Subsurface Sounding Research Articles

The long-wavelength thermal emission of the Pluto-Charon system fromHerschelobservations. Evidence for emissivity effects

Thermal observations of the Pluto-Charon system acquired by the Herschel Space Observatory in February 2012 are presented. They consist of photometric measurements with the PACS and SPIRE instruments (nine visits to the Pluto system each), covering six wavelengths from 70 to 500 $\mu$m altogether. The thermal light curve of Pluto-Charon is observed in all filters, albeit more marginally at 160 and especially 500 $\mu$m. Putting these data into the context of older ISO, Spitzer and ground-based observations indicates that the brightness temperature (T$_B$) of the system (rescaled to a common heliocentric distance) drastically decreases with increasing wavelength, from $\sim$53 K at 20 $\mu$m to $\sim$35 K at 500 $\mu$m, and perhaps ever less at longer wavelengths. Considering a variety of diurnal and/or seasonal thermophysical models, we show that T$_B$ values of 35 K are lower than any expected temperature for the dayside surface or subsurface of Pluto and Charon, implying a low surface emissivity. Based on multiterrain modeling, we infer a spectral emissivity that decreases steadily from 1 at 20-25 $\mu$m to $\sim$0.7 at 500~$\mu$m. This kind of behavior is usually not observed in asteroids (when proper allowance is made for subsurface sounding), but is found in several icy surfaces of the solar system. We tentatively identify that a combination of a strong dielectric constant and a considerable surface material transparency (typical penetration depth $\sim$1 cm) is responsible for the effect. Our results have implications for the interpretation of the temperature measurements by REX/New Horizons at 4.2 cm wavelength.

Space-based radar systems intended for subsurface sounding of Mars and Moon soils

Space-based radar systems intended for investigating the subsurface layers of Mars, Phobos, and Moon are discussed. The characteristics of domestic radar systems developed in preparing the space projects devoted to the study of Mars soils (Mars-96 mission), Phobos ground (Phobos 1 and 2 and Phobos-Grunt missions), and the Moon surface (Luna-Glob mission) are presented. The characteristics of a long-wave Mars advanced radar for subsurface and ionosphere sounding (MARSIS) (Mars Express project) and a long-wave shallow radar (ShaRad) system included in Mars Reconnaissance Orbiter, as well as the results of processing of radar measurement data, are presented.

Phase compensation of MARSIS subsurface sounding data and estimation of ionospheric properties: New insights from SHARAD results

Phase compensation of MARSIS subsurface sounding data and estimation of ionospheric properties: New insights from SHARAD results

Optimization of the Antennas of the EISS Radar Designed to Perform Deep Martian Subsurface Sounding

The Electromagnetic Investigation of SubSurface (EISS) instrument has been designed to get information on the morphology and geological structure of the Martian subsurface and search for potential liquid water reservoirs. EISS is an impulse radar operating from the Martian surface at central frequencies of a few megahertz in order to perform deep sounding of the subsurface. Particular attention has been paid to the design of the instrument's electrical antennas that need to transmit and receive the electromagnetic waves without distortion over the instrument's full frequency bandwidth (i.e, from 1 to 7 MHz). To fit into the mass and volume allocation, wire antennas made of identical loaded dipoles have been selected; they will be deployed on the surface by a mechanical mortarlike device. The resistive profile along the monopoles needs to be carefully chosen to ensure a proper behavior of the antenna once they are deployed on the surface. This paper deals with the performance of these electrical antennas and the optimization of their resistive profile. The study of the impact of the subsurface is performed on simulated data obtained by a numerical finite difference in time domain code. When available, experimental data show the good agreement with the theory. The studies performed show that a slightly suboptimal resistive profile will allow a correct operation of the instrument at the surface of Mars for any landing site.

Total electron content in the Martian atmosphere: A critical assessment of the Mars Express MARSIS data sets

AbstractThe total electron content (TEC) is one of the most useful parameters to evaluate the behavior of the Martian ionosphere because it contains information on the total amount of free electrons, the main component of the Martian ionospheric plasma. The Mars Express Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) radar is able to derive TEC from both of its operation modes: (1) the active ionospheric sounding (AIS) mode and (2) the subsurface mode. TEC estimates from the subsurface sounding mode can be computed from the same raw data independently using different algorithms, which should yield similar results. Significant differences on the dayside, however, have been found from two of the algorithms. Moreover, both algorithms seem also to disagree with the TEC results from the AIS mode. This paper gives a critical, quantitative, and independent assessment of these discrepancies and indicates the possible uncertainty of these databases. In addition, a comparison between the results given by the empirical model of the Martian ionosphere developed by Sánchez‐Cano et al. (2013) and the different data sets has been performed. The main result is that for solar zenith angles higher than 75°, where the maximum plasma frequency is typically small compared with the radar frequencies, the two subsurface algorithms can be confidently used. For solar zenith angles less than 75°, where the maximum plasma frequency is very close to the radar frequencies, both algorithms suffer limitations. Nevertheless, despite the solar zenith angle restrictions, the dayside TEC of one of the two algorithms is consistent with the modeled TEC.

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 40m antenna, acquiring data at altitudes lower than 1200km. 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 ≈10m 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.

The influence of relief on formation of reflected signals of subsurface sounding radar

Radar sounding of the surface and near-surface layer of the Moon by the RLK-L low-frequency radar complex from the orbiter module is planned for the Moon-Globe Russian mission. To forecast results of radar experiments, a simulation procedure of the reflection of the RLK-L radar signal by the Moon’s surface is designed. The 3D surface model, based on measurement results of the Lunar Orbiter Laser Altimeter (LOLA) of the Lunar Reconnaissance Orbiter mission was used in the calculations. The simulation results showed that the spectrum shape of the reflected signal depends on the relief type in the experimental area. Therefore, when the depth distribution of the permittivity of the geological media is determined, the topographic information should be taken into account.

1D-FDTD Characterization of Ionosphere Influence on Ground Penetrating Radar Data Inversion

A finite-difference time-domain (FDTD) simulator is employed to evaluate distortions induced by the ionosphere on chirp signals transmitted by orbiting ground penetrating radars like the Mars advanced radar for subsurface and ionosphere sounding (MARSIS) and the shallow radar (SHARAD). The main goal is to support the data inversion process, i.e., the estimation of the permittivity of subsurface layers. Also proposed is an approach to study the influence of the ionosphere on chirp signals for present and future missions. Since data inversion relies on both crust attenuation estimation and rough geometries compensation, procedures that could be both strongly influenced by the ionosphere, several ionosphere compensation schemes are compared and their impact on data inversion is discussed.

Pendugaan Struktur Bawah Permukaan Peninggalan Purbakala Situs Candi Jabung, Probolinggo, Indonesia Menggunakan Metode Geolistrik Resistivitas

The sounding of geoelectrical resistivity distribution using dipole-dipole configuration around the Jabung temple site located in the Jabung Candi village, Paiton, Probolinggo District, East Java province, Indonesia has been done by using Resistivitymeter OYO MacOhm. The aim of the research was to determine the distribution and depth of rock below the Jabung temple area also as an information for investigation and discovery efforts of ancient objects which are still burried. Aquisition are taken by ten lines and ±20.042 m 2 of coverage area. Line 1, 2, 3, 4, 5, 6 located around in Menara Sudut temple at length of measurement line12 m and at a distance of electrode spacing are 1 m, where lines 1 and 4 located in outcrop of Menara Sudut tample. While lines 7, 8, 9, and 10 located in all area of Jabung temple. Lines 7 and 8 have length of measurement lines 150 m with spacing 10 m, while lines 9 and 10 have length of measurement lines 200 m with spacing 4 m, where line 8 located pass to main Jabung tample. The processing of data was using RES2DINV software. Resistivity values that are used to determine the temple rock is the resistivity value of sandy clay. Base on geoelectrical investigation and interpretation shows the sandy clay as temple rock with resistivity value 33 Ω.m to 92.6 Ω.m on average depth of 1.79 m and the others remain of tample rock around the main Jabung tample. This research shows geoelectrical method is good idea to subsurface sounding especially for archeology case, it caused this method is simple and more cheap than ekskavation method.

Roughness and near‐surface density of Mars from SHARAD radar echoes

AbstractWe present a technique for estimating Mars topographic roughness on horizontal scales from about 10 m to 100 m using Shallow Radar (SHARAD) sounding data. Our results offer a view of surface properties complementary to Mars Orbiter Laser Altimeter (MOLA) pulse‐width or baseline roughness maps and can be compared to SHARAD peak‐echo properties to infer deviations from the average near‐surface density. Latitudinal averaging of SHARAD‐derived roughness over Arabia and Noachis Terrae shows good agreement with MOLA‐derived roughness and provides clear evidence for latitude‐dependent mantling deposits previously inferred from image data. In northwestern Gordii Dorsum, we find that bulk density in at least the upper few meters is significantly lower than in other units of the Medusae Fossae Formation. We observe the same behavior indicative of low near‐surface density in wind‐eroded crater fill in the southern highlands. Combining surface‐properties analysis, subsurface sounding, and high‐resolution optical images, we show that the Pavonis Mons fan‐shaped deposit differs significantly from lobate debris aprons which SHARAD has shown to be ice‐cored. There are no internal radar reflections from the smooth‐facies portion of the Pavonis Mons fan‐shaped deposit, and we suggest that these deposits are either quite thin or have little dielectric (i.e., density) contrast with the underlying terrain. Future application of these techniques can identify other low‐density units across Mars, assist in the mapping of regional volatile‐rich mantling units, and provide new constraints on the physical properties of the polar layered terrain.

Multimode/Multifrequency Low Frequency Airborne Radar Design

This work deals with the design of multimode/multifrequency airborne radar suitable for imaging and subsurface sounding. The system operates at relatively low frequencies in the band ranging from VHF to UHF. It is able to work in two different modalities: (i) nadir-looking sounder in the VHF band (163 MHz) and (ii) side-looking imager (SAR) in the UHF band with two channels at 450 MHz and 860 MHz. The radar has been completely designed by CO.Ri.S.T.A. for what concerns the RF and the electronic aspect, and by the University of Calabria for what concerns the design, realization, and test of SAR antennas. The radar has been installed on a civil helicopter and its operation has been validated in flight in both sounder and imager modality. Preliminary surveys have been carried out over different areas of Campania region, South Italy.

Martian ionogram scaling by the Object Tracking Method

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard the Mars Express (MEX) spacecraft started to collect data of the Martian topside ionosphere from May, 2005. By now a large amount of ionograms has been obtained. It is important to extract vertical ionospheric information effectively from the ionograms for further study. In this paper a new method, Object Tracking Method (OTM), is proposed to automatically extract the ionospheric electron density profiles by computer. This method is based on three algorithms, namely the Hough transform, region growing segmentation algorithm and moving objects detection method from video sequences. In processing ionosphere echoes are treated as moving objects. The identification ratio of OTM for the MARSIS ionograms is estimated to be around 90%.

Long-wave planetary radar: Radar sounding of the soil of Phobos in the Phobos-Grunt project

The specific features of the radar sounding of the soil of Phobos during the performance of the Russian Phobos-Grunt project have been considered. The parameters of the long-wave subsurface sounding radar designed in order to study the electrophysical characteristics of the soil of Phobos, reveal the depth structure, estimate the rock density, and perform radar mapping of the satellite relief and surface roughness have been justified. The scheme of the experimental sounding of the soil of Phobos is presented.

Radar Signal Propagation and Detection Through Ice

In this paper we describe the existing and planned radar measurements of the planetary bodies. The dielectric properties of water ice and other potential surface and subsurface materials are discussed, as well as their dependency on temperature and structure. We then evaluate the performance of subsurface sounding radars using these parameters. Finally we describe some laboratory technique to help interpret the radar data, presenting some results obtained using dielectric spectroscopy methods.

Influence of the ionospheric plasma density fluctuations on the subsurface sounding of the Martian soil by a synthetic aperture radar

We consider the problem of subsurface sounding of the planetary interior with an ultrawideband synthetic aperture radar through the ionosphere containing random density fluctuations. Numerical simulation is performed for a variety of typical parameters of the medium and the instrument. The impact of the ionospheric fluctuations on the sounding is estimated. The question of optimal choice of the synthetic aperture length is addressed.

Ionospheric corrections of MARSIS subsurface sounding signals with filters including collision frequency

Ionospheric corrections of Mars advanced radar for subsurface and ionosphere sounding (MARSIS) subsurface sounding signals are necessary before they can be further analyzed. Usually the ionosphere correction only considers the phase dispersion owing to the electron densities. In this paper we show that if the electron–neutral collision frequency is included in the correction filter, the signal-to-noise ratio of the processed signal can be further maximized and the spatial resolution of the signal be improved. Three different models of the ionosphere profile have been studied, and it is shown that a uniform slab model, of both densities and collisions, is feasible and probably the best choice when implementing the correction filter including collisions. The physical significance of the parameters obtained with the uniform model (equivalent parameters) is discussed, and it is shown that they are useful for the estimation of the real physical parameters of the ionosphere. We developed a recursive, random search algorithm to facilitate the realization of the correction process with the filter including collision frequency.

Electromagnetic compatibility (EMC) evaluation of the SELENE spacecraft for the lunar radar sounder (LRS) observations

Abstract In order to achieve the lunar subsurface sounding and planetary radio wave observations by the Lunar Radar Sounder (LRS) onboard the SELENE spacecraft, strict electromagnetic compatibility (EMC) requirements were applied for all instruments and the whole system of the spacecraft. In order to detect the lunar subsurface echoes from a depth of 5 km, the radiated emission (RE) limit was determined to be −10 dBμV/m and the common-mode (CM) current limit to be 20 dBμA. The EMC performance of the spacecraft was finally evaluated in the system EMC test held from Oct. 20 to Oct. 22, 2005. There is no broadband noise but some narrowband noises at a level above the CM-current limit in a frequency range from 4 to 6 MHz, in which radar soundings are operated. Based on the noise spectrum within 4–6 MHz, the noise level of FMCW radar sounder is estimated to be 14 dB lower than the CM-current limit. In the SELENE EMC test, the following new techniques were introduced: (1) systematic control and evaluation of CM-current noises were first performed to improve the spacecraft EMC performance; (2) onboard battery operation was utilized for reduction of ambient broadband noises during EMC measurements.

電磁気法探査（ＥＭ法探査）技術の現状と展望―地震探査との統合型解析に向けて―

Electromagnetic (EM) methods have been developed for estimating the apparent resistivity or conductivity of material composing subsurface structure depending on survey objectives, while seismic methods are applied mainly to understand geological structure or stratigraphy. Magnetotelluric subsurface sounding (MT) methods are proven tools detect high-conductivity anomalies in the Earth's interior; controlled source EM (CSEM) methods detect high-conductivity anomalies; and, nuclear magnetic resonance (NMR) methods estimate “the mean free path” of hydrogen atoms in various molecules composing underground materials. Regarding methodologies, EM methods frequently applied in practice are: (1) natural source MT methods, (2) artificial source MT or EM methods, and (3) borehole EM methods. The fundamental principles of these methods can be summarized as measuring the induction effects of a survey target using a natural or artificial electromagnetic source. Finally, we investigate examples of recent EM approaches in connection with seismic methods and discuss the integration of survey data from both methods as a key to exploring underground structures not only in terms of stratigraphic interpretation but also for estimating material physical properties.

Absorption of MARSIS radar signals: Solar energetic particles and the daytime ionosphere

We present observations from the subsurface sounding mode of the MARSIS instrument onboard Mars Express that imply radar wave absorption because of increased amounts of ionization in the upper Martian atmosphere during the fall of 2005. On at least two occasions these radar disruptions lasted for several days and we find that these periods are correlated with periods when other instruments indicate elevated levels of solar energetic particles. Another disruption lasted for over a month and we find that it was likely caused by a combination of solar activity and observing through the daytime ionosphere. There is no evidence in the present results for the constant ionospheric layer predicted to be created by the normal infall of cosmic dust, although the effects of enhanced infall during meteor showers remains uncertain. The effects of dust activity also remain uncertain but will be tested during the 2007 dust season.

Electromagnetic Propagation of GPR Signals in Martian Subsurface Scenarios Including Material Losses and Scattering

A study on the electromagnetic propagation in various models of the Martian subsurface is performed with a relevance to ground penetrating radar (GPR) operating onboard rover missions. Measurements of the electromagnetic properties of Mars soil simulants are obtained; on this basis, the attenuation features of the GPR signals are estimated, including both electric and magnetic losses. The effect on propagation of inhomogeneities inside the soil is also taken into account by means of a specific model with randomly distributed scatterers. The GPR performance in terms of resolution and maximum penetration depth is evaluated in the considered scenarios for different operating frequencies, thus providing a basic information for the design of systems for future subsurface sounding investigations on Mars