Purpose: Column Pulldown Corrector for Warm-Mission IRAC BCDs and CBCDs
Authors: Matthew Ashby (CfA) and Joseph Hora (CfA)
Date Contributed: 28 Jan 2010
System Requirements: Linux (32 or 64 bit)

This software is not considered part of the pipeline and no installation support from IRSA should be expected.

Information and Download

Download fixpulldown.tar (Tar File, 120 KB)

The IRAC warm-mission column pulldown corrector was written by M. Ashby and J. Hora of the IRAC instrument team. This software is is being made available "as is" for the astronomical community.

This program implements a second-order polynomial fit-and-subtract algorithm that is a significantly better match to the changed behavior of IRAC column pulldown in the presence of bright sources in the warm mission. The fitting is performed separately above and below the triggering pixels, instead of applying a single fit to the entire affected column. The algorithm has been tested on a variety of warm-mission data, including 3.6 and 4.5 micron frames with frame times ranging from 2 to 200 seconds. Better results may be obtained in some cases by applying the algorithm twice, because the convergence criteria were optimized for long exposures (e.g., the 100 sec CBCD frames taken for the SEDS Exploration program) rather than for the short exposures. The program works best when the observed field is free of diffuse emission, because it attempts to flatten and 'zero out' the median flux levels in a given column.

This software consists of a shell script called do_fixpulldown.sh, which serves as a front end that calls a second program called bandcor_warm. The intent is to make it possible to quickly process large numbers of either BCD or CBCD files in a non-interactive (batch) mode. Usage is as follows:

Compile the code with

cc bandcor_warm.c fitsio.c swapbytes.c -lm -o bandcor_warm

and, after the executable bandcor_warm and the shell script do_fixpulldown.sh have been put in the working directory, run the code with the following command:

do_fixpulldown.sh [value] [filelist]

where [value] specifies a threshold such that all columns containing pixels having values higher than the threshold will be treated with the column pulldown correction. [filelist] can be a text file containing the names of IRAC CBCD or BCD frames, or a string with wildcard characters. An example of valid usage is

do_fixpulldown.sh 20.0 @filelist.txt

Be aware that the input images are overwritten by the modified versions, but files will be modified ONLY if they contain at least one pixel exceeding the user-specified threshold. For more information, users can simply type

do_fixpulldown.sh

at the command line.