2. Imaging of overlap area between left and
right frames.
A few images appear to have a black strip across the bottom of the
image, followed by more image data, apparently discontinuous with the
data above the line. (An example of this is the image
mars/seq0179/c1248xxx/i811350l.img on volume MPIM_0002.) This
artifact is due to the way the image frames are laid out on the CCD
array. (See the DATASET.CAT file on this CD
for more information.) The subframing of these images was erroneously
commanded such that the area of six pixels of overlap between the left
and right frames was captured in the image. Normally this area is not
imaged.
3. ATMOS_FLAG images
There is a subset of the sun images known as "ATMOS FLAG" images.
(The image ids of these images can be identified from the ATMOS_FLAG
field in the COMMAND.TAB file.) For
these images, there was no predetermined starting line and sample for
image subframing; the IMP camera performed a Sun search, then
automatically subframed a 31 x 31 image centered on the Sun. The
starting line and starting sample of these automatically chosen
subframes was not returned in a timely enough manner to be correctly
correlated with the images. Therefore, no FIRST_LINE or
FIRST_LINE_SAMPLE values are available for these images.
4. Duplicate IMAGE_IDs
The IMAGE_IDs were intended to uniquely describe a set of observation
parameters used to command the acquisition of an image or series of
images. Unfortunately, in a few cases IMAGE_IDs were re-used with
different command parameters. The telemetry processing software was
not designed to keep track of these duplicate commands, so the older
values were over-written in the command table. We have attempted to
re-construct all of the original IMAGE_IDs and have added a
COMMAND_VERSION_NUMBER to the COMMAND.TAB file in the INDEX directory to reflect these multiple versions.
While we are fairly confident of the accuracy of the information
provided, we cannot guarantee that we have successfully recovered
every command, or that the command versions are always in the correct
order.
In cases where there are multiple IMAGE_IDs, it is not possible to directly correlate an individual image with the command that produced it. The only way this can be done is to manually compare each of the command parameters for those IMAGE_IDs with the values in the image label (or the EDRINDEX.TAB file). Note that because earlier versions of command parameters will disagree with the most recent version of a command as described in the command table, images with previous version IMAGE_IDs will have the TLM_CMD_DISCREPANCY_FLAG set to TRUE.
5. DN values in excess of 4095
The Mars Pathfinder IMP data is 12-bit data, and should nominally have
a DN range of 0 to 4095. However, due to the lossly JPEG compression
algorithm used on board the spacecraft, it is possible to generate DN
values in excess of 4095. The label item ERROR_PIXELS will identify
the number of pixels that have a DN value greater than this.
6. Coordinate systems
There has been a great deal of debate about which coordinate system
should be used to define camera pointing and solar position values.
The system chosen for this dataset, while not a Project defined
coordinate system, is believed to reflect the most common usage in the
planetary science community, and additionally matches the system used
for the Viking Lander data. Further details on the coordinate systems
are provided in the DATASET.CAT
file, which can be found in the CATALOG directory, and the IMP EDR Software Interface
Specification (EDRSIS), which can be found in the DOCUMENT directory.