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 fixed- length 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) : 162.5 + 91.4286 * item 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) ---- ---------------- ---- ---------------- 1 253.93 41 3911.07 2 345.36 42 4002.50 3 436.79 43 4093.93 4 528.21 44 4185.36 5 619.64 45 4276.79 6 711.07 46 4368.21 7 802.50 47 4459.64 8 893.93 48 4551.07 9 985.36 49 4642.50 10 1076.79 50 4733.93 11 1168.21 51 4825.36 12 1259.64 52 4916.79 13 1351.07 53 5008.21 14 1442.50 54 5099.64 15 1533.93 55 5191.07 16 1625.36 56 5282.50 17 1716.79 57 5373.93 18 1808.21 58 5465.36 19 1899.64 59 5556.79 20 1991.07 60 5648.21 21 2082.50 61 5739.64 22 2173.93 62 5831.07 23 2265.36 63 5922.50 24 2356.79 64 6013.93 25 2448.21 65 6105.36 26 2539.64 66 6196.79 27 2631.07 67 6288.21 28 2722.50 68 6379.64 29 2813.93 69 6471.07 30 2905.36 70 6562.50 31 2996.79 71 6653.93 32 3088.21 72 6745.36 33 3179.64 73 6836.79 34 3271.07 74 6928.21 35 3362.50 75 7019.64 36 3453.93 76 7111.07 37 3545.36 77 7202.50 38 3636.79 78 7293.93 39 3728.21 79 7385.36 40 3819.64 80 7476.79 ----------------------- ------------------------ * 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 * (162.5 + 91.4286 * item) 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.

Corrupted data have been flagged in data files where they occurred. The label file for each data product contains an entry to flag this condition.