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3 Data products
The general philosophy followed for the definition of ESO originated data products can be summarized as follows:
-
frame headers contain only information that is relevant to data reduction and analysis and is recorded in astronomy oriented units such as arc seconds for slit widths, etc. (see
section 9
);
-
frame headers contain the non-standard hierarchical keywords, but a tool is provided to translate headers from one semantic specification to another (e.g. hierarchical keywords with ESO names to e.g. IRAF–STSDAS naming conventions); the translation is table driven, the table itself can be provided by the user or by the observatory;
-
a number of log files record all information relevant to science operations; in particular, telescope operations, instrumental configuration, standard–reduction steps and atmospheric conditions are recorded (see section below);
-
a number of auxilliary files/ tables provide a user–friendly view of the data harvest both at the telescope and at home during post-observation data analysis.
This section describes the rules and guidelines applicable to data products covered in this document.
3.1 Observation frames
The ESO data acquisition system delivers observations in FITS format (see
[1]
). They conform to the following rules:
-
Storage Format
Each FITS file includes one or several exposures depending on the instrument/mode used.
- guideline-1
- Multiple windows are stored using the FITS IMAGE extension that allows to store several frames in one FITS file.
-
Headers
The FITS headers delivered by ESO consist of the following groups of keywords: primary keywords, world coordinate system (WCS) keywords, ESO hierarchical keywords, selected operations log entries and possibly comments. Each of these keyword groups is described in detail in the next sections.
- guideline-2
- Keyword values always reflect the actual setting of the parameter or function in question, as opposed to the value that was requested at setup.
-
At acquisition time, the FITS header of a given frame is assembled by the instrument Observation Software (OS) by collecting the contributions to the header from the different subsystems (TCS, INS, DET, etc). Each of these subsystems may contribute primary and/or hierarchical keywords.
- guideline-3
- Only optical elements insersecting the light path in a given exposure are recorded in the header.
- guideline-4
- Header records should be ordered such that primary keywords are listed first (at the header top), followed by hierarchical keywords (see SectionÝ4.3) sorted by category in the following order: DPR, OBS, TPL, GEN, TEL, INS, DET, ESO-LOG keywords, any other
3.2
Log files
The following log files are produced during telescope operations:
-
The
operations log
: records all major operations performed and their results (e.g. telescope presets, instrument operations, detector readouts and possible preprocessing); the operations log starts everyday at noon (UTC) and includes actions, acknowledgments, events and comments throughout the night.
-
The
configuration log
: records the overall configuration in effect during operations such as pointing models, mounted filters, adaptive and active optics parameters; configuration log entries are written at the start of operations (usually at the beginning of the night) to record the configuration in place, and during operations when configuration parameters change.
-
The
conditions log
: records main meteorological and seeing measurements, both ambient and within the dome; typically, ambient conditions would be checked by sensors periodically and their readings recorded in the log every
n
minutes.
-
The
reduction log
: records all standard reduction steps applied and results obtained.
All log files will be stored and archived in the VLT Archive Facility. From there they will be available for engineering monitoring and other needs (see
[5]
for further details). Extracts from each of the logs will be stored on the medium handed over to PI's as part of the standard data distribution procedure. Some log records may also be included in the headers – this is governed by the `class' attribute of a keyword in the corresponding dictionary (see
section 8.3
for more details).
- guideline-5
- By convention, all keywords that identify the configuration in place on a given night are recorded on the configuration log at the beginning of the night and whenever the configuration changes.
A detailed description of log files is given in
section 5
.
3.3 Observation preparation data and VLT parameter files
The preparation of observations, also called
Phase 2 Proposal Preparation
is supported by tools that assist the user in defining target and instrument requirements (see
[10]
). This information is grouped in units called
Observation Blocks
.
In spite of the fact that observation preparation tools will transparently generate observation block parameter files, these files will be editable by the user if she/he wishes to do so. Hence, these files are considered part of the observatory data interface.
The format and syntax of the VLT
Parameter Files
is used by the VLT Control Software (VCS) to store Setup files.
The format of VLT Parameter Files is described in
section 6
.
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Last updated: November 28, 1997
