Correlated radon and CO_2 variations near the San Andreas Fault

Correlations have been observed between groundwater radon and thoron concentrations and carbon dioxide discharges at the Lake Hughes station of the Caltech radon monitoring network. The Lake Hughes site is one of three radon monitoring stations located near the "big bend" segment of the San Andreas fault which began to record anomalous radon levels in August 1981. Two stations, Lake Hughes and Lytle Creek, recorded anomalous increases in radon while the third, Sky Forest, recorded an anomalous decrease. Several weeks after the onset of the anomaly, strongly correlated radon fluctuations began at Lake Hughes and Lytle Creek. These radon spikes also were found to be phase anti-correlated with barometric pressure fluctuations. Analyses of gas grab samples showed relatively high levels of CO_2 and ethylene in borehole air at Lake Hughes and Lytle Creek, while analyses of water samples showed relatively large increases in HCO_3^− at both sites. Isotopic analysis of one gas sample from Lake Hughes yielded a ^(13)C δ value of −22 ‰, which suggests that the CO_2 originates from the oxidation of organic material. The correlation in radon fluctuations at Lake Hughes and Lytle Creek and their common dependence on barometric pressure changes began shortly after the onset of the radon anomaly in August, and probably resulted from the simultaneous saturation of the water in these boreholes with carbon dioxide

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) after nine years of operation: a summary

Mars Express, the first European interplanetary mission, carries the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to search for ice and water in the Martian subsurface. Developed by an Italian–US team, MARSIS transmits low-frequency, wide-band radio pulses penetrating below the surface and reflected by dielectric discontinuities linked to structural or compositional changes. MARSIS is also a topside ionosphere sounder,transmitting a burst of short, narrow-band pulses at different frequencies that are reflected by plasma with varying densities at different altitudes.The radar operates since July 2005, after the successful deployment of its 40 m antenna, acquiring data at altitudes lower than 1200 km. Subsurface sounding (SS)data are processed on board by stacking together a batch of echoes acquired at the same frequency. Onground, SS data are further processed by correlating the received echo with the transmitted waveform and compensating de-focusing caused by the dispersive ionosphere. Ground processing of active ionospheric sounding (AIS)data consists in the reconstruction of the electron density profile as a function of altitude. MARSIS observed the internal structure of Planum Boreum outlining the Basal Unit, an icy deposit lying beneath the North Polar Layered Deposits thought to have formed in an epoch in which climate was markedly different from the current one.The total volume of ice in polar layered deposits could be estimated, and parts of the Southern residual ice cap were revealed to consist of 10 m of CO2 ice. Radar properties of the Vastitas Borealis Formation point to the presence of large quantities of ice buried beneath the surface. Observations of the ionosphere revealed the complex interplay between plasma, crustal magnetic field and solar wind, contributing to space weather studies at Mars. The presence of three-dimensional plasma structures in the ionosphere was revealed for the first time. MARSIS could successfully operate at Phobos, becoming the first instrument of its kind to observe an asteroid-like body. The main goal pursued by MARSIS, the search for liquid water beneath the surface, remains elusive. However, because of the many factors affecting detection and of the difficulties in identifying water in radar echoes, a definitive conclusion on its presence cannot yet be drawn

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) after nine years of operation: A summary

Mars Express, the first European interplanetary mission, carries the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) to search for ice and water in the Martian subsurface. Developed by an Italian-US team, MARSIS transmits low-frequency, wide-band radio pulses penetrating below the surface and reflected by dielectric discontinuities linked to structural or compositional changes. MARSIS is also a topside ionosphere sounder, transmitting a burst of short, narrow-band pulses at different frequencies that are reflected by plasma with varying densities at different altitudes. The radar operates since July 2005, after the successful deployment of its 40 m antenna, acquiring data at altitudes lower than 1200 km. Subsurface sounding (SS) data are processed on board by stacking together a batch of echoes acquired at the same frequency. On ground, SS data are further processed by correlating the received echo with the transmitted waveform and compensating de-focusing caused by the dispersive ionosphere. Ground processing of active ionospheric sounding (AIS) data consists in the reconstruction of the electron density profile as a function of altitude. MARSIS observed the internal structure of Planum Boreum outlining the Basal Unit, an icy deposit lying beneath the North Polar Layered Deposits thought to have formed in an epoch in which climate was markedly different from the current one. The total volume of ice in polar layered deposits could be estimated, and parts of the Southern residual ice cap were revealed to consist of ≈ 10 m of CO2 ice. Radar properties of the Vastitas Borealis Formation point to the presence of large quantities of ice buried beneath the surface. Observations of the ionosphere revealed the complex interplay between plasma, crustal magnetic field and solar wind, contributing to space weather studies at Mars. The presence of three-dimensional plasma structures in the ionosphere was revealed for the first time. MARSIS could successfully operate at Phobos, becoming the first instrument of its kind to observe an asteroid-like body. The main goal pursued by MARSIS, the search for liquid water beneath the surface, remains elusive. However, because of the many factors affecting detection and of the difficulties in identifying water in radar echoes, a definitive conclusion on its presence cannot yet be drawn

Radar Evidence of Subglacial Liquid Water on Mars

Strong radar echoes from the bottom of the martian southern polar deposits are interpreted as being due to the presence of liquid water under 1.5 km of ice

Range compression optimization for subsurface investigation in the MARSIS experiment

This work deals with the range compression applied to MARSIS (Mars Radar for Subsurface and Ionosphere Sounding) data proposing a new approach to improve the S/N after matched filtering for both surface and subsurface responses. It will be also illustrated how the geometric term correction can be performed on a particular class of data previously not correctable according to surface/subsurface theoretical models. Finally, it will be demonstrated how a better estimation of the volume scattering can be obtained. © 2012 IEEE

MARSIS AN EXPERIMENT OF MARS EXPRESS

The second of June 2003 a European space probe ,called Mars Express was launched to Mars. This has been the first European mission to the red Planet and for the first time in only about three years a complex spacecraft was designed built and launched. Among the eight experiments MARSIS is one of the most important if not the most important. It is a radar sounder designed primarily to find subsurface discontinuities that may be due to water in liquid, solid or permafrost forms. In order to penetrate the planet surface a relatively low frequency need to be used, consequently a very long dipole antenna is required. This arose a design challenge that in the end lead to a not proper solution for the antenna deployment. As a consequence the deployment of MARSIS antenna has been postponed until the end of June 2005. First data are being collected and analyzed. The main issues that caused the delay in the MARSIS antenna deployment will be reviewed. Also a description of Mars environmental models and MARSIS system description will be reported

Weighting network influence on the geometric term correction in MARSIS data inversion

Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) is a low frequency, pulse-limited radar sounder and altimeter selected by ESA as a payload of the Mars Express mission. This work retraces the processing that leads to the extraction of parameters needed to perform the data inversion pointing out an effect caused by the weighting network application in presence of volume scattering that could jeopardize the backscattering-related geometry interpretation on a specific set of data

Doppler analysis for data inversion and image processing in the MARSIS experiment

This paper is addressed to MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) signal analysis. The effect of tilted layers, detected within different Doppler filters, is taken into account in order to improve the quality and the quantity of the data set needed to perform the data inversion, that is the estimation of the dielectric constant of the materials composing the different detected interfaces. © 2011 IEEE

Image resolution enhancing in the MARSIS experiment

MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding) is a low frequency, pulse-limited radar sounder and altimeter selected by ESA as a payload of the Mars Express mission. Synthetic aperture technique is required to reduce the wide ground footprint (due to the low operating frequency and the small allowable antenna dimensions) and, thus, the unwanted echo from other surface objects. MARSIS primary objective is to detect, map and characterize subsurface material discontinuities in the upper crust of Mars. These may include boundaries of liquid water-bearing zones, icy layers and geologic structures. Past studies have shown polar caps stratifications, in terms of depth structure and composition, ground ice abundance and seasonal variations (thickness of seasonal deposits, thermal effects). MARSIS is the first instrument able to detect what lies beneath the surface of Mars. MARSIS operates with a very high fractional bandwidth: 1MHz bandwidth allows a vertical resolution of 150 m in free space which corresponds to a lower resolution in the subsurface, depending on the electromagnetic wave propagation speed in the crust. The centre frequency of the pulses transmitted by MARSIS can be set to 1.8 MHz, 3MHz, 4 MHz and 5MHz. On day side operations, it operates only in 4MHz and 5MHz due to the ionosphere plasma frequencies of Mars that reflects all the frequencies lower than 4 MHz. All the four carrier frequencies are available for subsurface sounding on night side. This paper propose a modified version of the well known stepped frequency processing to improve the vertical resolution of MARSIS in order to allow the detection of thinner interfaces that could not be discriminated by the present processing because of its coarse vertical resolution. In fact, range resolution in SAR images is inversely proportional to the transmitted signal bandwidth. Since there is a limit in the transmitted bandwidth that can be supported by the radar hardware, there is a limit in range resolution that can be achieved by processing the SAR data in conventional way. However, if the frequency band of the received signal is widened with a group of sub-pulses, close in frequency (e.g. 3Mhz and 4 MHz), and properly combined, the composite signal increases the bandwidth and hence the improvement in range resolution can be achieved. The algorithm proposed modifies the standard stepped frequency processing introducing ionosphere effects compensation necessary for a correct data processing . Thanks to improved data set it will be possible to have either a deeper knowledge of the subsurface stratifications as well as additional information about the nature of the volume scattering useful in the data inversion process (estimation of the materials composing the surface and the subsurface by the estimation of the dielectric constants)