pins		The GISMO multiplexing scheme is implemented in the time-domain
		Thus, the first channels of each SQUID are read out at the same
		time, followed by the second channel in each group etc. Thus,
		if there is any pickup of high-frequency signals in the
		multiplexing scheme, one could expect some correlated signals
		to be present on these virtual readout pin groups. There
		is little evidence for these, but the reduction of very faint
		compact sources may benefit from the additional decorrelation
		on these groups.





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6. Runs 1&2 Peculiarities
#####################################################################



  6.1 Coordinate Epochs



  6.2 Pointing



#####################################################################
6. Glossary of GISMO-specific options
#####################################################################

   date=YYYY-MM-DD	Specify the observing date (UT) in the format
			YYYY-MM-DD. This is used for constructing the IRAM 
			scan IDs by combining with scan numbers.
			You also need to specify the 'object' and 'datapath' 
			before CRUSH will be able to find scans by number.
			@See: 'datapath', 'object'

   object=<name>	Give the IRAM catalog name (case sensitive) of the 
			observed object. Use together with 'datapath' and 
			'date' to allow locating scans by serial numbers.
			@See: 'datapath', 'date'

   pcenter=<row>,<col>	@Expert
			Specify the pointing center as a row,col combination 
			on the array. There are 16 rows and 8 columns on the 
			GISMO array, and the numbering starts from 1. Thus, 
			the geometric center of the array corresponds to 
			8.5,4.5. This option is not used (ignored) if pixel
			positions are defined by the 'rcp' option (which is 
			default). In those cases, the pointing center can be 
			adjusted via the 'rcp.center' option.
			@See: 'rcp', 'rcp.center', 'pixelsize', 'rotation'


   pixelsize=<a>[,<b>]	@Expert
			Specify the size of the pixels for calculating pixel 
			positions based on a regular grid. A better way of 
			setting the pixel positions is through the 'rcp' 
			option. 
			The argument can be either a lateral size (in arcsec) 
			for square pixels, or two comma separated sizes for 
			rectangular pixels.
			@See: 'rcp', 'rotation', 'pcenter'

   rotation=<deg>	@Expert
			Specify the array rotation (in degrees), when pixel 
			positions are calculated from a regular grid. A better 
			way is to specify pixel positions via the 'rcp' option 
			their rotation via 'rcp.rotate'.
			@See: 'rcp', 'rcp.rotate', 'pixelsize'

   mux			@Alias: 'correlated.mux'
			@Expert
			Specifies the grouping of channels by the SQUID 
			multiplexing.
			@See: 'correlated.<?>'

   pins			@Alias: 'correlated.pins'
			@Expert
			Specifies the grouping of channels by their virtual 
			pin numbers in the multiplexing time domain.
			@See: 'correlated.<?>'

   pins.group=<n>	@Alias: 'correlated.pins.group'
			@Expert
			Because there are only four SQUID multiplexers in 
			GISMO, there is little redundancy among the pixels, 
			which are read out at exactly the same instant. This 
			option allows to group together <n> consecutive 
			samples, to combine pixels read in some time-interval.
			@See: 'pins'

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Copyright (C)2010 -- Attila Kovacs <kovacs@astro.umn.edu>

