| DATA_SET_DESCRIPTION |
This data set description was provided by Stephanie McLaughlin and
Dennis Wellnitz (University of Maryland), who participated in
the ground calibration tests of the Deep Impact instruments.
Data Set Overview
=================
This data set contains 2-dimensional spectral images acquired by the
High Resolution Instrument's Infrared Spectrometer (HRII) during the
the first preflight thermal-vacuum test (TV1) for Deep Impact.
TV1 was considered a dry run in preparation for the full, second
thermal-vacuum test (TV2) of the HRII instrument. The experiments
performed during TV1 were designed by the Ball Aerospace team with
input from the project's science team. TV1 was conducted by Don Hampton
and Jeff Van Cleve of Ball Aerospace. Several science team members
were present at all times to assist with the experiments and perform
real-time analysis of the data.
The main objectives of the TV1 were to:
- Perform tests at the 3 nominal operating temperatures of optical
bench: 128K, 135K, and 141K.
- Determine best focus at 128K.
- Measure the minimum and maximum wavelengths of the focal plane
array (FPA).
- Determine alignment of a spectral image on the FPA.
- Determine the spatial and spectral dispersion of the FPA.
- Obtain flat fields from various blackbody sources for preliminary
measurements of the response of the FPA at different wavelengths.
- Determine the non-linearity of the FPA.
- Activate the internal stimulator to be used as an in-flight
calibrator.
- Check for stray light.
To meet these objectives, the HRII was tested in the Ball 8
thermal-vacuum chamber; its shroud was cooled with liquid nitrogen
and its instrument plate was cooled with liquid helium. The
High Resolution telescope was simulated by an optical bench that
was setup outside the chamber and oriented such that light
produced by a source would enter the chamber's window and
illuminate the FPA. Various types of emission, absorption, and
black body sources were employed to test the FPA.
Daily tests are summarized in the following chart. Since TV1 was
a dry run, temperature logs were not created for the HRII's
optical bench and FPA. Instead, these temperatures were simply
recorded at the beginning of each test day.
FPA IR Opt.
Date/(DOY) Temp(K) Bench(K) Tests
---------- ------- ------- ---------------------------------
2002-06-27 120-113 155 First light on flight FPA with EM
(178) electronics; CO2 and H20 asborp-
tion lines visible; blackbody
radiation of room visible at
longer wavelengths
.
2002-06-28 90-88 125-123 At colder temperatures, signal
(179) visible across entire array;
Check test telescope boresight;
Tungsten source
2002-06-29 ~92 ~128 Focus test; Internal stimulator;
(180) Argon source; Darks
2002-06-30 ~92 ~128 Best focus achieved; Argon and
(181) Krypton sources; CO2 and H20
absorption lines; Darks; Various
blackbody sources for flats
2002-07-01 ~99 ~135 Argon and Krypton sources; Darks;
(182) Various blackbody sources for
flats; Tungsten source
2002-07-02 ~105 ~141 Argon and Krypton sources; Darks;
(183) Various blackbody sources for
flats; M filter for long wave-
length cutoff; Stray light;
Internal stimulator
For more information about the mission, the HRII instrument,
and the anticipated HRII flight data, see A'Hearn, et al. (2005)
[AHEARNETAL2005], Hampton, et al. (2005) [HAMPTONETAL2005], and
Klaasen, et al. (2005) [KLAASENETAL2005].
Parameters
==========
The image data are in units of raw data numbers. For TV1, all
seven of the HRII's image modes were tested:
Image MinExp X-Size Y-Size #Images
Mode# (sec) (pix) (pix) Output Binning Comments
----- ------ ------ ------ ------- ------- ----------------------
1 2.862 512 256 1 2x2
2 1.432 512 128 1 2x2
3 0.717 512 64 1 2x2
4 2.861 1024 512 1 1x1
5 2.865 512 256 1 2x2
6 1.432 1024 512 2 1x1 Reset then data frame
7 2.864 1024 512 1 1x1 Memory check mode
In this table, MinExp is the frame-to-frame minimum exposure times,
X-Size is spectral dimension and Y-Size is spatial dimension of the
FPA. For all image modes except 6, the reset frame is automatically
subtracted, on-chip, from the data frame and the result is output.
For more information about the image modes, see Hampton, et al. (2005)
[HAMPTONETAL2005].
Data
====
The data are in the form of FITS files with attached FITS headers
and detached PDS labels. One data files contains one HRII
2-dimensional image. The fastest-varying axis (X) is the spectral
dimension and slowest-varying axis (Y) is the spatial dimension
along the spectrometer's slit. TV1 data filenames have this format:
Iyymmdd_hhmmss_sss_xn.FIT where the 'yymmdd_hhmmss_sss' string the date,
time and subseconds stamp provided by the ground-support computer
when it stored the original data file. The clock on the ground-support
computer was set to local Mountain time. The 'x' string' is valued
with 'B' for HRII data and the 'n' string is only used for image
mode 6 (see the last paragraph in this section).
For TV1, the ground-support computer stored data files in a native
image format, called 'IMG'. The raw data numbers were 14-bit and
and left justified. A 100-byte image header was prepended to each
data array. The 'IMG' data were converted to FITS at the Deep Impact
Science Data Center (SDC) at Cornell University, using algorithms
developed by Ball Aerospace for testing of the instruments and to
allow real-time analysis of data during thermal-vacuum tests.
During the conversion, raw data numbers were right justified to
give the actual, true data numbers. Data in the 100-byte image header
are captured in the FITS header.
For HRII image mode 6, the ground-support computer stored a
3-dimensional data file: the first slice was the reset frame and
the second slice was the data frame. To avoid mixing product types
in this data archive for one instrument, the SDC split the reset
and read frames into two separate files, with the reset frame
receiving a filename suffix of '1' and the data frame receiving a
suffix of '2'. This split was also required for TV2 HRII mode 6.
However, by TV4, the ground-support computer was changed so that
each read and data frame were written to separate 2-dimensional
'IMG' files.
Also, HRII spectral images have reference rows and columns that
border the edges on the image array. These areas are not exposed
to light and are simply read out. The number of rows and columns
varies between the types of image modes.
.
Ancillary Data
==============
The DOCUMENT directory provides an image log recorded during TV1.
The log contains an entry for each image acquired during TV1 and
includes image parameters such as mode and experiment type. The
log includes a brief description of each type of experiment performed
during TV1 and a summary of experiments performed on each test date.
The DOCUMENT directory also provides daily reports written by the
test leaders and distributed to the test team and the science
team. The reports describe in detail the test activities as well
problems and successes encountered during TV1.
The DOCUMENT directory includes the local PDS data dictionary used
to produce the labels.
Media/Format
============
This data set is released as a logical data volume.
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