| CADC filenames | Suffixes | Description | Examples |
|---|
| RAW files |
| NXXXXXXXX_RAW | _raw | Raw Science,File This FITS file
contains the raw image data received from the spacecraft. One file
per exposure is created (a MULTIACCUM exposure is considered a single
exposure irrespective of the number of samples specified). | N4RK020B0_RAW |
| NXXXXXXXX_SPT | _spt | Support File This FITS file contains
supporting information about the observation, the spacecraft telemetry
and engineering data from the instrument that was recorded at the time
of the observation, including detector temperature measurements. | N4RK020B0_SPT |
| NXXXXXXXX_ASN | _asn | Association Table This file is a FITS
binary table that contains the list of datasets making up an association. | N4RK020B0_ASN |
| Calibrated files |
| NXXXXXXXX_CAL | _cal | Calibrated Science File This FITS
file contains the calibrated science data for an individual dataset,
and is produced by the pipeline calibration task calnica. The input to
calnica are the _raw images. For a MULTIACCUM exposure, this file contains
a single science image formed by combining the data from all samples. | N4RK020B0_CAL |
| NXXXXXXXX_IMA | _ima | Intermediate Multiaccum Science
File This FITS file is also produced by the pipeline task calnica and
contains the calibrated science data for all samples of a MULTIACCUM
dataset before the process of combining the individual readouts into
a single image has occurred. This file is only produced for MULTIACCUM
observations. | N4RK020B0_IMA |
| NXXXXXXXX_MOS | _mos | Mosaic Files These FITS
files contain the composite target and, for chopped pattern sequences,
background region images constructed by the pipeline task calnicb for an
associated set of observations. The input to calnicb are the calibrated
_cal images from calnica and the _asn association table. Target images
are co-added and background-subtracted. The value of the last character
of the rootname is 0 for targets, and 1 to 8 for background images. These
files are only produced for an associated set of observations. | N4RK020B0_MOS |
| NXXXXXXXX_ASC | _asc | Post-calibration Association Table
This table is produced by the pipeline calibration task calnicb, and is
the same as the association table _asn, with the addition of new columns
which report the offsets between different images of the mosaic or chop
pattern as calculated by calnicb, and the background levels computed
for each image. This file is only produced for an associated set of
observations. | N4RK020B0_ASC |
| NXXXXXXXX_TRL | _trl | Trailer File This
FITS ASCII table contains a log of the pipeline calibration processing
that was performed on individual datasets and mosaic products. | N4RK020B0_TRL |
| NXXXXXXXX_PDQ | _pdq | Processing Data Quality File
This FITS ASCII table provides quality information on the observation,
mostly on pointing and guide star lock. Possible problems encountered,
e.g., a loss of guide star lock or a guide star acquisition failure,
are reported here. | N4RK020B0_PDQ |
| NXXXXXXXX_EPC | _epc | Temperature Table This
FITS binary table is produced by the Engineering Data Processing System
(EDPS) as an aid for use in calibration and temperature monitoring. Nine
NICMOS Cooling System (NCS) mnemonics and five temperature sensors are
bundled together into an STSDAS FITS table. | N4RK020B0_EPC |
Note: The *_raw.fits, *_cal.fits, *_ima.fits, and *_mos.fits files are
all defined as science data files, as they contain the images of interest
for scientific analysis.
The data for an individual NICMOS science readout consist of five arrays,
each stored as a separate image extension in the FITS file. The five
data arrays represent:
- The science (SCI) image from the detector.
- An error (ERR) array containing an estimate of the statistical uncertainties (in units of 1) of the science data.
- An array of bit-encoded data quality (DQ) flags representing known status or problem conditions of the science data.
- An array containing the number of data samples (SAMP) that were used to compute each science image pixel value.
- An array containing the effective integration time (TIME) for each science image pixel.
Science Image
This image contains the data from the detector readout. In ACCUM and
BRIGHTOBJ modes the image received from the instrument is the result
of subtracting the initial from the final readouts of the exposure. In
MULTIACCUM mode the images received are the raw (unsubtracted) data
corresponding to each detector readout. In raw datasets the science array
is an integer (16-bit) image in units of DNs (counts). In calibrated
datasets it is a floating-point image in units of DNs per second
(count rates).
Error Image
The error image is a floating-point array containing an estimate of the
statistical uncertainty associated with each corresponding science image
pixel. This image is computed in the ground calibration pipeline task
calnica as a combination of detector read noise and Poisson noise in the
accumulated science image counts (see Chapter 3) and is expressed in terms
of 1 uncertainties. For calibrated MULTIACCUM images (i.e., *_cal.fits
files), the values of the error array are computed uncertainties in the
count rates derived from the linear fit to counts vs. exposure time from
the intermediate readouts.
Number of Samples Image
The SAMP image is an integer (16-bit) array containing the total number of
data samples that were used to compute the corresponding pixel values in
the science image. For ACCUM and BRIGHTOBJ modes, the number of samples
contributing to each pixel always has a value of 1 in the raw data
file. For MULTIACCUM mode the sample values in the raw and intermediate
data files are set to the number of readouts that contributed to the
corresponding science image
Because the number of samples in the raw images for MULTIACCUM, ACCUM and
BRIGHTOBJ modes is the same value for all pixels of an imset, the image
array is usually not created (to save on data volume), and the value of
the sample is stored in the header keyword PIXVALUE in the SAMP image
extension (see Table 2.4 below)
In MULTIACCUM calibrated data files (*_cal.fits) the SAMP array contains
the total number of valid samples used to compute the final science image
pixel value, obtained by combining the data from all the readouts and
rejecting cosmic ray hits and saturated pixels. In this case the sample
array may have different values at different pixel locations (less than
or equal to the total number of samples in the MULTIACCUM sequence),
depending on how many valid samples there are at each location
In the mosaic images (*_mos.fits), the data in the SAMP array
indicate the number of samples that were used from overlapping
images to compute the final science image pixel value
Integration Time Image
The TIME image is a floating-point array containing the effective
integration time associated with each corresponding science image pixel
value. These data are always computed in the ground calibration pipeline
for recording in the raw data file.
For ACCUM and BRIGHTOBJ mode observations, each pixel has the
same time value. For MULTIACCUM observations each pixel for a
given readout has the same time value in the raw and intermediate
data. In these cases, to save on data volume, the image array
is not created and the value of the time is stored in the header
keyword PIXVALUE in the TIME image extension (see Table 2.4).
In MULTIACCUM calibrated data files (*_cal.fits) the TIME array
contains the combined exposure time of all the readouts that
were used to compute the final science image pixel value, after
rejection of cosmic ray and saturated pixels from the intermediate
data. As in the case of the SAMP array, the TIME array can have
different values at different pixel locations, depending on how
many valid samples compose the final science image in each pixel.
In mosaic images (*_mos.fits), the TIME array values indicate the
total effective exposure time for all the data from overlapping
images that were used to compute the final science image pixel
values.
Auxiliary Data Files
The *_spt.fits, *_trl.fits, *_pdq.fits, *_asn.fits, and the *_asc.fits
files are termed auxiliary data files. They contain supporting
information on the observation, such as spacecraft telemetry and
engineering data, assessment of the quality of the observation,
calibration information, and information on the associations present
in the observations.
Association Tables
The association tables, *_asn.fits and *_asc.fits, are FITS binary
tables which are created when a particular observation generates
an association of datasets (see the discussion of "Associations" in
Appendix B). In particular, the *_asn.fits table is generated by OPUS1,
and contains the list of datasets which make up the association (e.g.,
from a dither or chop pattern). The *_asn.fits tables are the inputs to
the pipeline calnicb, which creates the mosaiced or background subtracted
images (*_mos.fits files) from the input datasets. All the datasets
must have been processed through the basic pipeline data reduction
(calnica) before being processed through calnicb. In addition to the
output science image(s), calnicb produces another association table
(*_asc.fits), which has the same content as the *_asn.fits table, along
with additional information on the offsets used by the pipeline for
reconstructing the science image and background values computed for
each image. For mosaics (dither patterns), there is only one final
image produced, with file name *0_mos.fits. For chop patterns, in
addition to the background-subtracted image of the target (*0_mos.fits),
an image for each background position is produced; the file names of
these background images are *1_mos.fits, *2_mos.fits,..., *8_mos.fits
(a maximum of eight independent background positions is obtainable with
the NICMOS patterns; see the NICMOS Instrument Handbook for details).
Support File
The support files, *_spt.fits, contain information about the observation
and engineering data from the instrument and spacecraft that was
recorded at the time of the observation. A support file can have
multiple FITS image extensions within the same file; in the case of a
MULTIACCUM observation there will be one extension for each readout
(i.e., each imset) in the science data file. Each extension in the
support file holds an integer (16-bit) image containing the data which
populates the *_spt.fits header keyword values. One example of useful
information from the support files is detector temperature information,
which can be important when matching DARK reference files to the images
(see, e.g., Section 4.1.3).
Trailer File
The trailer files, *_trl.fits, contain information on the calibration
steps executed by the pipelines and diagnostics issued during the
calibration. There is one *_trl.fits file produced for each dataset,
and, in the case of associations, one *_trl file for each NICMOS product
(i.e., each *_mos.fits file).
Processing Data Quality File
The processing data quality files, *_pdq.fits, contain general
information summarizing the observation, a data quality assessment
section, and a summary on the pointing and guide star lock. They state
whether problems were encountered during the observations, and, in case
they were, describe the nature of the problem. There is one *_pdq.fits
file produced for each dataset, and, in case of associations, one *_pdq
file for each NICMOS product (i.e., each *_mos.fits file).
Temperature Table
The temperature Tables, *_epc.fits, contain a set of 14 mnemonics
(sensors) extracted from the engineering telemetry. The time range of
the tables are over the duration of the corresponding observations. The
selected sensor used to monitor the temperature of the NICMOS detectors
is NDWTMP11, the temperature at the NIC1 mounting cup. A listing of the
individual table names and their location within the FITS table can be
obtained by using the IRAF/STSDAS task catfits. (See NICMOS ISR 2003-008
for more details.) Mnemonics in the temperature table *_epc.fits, report
temperature information within the NCS and five temperature sensors
within the NICMOS dewar. Table 2.7 presents a listing of the 14 NCS and
NICMOS telemetry temperature sensors.
|
(Subscribe to new public observations)
