Data Set Overview
=================
 
MARSIS Level 1b data products consist of the data produced
by the  instrument reconstructed from the scientific telemetry,
sorted by instrument state and data type, and provided
with spacecraft position, velocity and attitude information.
Any other spacecraft telemetry relevant for calibration and
processing (e.g. temperature of the receiver) is also be included.
 
 
Parameters
==========
 
MARSIS data are organized into groups of echoes called frames.
A frame contains one or more echoes, with or without on-board
processing. Each echo, depending on the kind of processing
it underwent, is recorded either as a time series of signal samples,
or as the complex spectrum of the signal itself produced
by means of a FFT. Scientific data in a frame are complemented
by a set of ancillary data, produced by the instrument and
recording parameter values used in pulse transmission,
echo reception and on-board processing.
 
 
Processing
==========
 
Level 1b processing starts from the telemetry data, as produced
by the C&DH system on the spacecraft and passed to the telemetry
subsystem:
data are still in the form of transfer frame packets organised
by contacts or ground tests data.
Processing starts by cleaning, merging and time-ordering the packets.
This means that duplicate data have been deleted, missing
packets are padded out, and the data are organised
by days (or orbits).
 Data then need to be sorted by instrument data types and instrument
modes.
 
MARSIS Level 1b processing orders data in a useful way for the
intended users (i.e. radar scientists) and applications
(i.e. quick look to monitor hardware performance and higher-level
processing), altering and manipulating them as little as possible
to avoid the risk of introducing errors and, at the same time,
including all necessary information from all relevant sources.
Level 1b data are in scientifically useful form,
i.e. individual spectra. These data are still uncalibrated.
 
MARSIS Level 1b data products consist of the data produced
by the instrument reconstructed from the scientific telemetry,
sorted by instrument state and data type, and provided
with spacecraft position, velocity and attitude information.
Any other spacecraft telemetry relevant for calibration and
Processing (e.g. temperature of the receiver) is also be included.
 
Level 1b processing requires the acquisition of MARSIS scientific
telemetry and any relevant spacecraft auxiliary data from the Mars
Express Data Disposition System (DDS) in ESOC, and of SPICE kernels
describing the spacecraft state and attitude from the Auxiliary Data
Conversion System (ADCS) in ESTEC.
 
Both instrument telemetry and ancillary data are stored at the PI
processing facility as they accumulate over the course of the mission,
to provide the capability to reprocess data in case of errors or to
accommodate new information referring to existing data sets.
 
Level 1b data distribution to the Co-Is and to the Mars Express
mission archive is performed by ASDC. It is required by ESA that data
products are delivered in batches of six-months worth
of data within six months from the last data take
(i.e. one year after the beginning of that particular data collection
period), but it is necessary that level 1b processing be completed
in a much shorter period, to allow enough time for level 2 data
processing and data analysis within the MARSIS team before
the expiration of the data proprietary period (which is the same
six-month time span).
 
 
Data
====
 
The MARS EXPRESS MARS MARSIS EXPERIMENT DATA RECORD V1.0 Data Set
contains scientific telemetry generated by the instrument,
edited to remove duplications, zero-padded for missing
packets, and correlated with geometric information needed to locate
observations in space and time. No other kind of processing is
applied to the data.
 
The list of EDR data Products is :
 
AIS_EDR : Active Ionosphere Sounding data frames with geometry
          information.
CAL_EDR : Data frames acquired in Calibration mode with geometry
          information.
RXO_EDR : Data frames acquired in Receive Only mode with geometry
          Information.
SSx_yyy_CMP_EDR : On-board processed Subsurface Sounding data
                 (either in Acquisition or Tracking state) with
                 geometry information
SSx_yyy_IND_EDR : Individual Echoes from Subsurface Sounding data
                 (either in Acquisition or Tracking state).
SSx_yyy_UNC_EDR : Uncompressed Subsurface Sounding data
                 (either in Acquisition or Tracking state).
SSx_yyy_RAW_EDR : Raw Subsurface Sounding data
                  (either in Acquisition or Tracking state).
Where   x   stands for a number between 1 and 5, while  yyy  stands
either for ACQ or TRK.
 
AIS_EDR, CAL_EDR, RXO_EDR and SSx_yyy_CMP_EDR Data Products
is made by two files, each of which contains a PDS binary TABLE
object preceded by a PDS attached label describing its structure.
The first file, called Frame file (FRM) contains the instrument
data proper, exactly in the same format (bit by bit) as they were
produced by the instrument.
Each frame corresponds to a record in the file,
which is also a row in the PDS binary TABLE object into which
frames are organised.
A Data Product contains all frames acquired using the same
instrument mode, in the same instrument state and after
the same type of on-board processing during a single orbit.
The second file constituting an EDR is called a Geometry file (GEO),
 and contains one record, corresponding to one line of the PDS binary
TABLE object into which data are organised, for every frame
in the corresponding FRM file.
 
Subsurface data from Individual Echoes are the unprocessed version
of data that are also down-linked in processed form.
A frame of Individual Echoes consists of a variable number
of raw echoes, because, to produce a constant along-track ground
resolution, synthetic aperture (Doppler) processing performed
on board requires a number of echoes that increases with altitude
of the spacecraft.
The Data Product consists in just one file containing a PDS header
and the data themselves, because any additional geometric information
would just duplicate similar information already provided in
SSx_yyy_CMP_EDR GEO data files.
File names contain the first ten digits of the spacecraft clock
count corresponding to the time at which data were acquired.
 
Each record in a file contains a single unprocessed echo,
preceded by auxiliary data and by a counter starting from 0 and
increasing by one at each new echo. Echoes are ordered according
to the time at which they were collected. Ancillary information is
produced once per frame, and is thus the same for all
echoes in a file: this duplication has been deemed necessary
to simplify the data structure as much as possible.
 
The number of echoes required in Doppler processing is a function
of frequency, as well as of spacecraft altitude.
In a dual-frequency mode, the exact number of echoes collected
at each frequency is contained in the Ancillary data and echoes
within a frame are ordered by frequency before being ordered in time.
 
Subsurface UNC data are the uncompressed version of data that are
also down-linked in fully processed form. Because they are structured
exactly as CMP data, the only difference being the compression of
individual echo samples from 4-byte IEEE real numbers to 1-byte
integers, it has been chosen to produce one Data Product per orbit,
just as for CMP data.
The Data Product consists in just one file containing a PDS header
and the data themselves, because any additional geometric information
would just duplicate similar information already provided in
SSx_yyy_CMP_EDR GEO data files.
File names contains  the four-digit number of the orbit at which
data were acquired.
The structure of UNC Data Products is identical to the one used
in CMP FRM files. Because UNC data are down-linked through a dump
of the flash memory, rather than through the scientific telemetry
of the instrument, they do not come with a full set of ancillary data
 
Subsurface Raw Data are the unprocessed version of data that are also
down-linked in processed form.
A frame of Raw Data consists of a variable number of raw echoes,
because, to produce a constant along-track ground resolution,
synthetic aperture (Doppler) processing performed on board requires
a number of echoes that increases with altitude of the spacecraft.
 
Because of this, it has been chosen to produce one Data Product
per each frame of Raw Data, rather than one per orbit, similarly to
Individual Echoes. The Data Product consists in just one file
containing a PDS header and the data themselves, because any
additional geometric information would just duplicate similar
information already provided in SSx_yyy_CMP_EDR GEO data files.
File names contain the first ten digits of the spacecraft clock
count corresponding to the time at which data were acquired.
 
The structure of RAW Data Products is identical to the one used in
IND files. Because RAW data are down-linked through a dump
of the flash memory, rather than through the scientific telemetry
of the instrument, they do not come with a full set of ancillary data.
 
 
Ancillary Data
==============
 
Each frame of MARSIS data (with the exception of frames
stored in flash memory) carries a 228 byte header of ancillary data,
containing necessary information for subsequent analysis
of the data and further processing.
The exact content of the ancillary data depends on instrument mode.
There are four major structure types of the ancillary data :
acquisition, tracking /
individual echoes for subsurface modes, calibration /
receive only and active ionosphere
 
 
Coordinate System
=================
 
Locations on the surface of Mars are expressed in planetocentric
coordinates. Longitude is comprised in the range 0 - 360 degrees.
 
 
Software
========
 
Marsis data products can be read by the PDS software NASAView, which
reads a PDS label and displays the associated image or table.
NASAView has been tested on both EDR and RDR data products.
 
 
Media/Format
============
 
The standard distribution format for the data is transfer through
Internet from the Planetary Science Archive of ESA, which can be
accessed at the following URL:
 
http://www.rssd.esa.int/psa

Review
======
 
These data have been reviewed by the instrument team and are of the
highest quality that can be generated at this time. Science results
based on these data have been published in journals. The dataset is
currently being reviewed by the Plannetary Science Archive of ESA.
 
 
Data Coverage and Quality
=========================
 
Data in this dataset have been acquired only in the last six months of
the nominal mission, because of the delay in the deployment of the
MARSIS antenna. Because of this, coverage is limited mainly to
southern latitudes.
 
Data quality in a data product label is indicated through the
DATA_QUALITY_ID element, and measures the integrity of the telemetry
stream from the instrument. The permitted values of DATA_QUALITY_ID
are the following:
 
-1: percentage of corrupted data not available
 0: no corrupted data
 1: less than 2% corrupted data
 2: less than 5% corrupted data
 3: less than 10% corrupted data
 4: more than 10% corrupted data
 
 
Limitations
===========
 
There are no known limitations at this time.
 
 
 
At this point you may add additional headings for other
relevant aspects
of the data set: Data Compression, Time-Tagging, etc.