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44.1 Science Data Files

If strfits was used to convert the HST Archive's FITS files (as described in Chapter 3), the image data will be in GEIS format. A directory listing (type dir within IRAF), will show that the files all have a nine-character rootname and a three-character suffix.

By definition, a dataset is the collection of all files produced by the Routine Science Data Processing (RSDP) pipeline for a single HST exposure. The files in a dataset all share the same nine-character rootname or IPPPSSOOT. As defined in Appendix B, the rootname follows a specific naming convention that allows each executed observation to be uniquely tied to the scheduling information from which it originated.

Each file in a dataset has a three-character suffix. For each instrument, this suffix uniquely identifies the file contents. The WF/PC-1 science data file sizes and suffixes are listed in Table 44.1 below.

WF/PC-1 Dataset Suffixes and File Sizes


File Contents

File Sizes

(full mode) 1

Raw Data Files


Raw science data

5 MB


Data quality for raw science data

5 MB


Extracted engineering data

90 KB


Data quality for extracted engineering data

90 KB


Standard header packet containing observation parameters

90 KB

Calibrated Data Files


Calibrated science data

10 MB


Data quality for calibrated science data

5 MB


Histogram of science data pixel values


Saturated pixel map


Trailer file

1 Area mode files are ~1/4 the size of Full mode.

Files whose suffixes end with the letter "h" (e.g., w0lo0105t.c1h) are ASCII header files. The header files contain keywords that describe the parameters used to take the observation, the processing of the data, and the properties of the image. Files whose suffixes end in the letter "d" (e.g., w0lo0105t.c1d) are binary data files; these files contain the data as well as the group keywords. A single GEIS image is composed of a header and data pair (e.g., the files w0lo0105t.c1h and w0lo0105t.c1d together represent a single image, retrieved as w0lo0105t_c1f.fits from the Archive).

The data quality file (.c1h) flags bad pixels; see Table 45.2 for a description of the data quality values and their meaning.

A single WF/PC-1 exposure is obtained as four images (less if fewer than four chips were read out). GEIS files use group format to keep all of the data from a given HST exposure together in a single image file. The data corresponding to each sub-image for the WF/PC-1 are stored sequentially in the groups of a single GEIS image. The header file for an image contains the information that applies to the observation as a whole (i.e., to all the groups in the image), viewable by paging the header. The group-specific (that is, chip-specific) keyword information is stored with the group data in the binary data file; group keywords are only accessible via specialized software such as the STSDAS tasks like hedit or imhead.

WF/PC-1 images are normally four-group images, groups 1-4 representing CCD chips WF1-WF4 or PC5-PC8, depending on the camera used; if only a subset of chips were read out, only a subset of groups will be present. The group keyword DETECTOR provides the identification number of the chip (1 through 8) stored in that group, regardless of the number of chips read out.

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Copyright © 1997, Association of Universities for Research in Astronomy. All rights reserved. Last updated: 01/14/98 16:04:09