QuickLook Data Reduction Pipeline - Keck Adaptive Optics Real Time Data Reduction Software

When observing with adaptive optics, it is often necessary to reduce the images in real-time to adapt to varying conditions and to adopt the correct observing strategy. For example, the integration time can vary with fluctuating Strehl ratio, or the adaptive optics system can be tuned to produce the same image quality on the PSF calibrator and on the object of scientific interest.

To this end, a ``QuickLook'' data reduction pipeline was developed at the W.M. Keck Observatory, designed specifically to reduce adaptive optics infrared observations. The pipeline allows the observer to clean-up the images cosmetically using of FITS keywords and a library of calibration files (darks, flat fields, etc.), to examine the images in many modes, to compute image quality parameters (FWHM, Strehl) and to piece various images together (in mosaics or shift and add). Furthermore, the pipeline accepts data acquired with various observing techniques (dithering, separate sky exposure, etc.).

In this paper, we describe the general philosophy, and general overlay of the pipeline. Different screens of the User Interface are shown to illustrate the principle and feel of the tool, and finally some examples of scientific targets reduced with the pipeline are presented to demonstrate the efficiency of the ``QuickLook'' data reduction tool.

1. Introduction - Pipeline

Schematically, the pipeline consists of 4 distinct steps: reducing the data (cosmetic, camera defects, noise, etc.); viewing and examining the data; extracting quantitative image quality estimates; and assembling the images with mosaicing or shift and adding.

**Figure 1:** Data reduction pipeline Look&Feel.
$\begin{figure} \epsscale{1.0} \plotone{P2-03a.eps} \end{figure}$

This is achieved with the QuickLook Data Reduction Pipeline, where all this can be done without typing a command at the keyboard: a menu driven set of applications, specific to this detector, are used in real-time to streamline adaptive optics observations.

2. Data Reduction

The data reduction consists of selecting an image frame (or series thereof) to reduce and a sky frame; there are a variety of ways to do this (extracting the sky from a dither pattern, combining various sky frames together, etc.) with a variety of interfaces.

Once the files are in the pipeline, all the relevant information is extracted from the FITS header, and the images are reduced: each frame is divided by the number of co-adds. If the integration time is different between the object and sky, the appropriate dark frame (if it exists) is subtracted from both, and the residual of both is normalized to a one second exposure. The images are then flat-fielded and dead-pixel corrected. An option can be toggled on or off to try to remove any periodic noise. Finally, some detector specific operations are performed (the quadrants are shifted by one pixel), the FITS headers are updated and the processed images are written to disk.

2.1. File Architecture

Each nightly directory contains two subdirectories named reduced and calib. All the reduced files go in the reduced directory, keeping their original filename with a suffix describing the processing they have undergone. The calib directory contains the most recent flat-fields, darks and dead pixel maps. The file name contains the information about the file parameters (e.g. flat_H.fits, dark_005.0s.fits).

3. Image Displays

3.1. XDisplay

3.2. XImExam

This program, entirely written in IDL, emulates most of the function of the IRAF ``imexamine'' routine. The major difference is the use of a widget wrapper: the main pull down menu indicates the action of the mouse as it is dragged across the main display window. Most parameters can be adjusted with interactive text areas. Some more advanced parameters can be modified by opening a dedicated window. The screens can be dumped into PostScript or GIF files, either individually or altogether.

The many functions available include: plotting rows, columns (or averages thereof) and histograms; printing image or area statistics and values; plotting contour maps (line or filled) and 3D surface plots (mesh or shaded), image magnification and demagnification, radial plots and Gaussian fitting, Look Up Table adjustments (as in saoimage), linear, square root, logarithmic or wrapped Intensity Transfer Table, etc.