2.3 Suffixes of Files Common to All Instruments

The suffix of an HST file identifies the type of data that it contains. Several types of file suffixes are common to all instruments. These common suffixes are briefly described below. Please refer to the appropriate chapter concerning data structure in the instrument-specific data handbooks for the definitions of the instrument-specific suffixes.

  • Trailer files (suffix "trl") are FITS files containing an ASCII table that logs the processing of a dataset through the data pipeline.
  • Support files (suffix "spt") are FITS files that contain information about the observation and engineering data from the instrument and spacecraft recorded at the time of the observation.
  • Observation logs (suffix ji* or cm*, aka "obslogs") are FITS files that contain information describing how the HST spacecraft behaved during a given observation. More information on these files is given in Chapter 5.

2.3.1 Historical File Structures

Old Version Observation Logs

The engineering telemetry, which is the basis of the observation logs, does not get reprocessed. Thus any significant change in its processing results in a different type of observation log. Such a change occurred in February 2003, when the existing Observation Monitoring System (OMS) was streamlined to reduce the software maintenance costs. Observation logs produced prior to this time have cm* suffixes and contain science specific information, in addition to the pointing information. Observation logs produced after this date have ji* suffixes and do not contain any instrument-specific information.

Observation log headers are divided into groups of keywords that deal with particular topics such as spacecraft data, background light, pointing control data, and line-of-sight jitter summary. The headers themselves provide short descriptions of each keyword. Observation log tables and images record spacecraft pointing information as a function of time. For more information on these files, consult Chapter 5.

PDQ Files

The suffix "pdq" denotes Post Observation Summary and Data Quality files which contain predicted as well as actual observation parameters extracted from the standard header and science headers. These files may also contain comments on any obvious features in the spectrum or image, as noted in the OPUS data assessment, or automatically extracted information about problems or oddities encountered during the observation or data processing. These comments may include correction to the keywords automatically placed in the obs logs files. Production of PDQ files was discontinued on May 9, 2002.

OCX Files

The suffix "ocx" denotes Observer Comment Files which were produced by STScI personnel to document the results of real-time commanding or monitoring of the observation, along with keywords and comments. Prior to April 17, 1992, OCX files were not always archived separately and, in some cases, were prepended to the trailer file. 

After early February 1995, OCX files were produced only when an observation was used to locate the target for an Interactive Target Acquisition. At this time, mission and spacecraft information were moved to the PDQ reports and the Observation Logs (OMS jitter image and jitter table). Like PDQ files, production of OCX files was discontinued on May 9, 2002.