Mars Exploration Rover (MER)
Software Interface Specification
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Interface Title: Mars Atmospheric Opacity Data
Set
Mission: MER
Date: June 19, 2003
Module ID: SIS-SCI017-MER
Version: Initial Release
JPL D-22853
Module Type (REFerence Only or MISsion-specific
info included): MIS
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Reference Module ID: N/A
Date: N/A
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SOST Generating Elements:
Mark Lemmon
Athena Science Team Member
Concurrence:
John Callas
MER Science Manager
Betty Sword
PDS Central Node Data Engineer
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Mars Exploration Rover (MER) Project
Mars Atmospheric Opacity Software Interface Specification
(SIS)
Initial Release
Prepared by: Edward A. Guinness
SIS Custodian
Paper copies of this document may not be current and should
not be relied on for official purposes. The current version
is in the MER Project Library at http://mars03-lib.jpl.nasa.gov, in the Controlled Documents and
Records folder.
JPL D-22853
June 19, 2003
Jet Propulsion Laboratory
California Institute of Technology
CHANGE LOG
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DATE
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SECTIONS CHANGED
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REASON FOR CHANGE
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REVISION
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4/11/03
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All
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First draft
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Draft
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6/19/03
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Title page
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Removed "draft in preparation"
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Initial Release
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TBD ITEMS
CONTENTS
CHANGE
LOG..............................................................................................................................
iii
TBD
ITEMS...................................................................................................................................
iv
CONTENTS...................................................................................................................................
v
LIST OF
TABLES........................................................................................................................
vi
ACRONYMS................................................................................................................................
vii
1.
INTRODUCTION.......................................................................................................................
1
1.1 Purpose and
Scope...........................................................................................................
1
1.2
Contents...............................................................................................................................
1
1.3 Applicable Documents and
Constraints...........................................................................
1
1.4 Relationships with Other
Interfaces...................................................................................
2
2. Data Product Characteristics and
Environment........................................ 2
2.1 Data Product
Overview......................................................................................................
2
2.2 Data
Processing.................................................................................................................
2
2.2.1 Data Processing
Level...............................................................................................
2
2.2.2 Data Product
Generation............................................................................................
3
2.2.3 Data
Flow.....................................................................................................................
4
2.2.4 Labeling and
Identification..........................................................................................
4
Standards Used in Generating Data
Products......................................................................
5
2.2.1 PDS
Standards...........................................................................................................
5
2.2.2 Time
Standards...........................................................................................................
5
2.2.3 Data Storage
Conventions.........................................................................................
5
2.3 Data
Validation...................................................................................................................
5
3. Detailed Data Product
Specifications...............................................................
5
3.1 Data Product Structure and
Organization........................................................................
5
3.2 Data Format
Description...................................................................................................
6
3.3 PDS Label
Description......................................................................................................
7
4. Applicable
Software....................................................................................................
7
4.1 Utility
Programs...................................................................................................................
7
4.2 Applicable PDS Software
Tools.......................................................................................
7
APPENDIX A - Sample Mars atmospheric opacity Label and data
file..... 8
PDS
Label.................................................................................................................................
8
Sample Data
File....................................................................................................................
10
aPPENDIX B - LABEL KEYWORD
DEFINITIONS.................................................................
1
LIST OF TABLES
Table 1. Processing Levels for Science Data
Sets........................................ 2
ACRONYMS
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ASCII
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American Standard Code for Information Interchange
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CODMAC
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Committee on Data Management and Computation
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EDR
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Experiment Data Record
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ISO
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International Standards Organization
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JPL
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Jet Propulsion Laboratory
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MER
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Mars Exploration Rover
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NASA
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National Aeronautics and Space Administration
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ODL
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Object Description Language
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OSS
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Operations Storage Server
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PDS
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Planetary Data System
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RDR
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Reduced Data Record
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SIS
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Software Interface Specification
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SOWG
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Science Operations Working Group
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STG
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Science Theme Group
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TBD
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To Be Determined
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The purpose of this data
product SIS is to provide users of the MER Mars atmospheric
opacity data product with a detailed description of the
product and a description of how it was generated,
including data sources and destinations. The product is an
ASCII table of Mars atmospheric opacity values as derived
from MER Pancam solar filter observations of the Sun. This
SIS is intended to provide enough information to enable
users to read and understand the data product. The users
for whom this SIS is intended are the scientists who will
analyze the data, including those associated with the MER
Project and those in the general planetary science
community.
This data product SIS describes how the Mars atmospheric
opacity data product is generated, formatted, labeled, and
uniquely identified. The document discusses standards used
in generating the product and software that may be used to
access the product. The data product structure and
organization is described in sufficient detail to enable a
user to read the product. Finally, an example of a data
product and the PDS label is provided, along with
definitions for the label keywords.
This Data Product SIS is responsive to the following MER
documents:
1. Mars Exploration Program Data Management Plan, R.
E. Arvidson, S. Slavney, and S. Nelson, Rev. 3, March 20,
2002.
2. Mars Exploration Rover Project Archive Generation,
Validation and Transfer Plan, R. E. Arvidson and S.
Slavney, JPL D-19658, March 22, 2002.
3. MER Project SIS - Camera Experiment Data Record
(EDR) and Reduced Data Record (RDR) Operations Data
Products, H. Mortensen, D. Alexander, JPL D-22846, Revision
B, January 24, 2003.
This SIS is also consistent with the following Planetary
Data System documents:
4. Planetary Data System Data Preparation Workbook,
Version 3.1, JPL D-7669, Part 1, February 1, 1995.
5. Planetary Data System Data Standards Reference,
Version 3.5, JPL D-7669, Part 2, October, 15, 2002
6. Planetary Science Data Dictionary Document, JPL
D-7116, August 28, 2002.
The reader is referred to the following documents for
additional information:
7. Smith, P. H., and M. Lemmon, Opacity of the Martian
atmosphere measured by the Imager for Mars Pathfinder,
J. Geophys. Res, 104, 8975-8995, 1999.
Finally, this SIS is meant to be consistent with the
contract negotiated between the MER Project and the Athena
Principal Investigator in which reduced data records and
documentation are explicitly defined as deliverable
products.
Changes to the Pancam EDR and/or RDR data products and the
SIS that describes these products [3] could affect the Mars
atmospheric opacity data product and/or this SIS. In
addition, changes to the processing tools used to generate
the Mars atmospheric opacity data product could affect both
the data product and this SIS.
A Mars atmospheric opacity data product consists of two
files, an ASCII formatted detached PDS label file and an
ASCII formatted data file. The data file contains values of
the Mars atmospheric opacity or optical depth derived from
MER Pancam images of the Sun acquired with the two solar
filters. The effective wavelengths of these filters are
440 and 880 nm. Each data file contains an ASCII table of
the derived atmospheric opacity for a given rover and
Pancam solar filter. Each table contains columns with the
source Pancam image identifier, the time of image
acquisition, the Mars season (Ls), Sun-Mars
distance, airmass, observed solar flux, and opacity.
This SIS used the Committee On Data Management And
Computation (CODMAC) data level numbering system to
describe the processing level of the Mars atmospheric
opacity data products. These data products are considered
CODMAC "Level 5" or "Derived Data" (equivalent to NASA
Level 2). The Mars atmospheric opacity data products are
generated from analysis of MER Pancam images. Refer to
Table 1 for a summary of the CODMAC and NASA data
processing levels.
Table 1. Processing
Levels for Science Data Sets
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NASA
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CODMAC
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Description
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Packet data
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Raw - Level 1
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Telemetry data stream as received at the ground
station, with science and engineering data
embedded.
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Level-0
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Edited - Level 2
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Instrument science data (e.g., raw voltages,
counts) at full resolution, time ordered, with
duplicates and transmission errors removed.
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Level 1-A
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Calibrated - Level 3
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Level 0 data that have been located in space and
may have been transformed (e.g., calibrated,
rearranged) in a reversible manner and packaged
with needed ancillary and auxiliary data (e.g.,
radiances with the calibration equations applied).
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Level 1-B
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Resampled - Level 4
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Irreversibly transformed (e.g., resampled,
remapped, calibrated) values of the instrument
measurements (e.g., radiances, magnetic field
strength).
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Level 1-C
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Derived - Level 5
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Level 1A or 1B data that have been resampled and
mapped onto uniform space-time grids. The data are
calibrated (i.e., radiometrically corrected) and
may have additional corrections applied (e.g.,
terrain correction).
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Level 2
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Derived - Level 5
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Geophysical parameters, generally derived from
Level 1 data, and located in space and time
commensurate with instrument location, pointing,
and sampling.
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Level 3
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Derived - Level 5
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Geophysical parameters mapped onto uniform
space-time grids.
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The Mars atmospheric opacity data products are produced by
the Atmospheres Science Theme Group (STG) of the MER
Science Operations Working Group (SOWG) using processing
procedures and software developed by Mark Lemmon, Texas
A&M Univ.
The data product is generated after each sol in which
opacity data is acquired. The generation is done in four
steps. First, the input parameters are set up. A list of
Pancam data products to be processed is read and associated
values are determined for Ls, the distance of
Mars from the Sun, the sol that the data were acquired, and
the actual elevation angle of the Sun. It is likely that
standard tools such as the NAIF toolkit will be used for
these computations. For each Pancam data product, the
airmass is computed by integration through a spherically
symmetric atmosphere with a scale height equivalent to the
gas scale height of the Martian atmosphere.
Second, the solar flux is extracted from each calibrated
Pancam data product. To do this, the background is
determined within an annulus at a fixed radius from the
center of the Sun in the image. That background is
subtracted, as it would lead to a significant departure
from Beers' Law at high airmasses. After background
subtraction, the solar flux is integrated over the image.
The presence of a few missing pixels (e.g., a Phobos
transit or a missing packet that only partly overlaps the
Sun) can be accommodated by the integration algorithm. The
presence of a large number of missing pixels or any
saturated pixels will result in the rejection of an image
(returning a flux and opacity of "-1.000").
Third, a relative calibration is derived. Data from the
afternoon of all sols during which more than 1 image was
acquired are considered, together with instrumental
uncertainties. The published calibration (Bell et al., in
prep.) is considered as a single datum with associated
uncertainty. The instrument response is varied, and a
single best-fit opacity is derived for each afternoon using
Beers' Law (I_observed = I_0 exp(-t h), where h = airmass).
A best-fitting responsivity is chosen by minimizing the
reduced C2 of the fit.
Fourth, the relative calibration is used to derive
opacities. All images are considered, and Beers' Law is
applied to every pair of I_observed and airmass. The
relative calibration method ensures that (1) substantial
calibration uncertainty is not propagated into uncertainty
in opacity once sufficient surface data are obtained, and
(2) that the processing transfers smoothly from using the
laboratory calibration when the first datasets are obtained
to using the relative calibration when enough surface data
exist.
The Mars atmospheric opacity data products are generated
from Pancam solar filter images. These images are
transferred from OSS to the Atmospheres STG workstations.
The most recent version of the appropriate opacity data
product is also obtained from OSS. Once a new version of an
opacity data product is generated, it is transferred back
to the OSS for access by other MER science and operations
team members. Updates to the Mars atmospheric opacity data
products will be made whenever new Pancam solar images are
acquired. After a science validation period, the Mars
atmospheric opacity data products are transferred to the
PDS for final validation and archiving in accordance with
the MER archive plan [2].
The opacity data products will be updated as new Pancam
solar filter images are acquired. Thus, the size of an
individual Mars atmospheric opacity data product will
increase over the course of the MER mission. The final
version of each data product will include opacity
determinations derived from a given rover and Pancam solar
filter covering the complete mission.
Each Mars atmospheric opacity data product is identified by
a unique filename, along with a unique product_id keyword
in the associated PDS label. The product filename adheres
to the ISO-9660 level II filename convention of 27.3
(maximum of 27 characters followed by a 3 character
extension), which is compliant with PDS standards [5]. The
product_id found in the PDS label is equal to the filename
without the extension.
The file naming scheme for the Mars atmospheric opacity
data products is formed by:
<rover>TAU<filter>_<sol>_<
date><version>.TAB
where:
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rover
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=
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(1 integer) MER rover mission identifier. Valid
values are "1" (MER-1) or "2" (MER-2).
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TAU
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=
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(3 alpha characters) Always TAU for atmospheric
opacity data
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filter
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=
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(3 integers) Effective wavelength of Pancam solar
filter. Valid values are "440" for left eye and
"880" for right eye.
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sol
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=
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(3 integers) Sol number of last data entry.
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date
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=
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(8 integers) Product creation date with format
yyyymmdd for year, month, and date.
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version
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=
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(1 alpha character). Product version identifier.
Value of "A" for first version of given product
creation date. Value increments for each new version
within a given day.
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TAB
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=
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(3 alpha characters) Always TAB to indicate a PDS
ASCII table structure.
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An example filename using this scheme would be:
2TAU880_040_20040214A.TAB.
The Mars atmospheric opacity data product complies with
Planetary Data System standards for file formats and
labels, as specified in the PDS Standards Reference [5] and
the Planetary Science Data Dictionary Document [6].
The PDS label for a Mars atmospheric opacity data product
uses keywords containing time values, such as start time
and stop time. Each time value standard is defined
according to the keyword definition. See Appendix B.
The Mars atmospheric opacity data product and detached PDS
label files are stored as ASCII text. Each line or record
in the files is terminated with a two-character sequence of
carriage return (<CR>, ASCII 13) and line feed
(<LF>, ASCII 10) to comply with PDS standards [5].
This line terminator sequence will allow the data files and
labels to be easily read on most computers, which recognize
either the carriage return, the line feed, or the
<CR>/<LF> sequence as an ASCII record
terminator.
Validation of Mars atmospheric opacity data product labels
includes checking for correct PDS syntax, for accepted
standard values of keywords, and for internal consistency
of label items.
The Atmospheres STG will periodically check the relative
calibration for internal consistency and will determine if
a different internal calibration is better suited to the
data obtained. Opacity derivations will be compared to
independent but indirect estimates of opacity from other
sources, such as the Pancam calibration target shadow
intensity.
Each Mars atmospheric opacity data product is structured as
two files; a detached PDS label file and a separate data
file. Both components are stored as ASCII text. Data within
the opacity data file is organized by time with the most
recent measurement being appended to the end of the file.
Each Mars atmospheric opacity data product consists of two
parts. The first part of the data file contains header
information, which includes parameter values used in the
opacity computations and column names for the data rows.
The second part of the file, starting at line 10 consists
of a PDS table object [5]. The table has eight columns and
a variable number of rows. There is one row for each
opacity measurement. The number of rows in a data product
will increase as new measurements of atmospheric opacity
are made. Each row is 88 bytes long including the carriage
return and line feed characters. All columns are
fixed-width as described in the PDS label and are also
delimited with commas. Text columns are surrounded by
double-quotes and are left-justified. Numeric columns are
right-justified. Table 2 contains the column definitions
for the opacity data product.
Table 2. Mars Atmospheric Opacity Column Definitions
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Column Number
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Name
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Data Type
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Description
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1
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Pancam Product_id
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Text
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Product identifier for the source Pancam image used
for the opacity measurement.
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2
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Solar Longitude
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Real
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Martian season in degrees past northern spring
equinox.
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3
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Solar Distance
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Real
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Mars-Sun distance in AU at time of observation.
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4
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Local Time
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Real
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Observation time in sols past the local midnight
preceding landing. The local solar time is given by
multiplying the fractional component by 24 hours. Sol
number is obtained by rounding up the local time
value. For example, noon on Sol 2 is given as local
time of 1.5.
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5
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Airmass Factor
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Real
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Airmass factor relative to the zenith. It can be
approximated as the secant of zenith angle for most
observations, but is computed using a 13-km scale
height to improve accuracy for low-Sun observations.
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6
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Solar Flux
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Real
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Observed solar flux after subtracting background in
units of W/m2/nm. Computed using Pancam
calibration parameters. A value of -1.0 indicates an
image that resulted in a non-measurement of opacity
(e.g., due to missing packet and/or data saturation).
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7
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Opacity Value
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Real
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Measured atmospheric opacity using the current best
relative calibration. A value of -1.0 indicates an
image that resulted in a non-measurement of opacity
(e.g., due to missing packet and/or data saturation).
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8
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Relative Opacity Error
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Real
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Relative error in the opacity measurement. A value
-1.0 indicates an image that resulted in a
non-measurement of opacity (e.g., due to missing
packet and/or data saturation).
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Each Mars atmospheric opacity data product has a detached
PDS label, which is stored as ASCII text. The PDS label is
object-oriented with keywords for product identification,
along with the data object definition. The data object
definition within the label contains descriptive
information needed to interpret or process the data.
PDS labels are written in Object Description Language (ODL)
[5]. PDS label statements have the form of "keyword =
value". Each label statement is terminated with a carriage
return character (ASCII 13) and a line feed character
(ASCII 10) sequence to allow the label to be read by many
operating systems. Pointer statements with the following
format are used to indicate the location of data objects in
the data product:
^object = location
where the carat character (^, also called a pointer) is
followed by the name of the specific data object. For
detached PDS labels, location is the name of the file that
contains data object and optionally the starting record
number of the data object within the file or byte offset
from the start of the file.
Appendix A lists an example PDS label for a Mars
atmospheric opacity data product, along with a sample data
file.
The ASCII format of the Mars atmospheric opacity data
product means that the data can be displayed using a text
editor. In addition, the use of the PDS table structure for
this data product means the data can be readily imported
into spreadsheet and plotting programs.
PDS-labeled tables can be viewed with the program NASAView,
developed by the PDS. NASAView is available in versions
that run on SUN/SOLARIS, Windows, and LINUX operating
systems. NASAView can be obtained from the PDS web site
http://pdsproto.jpl.nasa.gov/Distribution/license.html.
There is no charge for NASAView.
PDS_VERSION_ID = PDS3
/* FILE DATA ELEMENTS */
RECORD_TYPE = STREAM
FILE_RECORDS = TBD (9 + number of opacity
records)
^HEADER = ("NAME_OF_FILE", 1)
^TABLE = ("NAME_OF_FILE", 10)
/* IDENTIFICATION DATA ELEMENTS */
DATA_SET_ID =
"MER-M-PANCAM-5-ATMOS-OPACITY-V1.0"
PRODUCT_ID = "2TAU440_040_20040212A"
PRODUCT_TYPE = "OPACITY"
INSTRUMENT_HOST_ID = <MER1 or MER2>
INSTRUMENT_HOST_NAME = "MARS EXPLORATION ROVER 1"
(or 2)
FILTER_NAME = PANCAM_L8_440NM (or
PANCAM_R8_880NM)
INSTRUMENT_ID = PANCAM_LEFT (or
PANCAM_RIGHT)
MISSION_NAME = "MARS EXPLORATION ROVER"
TARGET_NAME = SUN
PRODUCT_CREATION_TIME = YYYY-MM-DDThh:mm:ss
START_TIME = YYYY-MM-DDThh:mm:ss
STOP_TIME = YYYY-MM-DDThh:mm:ss
OBJECT = HEADER
BYTES = UNK
RECORDS = 9
HEADER_TYPE = SPREADSHEET
INTERCHANGE_FORMAT = ASCII
DESCRIPTION = "The header contains key
parameter values
used in the opacity
computations, along
with column headings for
the table object."
END_OBJECT = TABLE_HEADER
OBJECT = TABLE
INTERCHANGE_FORMAT = ASCII
ROWS = TBD (number of opacity
records)
ROW_BYTES = 88
COLUMNS = 8
DESCRIPTION = "Tables containing the
opacity
determinations for a given
rover and
solar filter. Columns in
the table
are fixed-width and
separated by
commas. The start byte
and bytes
keywords of the column
definitions do
not include quotes or
commas in the table."
OBJECT = COLUMN
COLUMN_NUMBER = 1
NAME = PANCAM_PRODUCT_ID
DATA_TYPE = CHARACTER
START_BYTE = 2
BYTES = 27
DESCRIPTION = "The product_id of the
Pancam solar
filter image used for a
given opacity
determination."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 2
NAME = SOLAR_LONGITUDE
DATA_TYPE = ASCII_REAL
START_BYTE = 31
BYTES = 6
DESCRIPTION = "Martian season in degrees
past
northern spring equinox."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 3
NAME = SOLAR_DISTANCE
DATA_TYPE = ASCII_REAL
START_BYTE = 38
BYTES = 6
DESCRIPTION = "Mars-Sun distance in AU at
time of
observation."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 4
NAME = LOCAL_TIME
DATA_TYPE = ASCII_REAL
START_BYTE = 45
BYTES = 8
DESCRIPTION = "Observation time in sols
past the local
Midnight preceding
landing. The local
solar time is given by
multiplying the
fractional component by 24
hours.
Sol number is obtained by
rounding up
the local_time value. For
example, noon
on Sol 2 is given as
local_time of 1.5."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 5
NAME = AIRMASS
DATA_TYPE = ASCII_REAL
START_BYTE = 54
BYTES = 7
DESCRIPTION = "Airmass factor relative to
the
zenith. It can be
approximated as
the secant of zenith angle
for
most observations, but is
computed
using a 13-km scale height
to
improve accuracy for
low-Sun
observations."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 6
NAME = SOLAR_FLUX
DATA_TYPE = ASCII_REAL
START_BYTE = 62
BYTES = 8
DESCRIPTION = "Observed solar flux in W
m-2
nm-1 after subtracting
background light. Computed
using
Pancam calibration
parameters.
A value of -1.0 indicates
an image
that resulted in a
non-measurement
opacity (e.g., due to
missing packet
and/or data saturation)."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 7
NAME = ATMOSPHERIC_OPACITY
DATA_TYPE = ASCII_REAL
START_BYTE = 71
BYTES = 7
DESCRIPTION = "Measured atmospheric
opacity using
the current best relative
calibration.
A value of -1.0 indicates
an image
that resulted in a
non-measurement
opacity (e.g., due to
missing packet
and/or data saturation)."
END_OBJECT = COLUMN
OBJECT = COLUMN
COLUMN_NUMBER = 8
NAME = OPACITY_ERROR
DATA_TYPE = ASCII_REAL
START_BYTE = 79
BYTES = 8
DESCRIPTION = "Relative error in the
opacity
measurement.
A value of -1.0 indicates
an image
that resulted in a
non-measurement
opacity (e.g., due to
missing packet
and/or data saturation)."
END_OBJECT = COLUMN
END_OBJECT = TABLE
END
The sample data file listed below consists of two parts.
The first nine lines contains header information with
parameter values used in the opacity computations. The
header also includes the column names for the data rows.
The second part of the file, starting at line 10 contains
the opacity determinations.
MER opacity measurements for Pancam 440 nm solar filter
images.
Flux_1AU = 0.9876 W m-2 nm-1 in the current best fit.
Abs_Err = 0.025 (absolute error in tau derivation at AM=1).
The date of the current best fit is 2004-Jan-07 11:59:59
UTC.
N_ENTRIES = 3
Comments or questions to Mark Lemmon, lemmon@tamu.edu.
Product_ID, L_s, R_au, Sol,
AM, Flux, TAU, Rel_err
"1P123456787EDR010300062L8M1", 328.5, 1.561, 1.234,
1.123, 0.7291, 0.489, 0.015
"1P123456788EDR010300062L8M1", 328.5, 1.561, 1.456,
1.123, 0.7291, 0.489, 0.015
"1P123456789EDR010300062L8M1", 328.5, 1.561, 1.678,
1.123, -1.0, -1.000, -1.000