| DATA_SET_DESCRIPTION |
Stardust Navigation Camera Preflight Calibration Image Data Format:
===================================================================
Data Set Overview:
=================
This volume contains the results of the preflight calibration of
the Stardust Navigation Camera. The images were collected in an
attempt to mimic the environment that the camera would experience
during cruise and encounter with the comet Wild-2.
The images on this calibration volume 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, which 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.
Pixel storage requirements:
===========================
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 ending of each line must be taken into account.
Values to use when reading images with a RAW readers:
=====================================================
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 histrogram 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 begins. To compute the data offset, follow the
example above:
Offset = ( ^image_histogram - 1 ) * record_bytes.
Ex: Offset = ( 11 - 1) * 2092 = 20920
A Sample PDS Attached Image Label:
==================================
PDS_VERSION_ID = PDS3
/*** FILE FORMAT ***/
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 2092
FILE_RECORDS = 1034
/*** POINTERS TO OBJECTS IN FILE ***/
^IMAGE_HISTOGRAM = 3
^IMAGE = 11
/*** GENERAL DATA DESCRIPTION PARAMETERS ***/
MISSION_NAME = STARDUST
SPACECRAFT_NAME = STARDUST
DATA_SET_ID = STARDUST-CAL-NC-2-PREFLIGHT-V1.0
OBSERVATION_NAME = CALIBRATION AT MINUS 30 DEGRESS C
OBSERVATION_TYPE = -30
PRODUCT_ID = NC370034.IMG
ORIGINAL_PRODUCT_ID = usd9898-144754.pds
PRODUCER_INSTITUTION_NAME = JPL/ACT
PRODUCT_TYPE = EDR
SOFTWARE_NAME = ACT DMAPKTDECOM 1.0
MISSION_PHASE_NAME = PREFLIGHT CALIBRATION
TARGET_NAME = CALIMG
FRAME_SEQUENCE_NUMBER = 34
/*** TIME PARAMETERS ***/
START_TIME = 1998-04-08T14:47:54
STOP_TIME = N/A
PRODUCT_CREATION_TIME = 2000-02-25T02:06:51
/*** CAMERA RELATED PARAMETERS ***/
INSTRUMENT_NAME = NAVIGATION CAMERA
INSTRUMENT_ID = NC
EXPOSURE_DURATION = 0.020
CAL_LAMP_MODE_ID = OFF
QUANTIZATION_MODE_ID = OFF
FILTER_NUMBER = 7
FILTER_NAME = HiRes
CENTER_FILTER_WAVELENGTH = 596.4
FILTER_FWHM = 200.0
/*** CALIBRATION EQUIPMENT PARAMETERS ***/
MEASUREMENT_SOURCE_DESC = KEITHLY 607 ELECTROMETER
RADIANCE = 0.981
/*** TEMPERATURE PARAMETERS IN ***/
INSTRUMENT_TEMPERATURE = 306.95
FOCAL_PLANE_TEMPERATURE = 243.15
/*** DESCRIPTION OF OBJECTS CONTAINED IN THE FILE ***/
OBJECT = IMAGE_HISTOGRAM
ITEMS = 4096
DATA_TYPE = MSB_UNSIGNED_INTEGER
ITEM_BITS = 32
END_OBJECT = IMAGE_HISTOGRAM
OBJECT = IMAGE
LINES = 1024
LINE_SAMPLES = 1024
SAMPLE_TYPE = MSB_UNSIGNED_INTEGER
SAMPLE_BITS = 16
SAMPLE_BIT_MASK = 2#0000111111111111#
MAXIMUM = 3063
MINIMUM = 603
LINE_PREFIX_BYTES = 20
LINE_SUFFIX_BYTES = 24
MEAN = 859.588
STANDARD_DEVIATION = 64.9859
SATURATED_PIXELS = 0
CHECKSUM = 50501490
END_OBJECT = IMAGE
END
General notes regarding label:
==============================
* Strings appear in quotes.
* Integers and PDS Times do not take quotes.
* Lists are enclosed within {} type brackets.
* If a field is unknown, UNK may be entered.
* If a field is not applicable, N/A may be entered.
* Fields can spill freely, with or without white space, onto
following lines.
Definition of Keywords/Values from the PDS Data Dictionary:
===========================================================
PDS_VERSION_ID The pds_version_id keyword indicates the
version number of the PDS standards
documents that is valid when a data
product label is created. Values for
the PDS_VERSION_ID are formed by
appending the integer for the latest
version number to the letters 'PDS'.
Examples: PDS3, PDS4.
RECORD_TYPE The record_type keyword indicates the
record format of a file. Note: In
the PDS, when record_type is used in a
detached label file it always
describes its corresponding detached
data file, not the label file itself.
The use of record_type along with
other file-related data elements is
fully described in the PDS Standards
Reference.
RECORD_BYTES The record_bytes keyword indicates the
number of bytes in a physical file
record, including record terminators
and separators.
FILE_RECORDS The file_records keyword indicates the
number of physical file records,
including both label records and data
records.
^IMAGE_HISTOGRAM The image_histogram object represents
a pointer to the image histogram. The
value is in RECORD_BYTE units and
indicates that the data starts at the
beginning of the record mentioned. As
an example, if the pointer value is 4,
then the 3 records are populated with
other data. If the bytes per record
is 2092, the image histogram data
starts at byte 6276
^IMAGE The ^image pointer represents a byte
offset to the image data. The value
is in RECORD_BYTE units. As an
example, if the pointer value is 11,
and the bytes per record is 2092, the
image histogram data starts at byte
20920.
MISSION_NAME The mission_name element identifies a
major planetary mission or project. A
given planetary mission may be
associated with one or more
spacecraft.
SPACECRAFT_NAME The spacecraft_name element provides the
full, unabbreviated name of a spacecraft.
DATA_SET_ID The data_set_id element is a unique
alphanumeric identifier for a data set
or a data product. The data_set_id
value for a given data set or product
is constructed according to flight
project naming conventions. In most
cases the data_set_id is an
abbreviation of the data_set_name.
Example value:
STARDUST-CAL-NC-2-PREFLIGHT-V1.0.
Note: In the PDS, the values for both
data_set_id and data_set_name are
constructed according to standards
outlined in the Standards Reference.
OBSERVATION_NAME The observation_name element provides the
identifier for an observation or
sequence of commands. For this
dataset, this keyword has 3
possibilities, based on the day the
calibration was completed:
4/08/98 CALIBRATION AT MINUS 30 DEGRESS C
4/09/98 CALIBRATION AT MINUS 40 DEGRESS C
4/10/98 CALIBRATION AT MINUS 50 DEGRESS C
OBSERVATION_TYPE The observation_type element identifies
the general type of an observation.
This keyword has 3 possibilities,
based on the day the calibration was
completed:
4/08/98 -30
4/09/98 -40
4/10/98 -50
PRODUCT_ID The product_id data element represents
a permanent, unique identifier
assigned to a data product by its
producer. Note: In the PDS, the
value assigned to product_id must be
unique within its data set. This
value represents the actual name of
the image file on the archive. The
output directory is also available.
ORIGINAL_PRODUCT_ID The original_product_id element
provides the temporary product
identifier that was assigned to a
product during active flight
operations which was eventually
replaced by a permanent id (see
product_id). In this dataset, this
value represents the original filename
recorded by the calibration equipment.
This name can be linked back to the
original calibration log files.
PRODUCER_INSTITUTION_NAME The producer_institution_name element
identifies a university, research
center, NASA center or other
institution associated with the
production of a data set. This would
generally be an institution associated
with the element producer_full_name.
In this dataset, this field has the
value of JPL/ACT, described as: JPL =
Jet Propulsion Laboratory. ACT =
Applied Coherent Technology Corp.
PRODUCT_TYPE The product_type data element identifies
the type or category of a data product
within a data set. Examples: EDR,
UDR.
SOFTWARE_NAME The software_name element identifies
data processing software such as a
program or a program library.
MISSION_PHASE_NAME The mission_phase_name element provides
the commonly-used identifier of a
mission phase.
TARGET_NAME The target_name element identifies a
target. The target may be a planet,
satellite, ring, region, feature,
asteroid or comet. See target_type.
In this calibration dataset, the
target is CALIMG.
FRAME_SEQUENCE_NUMBER The frame_sequence_number element
indicates the location within a cycle
at which a specific frame occurs.
Frames are repeated in a specific
order within each cycle. In this
dataset, this value represents a
uniquly sequential identifier assigned
to each image of the archive.
START_TIME The start_time element provides the
date and time of the beginning of an
event or observation (whether it be a
spacecraft, ground-based, or system
event) in UTC system format.
Formation rule: YYYY-MM-DDThh:mm:ss.
STOP_TIME The stop_time element provides the
date and time of the end of an
observation or event (whether it be a
spacecraft, ground-based, or system
event) in UTC system format.
Formation rule: YYYY-MM-DDThh:mm:ss.
PRODUCT_CREATION_TIME The product_creation_time element
defines the UTC system format time
when a product was created. Formation
rule: YYYY-MM-DDThh:mm:ss.
INSTRUMENT_NAME The instrument_name element provides
the full name of an instrument. Note:
that the associated instrument_id
element provides an abbreviated name
or acronym for the instrument.
INSTRUMENT_HOST_NAME The instrument_host_name element
provides the full name of the host on
which an instrument is based. This
host can be either a spacecraft or an
earth base. Thus, the
instrument_host_name element can
contain values which are either
spacecraft_name values or
earth_base_name values.
INSTRUMENT_ID The instrument_id element provides an
abbreviated name or acronym which
identifies an instrument. Note: The
instrument_id is not a unique
identifier for a given instrument.
Note also that the associated
instrument_name element provides the
full name of the instrument.
EXPOSURE_DURATION The exposure_duration element provides
the value of the time interval between
the opening and closing of an
instrument aperture (such as a camera
shutter).
CAL_LAMP_MODE_ID The cal_lam_mode_id element provides
the value of the calibration lamp mode
at the time the image was acquired.
This value indicates whether the
calibration lamp was on or off at the
time the image was acquired.
QUANTIZATION_MODE_ID The quantization_mode_id element
provides the identifier for the
quantization mode used when the image
was acquired. This value indicates if
the original data was quantized at the
time the data was acquired. A value
of OFF indicates that the data was not
quantized, while a value of ON
indicates that the data was quantized.
In this dataset, this value indicates
that the image was compressed with a
hardware square-root compression
technique prior to transmission.
FILTER_NUMBER The filter_number element provides the
number of an instrument filter through
which an image or measurement was
acquired or which is associated with a
given instrument mode. Note: that the
filter_number is unique, while the
filter_name is not.
FILTER_NAME The filter_name element provides the
commonly- used name of the instrument
filter through which an image or
measurement was acquired or which is
associated with a given instrument
mode. Example values: RED, GREEN.
See also filter_number.
CENTER_FILTER_WAVELENGTH The center_filter_wavelength element
provides the mid_point wavelength
value between the minimum and maximum
instrument filter wavelength values.
FILTER_FWHM The filter_fwhm element provides the
measurement for the Full-width,
half-max value associated with the
filter. This is the width of the
filter transmission curve at the
point of half of the maximum
transmission value.
MEASUREMENT_SOURCE_DESC The measurement_source_desc element
describes the source of light used in
a laboratory-generated data set, or
the radar transmitter in the case of
radar astronomy experiments.
RADIANCE The radiance element describes the
amount of current recorded from the
photo-diode detector used to measure
the radiance output from the source
emitter.
INSTRUMENT_TEMPERATURE The instrument_temperature element
provides the temperature, in degrees
Celcius, of an instrument or some part
of an instrument.
FOCAL_PLANE_TEMPERATURE The focal_plane_temperature element
provides the temperature of the focal
plane array in degrees kelvin at the
time the observation was made.
OBJECT = IMAGE_HISTOGRAM The histogram object is a sequence of
numeric values that provides the
number of occurrences of a data value
or a range of data values in a data
object. The number of items in a
histogram will normally be equal to
the number of distinct values allowed
in a field of the data object. (For
example, an 8-bit integer field can
have 256 values. This would result in
a 256-item histogram.) Histograms may
be used to bin data, in which case an
offset and scaling factor indicate the
dynamic range of the data represented.
The following equation allows the
calculation of the range of each 'bin'
in the histogram. 'bin lower
boundary' = ('bin element' *
scaling_factor) + offset.
ITEMS The items element defines the number
of multiple, identical occurrences of
an single object, such as a column.
See also: repetitions. Note: In the
PDS, the data element ITEMS is used
for multiple occurrences of a single
object, such as a column. REPETITIONS
is used for multiple occurrences of a
repeating group of objects, such as a
container. For a fuller description
of the use of these data elements,
please refer to the Standards
Reference.
DATA_TYPE The data_type element supplies the
internal representation and/or
mathematical properties of a value
being stored. See also:
bit_data_type, general_data_type.
Note: In the PDS, users may find a
bit-level description of each data
type in the Standards Reference
document.
ITEM_BITS The item_bits element indicates the
number of bits allocated for a
particular bit data item. Note: In
the PDS, the item_bits element is used
when the items element specifies
multiple occurrences of an implied
item within a BIT_COLUMN object
definition.
END_OBJECT The end_object element terminates the
object description.
OBJECT = IMAGE A regular array of sample values.
Image objects are normally processed
with special display tools to produce
a visual representation of the sample
values. This is done by assigning
brightness levels or display colors to
the various sample values. Images are
composed of LINES and SAMPLES. They
may contain multiple bands, in one of
several storage orders.
Note: Additional engineering values
may be prepended or appended to each
LINE of an image, and are stored as
concatenated TABLE objects, which must
be named LINE_PREFIX and LINE_SUFFIX.
IMAGE objects may be associated with
other objects, including HISTOGRAMs,
PALETTEs, HISTORY, and TABLEs which
contain statistics, display
parameters, engineering values, or
other ancillary data.
LINES The lines element indicates the total
number of data instances along the
vertical axis of an image. Note: In
PDS label convention, the number of
lines is stored in a 32-bit integer
field. The minimum value of 0
indicates no data received.
LINE_SAMPLES The line_samples element indicates the
total number of data instances along
the horizontal axis of an image.
SAMPLE_TYPE The sample_type element indicates the
data storage representation of sample
value.
SAMPLE_BITS The sample_bits element indicates the
stored number of bits, or units of
binary information, contained in a
line_sample value.
SAMPLE_BIT_MASK The sample_bit_mask element identifies
the active bits in a sample. Note:
In the PDS, the domain of
sample_bit_mask is dependent upon the
currently-described value in the
sample_bits element and only applies
to integer values. For an 8-bit
sample where all bits are active the
sample_bit_mask would be 2#11111111#.
MAXIMUM The maximum element indicates the
largest value occurring in a given
instance of the data object.
MINIMUM The minimum element indicates the
smallest value occurring in a given
instance of the data object.
LINE_PREFIX_BYTES The line_prefix_bytes element
indicates the number of non-image
bytes at the beginning of each line.
The value must represent an integral
number of bytes.
LINE_SUFFIX_BYTES The line_suffix_bytes element
indicates the number of non-image
bytes at the end of each line. This
value must be an integral number of
bytes.
MEAN The mean element provides the average
of the DN values in the image array.
STANDARD_DEVIATION The standard_deviation element
provides the standard deviation of the
DN values in the image array.
SATURATED_PIXELS The saturated_pixels element provides
a count of the number of pixels in the
array which at the maximum DN value.
For this dataset, the non-quantized
data has a maximum value of 4095,
while the quantized data has a maximum
value of 255.
CHECKSUM The checksum element represents an
unsigned 32-bit sum of all data values
in a data object.
END End of the PDS Label.
Contact Information:
====================
For any questions regarding the data format of the archive, contact:
Howard Taylor
Applied Coherent Technology Corp
112 Elden Street, Suite K
Herndon, VA 20170
(818) 354-5401
taylor@actgate.com
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