Data files and electromagnetic simulation software used in the paper "Radar evidence of subglacial liquid water on Mars" By Orosei et al. (2018)

This archive contains radargrams, geometric information and visualizations of MARSIS radar observations over the area centered at 193°E, 81°S within Planum Australe, Mars, together with scripts and results of electromagnetic propagation simulations used to interpret the data. This archive contains everything needed to reproduce the results presented in the paper "Radar evidence of subglacial liquid water on Mars" by Orosei et al. (2018). The software made available in this archive consists of scripts written in the Matlab© computing language, and is provided "as is" without warranty of any kind, either express or implied. Queries on the content of the archive can be sent to Roberto Orosei (roberto.orosei@inaf.it).

Three types of MARSIS data files are contained in this archive:

* orbit_XXXXX_frequency_Y_MHz_radargram.csv, where XXXXX is the orbit number, and Y the frequency at which the radar was operating, in MHz. The file contains an ASCII table of real numbers separated by commas. The table has as many columns as the number of radar echoes acquired during the orbit (usually 3200), and 980 lines, one for each echo sample. Values are samples of the uncalibrated echo voltage, without phase information (i.e. positive real numbers instead of complex echo samples). Echo samples are acquired every 0.3571 microseconds (2.8 MHz sampling rate). The first sample of an echo is located at a round-trip time corresponding to an altitude of 25 km above the Martian IAU ellipsoid.

* orbit_XXXXX_frequency_Y_MHz_geometry.csv, where XXXXX is the orbit number, and Y the frequency at which the radar was operating, in MHz. The file contains an ASCII table of real numbers separated by commas. The table has as many rows as the number of radar echoes acquired during the orbit (usually 3200), and contains the following auxiliary parameters:

 - EPHEMERIS TIME - Number of seconds elapsed since Jan 1, 2000, 12:00 UTC corresponding to the time at which data collection for the current echo started.

 - MARS SOLAR LONGITUDE - Angle between the Mars-Sun line at the time corresponding to EPHEMERIS TIME and the Mars-Sun line at the vernal equinox, in degrees.

 - MARS SUN DISTANCE - Distance from the centre of Mars to centre of the Sun at the time corresponding to EPHEMERIS TIME, in Km.

 - SPACECRAFT ALTITUDE - Distance from the Mars Express spacecraft to the reference surface of the target body measured normal to the surface at the time corresponding to EPHEMERIS TIME, expressed in Km.

 - SUB-SPACECRAFT LONGITUDE - East longitude of the point on the target body that lies closest to the Mars Express spacecraft at the time corresponding to EPHEMERIS TIME, expressed in degrees and in the [ 0 -360 ] range.

 - SUB-SPACECRAFT LATITUDE - Planetocentric latitude of the point on the target body that lies directly beneath the Mars Express spacecraft at the time corresponding to EPHEMERIS TIME, expressed in degrees.

 - RADIAL VELOCITY - Radial component of the Mars Express spacecraft velocity vector in the reference frame of the target body at the time corresponding to EPHEMERIS TIME, expressed in Km/s.

 - TANGENTIAL VELOCITY - Tangential component of the Mars Express spacecraft velocity vector in the reference frame of the target body at the time corresponding to EPHEMERIS TIME, expressed in Km/s.

 - LOCAL TRUE SOLAR TIME - Angle between the extension of the vector from the Sun to Mars and the projection on Mars' ecliptic plane of a vector from the center of the target body and the point on the target body surface that lies directly beneath the Mars Express spacecraft at the time corresponding to EPHEMERIS TIME, expressed on a 24-hour clock with decimal fractions of the hour.

* orbit_XXXXX_frequency_Y_MHz.png, where XXXXX is the orbit number, and Y the frequency at which the radar was operating, in MHz. The file is a visualization of the corresponding radargram, of the spacecraft ground track during the observation, and of surface and subsurface echo power.

Electromagnetic propagation model and results consist of several files:

* model_Pss_over_Ps_ratio.m is a script written in the Matlab© computing language. It simulates the propagation of a MARSIS radar pulse through a model stratigraphy representing the Martian South Polar Layered Deposits (SPLD). The simulation is based on the solution of Maxwell's equations for a plane parallel stratigraphy, and it is thus one-dimensional. The SPLD are represented as an uniform layer of ice mixed with dust.

* figure_S5.m is a script written in the Matlab© computing language. It simulates the propagation of a MARSIS radar pulse through a model stratigraphy representing the Martian South Polar Layered Deposits (SPLD). The simulation is based on the solution of Maxwell's equations for a plane parallel stratigraphy, and it is thus one-dimensional. The SPLD are represented as an uniform layer of ice mixed with dust, either overlaid by or overlaying a layer of pure CO2 ice of variable thickness.

* fftvars.m is a function written in the Matlab© computing language and used by both "model_Pss_over_Ps_ratio.m" and "figure_S5.m". It computes vectors containing the correct time and frequency values for FFT computations.

* genrefl.m is a function written in the Matlab© computing language and used by both "model_Pss_over_Ps_ratio.m" and "figure_S5.m". It computes the frequency-dependent complex electromagnetic reflectivity of a plane parallel stratigraphy at normal incidence.

* GPR_1D_simulation.m is a function written in the Matlab© computing language and used by both "model_Pss_over_Ps_ratio.m" and "figure_S5.m". It simulates the radar echo produced by the propagation of a broadband signal in a plane parallel stratigraphy.

* matzler.m is a function written in the Matlab© computing language and used by both "model_Pss_over_Ps_ratio.m" and "figure_S5.m". It computes the relative dielectric permittivity of pure water ice (ice Ih) for any temperature and frequency according to formulas provided in Matzler (1998).

* maxgarmix.m is a function written in the Matlab© computing language and used by both "model_Pss_over_Ps_ratio.m" and "figure_S5.m". It computes the effective dielectric constant of a medium containing intrusions of different dielectric properties according to the Maxwell-Garnett dielectring mixing model.

* Pss_over_Ps_ratio_at_X_MHz_and_Y.YY_dust_fraction.csv is a comma-separated value file containing model results for subsurface to surface echo power ratio as a function of central frequency, basal temperature, dust content and basal permittivity. One file is produced for every value of the central frequency and of the dust fraction. The value of these two parameters for a given files are reported in the file name, where X is the frequency in MHz, and Y.YY is the dust fraction. Each file contains a matrix in which there is a row for every value of basal temperature from 170 K to 270 K, and a column for every value of basal permittivity from 4 to 100 with logarithmic spacing. Basal temperature and permittivity values are reported in different comma-separated value files called "basal_temperatures.csv" and "basal_permittivities.csv".

* basal_permittivities.csv is a comma-separated value file containing the values of basal permittivity corresponding to the columns of the model result matrixes contained in the files "Pss_over_Ps_ratio_at_X_MHz_and_Y.YY_dust_fraction.csv".

* basal_temperatures.csv is a comma-separated value file containing the values of basal temperature corresponding to the rowso of the model result matrixes contained in the files "Pss_over_Ps_ratio_at_X_MHz_and_Y.YY_dust_fraction.csv".