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![]() | HST Data Handbook for WFPC2 | ||||
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C.1 Observation Log Files
Observation log files associated with each HST dataset contain pointing and specialized engineering data taken during the observation. These data files are produced by the Observatory Monitoring System (OMS), an automated software system that interrogates the HST engineering telemetry and correlates the time-tagged engineering stream with HST's Science Mission Schedule (SMS), the seven-day command and event list that drives all spacecraft activities. This system reports the status of the instruments and observatory and flags discrepancies between planned and executed actions. OMS provides observers with information about guide star acquisition, pointing, and tracking that is not normally provided in the science headers.
The observation log files share the same rootname as the observation they are associated with, except for the final character, which for observation log files is always a "
Table C.1: OMS Observation Log Filesj
" (see appendix B for more on the names of HST data files). When OMS was installed in October 1994, it initially generated files with the suffixescmh
,cmj
,cmi
, which contained header information, high time resolution pointing data, and three-second average pointing data, respectively (see table C.1). OMS observation logs changed to thejih
/jid/jif
image format after August 1995, at which time thecmi
table was renamedjit
to keep the naming convention consistent. In the OMS version of August 1995,cmj
tables were replaced with a jitter image, which is a two-dimensional histogram of jitter excursions during the observation. The suffixes of the GEIS jitter image arejih
for the header andjid
for the image data. Thejit
table accompanies the jitter image. The header file of the image replaces thecmh
file but includes the same information with the addition of some image-related keywords.
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A detailed description of the observation log files can be found on-line:
http://www.stsci.edu/ftp/instrument_news/Observatory/
obslog/OL_1.html
October 1994 to August 1995 cmh
OMS header cmj
High time resolution (IRAF table) cmi
Three-second averages (IRAF table) _cmh.fits
Archived FITS file of cmh
_cmj.fits
Archived FITS file of cmj
_cmi.fits
Archived FITS file of cmi
August 1995 to February 1997 jih/jid
Two-dimensional histogram and header (GEIS) jit
Three-second averages (IRAF table)1 _jif.fits
Archived FITS file which bundles the jih/jid
files._jit.fits
Archived FITS file of jit
.February 1997 onward _jif.fits
Two-dimensional histogram (FITS) _jit.fits
Three-second averages table (FITS)
1 After May 11, 1995, the jit
tables for exposures shorter than 6 seconds contain higher-resolution, one-second average pointing data.
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Pointing and tracking information prior to October 1994 is not routinely available. Interested observers with data from this epoch, can send E-mail to
help@stsci.edu
.C.1.1 Observation Log File Contents (October 1994 version)
Observation logs created between October 1994 and August 1995 contain:
- rootname
j.cmh
: This ASCII header file contains the time interval, the rootname, averages of the pointing and spacecraft jitter, the guiding mode, guide star information, and alert or failure keywords. Figure C.1 shows a representative observation log header file.- rootname
j.cmj
: This table presents the data at the highest time resolution for the telemetry mode in use. It contains the reconstructed pointing, guide star coordinates, derived jitter at the instrument aperture, and guiding-related flags. The intent is: (1) to provide high-time resolution jitter data for deconvolution or for assessing small aperture pointing stability, and (2) to display the slew and tracking anomaly flags with the highest resolution. Table C.2 lists the table column heading, units and a brief definition.- rootname
j.cmi
: This table contains data that were averaged over three-second intervals. It includes the same information as the .cmj
table and also includes orbital data (e.g., latitude, longitude, limb angle, magnetic field values, etc.) and instrument-specific items. It is best suited for a quick-look assessment of pointing stability and for studying trends in telescope or instrument performance with orbital environment. Table C.3 lists the table column heading, units and a brief definition.- rootnamej_cmi
/j/h.fits
: The above three GEIS files are actually archived as FITS files. They may be worked with as such, or run through the STSDAS task strfits, to convert them.- Observation Log File Contents (August 1995 version)
- The contents of observation log files created between August 1995 and February 1997 are as follows:
- rootname
j.jih
: This GEIS header file, the analog to thecmh
file, contains the time interval, the rootname, averages of the pointing and spacecraft jitter, the guiding mode, guide star information, and alert or failure keywords. Figure C.1 shows a representative observation log header file.- rootname
j.jid
: This GEIS image-a significant enhancement of the oldcmj
file-presents a two-dimensional histogram of the pointing fluctuations during the observation. You can display it to visualize the spacecraft stability during you observation, and is information for deconvolutions and PSF analyses.- rootname
j.jit
: This table, the analog to thecmi
table, contains data that were averaged over three-second intervals. Its content is identical (see table C.3).- rootname
j_jif.fits
: FITS file that is actually the de-archived product. This file can be converted to thejih/jid
GEIS file via the strftis routine.- rootname
j_jit.fits
: The de-archived FITS file corresponding to thejit
IRAF table. It can be converted via strfits.C.1.2 Observation Log File Contents (February 1997 version)
The contents of observation log files created since February 1997 are as follows:
Table C.2: Contents of .
- rootname
j_jif.fits
: The de-archived FITS file. Unlike the previous OMS epoch, this FITS file does not bundle a GEIS file and cannot be converted with strfits. This was done to more closely correlate the observation log files with the STIS and NICMOS FITS files with extensions and associations. OMS will normally put all associated observation logs into a single file, to correspond to the associated science exposures. However, if even one science exposure is orphaned (not associated) then an individual observation log FITS file will be produced for every exposure in that association. For a description of STIS and NICMOS association files, see appendix B. All of the information contained in the oldcmh/jih
ASCII header is now available as keywords in the FITS files.- rootname
j_jit.fits
: The FITS file containing the table information. The comments for the_jif
file apply here as well.cmj
Table
Figure C.1: A Representative .jih
or .cmh
Header![]()
Figure C.2: Representative.jih
or.cmh
Header![]()
Table C.3: Contents of .jit or.cmi
Table, Three-Second Averaging
Space Telescope Science Institute http://www.stsci.edu Voice: (410) 338-1082 help@stsci.edu |
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