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

			      Attila Kovacs
			<attila[AT]submm.caltech.edu>

			Last updated: 11 Mar 2012



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

1. Introduction
2. Locating Scans
  2.1 By file names
  2.2 By scan numbers 
3. Automatic Pointing Corrections
  3.1 Setting an IRAM Pointing Model
  3.2 Differential Pointing Model
  3.3 Residual Pointing Corrections
4. Extinction Correction
5. GISMO-specific pixel divisions
6. Runs 1 & 2 Peculiarities
7. Glossary of GISMO-specific options






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1. Introduction
#####################################################################


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. Automatic Pointing Corrections
#####################################################################

A major improvement offered since crush 2.04 is the ability to apply automatic
pointing corrections, (a) via supplying a differential pointing model, and (b)
calculating residual pointing corrections based on the pointing log. The
combination of the two methods allows to reach pointing accuracies down to a 
few arcseconds. Below is a detailed explanation on how to use these methods.


3.1 Setting an IRAM Pointing Model
==================================

   You can use the 'pointing.model' option to specify a file containing the
   effective IRAM pointing constants. These are the P1 through P9 as decribed 
   by Greve, A., et al. A&A, 115, 379, (1996), and the two Nasmyth offsets P10 
   and P11. Additionally P12-P16 contain terms with 2AZ dependence, and 
   refraction correction. The argument of the 'pointing.model' option should be
   a file containing all relevant constants, one per line. E.g.:

	P1 = -3.15
	P2 = -8.41
	P3 = -0.18, -2.4, -4.2
	P4 = 0.1, 17.5, 0.4
	[...]
	P11 = 1.0

   As shown in the example above, each constant can have a single value to
   specify a static term, or a comma-separated list of 3 values for a time-
   variant dynamical model: the static term plus two dynamic terms, Pn0, PnC, 
   and PnS, from which the pointing constant Pn is calculated for a given UT 
   phase (in radians) as:

   	Pn = Pn0 + PnC * cos(UT) + PnS * sin(UT)

   Such dynamical constants can be a powerful way to cyclical variations of
   the pointing model due to a daily cycle (e.g. temperature cycle or heating
   cycle by the Sun). However, if you rather stick to just the static values
   you can set 'pointing.model.static' to ignore the dynamical terms even if
   those were defined.

   The actual pointing correction calculated from the supplied pointing model
   are reported on the console output during the processing of each scan.

   UPDATE: 31.01.2012 ---->

   The new GISMO FITS format (ver 1.7) now includes all IRAM coordinate 
   columns. As a result, crush uses the scanning offsets rather than absolute
   AZ/EL positions for mapping. This seems to solve the pointing problems
   experieced earlier, and provides excellent (<3" rms) pointing in both 
   directions with static pointing constants only. 


3.2. Differential Pointing Model
================================
   
   Instead of specifying the full pointing model, you can also use the 
   'pointing.model' option to set incremental corrections relative to the model
   used by IRAM during the observations, if you set the 
   'pointing.model.incremental' option as well. Then, for adjusting P4, P5, 
   P10, and P11, the file could contain the lines:

	P4 = 2.38
	P5 = -6.12
	P10 = -0.68
	P11 = 4.30

   Now, these values will be added to whatever pointing model was used during
   the observations to calculate pointing corrections. Otherwise, the behaviour
   is the same as described above.


3.3 Residual Pointing Corrections
=================================

   You can also apply residual pointing corrections based on observations
   of nearby pointing sources. It is preferred that you observe pointing
   sources frequently, and preferably at least once withing 30 minutes of all
   your science scans, and withing 15 degrees distance on the sky. The more 
   pointings you have and the closer they are in distance and time to your
   source, the more reliable will be the derived corrections, which are 
   weighted by their relative proximity on sky and in time.

   To apply residual corrections, use the 'pointing.table' option whose 
   argument should specify the pointing log file. Such log files, containing
   pointing information are automatically generated during GISMO runs. However,
   you should use an edited copy of this log, making sure to remove, or comment
   out, all entries with unsuitale pointings. E.g. remove all bogus pointing on
   very faint sources, where the automatic routine may hit a noise peak or
   spike rather than a real source. Remove also any pointing data on extended
   source, objects with multiple peaks or otherwise complex structure, etc.

   For the option to work, the pointing log must contain certain mandatory
   columns, such as 'id', 'UTh', 'AZd', 'Eld', 'pnt.X', 'pnt.Y', 'src.peak'
   'src.dpeak', and 'src.FWHM'. Refer to the main README for details.

   The residual corrections calculated from nearby pointing data are printed
   on the console during the processing of each scan, together with a quality
   indicator (qualities near or above 1 are considered good). 

   The residual corrections can be used together with a pointing model 
   (which is the preferred way to use this option), in which case increments 
   are calculated on top of the model predictions, or without a pointing model
   for an 'absolute' pointing correction. In either case, you can still specify
   an additional correction manually, if desired, via the 'pointing' option,
   as usual. The total combined correction (pointing model, incremental
   correction based on pointing logs, and manual setting via 'pointing') are
   displayed during the scan processing for verification.



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4. 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. (Addition: during the 2011 April run, we confirmed that the opacity
correction based on the radiometer and the atmospheric model works well even
up to 10mm of precipitable water vapor, yielding ~7% rms blind calibration!!!)

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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5. 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

   flips	A modality based on the 'mux' division of pixels, for 
		decorrelating the pairwise alternating currents on the SQUID
		muxes. By design nearby pixels on the readout have wriring 
		traces s.t. the direction of current is flipped between one
		set and the other.

   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



#####################################################################
7. 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'

   pointing.table=<file>	@Advanced
				@Since: 2.04
			Specify the reduction log file (produced via the 'log'
			option) to use for applying incremental pointing
			corrections base on the nearby pointing observations. 
			You can use this option together with 'pointing.model' 
			or separately. For more information see Section 3.2 
			(above).
			@See: 'pointing.model', 'pointing'

   pointing.model=<file>	@Expert
				@Since: 2.04
				Specify a file containing differential
			pointing constants (i.e. relative to those used by IRAM
			during the observations). See Section 3.1 (above) for
			details on the file format.
			@See: 'pointing.table', 'pointing'

   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'

   ver.[<range>]	@Since: 2.11
			@Expert
			Set options for specific FITS merge versions. E.g.
			
			  ver.[<1.7] pointing.model=old.model

			@See: 'ver'

   ver=X		@Since: 2.11
			@Expert
			Force setting the merge version to X, ignoring the
			value stored in the FITS.

------------------------------------------------------------------------------
Copyright (C)2012 -- Attila Kovacs <kovacs@astro.umn.edu>

