Quick Start Maunal for CRUSH.



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

	1. Installing CRUSH
	2. Running CRUSH
	3. Brightness Settings
	4. Time Constants
	5. SHARC2 In-band opacity
	6. Calibration
	7. High-Pass Filtering
	8. Extended Sources



1. Installing CRUSH
===================
Read INSTALL.


2. Running CRUSH
================

Run crush from within the directory. Most scans shold reduce properly 
without specifying any options. Sometimes you may wish to override some of 
the scan specific options, like pointing (-fazo=, -fzao=), or coordinate 
epoch (-epoch=) or rotator zero angle (-rot0=) which were recorded 
erratically during the January 2003 run. To see what options you have 
available run 'crush [options] -help', or simply 'crush' without any 
arguments. For available configuration keys, see crush.cfg.


3. Brightness Settings
======================

Setting the appropriate source brightness is crucial to getting the
result you want. Crush solves for terms (sky, bolometer drifts etc. --
and source model) sequentially. Generally speaking you want to solve for
these terms in order of the contained signal strength. While most of these
terms are thus ordered already, the only question remaining is where the
source you are observing fits into the picture. Crush 1.2 is smart enough
to determine this on its own (based on the first listed scan), and will do
that by default. If, however, you wish to retain more control, here is
what you can do.

There are two ways to set the source brightness. You can do this by 
loading one of the supplied configurations with the appropriate command 
line flag, or by defining the brightness directly. To use the 
configurations, the following flags are defined:
	
	-default	Any
	-bright		> 1,000 Jy
	-faint		100 mJy - 1 Jy (point like)
	-deep		< 100 mJy (point like)

Your other option is to set the brightness more directly either by the
SOURCE_BRIGHTNESS key in a config file (e.g.  crush.cfg), or by the
-brightness= option in the command line. The following values are
recommended:
	
	auto	Should be able to detect the correct brightness value
	       	on its own. This is default. If, however, it fails, or one 
		wishes to try a different value, then read on. Use 
		together with the -diameter= flag or SOURCE_DIAMETER= key
		for better estimates. (Default diameter of 30" should
	        work well for most but the most extended sources.)

	12	> 10,000 Jy
	11	1,000 - 10,000 Jy
	9	10 - 1,000 Jy
	8	1-10 Jy (extended)
	7	1-10 Jy (compact or low stability)
	5	100 mJy - 1 Jy (extended) 
	4	100 mJy - 1 Jy (point like or low stability)
	2       < 100 mJy (extended)
	0	< 100 mJy (point like)
		
These brackets are somewhat approximate (within an order of magnitude),
and are designed for the best 350um weather (tau(225GHz) < 0.05). As
tau(225GHz) approaches 0.1, you may safely increase all bracket fluxes by
an order of magnitude.


4. Time Constants
=================

Some models have characteristic time constants associated to them, which
determine how often is the model approximated on the data. These time
constants are given by an integer number that is a multiple of the
recorded frame rate (36ms frames are default). A value of 30 is equivalent
to ca. 1 second.

Most of these should be set optimally in crush.cfg, but you can choose to 
change them and see what happens. 

Values of 'auto' are interpreted for -driftT=, -row0T=, -muxT= and 
-regionT= flags (PIXEL_DRIFT_T, ROW_OFFSET_T, MUX_T, REGION_T keys), which 
when defined, will attempt to determine the optimal setting based on the 
first scan supplied. This is still somewhat experimental for the time 
being, so use it with care if really want to.

5. SHARC2 In-band opacity
=========================
A linear tau dependence can now be described to a parametric tau value. 
This is done by the TAU_LINEAR_DEPEND key or -tauScale= flag. Both take an 
argument of the form:
                                                                                
	id(A,B) where tau(id) = A * t + B
                                         where t is the tau parameter.
                                                                                
By default t is equivalent to the 225GHz tau. If you want to change this, 
and make the parameter to which other opacities are related become some 
other value, say the 350um tau, you can do this by setting the argument 
to:
                                                                                
	350um(1.0,0.0)
                                                                                
This will set tau(350um) = 1.0 * t + 0.0, that is t = tau(350um).
                                                                                
The reserved id's used by crush are:
                                                                                
	'225GHz'    to specify the 225 GHz radiometer tau.
	'350um'     to specify the 350 um dipper tau.
	'Sharc2'    to specify the tau in the Sharc2 pass-band.
                                                                                
By thefault 350um filter operation is assumed. If the data was taken by 
another filter setting, you must adjust the tau(Sharc2) value accordingly. 
You may do this by uncommenting the appropriate definition in crush.cfg 
(these are rather approximate for the time being), or by specifying it 
directly in the above described fashion.
                                                                                
Similarly, -tau225= and -tau350= flags have been replaced by the new flag 
-tau=id:value. E.g. to explicitly specify a 225GHz tau value of 0.042, use 
the flag: -tau=225GHz:0.042

Notice, that the TAU225 key in the output fits has also been changed to 
simply TAU, and is now carrying the in-band tau that is parametrized by 
the id 'Sharc2'.


6. Calibration
==============

DETECTOR_V_TO_JY configuration key or -Jy= option flag determine the
calibration. The Calibration is defined as the Voltage (V) at the detector
stage for a uniform gain pixel for a 1Jy per SHARC2 pixel area (4.85
arcsec^2) source (NOT 1Jy/beam!!!). The supplied calibration is derived
for Apr 2003, and is only approximately correct for other times, as
changes on the DSOS (Dish Surface Optimization System) were made
throughout 2003, affecting beam efficiencies, and due to an instrumental
change in SHARC2 itself (in Aug 2003) reducing the incident background on
the detector array, and thus affecting its overall responsivity. Work is
in progress to improve on the calibration to account for dependency on
background loading and elevation (beam efficiency).


7. High-Pass Filtering
======================

As of 1.2b6, there is a possibility of high-pass filtering the time 
stream. This may have benefits when the source is relatively compact, 
and/or the scanning speed is large. For s source with angular size D, and 
scanning speed v, you want to set the filter time scale >> D/v. The 
setting 'auto' will attempt to do just that by setting the time scale to 
10 D/v. Beware thuogh, that the high pass filtering may affect your 
calibration if as some components of the source will inevitably filter out 
as well (thuogh their contribution may be kept reasonably small by 
carefully selecting filtering parameters). However, high-pass filtering 
may present the only option for reasonably looking maps under poor 
stability, especially for large box scans with faint structures.
The filter is set by the -hipass= flag or "HIGH_PASS_FILTER" key. The 
value 'off' diables the filter (default).

8. Extended Sources
===================

Extended sources provide the most challenge, both because the redundancy 
of a larger scan pattern is lower -- making it harder to disentangle the 
various terms from the data, -- and often because some instrument specific 
terms (row dirfts) and sky stabilities (regional correlations) can 
interfere with faint extended source structures. Here's a little FAQ 
to help dealing ewith difficulties:

	Q: Baselines are not flat, what can I do?
	A: Your best bet is to change the brightness setting used
	   (with the -brightness= flag). If the brightness is 11 or 12, 
	   then the variation in the sky emission will be responsible 
	   for the baseline. Decrease it to < 11.
	   More likely, though, the baselines are due to gradients, row 
	   drifts and/or regional correlations, which happen on a faster
	   scale than what it takes for the scan pattern to cycle. To 
	   avoid this problem, you can either change the brightness such
	   that the source follows the suspect term(s), or increase the 
	   time constant of the suspect models to high enough values to
	   get rid of the unwanted interference. The first method will
	   likely be more effective, but can also filter large scale 
	   structures.
	   An alternative or complementary solution is to use the high 
	   pass filtering capability in the time stream (with the -hipass=
	   and -diameter= flags). See more above.
	   It may also help to add in scans with considerable parallactic 
	   angle rotation, if they exist, which will increase redundancy.	

	Q: There are negative ridges or regions around my compact sources. 
	   How can they be made to disappear?
	A: Either increase the brightness setting, with the -brightness= 
	   option, or try using the -Ifidel= flag together with the 
	   -cutoff= flag. The latter will focibly clip out negatives below
	   the desired cutoff level for the specified number of 
	   iterations.
	
	Q: Extended structure seems missing, where did it go?
	   Models like row drifts, bolometer drifts, regional correlations
	   will, unfortunately interfere with extended sources. 
	   Increaseing the brightness setting so that the source 
	   extraction precedes the suspect model will do away with the 
	   unwanted interference, but you may pay the price of heavier 
	   baselines in the map. Otherwise, you can try increasing the 
	   model time scale, for those that precede source extraction, 
	   to values that compare to the time necessary for the sweep
	   to cross the expected structure.
	   Also, if you are high-pass filtering, make sure it is done
	   on a time scale >> source crossing time.
