A time–domain electromagnetic sounder for detection and characterization of groundwater on Mars

Grimm, R. E.; Berdanier, Barry; Warden, Robert; Harrer, James; Demara, Raymond; Pfeiffer, James; Blohm, Richard

doi:10.1016/j.pss.2009.05.003

Cited by 14 publications

(10 citation statements)

References 19 publications

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“…In water‐altered and old volcanic units, future radar systems must overcome hundreds of decibels in attenuation to probe the originally desired kilometer depths. Therefore other geophysical techniques must be used to search for groundwater, such as active seismic Q [e.g., Tittmann , 1979; Olhoeft , 2003], magnetotellurics [e.g., Grimm , 2002; Delory et al , 2007], time domain electomagnetics [e.g., Grimm , 2002; Grimm et al , 2009], or surface nuclear magnetic resonance [e.g., Grimm , 2002, 2003]. Even in areas of low attenuation rates these geophysical techniques are necessary as radar alone cannot uniquely identify groundwater.…”

Section: Resultsmentioning

confidence: 99%

Radar penetrates only the youngest geological units on Mars

Stillman

Grimm

2011

J. Geophys. Res.

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[1] Signals from the Shallow Radar were intended to penetrate hundreds of meters or more into Mars, but subsurface reflections are abundant only in known or inferred ice-rich units and young (middle to late Amazonian), apparently pristine, volcanic units. As volcanic units age, fewer subsurface reflections are detected. Also, no subsurface reflections are detected from any northern hemisphere units inferred to be altered by water. We suggest that the general lack of subsurface reflections on Mars is not likely an indication that the shallow interior is devoid of structure and stratigraphy but rather an indication that dielectric contrasts cannot be detected due to signal attenuation originating from scattering and/or absorption. We constrained the attenuation rate in regions with no subsurface reflections to 0.065-0.27 dB/m. This corresponds to scattering losses from meter-scale fractures and/or lithologic density variations of 0.27-1.03 g/cm 3 . Alternatively, our laboratory measurements have shown that three monolayers of adsorbed water on 2.2-14 vol % smectite clays can completely absorb radar energy and would be equivalent to a global water layer just ∼0.2-0.6 m thick. We suggest that the increased attenuation in volcanic units comes from an increase in fracture density. Attenuation in water-altered units may be due to the greater heterogeneity in sedimentary units and/or chemical alteration that has formed high-surface-area smectites capable of holding the necessary amount of adsorbed water. Overall, the lack of widespread, deep subsurface reflections is due to the more Earth-like radar properties of Mars, as compared to the Moon-like properties that were anticipated.

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Section: Resultsmentioning

confidence: 99%

Radar penetrates only the youngest geological units on Mars

Stillman

Grimm

2011

J. Geophys. Res.

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“…Furthermore, they lack the mobility needed to achieve large-scale coverage. An alternative electromagnetic method for deep subsurface study is time-domain electromagnetic (TDEM) sounding [65], which works by inducing eddy currents in the subsurface and by measuring the magnetic fields produced by such currents. This technique allows the determination of subsurface conductivity, which increases by orders of magnitude in the presence of saline water, and can achieve deeper penetration than GPR at the cost of lower resolution.…”

Section: Discussionmentioning

confidence: 99%

The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives

Orosei

Ding

et al. 2020

Life

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Due to its significance in astrobiology, assessing the amount and state of liquid water present on Mars today has become one of the drivers of its exploration. Subglacial water was identified by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard the European Space Agency spacecraft Mars Express through the analysis of echoes, coming from a depth of about 1.5 km, which were stronger than surface echoes. The cause of this anomalous characteristic is the high relative permittivity of water-bearing materials, resulting in a high reflection coefficient. A determining factor in the occurrence of such strong echoes is the low attenuation of the MARSIS radar pulse in cold water ice, the main constituent of the Martian polar caps. The present analysis clarifies that the conditions causing exceptionally strong subsurface echoes occur solely in the Martian polar caps, and that the detection of subsurface water under a predominantly rocky surface layer using radar sounding will require thorough electromagnetic modeling, complicated by the lack of knowledge of many subsurface physical parameters. Higher-frequency radar sounders such as SHARAD cannot penetrate deep enough to detect basal echoes over the thickest part of the polar caps. Alternative methods such as rover-borne Ground Penetrating Radar and time-domain electromagnetic sounding are not capable of providing global coverage. MARSIS observations over the Martian polar caps have been limited by the need to downlink data before on-board processing, but their number will increase in coming years. The Chinese mission to Mars that is to be launched in 2020, Tianwen-1, will carry a subsurface sounding radar operating at frequencies that are close to those of MARSIS, and the expected signal-to-noise ratio of subsurface detection will likely be sufficient for identifying anomalously bright subsurface reflectors. The search for subsurface water through radar sounding is thus far from being concluded.

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“…ELF electromagnetic methods are particularly predisposed to examine the parameters of the Martian environment, as due to the low-conductivity surface of the planet (there is no liquid water at the planetary surface), they allow for deep penetration into the Martian ground, and due to low attenuation of these waves, they can be used to detect even relatively low-intensity signals. The electromagnetic sounding in the low frequency range is favorable for detection of deep subsurface water layers, which cannot be done using radar or seismic methods (Delory et al 2007;Grimm et al 2009). Using this technique the presence of groundwater at depths up to several kilometers below the surface can be investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, we propose an EM method that allows studying global properties of the Martian cavity as well as individual ELF sources. Such an approach is more robust than the one presented by Grimm et al (2009), since it allows surveying the atmosphere and the ground on the global scale, and as it is a passive technique, it does not require any antenna deployment system nor additional power supply to generate signals.…”

Section: Introductionmentioning

confidence: 99%

Extremely Low Frequency Electromagnetic Investigation on Mars

et al. 2016

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Natural electromagnetic (EM) signals of extremely low frequencies (ELF, 3 Hz-3 kHz) can be used to study many of the electromagnetic processes and properties occurring in the Martian environment. Sources of these signals, related to electrical activity in the atmosphere, are very significant since they can influence radio wave propagation on the planet, the atmospheric composition, and the ionospheric structure. In addition, such EM signals can be employed in many purposes such as: surveying the subsurface of Mars or studying the impact of the space weather on the Martian ionosphere. As ELF waves propagate on very long distances, it is possible to explore properties of the entire planet using single-station recordings. In this study, we propose an experiment that allows measuring ELF signals from the Martian surface. Such measurements can be used for detection of electric discharges in the atmosphere and water reservoirs in the planetary subsurface.

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A time–domain electromagnetic sounder for detection and characterization of groundwater on Mars

Cited by 14 publications

References 19 publications

Radar penetrates only the youngest geological units on Mars

Radar penetrates only the youngest geological units on Mars

The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives

Extremely Low Frequency Electromagnetic Investigation on Mars

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