Introduction
Flight Data Products (An Overview)
There are two data records of interest here which are merged post-
flight. The experiment data record comes down over the medium rate
telemetry channel (1.4 Mbits/sec) and consists primarily of CCD images from
the GLO spectrographs and imagers. Post flight, these images are put into
FITS format. A real time data stream from the shuttle contains everything
you ever wanted to know about the shuttle operations. This is called
ancillary data; we refer to it as UCAT data, derived from the official
name. We extract shuttle attitude, thruster firings, dead band limit
cycles, etc. The data rate is 18 Kbaud and gives most data on a one-second
time base. We also calculate several parameters of interest - like
geometric tangent height, solar zenith angle (SZA) at the orbiter, SZA at
the tangent point, etc.
File Structure
File names are generated with respect to the mission event time
(MET). For instance, the first file in the data directory is 2120801B
which means that the record was read out on day 2 at 12:08:01 MET. The
B identifies the detector. The first five letters A-E are the five
spectrographs, A being the red end. The imagers follow: F, G are the
two six-channel imagers, while H is the IR support imagere
Each CCD readout file has a standard FITS header which is attached
at the readout time. It contains all of the instrument characteristics,
the file name, several times to define the exposure, pointing
information, high voltage conditions, CCD read out parameters (how many
pixels were summed), etc.
The readout takes a fraction of a second, but still the file name
of successive related records, such as a set of simultaniously exposed
images, will change by one or two seconds. We have tools to work with
individual CCD's at the raw data level. Although raw data is not included
here, this point is relevant to the processing which takes place.
Directories:
All data files from a single instrument configuration are identified
as a data set and are grouped into one directory. For example, in a
typical orbit of limb observations there would be one dayglow data set and
one night airglow data set. The directory is named from the first file in
the series, 2_1208. The underscore indicates the mission was STS-53
(GLO1). For subsequent missions we use an A for the STS-63/GLO2 mission
(e.g. 2A1208), B for STS-69/GLO3 (e.g 2B1208), and C for STS-74/GLO4 (e.g.
2C1208).
Lists:
The software tools do their work by reference to lists of files
rather than the files themselves. For instance, a DOS directory sort on
spectrograph C (???????C.FIT) to a file C.LST will give the programs
access to all the C spectrograph data when LIST C is used to initiate a
process. Data processing proceeds in the order of files contained in C.LST.
Initial Data Processing
Once the FITS image data has been prepared in a DOS directory format, it is
sorted by name to be certain the data is in ascending time order, which is
expected by subsequent programs. The utility program GETMET produces a
listing (GETMET.DAT) containing each FITS file name in the directory. This
file is processed against the UCAT flight data record. The data in the FITS
headers are used to interpolate the UCAT data and prepare the parameters to
be returned and merged into the FITS headers in the GLO data file. The
returned file, UCAT.DAT, is then merged with the data files. The effect is
to expand the FITS headers and add the attitude and position data. The
merge process is followed by a procedure called MAKESET, which changes the
slightly different file names of related data so they can be identified as
a set. Although the data is recorded at nearly the same time, there are
enoughseconds involved that the file name of successive reads may be
different by one or two seconds. The utility MAKESET senses the first
record in the ascending series AB_____H and changes the names of succeeding
records to the prefix of first record resulting in a SET of spectra or
images. The real time is still preserved in the header. The MAKESET
program produces a MAKESET.LST which is the complete list of the data
"SETS" in the directory and includes selected UCAT data for each data set.
The MAKESET.LST is contained in each experiment data set. The MAKESET.LST
can be printed out across a page in condensed type (landscape format).
When all of the above steps have been performed on the data, the
experiment sets are corrected by leakage subtraction, hot pixel removal,
and brightness calibration. The data is then ready for analysis.
Last Updated: 29 January, 1996
This page is maintained by:
Jesus A.
Ramirez