lwscoadd

Name

lwscoadd -- Convert raw 6-dimensional LWS image to 2-D frame

Usage

lwscoadd input output

Parameters

input: List of input images to process. These must be 6-dimensional raw LWS images. Wildcards may be used to select multiple files. An "@"-file may also be used.
output: List of output co-added images to create. This may be either a list of files (in which case the number of input and output images must match), a directory name (in which case the output images will have the same names as the input images), or a blank string (legal only if the CL environment variable clobber=yes, in which case the output images will replace the input images).
verbose = yes: Flag which determines whether or not to echo the actions being taken.

Description

The lwscoadd task takes as input a raw image produced by the Long Wavelength Spectrometer (LWS) at the W. M. Keck Observatory (WMKO) and outputs an image which properly combines the various layers of the input. The raw LWS images have the following dimensions:

detector columns: Index of detector column or "x" coordinate, from 1 to 128.
detector rows: Index of detector row or "y" coordinate, from 1 to 128.
chpbeams: Index of chop beam, 1 for on-source and 2 for off-source.
savesets: Index of the save set; i.e., number of disk writes during a nod set.
nodbeams: Index of nod beam, 1 for on-source and 2 for off-source.
nodsets: Index of the nod set; i.e., number of nods during the exposure.

Processing consists solely of subtracting the appropriate chop-off beams from their corresponding chop-on beams, and subtracting nod-off layers from corresponding nod-on layers; i.e., taking the "double difference." Images are properly processed whether taken in stare, chop, or chop-nod mode.

Examples

To convert a single raw LWS image into an output image in the same directory:
```
	cl> lwscoadd lws00001.fits coadd00001.fits
```
To convert a single raw LWS image into an output image of the same name in a subdirectory named coadd/:
```
	cl> lwscoadd lws00001.fits coadd/
```
To replace all LWS images in the current directory with their co-added versions:
```
	cl> lwscoadd *.fits
```
This will only work if the CL environment variable clobber = yes.

Time Requirements

To process a 32MB raw LWS image on a lightly-loaded UltraSPARC 10 requires less than 4 seconds, which is much faster than equivalent IDL routines.

Algorithm

The algorithm can be described as follows:

    for( each line in the input image){
	set default sense to "positive";
	negate the sense if this layer represents the CHOP OFF beam;
	negate the sense if this layer represents the NOD OFF beam;
	add this line into the final array;
    }

Notes

Clobbering of the input image is supported if the CL environment variable clobber = yes. To disable clobbering, issue the command
```
	cl> reset clobber = no
```
on the IRAF command line, or in your loginuser.cl file.

Author

Gregory D. Wirth, W. M. Keck Observatory

Support

Send questions to the

Revisions

lwscoadd v1.1 1999-Oct-27: Fixed bug in lwscoadd() procedure: data array not zeroed
lwscoadd v1.0 1999-Oct-26: Original public release.
lwscoadd v0.0 1999-Jun-30: Original internal release.