| DATA_SET_DESCRIPTION |
Data Set Overview
=================
This data set contains raw pre-encounter and encounter images
taken by the Stardust Navigation Camera during the encounter
with comet Wild 2.
This version contains an error in the exposure times of some of
the images (see 'Exposure Duration' comments below). This error
has been corrected in Version 2.0 of the dataset.
Every image provided in this data set was taken as a part of a
particular imaging sequence, each of which is described in this
section by the NAVCAM Science Lead, Dr. Raymond L. Newburn, Jr.
For the complete list of images and their parameters, refer to
the data set's index table, INDEX/INDEX.TAB. For additional
notes on individual images also consult with the document ``Log
of Stardust NAVCAM Flight Images'', DOCUMENT/PIIMGLOG.PDF,
provided with this data set.
2003 JAN 28 12:33:36 -- Images 477-509
--------------------------------------
The primary purpose of images 477 through 507 was geometric
calibration of images taken through the periscope. Images 508
and 509 were tests of windowing, using a 151 x 151 window.
Photometric calibration of these was a secondary goal. The
target for all images was the Pleiades (M45, an open cluster).
For the primary purpose, the scan mirror was set at one degree
intervals from 0 through 20 degrees. All images showed a
significant amount of scattered light, but they still were
useful for geometric calibration of images taken through the
periscope. The images showed significant doubling with part of
the light coming through the periscope and part of it around
the periscope, the two images separated by about 17 pixels.
None of the images were of significant use for photometric
calibration.
2003 MAY 21 21:09:43 -- Images 510-513
--------------------------------------
After almost four months since the last image, this series of
four images (510-513) was intended as a check of the camera and
the state of its optical system. Image 510, taken through the
periscope, seemed to indicate severe contamination, both of the
periscope and the rest of the optical system. Image 511, taken
of the calibration lamp showed the lamp filament plainly but
also showed a very mottled background. This showed that there
was contamination of both the periscope and the camera optics.
The final images, off the periscope, seemed to indicate that
the camera was in better shape than the periscope. Clearly,
another heating cycle was needed to clean up the camera.
2003 OCT 08 22:11:21 -- Images 514-517
--------------------------------------
Much of the contamination seen in the images 4 1/2 months
earlier was on the periscope, which could not be heated without
turning the Sun on the battery immediately above it. This is
not permitted by spacecraft flight rules. We could, however,
turn the Sun on the camera radiator once again, if necessary.
Images 514 through 517 were an additional check on the state of
the camera, and the camera was found to be heavily
contaminated. The first image, of the calibration lamp, showed
it to be in much worse shape than it had been the previous May.
The other three images, of a star field and off the periscope,
were virtually blank, even with a five second exposure for two
of them.
2003 OCT 11 23:06:37 -- Images 518-521
--------------------------------------
On October 11 the previous cycle of images was repeated as
numbers 518 through 521. A few stars in the two 5 second
exposures indicated that the contamination was now ``only''
about 2 1/2 magnitudes (a factor of 10)! Just turning on the
CCD heater prior to this data set had helped, but not nearly as
much as needed, so commands were sent to put the Sun on the CCD
radiator once again.
2003 OCT 30 15:07:34 -- Images 522-525
--------------------------------------
Following a full heating with the Sun on the radiator and the
CCD and scan mechanism heaters turned on, this set of four
image (522 through 525) was meant to determine how successful
we had been in clearing off the contamination adhering to
camera components. We found that contamination had been reduced
from 2.5 magnitudes to about 0.5 magnitudes (a factor of ten to
a factor of 1.58 reduction in transmission). These much
improved images utilized exposures of one second, five seconds,
five seconds, and finally 20 milliseconds with the calibration
lamp turned on. For some reason, the calibration lamp didn't
seem to have been turned on. (This happened again just before
the Wild 2 encounter. It may have been caused by solar particle
radiation flipping a bit somewhere in the lamp or shutter logic
circuits.)
2003 NOV 08 16:15:03 -- Images 526-527
--------------------------------------
Images 526 and 527 were intended as shutter checks, because the
calibration lamp hadn't appeared in image 525. Image 526 was a
five second timed exposure on a star field. It appeared
perfectly normal. Image 527 tested the bulb mode, where the
shutter is commanded open and stays open until it receives the
close command. This method also worked perfectly. The lack of
an image of the calibration lamp in image 525 remains an
enigma.
2003 NOV 13 06:56:05 -- Images 528-530
--------------------------------------
Images 528, 529, and 530 were 3 second full frames exposed on
the encounter field. We were concerned about the number of
background stars available for optical navigation, this not
being the richest field in the sky. We also wanted to check,
once again, how much scattered light might confront us. As we
expected, there were no severe problems with scan mirror
settings of less then 170 degrees. Since these images were of
the encounter field, chief optical navigator Shyam Bhaskaran
scanned a frame looking for Wild 2. There seemed to be
something at about the correct position. He co-added the three
frames and was convinced he had found Wild 2. Others present at
his request were even more sure that he had found the comet.
These were the first images taken to search for Wild 2, and the
project heaved a huge sigh of collective relief at the comet
having been located in nearly the predicted place more than six
weeks before the encounter.
2003 NOV 17 16:59:59 -- Images 531-555
--------------------------------------
Images 531 through 555 were a test of windowing and pattern
matching. All images in this group used four 51 x 51 pixel
windows, three on stars and one on the expected position of
Wild 2. Image 532, if it ever existed, was not transmitted to
the ground. The proper windows were created in every case, but
the pattern matching varied from no match, to matched with
stars near the edge of the window to stars nearly centered. All
were taken with exposures of 5 seconds (531 through 550) or 15
seconds (551 through 555). Individually, none provided an
obvious image of Wild 2.
2003 NOV 20 17:00:00 -- Images 556-558
--------------------------------------
This was a set of three full frame images. The first of them,
556, was missing some packets and was a bit of a mess. The
other two were fine 5 second and 15 images and served to
confirm quite definitely the presence and location of Wild 2.
Needless to say, having definitely acquired the location of
Wild 2 this early was a huge relief to the STARDUST team.
2003 NOV 24 04:00:00 -- Images 559-583
--------------------------------------
Images 559 through 583 were windowed images, in this case three
51 x 51 images and one 71 x 71 image, the latter the window on
the predicted comet position. Twenty of these were 5 second
exposures and five were 15 second exposures. Eight images were
not pattern matched, while the other 17 seemed to work
perfectly. The image of Wild 2 can be seen in each individual 71
x 71 image, that is properly locked, by using a bit of stretch.
2003 NOV 27 17:00:00 -- Images 584-608
--------------------------------------
Images 584 through 608 were a repeat of the previous set,
except they were divided into 10 at five second exposures and
15 at fifteen second exposures. The same window sizes were
used, 51 x 51 for the stars and 71 x 71 for the comet. This
time only five did not lock up (pattern match). These images
were intended for optical navigation, as was the previous set.
2003 DEC 01 05:00:24 -- Images 609-633
--------------------------------------
Images 609 through 633 were intended to be another set of 25
optical navigation images using three 51 x 51 pixel images and
one 71 x 71 pixel image. Only four of them achieved pattern
matching, however, and those were very poorly centered. These
were of little use.
2003 DEC 04 10:44:18 -- Images 634-673
--------------------------------------
Images 634 through 673 were periscope checks, intended to see
how well the spacecraft could be guided when it had to be
pointed in the ram direction. The first nine frames were full
frame 5 second exposures at a scan mirror angle of 1.94
degrees. All exhibited considerable scattered light. The next
four images were again full frame, but this time at a scan
mirror angle of 1.57 degrees. The exposures were 15, 7.5, 5,
and 3 seconds. Again there was a great deal of scattered light.
The remainder of the frames were taken at a mirror angle of
16.82 degrees. The first two of these were again full frames
using a 15 second exposure. The remainder were all windowed,
using three 51 x 51 pixel sizes and one using 71 x 71 pixels.
They utilized exposures of 5 seconds or 15 seconds. All of
these contained a great deal of scattered light, and none were
successful in pattern matching.
2003 DEC 08 13:00:00 -- Images 674-698
--------------------------------------
The next set of 25 images, 674 through 698, were taken off
periscope at a scan mirror angle of 34.24 degrees. All were
windowed with three windows 51 x 51 pixels and one window 71 x
71 pixels. The first five images had five second exposures, the
next five had 10 second exposures, and the final 15 used 15
second exposures. The first five images did not achieve lock,
nor did the last of the 10 second exposures. The first four 10
second exposures and all of the 15 second exposures achieved a
good lock.
2003 DEC 09 05:00:00 -- Images 699-724
--------------------------------------
This set of 25 images (699 through 724) was taken strictly for
optical navigation purposes. The first five received an
exposure of 5 seconds, the second five 10 seconds, and the
third, a group of 15, received an exposure of 15 seconds.
Pattern matching was not achieved on the first five (699-703),
nor on 705, 706, 708, 710, 714, 716, 718, 722, or 723. Image
724 which is a full frame, shows considerable scattered light
as well as a strange artifact of several adjacent columns. This
artifact also appears in the other images of this group, but
fortunately it does not cross any of the windows. Looking back,
the artifact apparently first appeared in image 701. All of
this still left 11 good images for optical navigation purposes.
P/Wild 2 still is an easy target in the 71 x 71 window of each
image.
2003 DEC 10 05:00:00 -- Images 725-749
--------------------------------------
This set of 25 images (725 through 749) again was taken
strictly for optical navigation purposes. The first five
received an exposure of 5 seconds, the second five 10 seconds,
and the third, a group of 15, received an exposure of 15
seconds. Pattern matching was achieved on only four windows,
730, 732, 734, and 738. The artifact, first seen in image 701,
is apparent in this set of images as well.
2003 DEC 11 05:00:00 -- Images 750-774
--------------------------------------
This set of 25 images (750 through 774) again was taken
strictly for optical navigation purposes. The first five
received an exposure of 5 seconds, the second five 10 seconds,
and the third, a group of 15, received an exposure of 15
seconds. Pattern matching was achieved on only five images, 755
through 759. The artifact, first seen in image 701, is apparent
in this set of images as well, but seems to be fading.
2003 DEC 12 11:59:59 -- Images 775-800
--------------------------------------
This set of images, 775 to 800, was another set taken just like
previous sets except the scan mirror was set at an angle of
31.84 degrees. Again exposures were set at 5 seconds for the
first five, 10 seconds for the second five, and 15 seconds for
the final fifteen. The first fourteen of the 15 second
exposures were windowed, three at 51 x 51 pixels and one at 71
x 71 pixels. The last image was a full frame. The pattern was
not matched on ANY of the windowed images. So we were left with
only one image, number 800, and that had severe scattered light
problems.
2003 DEC 13 05:59:59 -- Images 801-825
--------------------------------------
This set of images, 801 to 825, was another set taken just like
previous sets except the scan mirror was set at an angle of
31.43 degrees and the final image was also windowed. Again
exposures were set at 5 seconds for the first five, 10 seconds
for the second five, and 15 seconds for the final fifteen. All
25 exposures were windowed, three windows at 51 x 51 pixels and
one at 71 x 71 pixels. The pattern was not matched on any of
the first 24 images. So we were left with only one properly
pattern matched image, number 825, which showed the comet quite
clearly.
2003 DEC 14 12:00:00 -- Images 826-850
--------------------------------------
This set of images, 826 to 850, was another set taken just like
earlier sets, except the scan mirror was set at an angle of
30.63 degrees and the final image again was windowed. Again
exposures were set at 5 seconds for the first five, 10 seconds
for the second five, and 15 seconds for the final fifteen. All
25 exposures were windowed, three windows at 51 x 51 pixels and
one at 71 x 71 pixels. One image, 835, was missing many
packets. Two windows were missing entirely and the third was
only partially present. The pattern was matched on only five
images, 831, 833, 839, 847, and 850.
2003 DEC 15 12:00:00 -- Images 851-853
--------------------------------------
Realizing the poor yield of the pattern matching program with
small windows, it was decided to use fewer but much larger
windows, 201 x 201, and not to attempt pattern matching. Image
851 utilized three of these much larger windows. Image 852 used
two 201 x 201 windows and one 1 x 1 image, which significantly
reduced the amount of data to be returned. Image 853 once again
used three 201 x 210 windows. All were 15 second exposures at
30.69 degrees scan mirror setting, and all showed the comet.
2003 DEC 16 05:00:00 -- Images 854-856
--------------------------------------
The December 16 set of Op Nav images was composed of three 201
x 201 pixel windows, 854, 855, and 856. These were all 15
second exposures at a scan mirror angle of 30.29 degrees. The
only significant problem was that the bad columns, that first
appeared in image 701, fell right across two of the windows,
which were set a bit too far to the right in the frame.
2003 DEC 17 05:00:00 -- Images 857-859
--------------------------------------
The December 17 set of Op Nav images was composed once again of
two 201 x 201 pixel windows and one 1 x 1 pixel window. These
are numbered as windows 857, 858, and 859. All were 15 second
exposures at a scan mirror angle of 29.65 degrees. All were
properly placed, with the bad columns now falling between
windows.
2003 DEC 18 04:00:00 -- Images 860-876
--------------------------------------
The sequence of December 18 was meant to serve two purposes.
The first 14 full frame uncompressed images were meant to
photometrically calibrate the camera for the encounter, now
only two weeks off. Images 860 and 873 are bias frames. Images
861 through 869 were off periscope images taken at a scan
mirror setting of 23.98 degrees. Images 870, 871, and 872
included the periscope in the light path with the scan mirror
set at 0.20 degrees. The final three frames, 874, 875, and 876
were meant to further understand periscope use when it included
light both through the periscope and around it. The sad thing
is that none of these images were of significant use. All
contained many thousands of hot pixels as well as a generally
high background level. The camera electronics had been left
turned on to prevent possible failure due to excessive on and
off cycles, the time when most electronics fail, if they are
going to do so. Hereafter the electronics were turned off when
not in use, and everything worked just fine. There was now no
time for an additional photometric calibration before
encounter, so it was decided to go with just the planned
post-encounter photometric calibration.
2003 DEC 19 12:00:00 -- Images 877-879
--------------------------------------
Images 877 through 879 were once again for optical navigation.
These images all used 15 second exposures with the scan mirror
set at 28.40 degrees. Wild 2 was now quite easy to see on each
individual frame.
2003 DEC 20 12:00:00 -- Images 880-882
--------------------------------------
Images 880 through 882 were once again for optical navigation.
These images all used 15 second exposures with the scan mirror
set at 27.88 degrees. Wild 2 was now quite easy to see on each
individual frame.
2003 DEC 21 11:59:59 -- Images 883-885
--------------------------------------
Images 883 through 885 were once again for optical navigation.
These images all used 15 second exposures with the scan mirror
set at 27.25 degrees. Wild 2 is now quite easy to see on each
individual frame.
2003 DEC 22 03:59:59 -- Images 886-889
--------------------------------------
Images 886, 887, and 888 were again for optical navigation.
Image 989 does not exist for unknown reasons. These images all
used 15 second exposures with the scan mirror set at 26.96
degrees. All continued to use three 201 x 201 pixel windowing.
2003 DEC 24 03:00:44 -- Images 890-906
--------------------------------------
Images 890 through 906 were still taken for optical navigation.
All images were taken with a 20 second exposure at a scan
mirror angle of 24.10 degrees. All consist of three windows,
now 301 x 301 pixels in size.
2003 DEC 25 02:00:44 -- Images 907-924
--------------------------------------
Images 907 through 924 were still taken for optical navigation.
All images were taken with a 20 second exposure at a scan
mirror angle of 24.10 degrees. All were meant to consist of
three windows, again 301 x 301 pixels in size. Image 907 does
not exist. Images 908, 909, and 910 are all incomplete,
consisting in each case of a single incomplete window. The
remainder of the images are very good normal frames. Since new
data were being taken every day, no attempt was made to
retransmit the incomplete images.
2003 DEC 26 03:00:45 -- Images 925-942
--------------------------------------
Images 925 through 942 were still taken for optical navigation.
All images were taken with a 20 second exposure at a scan
mirror angle of 23.57 degrees. All were meant to consist of
three windows, again 301 x 301 pixels in size. Image 925 does
not exist. Images 927 through 930 are also missing for unknown
reasons. The remainder, 931 through 942 are excellent. Again no
attempt was made to retransmit the missing images, if in fact
they ever existed. So many images were being taken that it was
pretty easy to lose track of which had and which had not been
taken. It was always much safer to skip a few numbers than to
give two images the same number.
2003 DEC 26 16:00:00 -- Images 943-960
--------------------------------------
This set of images made up the second optical navigation
sequence of December 26, as optical navigation prepared for the
final TCMs, if they proved necessary. They are images 943
through 960, consisting of 20 second exposures at a scan mirror
angle of 23.30 degrees. Each consisted of three 301 x 301
windows. All turned out quite well.
2003 DEC 28 02:01:30 -- Images 961-978
--------------------------------------
Following a day ``off'' when an additional heating cycle was
carried out for a decontamination of the camera, optical
navigation images were resumed, images which also determined
the then current state of the camera. Images 961 and 962 appear
not to exist. Image 963 appears to consist of one window with
many missing packets. Images 964 and 965 have single partial
windows, each with many missing packets. Image 967 consists of
two windows, only one of which is complete, but the complete
window does contain a usable image of the comet. Images 966
and 968 through 978 have the normal three windows of 301 x 301
pixels. Three of these have 20 second exposures and nine were
given 10 second exposures. All were taken with the scan mirror
at 22.49 degrees.
2003 DEC 29 05:00:00 -- Images 979-996
--------------------------------------
In the series of images 979 through 996, only 983 and 984 are
missing packets. All images were acquired at a scan mirror
angle of 21.87 degrees. Images 979 through 982 and 985 through
987 were given 20 second exposures, while 988 through 996
received 10 second exposures. All complete images had three 301
x 301 pixel windows.
2003 DEC 30 05:27:15 -- Images 997-1014
---------------------------------------
Images 997 through 999 were missing the first packet, thereby
ruining each entire image. In this hectic period, no attempt
was made to reconstruct them. Image 1000 consisted of one
normal 301 x 301 pixel window and two 1 x 1 pixel windows. The
image of Wild2 was in one of the latter. Images 1001 through
1014 were normal, each having three 301 x 301 windows. The
first five good frames received 20 second exposures, and the
last nine were all 10 second exposures. These, of course, were
again taken for optical navigation purposes.
2003 DEC 30 22:35:15 -- Images 1015-1032
----------------------------------------
The second set of December 30 images probably included 1015
through 1021, which are missing. I say this because there are
only two images with 20 second exposures instead of the usual
nine. The two 20 second images are 1022 and 1023. These are
followed by 1024 through 1032, which are 10 second exposures.
All were taken at a scan mirror angle of 21.00 degrees and with
three 301 x 301 pixel windows.
2003 DEC 31 07:00:00 -- Images 1033-1050
----------------------------------------
Images 1033 through 1050 constituted the first set of December
31 exposures. All were taken at a scan mirror angle of 20.77
degrees and with three 301 x 301 pixel windows. The first nine
were 20 second exposures and the second nine were 10 second
exposures.
2003 DEC 31 20:18:00 -- Images 1051-1058
----------------------------------------
The second set of December 31 images consisted of eight images
numbered 1051 through 1058. The first four were 15 second
exposures, the second four 10 seconds. All utilized a scan
mirror of 24.49 degrees. Each consisted of three windows of 291
x 291 pixels.
2004 JAN 01 00:18:00 -- Images 1059-1066
----------------------------------------
The first set of January 1 images, 1059 through 1066, were
taken at a scan mirror angle of 24.49 degrees. All were
windowed images using three 291 x 291 pixels with a scan mirror
angle of 24.49 degrees. The first four were 15 second
exposures, the second four, 10 second exposures.
2004 JAN 01 05:18:00 -- Images 1067-1074
----------------------------------------
The second set of January 1 images, 1067 through 1074, were
also taken at a scan mirror angle of 24.49 degrees. All were
windowed images using three 291 x 291 pixels with a scan mirror
angle of 24.49 degrees. The first four were 15 second
exposures, the second four, 10 second exposures.
2004 JAN 01 08:18:00 -- Images 1075-1082
----------------------------------------
The third set of January 1 images, 1075 through 1082, once
again were taken at a scan mirror angle of 24.49 degrees. All
were windowed images using three 291 x 291 pixels with a scan
mirror angle of 24.49 degrees. The first four were 15 second
exposures, the second four, 10 second exposures.
2004 JAN 01 12:18:00 -- Images 1083-1090
----------------------------------------
The fourth set of January 1 images, 1083 through 1090, once
again were taken at a scan mirror angle of 24.49 degrees. All
were windowed images using three 291 x 291 pixels with a scan
mirror angle of 24.49 degrees. The first four were 15 second
exposures, the second four, 10 second exposures.
2004 JAN 01 16:18:00 -- Images 1091-1098
----------------------------------------
The fifth set of January 1 images, 1091 through 1098, once
again were taken at a scan mirror angle of 24.49 degrees. All
were windowed images using three 291 x 291 pixels with a scan
mirror angle of 24.49 degrees. The first four were 15 second
exposures, the second four, 10 second exposures.
2004 JAN 01 21:18:44 -- Images 1099-1106
----------------------------------------
The sixth set of January 1 images, 1099 through 1106, were
taken at a scan mirror angle of 24.49 degrees. All were
windowed images using three 291 x 291 pixel windows. Image 1099
was missing. Image 1100 had two windows, but only the image
containing the comet was complete. Images through 1102 were 15
second exposures, the last four were 10 second exposures.
2004 JAN 02 05:18:44 -- Images 1107-1122
----------------------------------------
Images 1107 through 1115, one complete set, are missing. The
final set of optical navigation images, numbered 1116 through
1122, were acquired using three 291 x 291 pixel windows and a
scan mirror angle of 24.49 degrees. The first three utilized 15
second exposures and the final four 10 second exposures.
2004 JAN 02 18:54:28 -- Images 2000-2115 -- Wild 2 Encounter Set
----------------------------------------------------------------
Images 2005 through 2115 are the 81P/Wild 2 encounter set.
There are 72 complete images in this set, the missing numbers
having been used only to establish the auto-tracking on the
nucleus. There was sufficient memory only for the 72 images. It
is the nature of the shutter that alternate exposures are 1.65
milliseconds shorter than the set exposure time. The even
numbered images are the shorter ones taken during the
encounter. We were quite limited in the number of changes that
could be made in the exposure time, so most were taken at
settings of either 100 milliseconds (actually 98.35
milliseconds) or 10 milliseconds. Many of the longer exposures
were saturated, but these serve very well to bring out the many
jets of gas and dust ejected by the comet. Scan mirror angles
ranged from 1.37 degrees for image 2005 through 176.05 degrees
for image 2115. The images with the mirror at more than 170
degrees all exhibit a great deal of scattered light, probably
from the sample return capsule. There are lesser amounts of
scattered light on images back to about 160 degrees. There is a
problem with images taken near 0 degrees as well, from light
scattered from the launch vehicle adapter ring which actually
occludes a bit of the periscope.
2004 JAN 13 02:24:28 -- Images 2116-2130
----------------------------------------
Images 2116 through 2130 were taken to attempt to calibrate all
of the images, to check the post-encounter state of the
periscope, and to check the calibration lamp, which appeared to
have failed pre-encounter. Images 2116 and 2129 were bias
frames. Images 2117 through 2125 constituted the very limited
calibration set. Images 2126 through 2128 were for the
periscope check, and 2130 was the calibration lamp check. The
calibration images all were taken at scan mirror angles near 24
degrees, four with 1 second exposures, four with 5 second
exposures and one with a 15 second exposure. All were
uncompressed full frame images. The periscope checks were done
at an angle of -0.10 degrees and were full of scattered light.
This was expected to some extent, but the very mottled
appearance of the images indicated that one or both mirrors of
the periscope were thoroughly sandblasted by the passage
through the Wild 2 coma. The check of the calibration lamp
unfortunately was done with a 1 second exposure rather than 20
milliseconds. It was obviously working just fine, since every
pixel in the frame was saturated.
Processing
==========
The images in this data set were created by the DMAPKTDECOM
program developed by Applied Coherent Technology Corp, Herndon,
Virginia and operated by the Stardust Data Management and Archive
Team at JPL, Pasadena, California. This program assembled images
from raw telemetry packets sent down by the spacecraft and
populated the images labels with housekeeping values, decommutated
the binary image headers, and computed geometry parameters using
SPICE kernels. This program did not apply correction of any kind
to the image data.
In the cases when only certain sections of the detector were
downlinked, the program filled the pixels in the image
corresponding to the areas for which data had not been downlinked
with hex null values (i.e., zeroes). In such images window
objects define the areas containing non-null data.
Data
====
The images in this data set are in standard PDS format. Each file
includes an attached PDS label at the beginning of the file,
followed by a histogram, and ending with the image itself. The
PDS label contains two OBJECT definitions that describe the
storage requirements for both the histogram and image objects.
The label also describes the circumstances surrounding the
collection of the calibration image. This meta-data is in keyword
and value pairs and each of these keywords is described at the
end of this document.
Camera Description
------------------
The camera has a 1024x1024 array as the active portion of the
CCD. The images that are stored on this volume, however, contain
more than just the active portion of the CCD. Each line contains
a sync pattern, a line counter, 12 baseline stabilization pixels,
the 1024 pixels from the active portion of the CCD, and finally 8
over-clock pixels used to measure the quantum efficiency. The
number of rows for each image is always 1024, no matter what
compression mode is used, but the number of columns for each
image depends on the compression mode used.
Compression Modes
-----------------
The NAVCAM images can be either 8-bit or 12-bit data. The 12-bit
data is commonly referred to as 'uncompressed data', while the
8-bit is referred to as 'compressed data'. This compression is
accomplished by a 12-bit to 8-bit square-root look-up-table
compression method, which is implemented in the hardware of the
camera electronics. This compression is lossy and the estimate of
the 12-bit image can be recovered using the look-up table
mentioned in Appendix 3 of the Calibration Document. Both the
image and histogram portions of the data file require different
amounts of storage space, dependent on the compression mode used.
In uncompressed mode with 12-bit data, the pixels are expressed
in two bytes, as 16 bits per pixel. The upper nibble of the most
significant byte is always zero for these images. In compressed
mode with 8-bit data, the pixels are expressed in a single byte.
Number of Columns within Each Row
---------------------------------
The general form of each line for each image is fixed. The row of
data from the camera can be categorized into five different
regions:
1. Sync Pattern Always 2 bytes, with value 0x0000
2. Line Counter Always 2 bytes, values from 0 to
1023
3. 8 BLS pixels (*) Baseline Stabilization pixels,
either 1 or 2 bytes per pixel
4. 1024 image pixels (*) Either 1 or 2 bytes per pixel
5. 12 over-clock pixels (*) Used to measure quantum
efficiency, either 1 or 2 bytes
per pixel
(*) The pixels are either 1 or 2 bytes per pixel dependent on
the compression mode. Uncompressed, 12-bit images require
2 bytes per pixel, while compressed 8-bit images require 1
byte per pixel.
For the uncompressed, 12-bit data, each row contains 1046
'pixels' of data, which is exactly 2092 bytes. This is 2 bytes
for the sync, 2 bytes for the line counter, 8 pixels at 2 bytes
per pixel, 1024 pixels at 2 bytes per pixel and, finally, 12
pixels at 2 bytes per pixel. In equation form:
bytes_per_uncompressed_line = 2 + 2 + 2 * (8 + 1024 + 12) = 2092
For the compressed, 8-bit data, each row contains 1048 'pixels'
of data, which is exactly 1048 bytes. This is 2 bytes for the
sync, 2 bytes for the line counter, 8 pixels at 1 byte per
pixel, 1024 pixels at 1 bytes per pixel and, finally, 12 pixels
at 1 bytes per pixel. In equation form:
bytes_per_compressed_line = 2 + 2 + 1 * (8 + 1024 + 12) = 1048
Reading with RAW Image Readers
------------------------------
When using any of the supported PDS readers, this extra data at
the beginning and end of the line is not displayed, but when
reading these images with a raw raster-scan style reader, this
extra data at the beginning and end of each line must be taken
into account.
When reading images with raw readers, use the following values:
Compression Mode # Rows # Columns Data Type
---------------- ------ --------- -----------------------------
Compressed 1024 1048 BYTE data
Uncompressed 1024 1046 MSB_Unsigned_integer (16-bit)
Finding the Offset to the Data within the File
----------------------------------------------
When trying to read the histogram or image arrays from the file
using a RAW reader, the reader must first skip all of the
information before the object to be read. As an example, to
read the image object using a raw reader, the reader must first
skip the PDS attached header, as well as the histogram data. To
determine the amount of data to skip, examine two keyword pairs
from the attached label.
To advance to the beginning of the histogram data, examine the
following keywords:
RECORD_BYTES = 2092
^IMAGE_HISTOGRAM = 3
The first keyword defines the number of bytes within each
record, while the second keyword indicates at which record the
data begins. In this example, the data starts in record #3.
This indicates that 2 other records contain data prior to the
start of the histogram data. To compute the data offset,
account for 2 records of data: in this example, the offset is
(3-1)*2092 = 4184.
To advance to the beginning of the image data, examine the
following keywords:
RECORD_BYTES = 2092
^IMAGE = 11
As in the previous example, the first keyword defines the number
of bytes within each record. The second keyword indicates the
record at which the image data begin. To compute the data
offset, follow the example above:
Offset = ( ^image_histogram - 1 ) * record_bytes.
Example:
Offset = ( 11 - 1 ) * 2092 = 20920
Exposure Durations
------------------
NOTE: Below it states that the exposure times have been
adjusted so that the correct times are given in the labels.
This is incorrect. The labels in this version of the data
still contain the downlinked times. The exposure times have
been corrected in Version 2.0 of this dataset
(SDU-C-NAVCAM-2-EDR-WILD2-V2.0).
The double-bladed shutter utilized by the camera has the property
that in one direction the exposures are 1.65 ms shorter than in
the other. Therefore a setting of 5 ms, which is the shortest
possible, results in alternate 5 and 3.35 ms exposures, those at
25 ms, alternate 25 and 23.35 ms exposures, and so on.
Occasionally bias frames, which do not require shutter action,
are transmitted to Earth. This changes the ``parity.''
While not always the case, for Wild 2 image sequences the even
numbered images have the shorter exposures. The downlinked
exposures for these images have been adjusted and the correct
exposure duration values are provided in the labels.
Target Name in the Image Labels
-------------------------------
The target name in the image labels was set only for the images
where the target is either seen in the image or computed to be
with the camera field of view. For all other images the target
name was set to ``N/A''.
Consequently the label geometry items pertaining to the target
-- spacecraft-target position, velocity and distance, pixel
scales, and phase angle -- are only supplied for the images where
target name is not ``N/A'' and were computed for that specified
target.
Windowed Images
---------------
The IMAGE size parameter in the image label reflects the size
of the detector, however in some cases data from only certain
sections of the detector were downlinked. In these cases the
pixels in the image corresponding to the areas for which data
had not been downlinked are filled with hex null values (i.e.,
zeroes). WINDOW objects define the areas containing non-null
data.
Noise in the Images
-------------------
If the images are stretched to the limit, regular wide
horizontal stripes appear in every image at the level of 1 to 2
dn above background. These appear to be the product of coherent
noise somewhere in the data stream or from a power supply.
Their source is unknown.
Unresolved Liens on the Data
----------------------------
Several errata concerning the format of the data noted during
peer-review have not been applied to the data because of
funding and resource limitations. In general these errata do
not cause significant problems with software designed to read
PDS images, but users should be aware of these format issues
should software problems arise.
One of the liens that was not addressed was a request to
include the LINE_DISPLAY_DIRECTION, SAMPLE_DISPLAY_DIRECTION
and AXIS_ORDER_TYPE keywords in the image labels. Users should
be aware that the images are oriented in such a way that the
PDS Data Dictionary definition of, for example, TWIST_ANGLE is
not the correct interpretation for these images. User should
note carefully the explanations provided in the ``Coordinate
System'' section of this description and in the documentation
for this data set regarding image orientation and the
definitions of the angles used in the image labels.
Ancillary Data
==============
The geometry items included in the image labels were computed
using the following SPICE kernels archived in the Stardust SPICE
data set, SDU-C-SPICE-6-V1.0:
Kernel Type File Name
------------ ---------------------
LSK naif0007.tls
PCK pck00007.tpc
SCLK sdu_sclkscet_00105.tsc
FK sdu_v17.tf
IK sdu_navcam_v21.ti
SPK sdu_l_2003_w2.bsp
SPK sdu_w2_opnav.bsp
CK (s/c) sdu_sc_rec_2003_w2_v2.bc
CK (s/c) sdu_sc_rec_w2_opnav.bc
CK (camera) sdu_nc_rec_v2.bc
Coordinate System
=================
Geometric Parameter Reference Frame
-----------------------------------
Earth Mean Equator and Vernal Equinox of J2000 is the inertial
reference system used to specify observational geometry items
provided in the image labels. Geometric parameters are based on
best available SPICE data at time of image creation.
Epoch of Geometric Parameters
-----------------------------
All geometric parameters provided in the image labels were
computed at the epoch specified in the START_TIME label field.
Flip Required to Achieve ``As Seen By Observer'' Display
--------------------------------------------------------
Since the optical path of the camera includes a mirror and the
flight and image production s/w do not compensate for the flip
that this mirror introduces, the images displayed in normal
left-to-right sample, top-to-bottom line fashion have to be
transposed (flipped about left-top/right-bottom diagonal) in
order to appear as an observer located on the spacecraft would
see it.
The need to perform the flip and the type of the flip could
have been identified by including the following two keywords
in the image labels:
SAMPLE_DISPLAY_DIRECTION = 'DOWN'
LINE_DISPLAY_DIRECTION = 'RIGHT'
TWIST_ANGLE Provided in the Label
---------------------------------
Users should be aware that the PDS Data Dictionary definition
of TWIST_ANGLE is not the correct interpretation for the
TWIST_ANGLE provided in the image labels. For the NAVCAM images
it is the angle between the leftward direction (in left-right,
top-down displayed, un-flipped image) and projection of the EME
J2000 +Z axis onto the image plane, measured clockwise.
Quaternion Provided in the Label
--------------------------------
The quaternion provided in the image label is an engineering,
or alternative, ``non-SPICE'' style, quaternion providing the
rotation from Earth Mean Equator and Vernal Equinox of J2000
inertial reference frame into the Stardust spacecraft frame.
Note that although this quaternion was downlinked in the binary
image header and included in the image label, it was not used
directly to compute any of the geometry parameters. Instead it
was converted to a SPICE-style quaternion and written to a
C-Kernel file, which was then used by the DMAPKTDECOM program
to calculate observation geometry.
Software
========
The images in this data set are in standard PDS format and,
therefore, can be viewed by a number of PDS-provided and
commercial programs. For this reason no special software is
provided with this data set.
Contact Information
===================
For any questions regarding the data format of the archive,
contact Stardust NAVCAM Science Lead:
Dr. Raymond L. Newburn, Jr.
Phone: +1 (818) 354-2319
Electronic mail address: Ray.L.Newburn@jpl.nasa.gov
MAIL STOP 264-379
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Drive
Pasadena, CA, 91109-8099
USA
or Stardust Data Management and Archive Team (SDMA):
Charles H. Acton, Jr.
Phone: +1 (818) 354-3869
Electronic mail address: Charles.Acton@jpl.nasa.gov
Boris V. Semenov
Phone: +1 (818) 354-8136
Electronic mail address: Boris.Semenov@jpl.nasa.gov
MAIL STOP 301-125L
Jet Propulsion Laboratory
California Institute of Technology
4800 Oak Grove Drive
Pasadena, CA, 91109-8099
USA
|
.png)
.png)
