ESA/UPV-EHU/DADPS
Mars Express
VMC
Visual Monitoring Camera
Experiment to Archive
Interface Control Document
(EAICD)
V1.1
Contents
List of Figures 4
List of Tables 4
Acronyms 4
1. Introduction 5
1.1 Purpose and Scope 5
1.2 Contents 5
1.3 Applicable Documents 5
1.4 Reference Documents 5
2. The Visual Monitoring Camera 6
2.1 Description 6
2.2 Main Instrument Characteristics 6
2.3 Data Description 6
2.3.1 Raw Telemetry and Housekeeping data 7
2.3.2 Archive Data types 8
2.4 Science Applications 10
2.5 Opening the data 10
2.6 Known image artifacts 10
2.7 Geometry 11
3. VMC Product Generation 11
3.1 VMC Data Archive Pipeline 11
4. Archive Format and Content 12
4.1 Format and Conventions 12
4.1.1 Deliveries 12
4.1.2 Data Set ID Formation 13
4.1.3 Data Directory Naming Convention 14
4.1.4 File naming Convention 14
4.2 Standards Used in the Data Product Generation 14
4.2.1 PDS Standard 14
4.2.2 Time Standard 15
4.2.3 Reference Systems 15
4.2.4 Data Validation 15
4.2.5 Data Set 15
4.2.6 Directories 16
5. Detailed Interface Specifications 18
5.1 Data Product Design 18
5.1.1 Raw Data Products 18
5.1.2 Calibrated data products 18
5.2 Label 18
PDS version 18
File Characteristics 19
Data Object Pointers 19
Identification 19
Instrument and Detector Parameters 23
Geometry Information 23
Image Calibration, Timing and Resolution details 24
Additional information 26
Data Object Definition 27
Appendix A: Complete Data Label 29
List of Figures
Figure 1: XML Telemetry entry example 7
Figure 2: Debayering process. 8
Figure 3: Flowchart of the full VMC data pipeline used to process raw
and calibrated data products, as well as browse images. 11
Figure 4: Archive folder structure. YYYY corresponds to year, MM to
month, DD to day, TTTT to the start time of the observation and XXXX
to the end time of the observation. 16
List of Tables
Table 1 - Mars Express Mission Phases 12
Acronyms
CMOS
Complementary Metal-Oxide-Semiconductor
DADPS
DN
Dias Almeida Data Processing and Systems
Digital Number
EAICD
Experiment to Archive Interface Control Document
ESA
European Space Agency
FOV
HK
IAU
Field Of View
HouseKeeping data
International Astronomical Union
MEX
Mars EXpress
PDS
Planetary Data System
UPV-EHU
University of the Basque Country (Spain) (Universidad del Pais Vasco -
Euskal Herriko Unibertsitatea)
TM
VMC
TeleMetry data
Visual Monitoring Camera
1. Introduction
1.1 Purpose and Scope
The Experiment to Archive Interface Control Document (EAICD) serves as
the companion document to the Mars Express Visual Monitoring Camera
datasets. With it, the intended readers should be able to make use of
these datasets for scientific purposes.
1.2 Contents
Described in this document are:
* The data itself, with information about how it evolves from the
moment it is acquired to its format in the archive.
* Details of the auxiliary constructions around the data.
* The file structure, naming conventions and metadata associated with
the data products.
1.3 Applicable Documents
[PDS-SR] Planetary Data System Standards Reference, v3.8. 27 February
2009.
1.4 Reference Documents
[VMC-UM] ESA VMC Flight User Manual 4.2. 2003
[VMC-DB] RE-VMC-0050-OIP/07. MEX-VMC Debayering Raw Images and
Conversion to RGB images. OIP Sensor Systems. Issue 1. 2007
[VMC-OR] Ormstom, T. et al. An ordinary camera in an extraordinary
location: Outreach with the Mars Webcam. Acta Astronautica 2018.
https://doi.org/10.1016/j.actaastro.2011.04.015
[VMC-SL] Sanchez-Lavega, A. et al. Limb clouds and dust on Mars from
images obtained by the Visual Monitoring Camera (VMC) onboard Mars
Express. 2018. https://doi.org/10.1016/j.icarus.2017.07.026
[VMC-HBa] Hernández-Bernal, J. et al. The 2018 Martian Global Dust
Storm Over the South Polar Region Studied With MEx/VMC. Geophysical
Research Letters 2019. https://doi.org/10.1029/2019GL084266
[VMC-HBb] Hernández-Bernal, J. et al. Clouds in the night side of
Mars: an analysis using Mars Express VMC. EPSC, 2018.
[VMC-RA] Ravanis, E. et al. From engineering to science: Mars
Express Visual Monitoring Camera's first science data release.
EPSC, 2020.
2. The Visual Monitoring Camera
2.1 Description
The Visual Monitoring Camera (VMC) on board Mars Express was primarily
put on the spacecraft to monitor the Beagle 2 lander release (see
[VMC-UM]). It performed this task successfully, despite the failure of
the Beagle 2 lander itself, and no use of the camera as a science
instrument was foreseen.
In 2007, engineers from the Mars Express Flight Control Team switched
VMC back on again to begin taking observations for outreach and
educational purposes, whenever those observations did not interfere
with the operations of science instruments (see [VMC-OR]). Since the
VMC images are quite small in data volume, it was possible to acquire
some images without impacting the rest of the Mars Express Payload.
Finally in 2016 it was understood that there was scientific value to
the VMC data (see [VMC-SL]), and the camera was given the status of a
scientific instrument on Mars Express. Science operations for the
instrument has been based at the European Space Astronomy Centre in
Madrid since summer 2018, and the scientific leadership is based at
the University of Pais Vasco (UPV/EHU) in Bilbao, Spain. The VMC
camera is able to monitor large scale atmospheric phenomena, and
provides valuable context to other instruments.
2.2 Main Instrument Characteristics
The values provided here are the result of the instrument calibration
performed by UPV/EHU and are updated with respect to those previously
published in reference documentation. The operational values and most
updated versions are maintained in the SPICE reference frame kernels
(FK) and instrument kernels (IK):
ftp://spiftp.esac.esa.int/data/SPICE/MARS-EXPRESS/kernels
Focal length: 12.3 mm
Focal ratio (F/#): 5
FOV: 41.38º x 31.04º.
Instantaneous FOV: 0.00112859 rads/pixel
Wavelength range: 400 - 650 nm
Detector: 640x480 pixel CMOS
Pixel pitch: 14 µm pixel pitch
2.3 Data Description
VMC has a 640 x 480 pixel array with a Bayer filter on top (see
[VMC-UM], [VMC-DB] and [VMC-RA]).
For the Archive there are two main products of the VMC, these being
the raw data and the calibrated data. VMC takes images by default in
grayscale but colour is added using a Bayer Matrix (explained in
section 2.3.2).
2.3.1 Raw Telemetry and Housekeeping data
This data is not archived, but is described here for completion. This
refers to the original data obtained by the instrument and the
spacecraft, which is converted into the archive products described
later.
Raw Telemetry Data
The original raw telemetry data from the instrument comes as a byte
stream with no header. The byte stream has the digital number (DN)
intensity of each pixel in the sensor stored as 1 byte (8 bit). The
sensor has a Bayer filter on top, therefore each pixel is for a
different colour. The Bayer Pattern is RGGB. The byte stream is stored
in a binary file produced by the European Space Operations Centre
(ESOC) with a raw extension.
Housekeeping Data
In order to produce the Raw and Calibrated Data for the archive, some
of the instrument and spacecraft housekeeping telemetry (HK) is used.
These are produced as XML ASCII files. One XML is created for one
observation (Instrument ON - Images Acquisition - Instrument OFF).
The following is a sample of one of the XML entries, corresponding to
one image (each file includes entries for each image acquired during
one observation):
16-261_02.17.31_VMC_Img_No_1.raw
16-261T02:17:31.302Z
14.00
-13.0
Figure 1: XML Telemetry entry example
is the XML tag for the image object.
is the file name of the ESOC produced file
The name is as follows:
YY-DOY_HH:MM:SS_VMC_Img_No_X.raw
YY - is the year
DOY - is the day of the year
HH - Hours
MM - Minutes
SS - Seconds
X - image counter of the observation
is the time the sensor was exposed for the image
acquisition in milliseconds.
VMC internal temperature in degrees.
2.3.2 Archive Data types
In this section we describe how the raw and calibrated VMC data is
generated and in what format.
Raw Image Data with PNG Browse file
The VMC Archive data products are in .RAW image format.
As stated in the Raw Telemetry Data section, the original data has
the information of each physical pixel in a byte stream corresponding
to the colour filter on top of it following the Bayer pattern. The
archived raw files are codified as unsigned integers with 8 bits,
which means that their values range from 0 to 255. The pixels are
read row by row, starting in the top left corner of the image and
finishing in the bottom right corner. In some rare cases, there are
missing bytes at the end of the file, and these are drawn as black.
The file size is 640 x 480 bytes, corresponding to 307200 bytes, or
300 KB.
The browse products are provided for quick-look purposes in PNG
format, which is a direct conversion of the raw product into an image
with the Bayer pattern solved (see [VMC-DB]). Each PNG pixel has
information for Red, Green and Blue. In order to keep the scientific
fidelity, the way the images are processed is that each pixel keeps
its original value for the corresponding Bayer grid colour and
interpolated values are calculated by averaging the available
adjacent pixels of the target original colour (either 2 or 4 pixels,
see also Figure 2).
Figure 2: Debayering process. Coloured squares indicate pixels that
keep their original value, grey boxes indicate where that colour
channel is interpolated from the surrounding pixels.
In the Debayering process (see [VMC-DB]), each pixel keeps its
original value for the corresponding colour on the Bayer filter grid,
and for the other colour channels, the value is interpolated from the
surrounding pixels. On the diagram in the final column, the coloured
squares (red, green and blue) represents an original colour value, and
the grey colour represents an interpolated value for that colour
channel.
This means that:
o Red in green pixels is interpolated from only 2 available adjacent
red pixels.
o Red in blue pixels from up to 4 pixels.
o Green in red pixels from up to 4 pixels.
o Green in blue pixels from up to 4 pixels
o Blue in red pixels, from up to 4 pixels.
o Blue in green pixels, from 1 or 2 pixels.
Note that this interpolation algorithm has limitations at the borders,
in particular in the 2 pixel margin around each image, which should be
handled carefully and taken into account for the scientific
interpretation of the images.
Calibrated FITS data with PNG Browse
No on-ground calibration exists for the VMC camera and so in-flight
calibration has been performed.
The master dark current file is made from images of dark sky. The dark
has a mean value of 2.4 DN, and only 0.1% of pixels have values >4 DN.
Currently, the same dark current file is used for all exposures and
temperatures.
The flat-field file was created using dark-corrected images of flat
portions of Mars that were well and uniformly illuminated, as free as
possible from large structures, and as flat as possible (e.g. taken at
pericentre, in the northern plains of Mars). Sigma-clipping was
performed that rejected pixels two standard deviations away from the
mean value of the pixels across all the images for darker images, and
4 standard deviations away for higher pixel value images, so that
images with poorer illumination had less influence on the final master
flat. Once this sigma-clipping was performed, the remaining pixels
were averaged across all the images and then normalised to create the
master flat-field file. This was done by averaging the counts of the
central portion of the images (typically the most well illuminated) to
1 and then dividing all the pixels of the master flat by that number.
This flat-field calibration may be improved in future as we take more
observations, but the current flat field has provided good results so
far (see reference list for example publications).
In the BROWSE calibrated products, the vignetting effect produced by
the camera is not corrected (though such correction is done for the
DATA products using the flat-field image), as these PNGs cannot save
values above 255, but the BROWSE products are not intended to be used
for scientific purposes.
The process of calibration in the processing pipeline for the Level 3
DATA products is as follows: first, all saturated (=255 and above) are
converted to NAN ('Not a Number') so that they are removed from the
calibration, then the dark current file is subtracted, and the result
is divided by the flat. This is illustrated later in Figure 3. Both
the flat-field and dark-current file used are provided in the CALIB
directory.
2.4 Science Applications
The main science applications that are envisaged focus on global
climate monitoring and include the following:
* Cloud monitoring
* Dust monitoring
* Limb monitoring
* Winds and dynamical phenomena
* High clouds at terminator
* Surface ice coverage
* Synergies with other payloads on Mars Express.
These are made possible by the wide field of view of VMC which can
therefore image large areas of Mars at once (allowing for the study
of regional to global scale atmospheric phenomena) and the capability
to take various images with a repetition time of less than 1 minute,
allowing observations of the same area which can be used to identify
and monitor dynamic atmospheric features (dust and cloud tracking,
wind measurements, etc). See the reference publications for more
information [VMC-OR], [VMC-SL], [VMC-HBa], [VMC-HBb], [VMC-RA].
2.5 Opening the data
FITs files are typically opened using Python. The ‘Astropy’ library is
required.
DS9 is a popular free software for astronomical images which can also
be used for opening VMC FITs data products. When opening the files,
DS9 takes the first layer of the FITs file (the calibrated layer), and
detects that it contains three dimensions (more than one colour
channel). DS9 then opens a "Cube" window to handle the three
dimensions. In the menu "Axes order", the user must select "2 3 1",
and then the first channel (red) appears in the viewer. In the "Cube"
window, it is possible to switch the channel. Once the image is in the
viewer, several operations can be performed, including exporting to an
image format.
2.6 Known image artifacts
We note here various artifacts that are still present in the data
after the calibration process and that will hopefully be addressed in
future updates of the calibration pipeline, which will be released and
distributed in the
PSA whenever they become available.
* The "main" artifact is in the right half of the VMC images. This is
believed to be a consequence of the Beagle 2 release. It appears as a
large flat-field value and those pixels cannot currently be
calculated. As a result, there are sometimes white squares in the
BROWSE products that are saturated values around this artifact.
* There is a horizontal "line" artifact which appears in some images.
It typically appears on the top of the image, but its exact
positioning changes depending on exposure. Taking the first horizontal
line as 0, this artifact line is always in an odd (1,3,5,7,...) number
line. In most cases, the line position can be determined as:
N=2.5*exposure (in milliseconds).
* There is a background "glare" in images. This glare is not present
when we image dark sky. This glare does not grow linearly with
exposure, and thus it is unlikely to be an internal reflection of
optical origin, but instead likely has an electronic origin. This
glare may be corrected in future releases, but no photometrically
reliable correction has been developed so far. The typical DN of this
glare is around 7, but occasionally it can reach up to DN~15.
2.7 Geometry
Only basic geometry information (latitude, longitude and distance) has
been added in the PDS Labels so far. All geometry computations are
based on the spacecraft ephemeris and orientation provided via the
SPICE service in the web and FTP repository below:
* https://www.cosmos.esa.int/web/spice/spice-for-mex
* ftp://spiftp.esac.esa.int/data/SPICE/MARS-EXPRESS/kernels
A full geometry calibration pipeline for VMC is currently under
development and it may be included in a future data release for the
PSA. Some preliminary details of the geometry calibration performed so
far for specific research are accessible via the reference papers
Hernandez-Bernal et al. [VMC-HBa and VMC-HBb]. Note however that this
is still under development and therefore some of the geometry
information may differ in each of the research works.
3. VMC Product Generation
3.1 VMC Data Archive Pipeline
The VMC data is assembled on ground as raw data product images. These
products are a bitstream of all the pixels as collected by the VMC
sensor (see 2.3 Data Description).
The resulting products will be described in more detail in the
following sections. In order to produce these products from the raw
data, a pipeline was made that uses the raw data as well as telemetry
parameters, namely the acquisition time, the exposure duration, and
the VMC temperature. The pipeline design is shown in Figure 3.
Figure 3: Flowchart of the full VMC data pipeline used to process raw
and calibrated data products, as well as browse images.
Before the dark current correction is applied, the raw data products
of the VMC dataset are stored, these being the level 2 outputs. The
dark-corrected and flat-fielded data are the derived data products,
which are the level 3 outputs.
4. Archive Format and Content
This chapter describes the archive structure, naming conventions for
directories and data products, and a high-level description of the
products.
Detailed product descriptions will be found in the Section 5 Detailed
Interface Specifications.
4.1 Format and Conventions
4.1.1 Deliveries
Deliveries will be done every six months for data that was acquired
six months before. These datasets will correspond to a given Mars
Express mission phase as shown in Table 1.
Table 1 - Mars Express Mission Phases
Mission Phase
Dates
Orbit Numbers
Nominal
4 Jan 2004 - 30 Nov 2005
1 - 2418
EXT1
1 Dec 2005 - 31 Oct 2007
2419 - 4918
EXT2
1 Nov 2007 - 30 Apr 2009
4919 - 6836
EXT3
1 May 2009 - 31 Dec 2012
6837 - 11453
EXT4
1 Jan 2013 - 31 Dec 2014
11454 - 13960
EXT5
1 Jan 2015 - 31 Dec 2016
13961 - 16468
EXT6
1 Jan 2017 - 31 Dec 2018
16469 - 18975
EXT7
1 Jan 2019 - 31 Dec 2020
18976 - Ongoing
4.1.2 Data Set ID Formation
This is the identification (ID) for the dataset.
The following datasets are currently envisaged:
* MEX VMC Raw Mars Data
* MEX VMC Calibrated Mars Data
The naming convention will follow the rule:
MEX-M-VMC-N-TTT-XXXX-Vn.n
Where:
o MEX - Mars Express
o M - Image Target Mars
o VMC - Visual Monitoring Camera
o N - data processing level number.
* 2 - Raw Data - Edited data in the PDS dictionary
* 3 - Derived Data - Calibrated data in the PDS dictionary
o TTT - type of data.
* EDR - Experiment Data Record (EDR) as defined in the PDS standard
(AD2). It will be used for the raw data.
* RDR - Reduced Data Record (RDR) as defined in the PDS standard
(AD2). It will be used for the radiometric calibrated data.
o XXXX - is the description of the data set. Typically the mission
phase as defined by the project. For VMC it will be one of the mission
extensions in the format:
* EXT# - See Table 1
o Vn.n - Version number of the data set, which is usually 1.0. This is
updated when data needs to be reprocessed. For large updates the first
number is updated. For small corrections the second number is updated.
See RELEASE_ID and REVISION_ID keywords for further information.
4.1.3 Data Directory Naming Convention
There will be t levels for the data archive. The data will be
separated by Year, then month, ending in observation folders.
YYYY --> YYYYMM --> YYYYMMDD_HHMM_hhmm
* YYYY : 4 digits denominating the data acquisition year
* MM : 2 digits denominating the month acquisition of said year
* DD : 2 digits denominating the day of acquisition of that month
* HHMM : start time of the observation (hours, minutes)
* hhmm : end time of the observation (hours, minutes)
4.1.4 File naming Convention
A unique file name identifier is used for each of the VMC images,
using the following format:
VMC_TL_YYMMDD_hhmmss_ccc.PNG
* VMC - Visual Monitoring Camera
* T - Purpose of data. S stands for Science.
* L - Data type
o E - Experiment Data Records (raw data)
o R - Reduced Data Records (radiometrically calibrated)
o M - Master Data Records (masters for calibration)
* YY - Year
* MM - Month
* DD - Day
* hh - hours
* mm - minutes
* ss - seconds
* ccc - counter of the image within an observation series
4.2 Standards Used in the Data Product Generation
4.2.1 PDS Standard
All files, labels, and keywords follow the PDS 3.8 standard.
4.2.2 Time Standard
The CCSDS time standard as described in the PDS standard is
used.
4.2.3 Reference Systems
Mars Body Fixed frame (IAU Mars) in Earth Mean Equatorial J2000
reference system is used.
4.2.4 Data Validation
Validated using PSA PVV software and reviewed internally.
4.2.5 Data Set
Each Dataset will include an entire mission phase as shown in
Table 1.
4.2.6 Directories
The directory structure envisaged for the VMC data sets is the
following:
Figure 4: Archive folder structure. YYYY corresponds to year, MM to
month, DD to day, TTTT to the start time of the observation and XXXX
to the end time of the observation.
Root Directory
Contains a readme file explaining the dataset and the voldesc.cat
catalog file, which lists all the catalogs in the volume.
Browse Directory
Contains versions of the data files used to facilitate browsing
through images on the PSA (see section 5.3 SOURCE_PRODUCT_ID).
Catalog Directory
Contains the catalog files.
It includes:
* DATASET.CAT - Describes the dataset
* INST.CAT - Describes the instrument
* INSTHOST.CAT - Describes the MEX spacecraft
* MISSION.CAT - Describes the MEX mission
* PERSON.CAT - List of people involved with the instrument
* REFERENCE.CAT - Lists all publications referenced in the other
catalog files
* RELEASE.CAT- Describes the individual releases that make the dataset
* SOFTWARE.CAT - Describes the software included in the dataset
Calib Directory
Contains the flat-field file and dark-current file used for the Level
3 calibration, in FITS format.
Index Directory
Contains the Dataset index file (INDEX.LBL and INDEX.TAB) that list
all the files in the dataset, as well as the BROWSE index files
(BROWSE_INDEX.LBL, BROWSE_INDEX.TAB).
Document Directory
Contains the Experiment to Archive Interface Control Document (EAICD)
- this document, and other accompanying documents, in this case the
VMC Flight User Manual and a document on the debayering technique.
Data Directory
Raw or Calibrated data depending on the Volume.
5. Detailed Interface Specifications
5.1 Data Product Design
Each product archived has a corresponding detached label.
5.1.1 Raw Data Products
Raw products are as described in section 2.3.2 and are archived with
a detached label (see section 5.2).
5.1.2 Calibrated data products
Calibrated data products are archived as a FITS data product with
extension FIT. The FITS data product consists of a header and 2
layers. The first layer includes the calibrated values, and the second
layer includes the raw values. The raw layer is not debayered, instead
it contains only one channel, and is codified as unsigned integers of
8 bits. The calibrated layer is debayered, it consists of 3 channels
and the codification is float32. Negative values indicate saturated
values. Due to a vignetting effect inherent to VMC images, which is
corrected when the flat-field is applied, some values away from the
centre of the image may go above 255 (but these values are
photometrically correct). As mentioned before, the surrounding 2 pixel
border of the images should only be used with caution for scientific
purposes. Additionally, although calibrated values are stored as
floating comma values, this is not the real precision of the values.
There is a level of uncertainty here which is currently not
calculated, however this uncertainty does not prevent the use of VMC
data for scientific purposes.The Level 3 PNGs are BROWSE products and
should not be used for anything relating to photometry. The correction
of the vignetting effect is undone for these BROWSE images so that the
values can be stored in 8 bits (which does not allow for values above
255). These PNGs are colour-enhanced and include a sharpening filter
to enhance the contrast, as well as a median filter to reduce noise.
These filters may produce artefacts in some cases, and therefore these
products are not intended for science (instead, the RAW and FITS
products should be used).
5.2 Label
This section describes each keyword used in the label.
PDS version
PDS_VERSION_ID = PDS3
PDS_VERSION_ID
Version of PDS for the VMC data.
File Characteristics
FILE_NAME = "VMC_SR_170128_141328_003.RAW"
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 1920
FILE_RECORDS = 480
FILE_NAME
Name of the image data product according to the naming convention
specified earlier in this document in 4.1.4 File naming Convention.
RECORD_TYPE
It is always FIXED_LENGTH.
RECORD_BYTES
Size of one line of the image in bytes. For RAW data products, this
number is 640. For PNG browse products, this number is 1920. For FITS
data products, this number is 6240.
FILE_RECORDS
One record for each image line. This value will always be 480.
Data Object Pointers
^IMAGE = "VMC_SR_160229_201108_0011.RAW"
^IMAGE
Location of the data/image object file. This will be the filename of
the object to which the label pertains. It will be in the same
directory as the label.
Identification
RELEASE_ID = 0001
REVISION_ID = 0000
DATA_SET_ID = "MEX-M-VMC-2-EDR-EXT6-V1.0"
DATA_SET_NAME = "MEX MARS VMC RAW DATA EXT6 V1.0"
PRODUCT_ID = "MEXVMC_1700400003"
SOURCE_PRODUCT_ID = "MEXVMC_1700400003"
PRODUCT_CREATION_TIME = 2020-01-15T15:38:39
INSTRUMENT_HOST_ID = "MEX"
INSTRUMENT_HOST_NAME = "MARS EXPRESS"
TARGET_NAME = "MARS"
IMAGE_TIME = 2017-01-28T14:13:28.004
START_TIME = 2017-01-28T14:13:28.004
STOP_TIME = 2017-01-28T14:13:28.011
PRODUCER_ID = "ESA_UPV-EHU_DADPS"
PRODUCER_FULL_NAME = "ELENI RAVANIS AND JORGE HERNANDEZ-BERNAL"
RELEASE_ID
Release one has value 0001. Only one release is intended, however any
subsequent releases will have sequential numbering if necessary.
REVISION_ID
Value from 0000 to 9999 to reflect updates to the release with updated
data products or to correct mistakes.
DATA_SET_ID
To be set in accordance to the 4.1.2 Data Set ID Formation
section of this document.
DATA_SET_NAME
It has two possible values:
MEX MARS VMC RAW DATA EXTX V1.x
MEX MARS VMC CALIBRATED DATA EXTX V1.x
Where EXTX indicates the mission extension number of the
dataset and x represents the revision.
PRODUCT_ID
Unique identifier for each data product. This uses the following
format:
MEXVMC_YYNNNNSSSS
Where:
* MEXVMC indicates the Mars Express Visual Monitoring Camera
* YY indicates the year
* NNNN indicates the observation number within that year
* SSSS indicates the image number within that observation.
SOURCE_PRODUCT_ID
For PNG BROWSE images, this refers to the source data product.
PRODUCT_CREATION_TIME
Time when the data product was created in UTC.
YYYY-MM-DDTHH:MM:SS
Where:
* YYYY - year
* MM - month
* DD - day
* T - separator, always T
* HH - hours
* MM - minutes
* SS - seconds.
INSTRUMENT_HOST_ID
It will always be "MEX".
INSTRUMENT_HOST_NAME
It will always be "MARS_EXPRESS".
TARGET_NAME
It will always be "MARS". Note that some images are deliberately
targeted at background stars, Phobos, Deimos, Earth or other planets
for calibration purposes but these may not be specified in this
keyword explicitly. There is also an observation of Beagle 2 in 2003.
IMAGE_TIME
Time when the image was acquired.
YYYY-MM-DDTHH:MM:SS.sss
Where:
* YYYY - year
* MM - month
* DD - day
* T - separator, always T
* HH - hours
* MM - minutes
* SS - seconds
* sss - milliseconds.
START_TIME
Same as the IMAGE_TIME. Both are kept in case for some reason times
need to be adjusted (e.g. system latency).
YYYY-MM-DDTHH:MM:SS.sss
Where:
* YYYY - year
* MM - month
* DD - day
* T - separator, always T
* HH - hours
* MM - minutes
* SS - seconds
* sss - milliseconds.
STOP_TIME
START_TIME plus the exposure time. Start and stop time will only be
different if the exposure time is longer than one second.
YYYY-MM-DDTHH:MM:SS.sss
Where:
* YYYY - year
* MM - month
* DD - day
* T - separator, always T
* HH - hours
* MM - minutes
* SS - seconds
* sss - milliseconds.
PRODUCER_ID
It will always be "ESA_UPV-EHU_DADPS", which stands for European
Space Agency, Universidad del Pais Vasco - Euskal Herriko
Unibertsitatea, Dias Almeida Data Processing Systems.
PRODUCER_FULL_NAME
Producers of the datasets, e.g. "ELENI RAVANIS AND JORGE
HERNANDEZ-BERNAL"
Instrument and Detector Parameters
INSTRUMENT_ID = "VMC"
INSTRUMENT_NAME = "VISUAL MONITORING CAMERA"
EXPOSURE_DURATION = 14.00
INSTRUMENT_TEMPERATURE = -13.0
INSTRUMENT_TYPE = "IMAGING CAMERA"
INSTRUMENT_ID
It will always be "VMC".
INSTRUMENT_NAME
It will always be "VISUAL MONITORING CAMERA".
EXPOSURE_DURATION
Exposure time in milliseconds.
INSTRUMENT_TEMPERATURE
Temperature as recorded by the instrument sensor in degrees Celsius,
or "N/A" when this information is not available.
INSTRUMENT_TYPE
It will always be "IMAGING CAMERA".
Geometry Information
COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING"
SUB_SPACECRAFT_LONGITUDE= 103.981
SUB_SPACECRAFT_LATITUDE= -47.673
CENTRAL_BODY_DISTANCE= 13257.315
COORDINATE_SYSTEM_TYPE
This will always be "BODY-FIXED ROTATING". In our case coordinates
correspond to the IAU Mars reference frame.
SUB_SPACECRAFT_LONGITUDE
Longitude of the sub-spacecraft point. The sub-spacecraft point is
that point on a body's reference surface where a line from the
spacecraft centre to the body centre intersects the surface.
SUB_SPACECRAFT_LATITUDE
Latitude of the sub-spacecraft point. The sub-spacecraft point is that
point on a body which lies directly beneath the spacecraft.
CENTRAL_BODY_DISTANCE
This is the distance from the spacecraft to the centre of a primary
target in kilometres.
Image Calibration, Timing and Resolution details
DARK_CURRENT_CORRECTION_FLAG = "TRUE"
DARK_CURRENT_FILE_NAME = "DARK_2020.FIT"
FLAT_FIELD_CORRECTION_FLAG = "TRUE"
FLAT_FIELD_FILE_NAME = "FLAT_2020.FIT"
SOLAR_LONGITUDE = 123.4
/*MARTIAN_YEAR = 34 */
/*NADIR_RESOLUTION = 11.1
LIMB_RESOLUTION = 14.5
SEE VMC EAICD FOR DETAILS*/
DARK_CURRENT_CORRECTION_FLAG
Flag to indicate if the data is dark corrected or not. It has two
possible values:
"FALSE" - Not corrected
"TRUE" - Corrected
DARK_CURRENT_FILE_NAME
Name of the dark current image file used to correct the data (or "N/A"
when this doesn't apply).
FLAT_FIELD_CORRECTION_FLAG
Flag to indicate if the data is flat fielded or not. It has two
possible values:
"FALSE" - Not corrected
"TRUE" - Corrected
FLAT_FIELD_FILE_NAME
Name of the flat field image file used to correct the data (or "N/A"
when this doesn’t apply).
SOLAR_LONGITUDE
The solar longitude of Mars (Ls) when the image was taken, to one
decimal place.
/*MARTIAN_YEAR */
The Martian year that the image was taken in.
/*NADIR_RESOLUTION */
This is the pixel width in kilometres, measured at the sub-spacecraft
point, that is the nadir point with emission angle zero, considering
the planet as a sphere with a radius of 3390 km. Nadir resolution is
simply a function of the sub-SC altitude and is independent of the
camera orientation. This nadir resolution is provided as a reference
of the maximum horizontal resolution that would be possible, but it
may not correspond to the maximum resolution in the image, in
particular if the nadir point is not within the image. The projected
spatial coverage of each pixel on the planet would need to be
corrected by the distance and emission angle of each pixel in the
image.
/*LIMB_RESOLUTION */
This is the pixel width in kilometers, measured at the planet limb,
that is in the horizon line with emission angle 90 degrees, which is a
circle considering the planet as a sphere of radius 3390 km. Limb
resolution is simply computed as a function of the distance between
the spacecraft and the planet limb circle, independently of the
camera orientation. This limb resolution is a valid reference for
all the horizon line, even if the limb may not be present in the
image. This resolution provides both the pixel vertical resolution in
the atmosphere, and the minimum horizontal spatial resolution in the
surface, without taking into account the pixel projection on the
planet due to the large emission angle (90 degrees). Given the wide
field of view of VMC, the difference between maximum (nadir) and
minimum (limb) horizontal resolution in a VMC image can be
considerable, and so these values provide a resolution range that can
be useful for the user.
Additional information
ORBIT_NUMBER = 16474
/*OBSERVATION_ID = "170001"*/
OBSERVATION_NAME = "2017-01-02_08.35-08.47"
PRODUCT_NAME = " 17-002_08.38.03_VMC_Img_No_1 "
ORBIT NUMBER
The orbit number in which the observation was acquired. In the rare
case where an observation spans 2 orbits, this will be the orbit
number where the observation started.
OBSERVATION_ID
This is a unique number for each observation. This keyword is
commented out, therefore not read by the PSA, but is useful for the
VMC science team. It uses the following format:
YYNNNN
Where:
* YY indicates the year
* NNNN indicates the observation number within that year.
OBSERVATION NAME
This identifier contains the year, month, day, start time and end time
of the observation, and also corresponds to the observations as they
are uploaded to the Flickr page. It uses the following format:
YYYY-MM-DD_HH:MM-hh:mm
Where:
* YYYY - year
* MM - month
* DD - day
* HH - hour of START time of the observation
* MM - minute for the START time of the observation
* hh - hour for the STOP time of the observation
* mm - minute for the STOP time of the observation
PRODUCT NAME
This identifier contains the year, month, day, start time and end time
of each image, and also corresponds to the individual images as they
are uploaded to the Flickr page. It uses the following format:
YY-DOY_hh_mm_ss_Img_No_S
Where:
* YY - year
* DOY - day of the year
* hh - hour for the start time of the observation
* mm - minute for the start time of the observation
* ss - second for the start time of the observation
* S - number of the image within that observation
Data Object Definition
OBJECT = IMAGE
LINES = 480
LINE_SAMPLES = 640
BANDS = 3
BAND_SEQUENCE = "(RED,GREEN,BLUE)"
BAND_STORAGE_TYPE = BAND_SEQUENTIAL
SAMPLE_TYPE = UNSIGNED_INTEGER
SAMPLE_BITS = 8
END_OBJECT = IMAGE
OBJECT and END_OBJECT
Mark the start and end of the IMAGE Object.
LINES
Number of instances along the vertical axis of an image. It will
always be 480.
LINE_SAMPLES
Number of instances along the horizontal axis of an image. It will
always be 640.
BANDS
Number of bands in a single image. This is 3 for the PNG images and
the calibrated data layer of the FITS products, and 1 for the RAW data
and raw data layer of the FITS.
BAND_SEQUENCE
Identification of the different bands. Where this keyword appears, it
will always be "(RED,GREEN,BLUE)".
BAND_STORAGE_TYPE
It will always be BAND_SEQUENTIAL.
SAMPLE_TYPE
Data Storage representation of sample value. It will always be
"UNSIGNED_INTEGER"
SAMPLE_BITS
Sample value number of bits for each band. For the RAW and PNG files
this is 8, for the FITS calibrated layer this is 32.
Appendix A: Complete Data Label
PDS_VERSION_ID = PDS3
FILE_NAME = "VMC_SR_170102_083802_001.FIT"
RECORD_TYPE = FIXED_LENGTH
RECORD_BYTES = 6240
FILE_RECORDS = 480
^IMAGE = "VMC_SR_170102_083802_001.FIT"
RELEASE_ID = 0001
REVISION_ID = 0000
DATA_SET_ID = "MEX-M-VMC-3-RDR-EXT6-V1.0"
DATA_SET_NAME = "MEX MARS VMC CALIBRATED DATA EXT6 V1.0"
PROCESSING_LEVEL_ID = "3"
PRODUCT_ID = "MEXVMC_1700010001"
PRODUCT_CREATION_TIME = 2020-09-11T20:24:10
INSTRUMENT_HOST_ID = "MEX"
INSTRUMENT_HOST_NAME = "MARS EXPRESS"
TARGET_NAME = "MARS"
IMAGE_TIME = 2017-01-02T08:38:02.000
START_TIME = 2017-01-02T08:38:02.000
STOP_TIME = 2017-01-02T08:38:02.000
PRODUCER_ID = "ESA_UPV-EHU_DADPS"
PRODUCER_FULL_NAME = "ELENI RAVANIS AND
JORGE HERNANDEZ-BERNAL"
INSTRUMENT_ID = "VMC"
INSTRUMENT_NAME = "VISUAL MONITORING CAMERA"
EXPOSURE_DURATION = 14.00
INSTRUMENT_TEMPERATURE = -13.0
INSTRUMENT_TYPE = "IMAGING CAMERA"
DARK_CURRENT_CORRECTION_FLAG = "TRUE"
DARK_CURRENT_FILE_NAME = "DARK_2020.FIT"
FLAT_FIELD_CORRECTION_FLAG = "TRUE"
FLAT_FIELD_FILE_NAME = "FLAT_2020.FIT"
SOLAR_LONGITUDE = 291.7
/*MARTIAN_YEAR = 33 */
/*NADIR_RESOLUTION = 11.3
LIMB_RESOLUTION = 14.7
SEE VMC EAICD FOR DETAILS*/
COORDINATE_SYSTEM_TYPE = "BODY-FIXED ROTATING"
SUB_SPACECRAFT_LONGITUDE= 8.711
SUB_SPACECRAFT_LATITUDE= -32.722
CENTRAL_BODY_DISTANCE= 13434.808
ORBIT_NUMBER = 16474
/*OBSERVATION_ID = "170001"*/
OBSERVATION_NAME = "2017-01-02_08.35-08.47"
PRODUCT_NAME = "17-002_08.38.02_VMC_Img_No_1"
OBJECT = IMAGE
LINES = 480
LINE_SAMPLES = 640
BANDS = 3
BAND_SEQUENCE = "(RED, GREEN, BLUE)"
BAND_STORAGE_TYPE = SAMPLE_INTERLEAVED
SAMPLE_TYPE = IEEE_REAL
SAMPLE_BITS = 32
END_OBJECT = IMAGE
OBJECT = IMAGE
LINES = 480
LINE_SAMPLES = 640
BANDS = 1
BAND_STORAGE_TYPE = BAND_SEQUENTIAL
SAMPLE_TYPE = UNSIGNED_INTEGER
SAMPLE_BITS = 8
END_OBJECT = IMAGE
ESA/UPV-EHU/DADPS00