Quick-Look Data Inspection Tools

Once data have been acquired, there are some simple image inspection tasks you can perform to quickly assess the image quality. These tools answer the questions:

  1. What do the images look like?
  2. What was the mean seeing (FWHM) during the exposure?
  3. What is the sky level?
  4. Are the images round?

etc. These are not meant as analysis per se, but to judge whether or not the data are any good in a global sense (e.g., if an SDT program requires <1-arcsec seeing and the seeing has degraded to 2-arcsec, maybe something else should be done - like checking the wavefront or going to a poor-seeing target instead).

These tools assume you are familiar with how to use IRAF.

Table of Contents

Basic IRAF Setup

Open an xgterm and ds9 window using the icons on the applications panel at the top of the left screen. Iraf should already be set up in the /home/sdtobs/iraf directory. There you will find the login.cl file, uparm directory, etc. If you make any changes to the basic installation, please send a note to observe@lbto.arizona.edu describing the changes.

LBTtools

Some tasks which are useful to list and display images while at the telescope have been incorporated into the LBTtools package maintained by LBTO staff. These are currently installed in the directory /home/lbcobs/dthompson/iraf/LBTtools and loaded by the loginuser.cl file in the sdtobs account, but do not appear in the initial package list. Any suggestions or contributions to this package can be sent to observe@lbto.arizona.edu.

The tasks within the LBTtools package make use of some parameters common to a night's data, and thus the LBTtools parameter set needs to be edited. The tasks within the package also assume a specific subdirectory structure to aid in organization and bookkeeping. So, to set up for use of the LBTtools package:

  • change directory to a working directory:
    • cd /scratch
    • mkdir <UTDate>
    • cd <UTDate>
  • Load the mscred package
  • Edit the parameters for the LBTtools package: type epar LBTtools and specify the following:
    • camera (LBCB);
    • UT date in the format yyyymmdd ;
    • path to the archived images (/Repository); and
    • calibration data directory (leave this as /home/lbcobs/LBT.Calib/)
  • Type LBTtools to load the package
  • Run the task prepdir to set up subdirectories for storing the raw (RAWdata), dark-subtracted (DSdata) and flat fielded data (FFdata) and for the logs (LOGs) and other information (Misc). At the moment, only LOGs and Misc are used by LBTtools tasks.

Quick-Look Inspection Tasks

1. Where are the data?

Starting 2007 Jan 17, all of the raw LBC data are written in the /Repository directory. It is common practice at the start of each night to move the prior night's data to a subdirectory named by the UTDate to reduce the clutter in the main directory.

2. What is in each file?

Alist is an LBTtools task that lists the last N images in the archive and any of the following information:
  • imginfo [timestamp, object name, OB name, exposure time, filter, RA, DEC, PA, Rotator Angle]
  • mirror [mirror position coefficients, for collimation]
  • zernike [Zernicke coefficients in effect for that image]
  • environ [temperature, pressure, and humidity]
Output can be redirected to a file to create a log of the night's observations. Normally only imginfo is needed.

You can also hselect on the images in the Repository directly with:

hselect /Repository/lbcb.*fits[1] $I,objname,obsra,obsdec,exptime,airmass yes

results in

 lbcb.20070112.070915.fits[1]    dark    120.235
 lbcb.20070112.073449.fits[1]    NGC2366 07:28:54.8      +69:12:56.9     60.235  1.24422
 lbcb.20070112.073636.fits[1]    NGC2366 07:29:00.5      +69:13:22.6     60.235  1.24453
 lbcb.20070112.073821.fits[1]    NGC2366 07:28:56.7      +69:13:35.6     60.234  1.24480
 lbcb.20070112.074007.fits[1]    NGC2366 07:28:52.1      +69:13:34.3     60.235  1.24504
 lbcb.20070112.074308.fits[1]    NGC2366 07:28:54.7      +69:12:57.0     36.234  1.24533
 lbcb.20070112.222320.fits[1]    dark    18:37:29.5      +20:41:49.8     0.129   1.65619
 lbcb.20070112.222354.fits[1]    dark    18:37:29.9      +20:41:51.8     0.129   1.66095
and so forth.

3. How do I display an image?

qdisp is an LBTtools task to display an image with mscdisplay and optionally enter mscexam. Images are referred to only by their timestamp hhmmss.

4. How do I measure the mean seeing and sky levels?

On the LBT computers in /home/sdtobs/iraf, there is a script named lbcFWHM.cl. It is loaded on startup of iraf by the loginuser.cl file. To run it in IRAF:

  cl> lbcFWHM /Repository/lbcb.20070117.041619.fits
  image   mean median sky nstar
  tmp.fits  5.09 5.12 10326.47 181

This script measures the mean and median FWHMs of stars in the top half of chip-2 (this is about in the center of the LBC field of view). It only takes a few seconds and shows the average FWHM is about 5 pixels.

Four (4) numbers are printed: mean FWHM of stars, median FWHM of stars, the median sky level and the number of stars used to compute the mean and median FWHM. The program knows to ignore extended objects (defined as FWHM>9 pixels). Note that it will fail if there are fewer than 2 stars in the image segment.

If you want to measure the mean seeing and sky levels in all 4 chips:
  cl>msred
  ms> lbcFWHM lbcb.20070117.041619.fits full=1
  image       mean median  sky nstar
  tmp_1.fits  5.08 5.06 9918.33 417
  tmp_2.fits  5.21 5.25 10343.61 369
  ...
  ...
It takes about 50 seconds to do a full image.

Note that the FWHMs are measured on raw the images assuming a Gaussian, so the values could be off, but it should be good enough for real-time assessment of image quality.

5. How do I make more detailed image-quality measurements?

If you want to make radial plots of stars, contour maps, etc., you can use the mscexamine task:
  cl> mscred
  qdisp 050103
  mscexamine
The mscexamine task works more or less like imexamine, but it knows how to work with the mosaic image display.

R. Pogge, X. Fan, D. Thompson, 2007 Jan 20
Topic revision: r4 - 24 Jan 2007, pogge
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