Data Set Overview: MARSIS Level 1b data products consist of the data producedby the instrument reconstructed from the scientific telemetry,sorted by instrument state and data type, and providedwith spacecraft position, velocity and attitude information.Any other spacecraft telemetry relevant for calibration andprocessing (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-boardprocessing. Each echo, depending on the kind of processingit underwent, is recorded either as a time series of signal samples,or as the complex spectrum of the signal itself producedby means of a FFT. Scientific data in a frame are complementedby a set of ancillary data, produced by the instrument andrecording parameter values used in pulse transmission,echo reception and on-board processing.  Processing: Level 1b processing starts from the telemetry data, as producedby the C&DH system on the spacecraft and passed to the telemetrysubsystem:data are still in the form of transfer frame packets organisedby contacts or ground tests data.Processing starts by cleaning, merging and time-ordering the packets.This means that duplicate data have been deleted, missingpackets are padded out, and the data are organisedby days (or orbits). Data then need to be sorted by instrument data types and instrumentmodes. MARSIS Level 1b processing orders data in a useful way for theintended users (i.e. radar scientists) and applications(i.e. quick look to monitor hardware performance and higher-levelprocessing), altering and manipulating them as little as possibleto 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 producedby the instrument reconstructed from the scientific telemetry,sorted by instrument state and data type, and providedwith spacecraft position, velocity and attitude information.Any other spacecraft telemetry relevant for calibration andProcessing (e.g. temperature of the receiver) is also be included. Level 1b processing requires the acquisition of MARSIS scientifictelemetry and any relevant spacecraft auxiliary data from the MarsExpress Data Disposition System (DDS) in ESOC, and of SPICE kernelsdescribing the spacecraft state and attitude from the Auxiliary DataConversion System (ADCS) in ESTEC. Both instrument telemetry and ancillary data are stored at the PIprocessing facility as they accumulate over the course of the mission,to provide the capability to reprocess data in case of errors or toaccommodate new information referring to existing data sets. Level 1b data distribution to the Co-Is and to the Mars Expressmission archive is performed by ASDC. It is required by ESA that dataproducts are delivered in batches of six-months worthof data within six months from the last data take(i.e. one year after the beginning of that particular data collectionperiod), but it is necessary that level 1b processing be completedin a much shorter period, to allow enough time for level 2 dataprocessing and data analysis within the MARSIS team beforethe expiration of the data proprietary period (which is the samesix-month time span).  Data: The MARS EXPRESS MARS MARSIS EXPERIMENT DATA RECORD V1.0 Data Setcontains scientific telemetry generated by the instrument,edited to remove duplications, zero-padded for missingpackets, and correlated with geometric information needed to locateobservations in space and time. No other kind of processing isapplied 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 informationSSx_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 standseither for ACQ or TRK. AIS_EDR, CAL_EDR, RXO_EDR and SSx_yyy_CMP_EDR Data Productsis made by two files, each of which contains a PDS binary TABLEobject preceded by a PDS attached label describing its structure.The first file, called Frame file (FRM) contains the instrumentdata proper, exactly in the same format (bit by bit) as they wereproduced by the instrument.Each frame corresponds to a record in the file,which is also a row in the PDS binary TABLE object into whichframes are organised.A Data Product contains all frames acquired using the sameinstrument mode, in the same instrument state and afterthe 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 binaryTABLE object into which data are organised, for every framein the corresponding FRM file. Subsurface data from Individual Echoes are the unprocessed versionof data that are also down-linked in processed form.A frame of Individual Echoes consists of a variable numberof raw echoes, because, to produce a constant along-track groundresolution, synthetic aperture (Doppler) processing performedon board requires a number of echoes that increases with altitudeof the spacecraft.The Data Product consists in just one file containing a PDS headerand the data themselves, because any additional geometric informationwould just duplicate similar information already provided inSSx_yyy_CMP_EDR GEO data files.File names contain the first ten digits of the spacecraft clockcount 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 andincreasing by one at each new echo. Echoes are ordered accordingto the time at which they were collected. Ancillary information isproduced once per frame, and is thus the same for allechoes in a file: this duplication has been deemed necessaryto simplify the data structure as much as possible. The number of echoes required in Doppler processing is a functionof frequency, as well as of spacecraft altitude.In a dual-frequency mode, the exact number of echoes collectedat each frequency is contained in the Ancillary data and echoeswithin a frame are ordered by frequency before being ordered in time. Subsurface UNC data are the uncompressed version of data that arealso down-linked in fully processed form. Because they are structuredexactly as CMP data, the only difference being the compression ofindividual echo samples from 4-byte IEEE real numbers to 1-byteintegers, 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 headerand the data themselves, because any additional geometric informationwould just duplicate similar information already provided inSSx_yyy_CMP_EDR GEO data files.File names contains the four-digit number of the orbit at whichdata were acquired.The structure of UNC Data Products is identical to the one usedin CMP FRM files. Because UNC data are down-linked through a dumpof the flash memory, rather than through the scientific telemetryof the instrument, they do not come with a full set of ancillary data Subsurface Raw Data are the unprocessed version of data that are alsodown-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 requiresa number of echoes that increases with altitude of the spacecraft. Because of this, it has been chosen to produce one Data Productper each frame of Raw Data, rather than one per orbit, similarly toIndividual Echoes. The Data Product consists in just one filecontaining a PDS header and the data themselves, because anyadditional geometric information would just duplicate similarinformation already provided in SSx_yyy_CMP_EDR GEO data files.File names contain the first ten digits of the spacecraft clockcount corresponding to the time at which data were acquired. The structure of RAW Data Products is identical to the one used inIND files. Because RAW data are down-linked through a dumpof the flash memory, rather than through the scientific telemetryof the instrument, they do not come with a full set of ancillary data.  Ancillary Data: Each frame of MARSIS data (with the exception of framesstored in flash memory) carries a 228 byte header of ancillary data,containing necessary information for subsequent analysisof 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 planetocentriccoordinates. Longitude is comprised in the range 0 - 360 degrees.  Software: Marsis data products can be read by the PDS software NASAView, whichreads 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 throughInternet from the Planetary Science Archive of ESA, which can beaccessed at the following URL: http://www.rssd.esa.int/psa

Review: These data have been reviewed by the instrument team and are of thehighest quality that can be generated at this time. Science resultsbased on these data have been published in journals. The dataset iscurrently 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 ofthe nominal mission, because of the delay in the deployment of theMARSIS antenna. Because of this, coverage is limited mainly tosouthern latitudes. Data quality in a data product label is indicated through theDATA_QUALITY_ID element, and measures the integrity of the telemetrystream from the instrument. The permitted values of DATA_QUALITY_IDare 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 otherrelevant aspectsof the data set: Data Compression, Time-Tagging, etc.