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 raw images acquired by the Imaging Targeting Sensor's Visible CCD (ITS) during the third preflight thermal-vacuum test (TV3) for Deep Impact. The experiments performed during TV3 were designed by the Ball Aerospace team with input from the science team. TV3 was conducted by Don Hampton 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 objective of the TV3 was to test and obtain calibration data of the ITS at or below the expected operating temperature, 243K, during the encounter with comet Tempel 1. Tested calibrations were designed to:  - Determine best focus - Test the photo-response of the CCD by using several calibrated blackbody sources and obtain flats - Measure linearity of the CCD - Measure dark current as the CCD cooled - Measure bias  To meet these objectives, the ITS was tested in the Ball 8 thermal-vacuum chamber; its shroud was cooled with liquid nitrogen. An optical test bench was setup outside the chamber and oriented such that light produced by a source would enter the chamber's window and into the ITS telescope. Various types of visible-wavelength sources were used to test the ITS.  TV3 activities are summarized in the following chart.  Date Range/(DOY) Tests ------------------------- ---------------------------------------- 2003-01-16 to 2003-01-23 Warm tests of the ITS in a clean (016-023) room including horizontal focus, astigmatism, geometric distortions, illumination by a blackbody  2003-01-24 ITS instrument package installed (024) in the Ball 8 thermal-vacuum chamber  2003-01-25 to 2003-01-26 Instrument bakeout (025-026)  2003-01-27 to 2003-01-29 Instrument cooldown; Dark current; (027-029) Images of the interior of the TV chamber, a uniform source  2003-01-30 Instrument is cold (226-233K); (030) Flats using various blackbody sources; Bias; Linearity; Latency; Dark current  For more information about the mission, the ITS instrument, the anticipated flight data, and the cratering experiment, see A'Hearn, et al. (2005) [AHEARNETAL2005], Hampton, et al. (2005) [HAMPTONETAL2005], Klaasen, et al. (2005) [KLAASENETAL2005], Richardson, et al. (2005) [RICHARDSONETAL2005], and Schultz and Ernst (2005) [SCHULTZ&ERNST2005].  Parameters:  The image data are in units of raw data numbers. For TV3, all nine of the image modes, also known as instrument modes, for the ITS were tested:  Image MinExp X-Size Y-Size Mode# (ms) (pix) (pix) Binning Comments ----- ------ ------ ------ ------- ------------------------- 1 3.5 1024 1024 1x1 Shuttered 2 3.5 512 512 1x1 Shuttered 3 3.5 256 256 1x1 Shuttered 4 217.8 256 256 1x1 Not shuttered 5 3.5 128 128 1x1 Shuttered 6 98.4 128 128 1x1 Not shuttered 7 47.4 64 64 1x1 Not shuttered 8 47.4 64 64 1x1 Not shuttered,no overscan 9 3.5 1024 1024 1x1 Shuttered; diagnostic  In this table, MinExp is the minimum exposure time and the term shuttered means the light blocker in the ITS instrument is always used (opened and closed). For all modes, additional exposure time can be commanded. For unshuttered modes, a delay time (duration to wait before the start of the CCD readout) can also be commanded. For more information about the image modes, see Hampton, et al. (2005) [HAMPTONETAL2005].  Data:  Images ------  The data are in the form of FITS files with attached FITS headers and detached PDS labels. One data files contains one ITS image. The fastest-varying axis is considered the X axis and the slowest-varying, the Y axis. TV3 data filenames have this format: Iyymmdd_hhmmss_sss_x.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 'A' for CCD data.  For TV3, 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 pre-pended 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.  All images ITS image modes except 8 and 9 have overclock data in the outermost rows and columns of the image array.  Instrument Temperatures -----------------------  Temperatures at various locations on the ITS were automatically recorded about every 5 minutes by a thermister monitor, a computer. Temperature data, in fixed-width ASCII table format, is available in the DATA/TEMP_LOG. Time stamps in the temperature file are within several minutes of the time stamps in the FITS filenames.  .Ancillary Data:  The DOCUMENT directory provides an image log recorded during TV3. The log contains an entry for each image acquired during TV3 and includes image parameters such as mode and experiment type. The log includes a brief description of each type of experiment performed during TV3 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 TV3.  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.

1) The time stamp in the FITS filename can vary by several tens of seconds of the actual time the image was acquired.  2) Instrument temperatures should be extracted from the temperature table provided in this archive. While some temperatures appear in the PDS labels, these values were extracted from the FITS headers and are not reliable because of uncertainties about how the measurements were being recorded by the ground-support equipment used during TV3. However, temperatures recorded by the thermister monitor and provided in the temperature table are reliable according to Ball Areospace engineers and science team members who have used these data.  3) The project elected store and archive ITS FITS images from flight with the sky orientation during the approach to Tempel 1: East is to the left and North is up. However, ITS FITS images from TV3 were stored in the engineering orientation with East to the right and North up. When comparing ITS FITS images from TV3 to those acquired during flight, a left-to-right flip about the y axis is required for the TV3 data.  4) The images in this archive were used extensively by the science team and Ball Aerospace engineers to verify the instruments were operating within requirements and to calibrate the instruments. These data were reviewed internally by the Deep Impact project before release to the planetary community.