| Description |
Data Set Overview ================= MARSIS Level 2 data products consist of Level 1b data that have been uncompressed, corrected for Automated Gain Control, aligned to a reference altitude and, except for data acquired using the SS2 mode, range-processed after correcting for the distortion of the transmitted signal caused by the ionosphere. Echoes collected in the acquisition (ACQ) phase, having a much smaller bandwidth, do not have a vertical resolution sufficient for scientific analysis, and thus are not used in generating Reduced Data Records. Geometric information needed to locate observations in space and time is also provided in the Data Set. Parameters ========== MARSIS data are the result of the processing of groups of echoes called frames. A frame is produced by the coherent summation of many tens of echoes. Each frame is recorded as a time series of complex signal samples. Scientific data in a frame are complemented by a set of engineering data, produced by the instrument and recording parameter values used in pulse transmission, echo reception and on-board processing, and by geometric information needed to locate observations in space and time. Processing ========== Level 2 processing of subsurface sounding data consists of several steps, needed to convert the instrument telemetry into a collection of radar echoes that can be used for geological analysis and interpretation of the Martian subsurface. These are: Data de-compression: 8-bit spectrum samples are converted back to 4-byte real numbers. AGC compensation: the gain scaling factor, applied during Automated Gain Compensation, is applied to the data. Receiving time compensation: echoes are shifted in time to refer them to a common altitude above the Martian ellipsoid. Range compression: the received signal is convolved with the transmitted signal to increase range resolution and signal-to-noise ratio. Ionosphere distortion correction: an algorithm to correct ionosphere dispersion of the signal, called contrast method, is applied to the data. Depending on the instrument mode, some of the above steps may not apply (for example, range processing is performed on board in mode SS2). The final result is a file containing all complex echoes collected by MARSIS in the course of a single orbit. Data ==== Data Products need to accommodate the different data structures produced by different subsurface sounding modes of the instrument. There is a single type of Data Product specialized into five different subtypes, one for each subsurface sounding mode: R_SSx Subsurface Sounding data that have been uncompressed, calibrated and range-processed, together with geometry information Where x stands for a number between 1 and 5. SSx_RDR Data Products consist of two files, one of which contains a PDS binary TABLE object while the other is a PDS label describing its structure. The first file contains the instrument data proper, organised into frames. 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 tracking (TRK) state during a single orbit. Ancillary Data ============== No Ancillary data are provided. Coordinate System ================= Locations on the surface of Mars are expressed in planetocentric coordinates. Longitude increases to the East and 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. 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.cosmos.esa.int/web/psa/psa-introduction Confidence Level Overview ========================= This data set contains all data for the Mars Express MARSIS for the interval described above. Every effort has been made to ensure that all data returned by the spacecraft is included and that processing is accurate. Review ====== The MARSIS EDR data have been reviewed internally by the Mars Express MARSIS team prior to release to the PDS. The data set has been also peer reviewed by the PSA. 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 median of the total echo power across the orbit. The permitted values of DATA_QUALITY_ID are the following: 0: data quality unknown 1: median data quality index in the bottom 25% of computed values 2: median data quality index in the bottom 50% of computed values 3: median data quality index in the top 50% of computed values 4: median data quality index in the top 25% of computed values For instrument mode transmitting at two different frequencies, DATA_QUALITY_ID reports a value for every frequency. Limitations =========== There are no known limitations at this time. |
| Mission Description |
Mission Overview ================ Mars Express was the first flexible mission of the revised long-term ESA Science Programme Horizons 2000 and was launched to the planet Mars from Baikonur (Kazakhstan) on June 2nd 2003. A Soyuz-Fregat launcher injected the Mars Express total mass of about 1200 kg into Mars transfer orbit. Details about the mission launch sequence and profile can be obtained from the Mission Plan (MEX-MMT-RP-0221) and from the Consolidated Report on Mission Analysis (CREMA)(MEX-ESC-RP- 5500). The mission consisted of (i) a 3-axis stabilized orbiter with a fixed high-gain antenna and body-mounted instruments, and (ii) a lander named BEAGLE-2, and was dedicated to the orbital and in-situ study of the interior, subsurface, surface and atmosphere of the planet. After ejection of a small lander on 18 December 2003 and Mars orbit insertion (MOI) on 25 December 2003, the orbiter experiments began the acquisition of scientific data from Mars and its environment in a polar elliptical orbit. The nominal mission lifetime for the orbiter was 687 days following Mars orbit insertion, starting after a 5 months cruise. The nominal science phase was extended (tbc) for another Martian year in order to complement earlier observations and allow data relay communications for various potential Mars landers up to 2008, provided that the spacecraft resources permit it. The Mars Express spacecraft represented the core of the mission, being scientifically justified on its own by investigations such as high- resolution imaging and mineralogical mapping of the surface, radar sounding of the subsurface structure down to the permafrost, precise determination of the atmospheric circulation and composition, and study of the interaction of the atmosphere with the interplanetary medium. The broad scientific objectives of the orbiter payload are briefly listed thereafter and are given more extensively in the experiment publications contained in ESAs Special Publication Series. See NEUKUM&JAUMANN2004, BIBRINGETAL2004, PICARDIETAL2004, FORMISANOETAL2004, BERTAUXETAL2004, PAETZOLDETAL2004 and PULLANETAL2004. The Mars Express lander Beagle-2 was ejected towards the Mars surface on 19 December 2003, six days before the orbiters capture manoeuvre. The probe mass was limited to about 70 kg by the mission constraints, which led to a landed mass of 32 kg. The complete experimental package was weighed in approximately at 9kg. The landers highly integrated scientific payload was supposed to focus on finding whether there is convincing evidence for past life on Mars or assessing if the conditions were ever suitable. Following safe landing on Mars, this lander mission would have conducted dedicated studies of the geology, mineralogy, geochemistry, meteorology and exobiology of the immediate landing site located in Isidis Planitia (90.74?E, 11.6?N), as well as studies of the chemistry of the Martian atmosphere. Surface operations were planned to last about 180 sols or Martian days ( about 6 months on Earth), see SIMSETAL1999. As no communication could be established to the BEAGLE-2 lander, it was considered lost in February 2004 after an extensive search. A nominal launch of Mars Express allowed the modify the orbit to a G3-ubeq100 orbit. The G3-ubeq100 orbit is an elliptical orbit, starting with the sub-spacecraft point at pericentre at the equator and a sun ^ation of 60 degrees. At the beginning of the mission, the pericentre moves southward with a shift of 0.54 degree per day. At the same time the pericentre steps towards the terminator which will be reached after about 4 months, giving the optical instruments optimal observing conditions during this initial period. Throughout this initial phase lasting until mid- May 2004, the downlink rate will decrease from 114 kbit/s to 38 kbit/s. After an orbit change manoeuvre on 06 May 2004 the pericentre latitude motion is increased to guarantee a 50/50 balance between dayside and nightside operations. With this manoeuvre, the apocentre altitude is lowered from 14887 km to 13448 km, the orbital period lowered from ~7.6 hours to 6.645 hours, and the pericentre latitude drift slightly increased to 0.64 degree per day. After 150 days, at the beginning of June 2004, the South pole region was reached with the pericentre already behind the terminator. Following, the pericentre moves northward with the Sun ^ation increasing. Thus, the optical instruments covered the Northern Mars hemisphere under good illumination conditions from mid-September 2004 to March 2005. During the next mission phase, lasting until July 2005, the pericentre was again in the dark. It covered the North polar region and moves southward. Finally, throughout the last 4 months of the nominal mission, the pericentre was back to daylight and moves from the equator to the South pole, and the downlink rate reached its highest rate of 228 kbit/s. The osculating orbit elements for the eq100 orbit are listed below: Epoch 2004:1:13 - 15:56:0.096 Pericentre (rel. sphere of 3397.2 km) 279.29 km Apocentre (rel. sphere) 11634.48 km Semimajor axis 9354.09 km Eccentricity 0.60696 Inclination 86.583 Right ascension of ascending node 228.774 Argument of pericentre 357.981 True anomaly -0.001 Mission Phases ============== The mission phases are defined as: (i) Pre-launch, Launch and Early Operations activities, including (1) science observation planning; (2) payload assembly, integration and testing; (3) payload data processing software design, development and testing; (4) payload calibration; (5) data archive definition and planning; (6) launch campaign. (ii) Near-Earth verification (EV) phase, including (1) commissioning of the orbiter spacecraft; (2) verification of the payload status; (3) early commissioning of payload. (iii) Interplanetary cruise (IC) phase (1) payload checkouts (2) trajectory corrections (iv) Mars arrival and orbit insertion (MOI) (1) Mars arrival preparation; (2) lander ejection; (3) orbit insertion; (4) operational orbit reached and declared; (5) no payload activities. (v) Mars commissioning phase (1) final instrument commissioning, (2) first science results, (3) change of orbital plane. (vi) Routine phase; Opportunities for dawn/dusk observations, mostly spectroscopy and photometry. This phase continued into a low data rate phase (night time; favorable for radar and spectrometers). Then daylight time, and went into a higher data rate period (medium illumination, zenith, then decreasing illumination conditions). Observational conditions were most favorable for the optical imaging instruments at the end of the routine phase, when both data downlink rate and Sun ^ation are high. (vii) MARSIS Deployment The dates of the MARSIS antenna deployment is not known as of writing this catalogue file. (viii) Extended operations phase A mission extension will be proposed in early 2005 to the Science Programme Committee (SPC). (ix) Post-mission phase (final data archival). Science Subphases ================= For the purpose of structuring further the payload operations planning, the mission phases are further divided into science subphases. The science subphases are defined according to operational restrictions, the main operational restrictions being the downlink rate and the Sun ^ation. The Mars Commissioning Phase and the Mars Routine Phase are therefore divided into a number of science subphases using various combinations of Sun ^ations and available downlink bit rates. The discrete downlink rates available throughout the nominal mission are: - 28 kbits/seconds - 38 kbits/seconds - 45 kbits/seconds - 57 kbits/seconds - 76 kbits/seconds - 91 kbits/seconds - 114 kbits/seconds - 152 kbits/seconds - 182 kbits/seconds - 228 kbits/seconds The adopted Sun ^ation coding convention is as follows: - HSE for High Sun Elevation (> 60 degrees) - MSE for Medium Sun Elevation (between 20 and 60 degrees) - LSE for Low Sun Elevation (between -15 and 20 degrees) - NSE for Negative Sun Elevation (< -15 degrees) The science subphase naming convention is as follows: - Science Phase - Sun Elevation Code - Downlink Rate - Science Subphase Repetition Number The following tables gives the available Science Subphases: NAME START END ORBITS BIT SUN RATE ELE ---------------------------------------------------------- MC Phase 0 2003-12-30 - 2004-01-13 1 - 16 MC Phase 1 2004-01-13 - 2004-01-28 17 - 58 114 59 MC Phase 2 2004-01-28 - 2004-02-12 59 - 105 91 69 MC Phase 3 2004-02-12 - 2004-03-15 106 - 208 76 71 MC Phase 4 2004-03-15 - 2004-04-06 209 - 278 57 51 MC Phase 5 2004-04-06 - 2004-04-20 279 - 320 45 33 MC Phase 6 2004-04-20 - 2004-06-04 321 - 475 38 22 MR Phase 1 2004-06-05 - 2004-08-16 476 - 733 28 -13 MR Phase 2 2004-08-16 - 2004-10-16 734 - 951 28 -26 MR Phase 3 2004-10-16 - 2005-01-07 952 - 1250 28 16 MR Phase 4 2004-01-08 - 2005-03-05 1251 - 1454 45 63 MR Phase 5 2004-03-05 - 2005-03-24 1455 - 1522 76 16 MR Phase 6 2004-03-25 - 2005-07-15 1523 - 1915 91 0 The data rate is given in kbit per seconds and represents the minimal data rate during the subphase. The sun ^ation is given in degrees and represents the rate at the beginning of the subphase. Detailed information on the science subphases can be found in MEX-EST-PL-13128. |
