| Description |
Data Set Overview ================= The Mars Express Mars Advanced Radar for Subsurface and Active Ionospheric Sounding (MARSIS) data set includes all spectral information calibrated in units of spectral density for the Active Ionospheric Sounder over the Mars Express mission. This data set includes calibrated values for each transmit event and the corresponding temporal data for each frequency channel. Parameters ========== This data set comprises the electric field spectral densities obtained via the electric dipole antenna sensor. Processing ========== Data in this data set were processed by the use of a number of software programs. These programs re-assembled and de-compressed the raw telemetry data. These raw values were then calibrated into physical units: power received by the electric antenna. The data products were calibrated using the best calibration tables and algorithms available at the time of data archiving. Should a significant improvement in calibration become available, an erratum will be noted in the erratum section. Later versions of the products may contain better calibrations. Data ==== The AIS calibrated full resolution data set includes several binary tables of wave spectra as a function of time from each of the various transmit events. Each table will contain fixedlength records including columns for time, transmit frequency, and spectral densities from the temporal measurements. The number of transmit frequencies is constant at 160 frequencies per frame and the number of samples per transmit frequency is constant at 80 per transmit pulse. Interpreting the provided intensities as remote emissions requires knowledge of the time delay between the emitted pulse and the measured electric spectral density. The time offsets from the onset of the transmit pulse until the measurement of each spectral density value may be found from the relation: delay time (microseconds) = 167.443 + 91.4286 * (item-1) where item is the ITEM number from the SPECTRAL density column of the AIS_TABLE data products. The first item value is 1, not 0. To make this more explicit these time values are pre-calculated in the table below. ITEM* Delay (microsec) ITEM* Delay (microsec) ---- ---------------- ---- ---------------1 167.44 41 3824.59 2 258.87 42 3916.02 3 350.30 43 4007.44 4 441.73 44 4098.87 5 533.16 45 4190.30 6 624.59 46 4281.73 7 716.01 47 4373.16 8 807.44 48 4464.59 9 898.87 49 4556.02 10 990.30 50 4647.44 11 1081.73 51 4738.87 12 1173.16 52 4830.30 13 1264.59 53 4921.73 14 1356.01 54 5013.16 15 1447.44 55 5104.59 16 1538.87 56 5196.02 17 1630.30 57 5287.44 18 1721.73 58 5378.87 19 1813.16 59 5470.30 20 1904.59 60 5561.73 21 1996.02 61 5653.16 22 2087.44 62 5744.59 23 2178.87 63 5836.02 24 2270.30 64 5927.44 25 2361.73 65 6018.87 26 2453.16 66 6110.30 27 2544.59 67 6201.73 28 2636.02 68 6293.16 29 2727.44 69 6384.59 30 2818.87 70 6476.02 31 2910.30 71 6567.45 32 3001.73 72 6658.87 33 3093.16 73 6750.30 34 3184.59 74 6841.73 35 3276.02 75 6933.16 36 3367.44 76 7024.59 37 3458.87 77 7116.02 38 3550.30 78 7207.45 39 3641.73 79 7298.87 40 3733.16 80 7390.30 ----------------------- -----------------------* Here ITEM refers to the ITEM number of the column named SPECTRAL_DENSITY in the AIS_TABLE of the data products on this volume. A basic method for determining the range at which an emission was generated is to multiply the delays above with 1/2 the speed of light in a vacuum. apparent range (kilometers) = 0.1499 * (167.443 + 91.4286 * (item-1)) The assumption that the signal propagates at the speed of light in a vacuum does not hold when the pulse traverses regions where the local plasma frequency is near the pulse frequency. For more information on these effects and more see the file: AIS_SIGNAL_PROCESSING_REQ.PDF in the DOCUMENT directory of this volume. Ancillary Data ============== No Ancillary data are provided. Coordinate System ================= The data in this data set are measurements of wave electric fields measured by the MARSIS electric sensors. These fields are presented as detected by the sensors and are not rotated into any other coordinate system. If desired the SPICE kernels can be used with the SPICE toolkit to convert from the spacecraft frame to virtually any frame which may be of use in analyzing these data. However, for many purposes, the wave amplitudes are extremely useful and may be entirely adequate with no coordinate transformations at all. Software ======== Sample code is provided with these data which demonstrates how to read these files in order to build a set of time-ordered wave spectra. The sample code and algorithms are found in the SOFTWARE directory. Confidence Level Overview ========================= This data set contains all active ionospheric calibrated data for the Mars Express MARSIS for the interval described above. Every effort has been made to ensure that all data returned to Iowa from the spacecraft is included and that the calibration is accurate. Review ====== The MARSIS active ionospheric sounder data will be reviewed internally by the Mars Express MARSIS team prior to release to the PDS. The data set will also be peer reviewed by the PDS. Data Coverage and Quality ========================= All data in the stated interval are included to the best of our knowledge and attempts to determine completeness. In general, the instrument was operated only briefly during early cruise phase for the purpose of Antenna deployment and periodic instrument health. During this time, flight restrictions precluded any transmit events and hence no science data. Beginning in June of 2005 commissioning of the instrument commenced more-or-less continuously for about a month. During this period instrument gain settings and transmit frequencies were optimized for maximum signal-to-noise ratios as well as avoidance of interference generated by the spacecraft and by other instruments. Limitations =========== One measurement quality issue deals with the data compression algorithm used by the MARSIS onboard processor, which generates values of zero when the measured AIS values should be small but non-zero. |
| 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-RP5500). 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. |
