Subsurface Sounding Research Articles

Observations of Igneous Subsurface Stratigraphy during the Jezero Crater Floor Rapid Traverse from the RIMFAX Ground-penetrating Radar

Perseverance traversed the eastern, northern, and western margins of the Séítah formation inlier on the rover’s western fan front approach. Mapping the stratigraphy and extent of the Máaz and Séítah formations is key to understanding the depositional history and timing of crater floor resurfacing events. Perseverance's rapid progress across the Jezero crater floor between the Octavia E. Butler landing site and the western fan front resulted in limited contextual images of the deposits from the Navigation Camera and Mast Camera Zoom. By combining the limited surface images with continuous subsurface sounding by the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) ground-penetrating radar, Jezero crater floor stratigraphy was inferred along this rapid traverse. We produced the first subsurface map of the Máaz formation thickness and elevation of the buried Séítah formation for 2.3 km of the rapid traverse. Three distinct reflector packets were observed in RIMFAX profiles interspersed with regions of low-radar reflectivity. We interpret these reflector packets with increasing depth to be the Roubion member of the Máaz formation (covered in places with regolith), the Rochette member, and the Séítah formation. We found a median permittivity of 9.0 and bulk density of 3.2 g cm−3 from hyperbola fits to RIMFAX profiles, which suggests a mafic composition for Máaz and Séítah. The low-radar reflectivity regions within each reflector packet could indicate potential depositional hiatuses where low-density material like sediment or regolith could have accumulated between successive Máaz formation lava flows and the Séítah formation at depth.

Analysis of Superresolution Methods in the Application to the Subsurface Sounding Radar for Detecting Hidden Objects

Adaptive methods have been developed for generating a radar image of a probed surface area. A block diagram of a subsurface sounding radar is described. The results of modeling and experimental studies are presented. Their use makes it possible to develop a subsurface sensing radar capable of effectively identifying hidden objects in concrete walls, as well as detecting cracks, voids and defects in the walls of buildings and structures, snow debris and avalanches, underground communications and organic bodies in the ground.

Near-field resonant microwave sensing in the diagnostics of bovine mastitis

The purpose of this work is to analyze the possibilities of evaluating the dielectric parameters of the mammary gland of cows in the diagnosis of mastitis. The study was performed on animals from a number of farms in the Nizhny Novgorod and Kirov regions. A total of 269 mature cows were examined, 185 of which were healthy, 53 individuals had subclinical mastitis, and 31 had a clinically manifested form of the disease. The animals were examined once, by instrumental analysis of the dielectric parameters of the tissues of each lobe of the udder of the animal. The study was carried out using a software and hardware complex, which makes it possible to evaluate the dielectric permittivity of a biological object by the method of near-field resonant microwave sensing. As a result of our research, we have for the first time formed a physiological “pattern” of the dielectric permeability of the skin and breast tissues of actively lactating cows, taking into account the features of the morphological structure of the udder at a significant depth of subsurface sounding (20 mm). It was found that the presence of a focus of inflammation (both in the form of subclinical and manifesting mastitis) leads to a significant increase in dielectric constant (by 12.4 and 26.9%, respectively). At the same time, in healthy cows, the hydration level of tissues of various udder lobes is almost uniform, as evidenced by the values of the dielectric gain coefficient close to one. In the case of the formation of a mastitis focus in one or some parts of the udder, uniformity is violated, and the dielectric constant gradient can be up to 31% with a corresponding increase in the developed coefficient.

Overview of Promising Solutions in Subsurface Sounding Equipment.

This overview analyzes current advances in the equipment for detecting various subsurface metal and metal-containing objects. Various metal detector types are discussed alongside their operation principles, properties, and capabilities. Following the analysis of conventional metal detectors, promising design and technical solutions are explored, implementing new physical metal detector operation principles that have not been used before for this equipment class. The information provided allows for evaluating new metal detector concepts developed to improve the sensitivity and accuracy of detecting equipment.

Влияние климатических и гидрологических изменений на лесорастительные условия речных пойм Донского бассейна

The article deals with the problem of floodplain forest degradation in the steppe zone, using the Don basin’s rivers as an example. The floodplains of the Khoper, Buzuluk, Ilovlya, Medveditsa, and Chir rivers were the key objects of the study. Identification of the landscape-hydrogeological conditions of river floodplains was carried out using the profiling method. In total, five transverse landscape profiles were laid in the floodplains of the listed rivers, along which leveling was carried out to build a hypsometric profile and a comprehensive soil and plant description. For the arid zone rivers, ground feeding is an important source of moisture in addition to atmospheric. Therefore, one of the main tasks was to determine the groundwater level using subsurface sounding (georadar). The analysis of the maximum levels of data for spring floods showed a trend of decreasing the height of floods since the late 1990s. Comparison of these data with the hypsometric profile and radar survey data revealed that the provision of complete flooding of floodplains occurs once every 10–20 years. The absence of annual complete flooding of floodplains with water has led to a decrease in the groundwater level to 5–6 m, which is an unfavorable factor for the development of woody vegetation. The climatic and hydrological conditions of the steppe zone considered in the article are unfavorable for the development of woody vegetation since they do not correspond to the conditions of its initial formation. In view of the existing conditions and the identified trends in the reduction of floods and the fall of the groundwater level, it is possible to predict a further reduction and redistribution of the forest cover of the Don basin’s river floodplains.

Range resolution enhancement of SHAllow RADar (SHARAD) data via bandwidth extrapolation technique: Enabling new features detection and improving geophysical investigation

The SHAllow RADar (SHARAD) is a subsurface sounding radar provided by the Italian Space Agency (ASI) as a facility instrument for NASA's Mars Reconnaissance Orbiter (MRO) mission, the second longest-lived mission to orbit Mars after Mars Odyssey. Developed by an Italian-US Team, SHARAD was designed to investigate to depth of up to one kilometer in the Martian subsurface and to map dielectric discontinuities associated with compositional and/or structural changes. The radar mapping began in November 2006 and, after 16 years of operations, SHARAD has mapped most of the planet's surface (∼55%), contributing a data volume for the entire MRO mission that exceeds that of all the past Mars missions combined.Designed to complement the lower-frequency, relatively narrower bandwidth capability of the MARSIS sounding radar, SHARAD emits an 85μs, frequency-modulated (10 MHz) chirp at a central frequency of 20 MHz to increase the signal-to-noise ratio (SNR) and achieve a finer resolution compared to MARSIS. On the ground, echoes recorded by the radar are range compressed using conventional pulse compression techniques yielding a nominal range resolution of 15 m (vacuum, 5–8 m in typical Martian materials). Additionally, synthetic aperture processing is performed in along-track to increase the resolution up to 300–500 m.Throughout the entire mission duration, SHARAD provided a diverse and extensive range of imaging data. It was able to observe the internal structures of Planum Boreum and Planum Australe, two icy deposits that contain the North and South Polar Layered Deposits (NPLD-SPLD), thought to contain valuable information about the planet's past climate. The radar unveiled the massive deposits of buried CO2 ice below the southern residual ice cap (SRIC), which confirmed the influence of the planet obliquity and insolation in the accumulation of dry ice. Furthermore, it revealed the intricate lava flows structures in the Tharsis Volcanic region, suggesting that the planet experienced deposition by multiple volcanic episodes.However, radar resolution often poses a limitation for subsurface investigations in many regions. Only recently, processing techniques have focused on enhancing SHARAD radargrams vertical resolution by implementing the Bandwidth Extrapolation (BWE) technique. This approach has demonstrated an improvement of the vertical resolution while preserving the time-of-arrival (TOA) and amplitude of the detected echoes. The resulting super-resolved data products exhibit better separation between radar returns, thus improving the overall understanding of the investigated terrains. The obtained results demonstrate the value of implementing the BWE techniques in the data processing pipeline whenever radar sounders are involved.

Design and verification of flexible penetrometer for planetary subsurface exploration

In-situ extraction of geological information from planetary subsurfaces is of great importance. To achieve this goal with low power consumption and deep penetration, a novel subsurface sounding system for planetary regolith exploration is proposed based on the operating principle of tape measures. Penetration model analysis and validation were conducted. The penetration mechanics of the penetrator head and body were modeled separately, and static penetration tests were performed to verify the feasibility of the penetrator and modify the penetration load model. As the structural design of the penetrator was completed, a cam-based impact clamping scheme was proposed. The impact system dynamics model was established to analyze the effect of pene-tration resistance and kinetic parameters on the penetration capability of the penetrator. The principle prototype of the penetrator was developed, and a load-free simulated planetary regolith penetration test system was built to verify the correctness of the design. This study may provide technical support for the future application of flexible detectors in planetary exploration.

Fluid Migration through Permafrost and the Pool of Greenhouse Gases in Frozen Soils of an Oil and Gas Field

Most methane (CH4) and carbon dioxide (CO2) emissions originate from the biodegradation of organic matter of soils and of degrading permafrost in the Arctic. However, there is limited evidence of the activity of geological sources, and little understanding of the pathways of migration of gaseous fluids through the porous mineral matrix filled with ice. We estimated the effect of geological factors on the winter storage of the greenhouse gases in frozen soils by statistical analysis of the geodatabase, which combined a field gas survey of frozen soils, subsurface sounding, and remote sensing data. Frozen soils stored on average 0.016 g CH4 m−3 and 11.5 g CO2 m−3. Microseeps, recognized by isolated anomalies of helium, had 30% higher CH4 concentrations. Lineaments marking margins of tectonic blocks were estimated to have 300% higher CH4 concentrations. High concentrations of propane and ethane indicated the contribution of diffuse fluid flow from hydrocarbon-bearing beds on 95% of the 130 km2 study area. In addition to the fluid contribution, we estimated an overwintering pool of greenhouse gases in frozen soil for the first time. Being at least 0.01–0.1% of the soil organic matter mass, these gaseous forms of carbon can be critical for the early-summer Arctic ecosystem functioning.

Effects of Ionospheric Inhomogeneities on Remote Sensing of the Earth by Space‐Borne P‐Band SAR

AbstractNumerical modeling of the effect of the polarization vector rotation in the ionospheric plasma on the radio waves of the high frequency range is performed. The relevance of the work is associated with the creation of space‐based P‐band synthetic aperture radars (SARs) for the Biomass mission and the MKS‐RSA (P) experiment on board ISS station. These instruments are intended for surface and subsurface sounding of the Earth and their readings are strongly influenced by the ionosphere. Another problem of EM propagation is the reconstruction of the profile e‐ionospheric plasma density by radio tomography methods. The source of radiation is located on the moving spacecraft at a distance of 400 km from the Earth's surface. The angle of rays inclination varies from 150 to 30° relative to the horizontal axis. The receiver is located on the surface of the Earth. Three spherical two‐layer models of the ionosphere are compared. To determine the ray paths, a bi‐characteristic system of equations is used. The dependence of the aiming angle deviation on group time is investigated. The phase variation due to the influence of the ionosphere and the angle of the Faraday rotation are studied. It is shown that the changes in the Faraday rotation angle for the selected parameters lie in the range from 6° to 54°, which will have a strong impact on the operation of the P‐band SAR and requires a sufficiently accurate quantitative account of the variability of the angle when probing vegetation and soil covers.

A New Method for Retrieving Electron Density Profiles from the MARSIS Ionograms

The Martian ionosphere was actively detected by Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard the Mars Express. The detected echo signal of the MARSIS at an epoch is presented as a function of frequency and time delay to form an ionogram. Some MARSIS ionograms have been processed to obtain the electron density profiles of the Martian topside ionosphere. Unfortunately, more than half of the records cannot be processed with current methods due to the lack of local plasma density information at spacecraft altitude. In this work, we employ a piece-wise exponent to describe the electron density profile of the Martian topside ionosphere. The piece-wise exponent used in our method can reasonably capture the altitude structure of the Martian topside ionosphere, which has been validated with the MGS and MAVEN data. In an altitude regime of lower than 200 km, the average absolute height error of the same electron density between MGS data and fitted profiles is 0.006 km, and the average relative error is 0.008%. In an altitude regime of higher than 200 km, the average absolute height error of the same electron density between MGS data and fitted profiles is 0.55 km, and the average relative error is −0.1%. Based on the altitude structure knowledge of the Martian topside ionosphere, we put forward a new method to invert electron density profiles from MARSIS ionograms with/without local plasma density information. Compared with the previous results, the average absolute difference in the peak height of the retrieved profile is 7.38 km, within the margin of the MARSIS height resolution of 13.8 km. The average relative difference is only 3%. The application of the new method can greatly improve the utilization rate of MARSIS ionogram records.

Flight Experiment Validation of Altitude Measurement Performance of MOSIR on Tianwen-1 Orbiter

The MOSIR (Mars Orbiter Subsurface Investigation Radar) is one of the scientific payloads carried by the Tianwen-1 orbiter. MOSIR conducted a ground experiment in the desert near Dengkou County, northern China, before the launch of the Tianwen-1 satellite. The MOSIR prototype was suspended from a hot air balloon and flew over a flat region at an altitude of 2500–3300 m. This experiment aimed to verify the system performance and data processing. The data collected in subsurface sounding mode is performed range compression, and the altitude measurement data removes invalid data. After processing, the altitude measurement results of two operating modes are analyzed and compared with that of the Global Position System (GPS), which verifies the accuracy of the altitude measurement.

Airborne Ground Penetrating Radar, Field Test

Deployment of a ground penetrating radar (GPR) on a flying machine allows one to substantially extend the application area of this geophysical method and to simplify carrying out large surveys of dangerous and hard-to-reach terrain, where usual ground-based methods are hardly applied. There is a necessity to promote investigations in this direction by modifying hardware characteristics and developing specific proceeding algorithms. For this purpose, we upgraded commercial ground-based subsurface sounding hardware and performed corresponding computer simulation and real experiments. Finally, the first experimental flights were done with the constructed GPR prototype mounted on a helicopter. Using our experience in the development of ground-based GPR and the results of numerical simulations, an appropriate configuration of antennas and their placing on the flying machine were chosen. Computer modeling allowed us to select an optimal resistive loading of transmitter and receiver dipoles; calculate radiation patterns on fixed frequencies; analyze the efficiency of different conductor diameters in antenna circuit; calculate cross-coupling of transmitting and receiving antennas with the helicopter. Preliminary laboratory experiments to check the efficiency of the designed system were performed on an urban building site, using a tower crane with the horizontal jib to operate the measuring system in the air above the ground area to be sounded. Both signals from the surface and subsurface objects were recorded. To interpret the results, numerical modeling was carried out. A two-dimensional model of our experiment was simulated, it matches well the experimental data. Laboratory experiments provided an opportunity to estimate the level of spurious reflections from the external objects, which helps to recognize weak signals from subsurface objects in GPR surveys under live conditions.

Modeling of the reflected signal of a ground penetrating radar

The objective of this paper is the simplified model of the reflected signal during subsurface sounding. Physical processes which influence the propagation of the electromagnetic wave are examined in the article. The process of accounting for reflecting local objects situated in the path of the sounding signal propagation is explained in the article. The proposed model is implemented in MatLab software.

Simulation of the radar signal reflection from the lunar surface

To determine the structure and mineralogical composition of lunar subsurface a radar complex RLK-L will be installed on the “Luna-26” spacecraft. The inverse problem solution of subsurface sounding will be more accurate if all factors affecting the shape of the reflected signal are taken into account. Topography is one such factor. The article deals with modelling the reflection of a radio signal from a rough surface. An analysis of a series of numerical experiments showed that destruction of high frequency part of the spectrum depends on the dispersion of the inhomogeneities’ heights in reflection spot. The simulation results are consistent with previously performed experimental measurements and well-known theoretical estimates. Therefore, in radar experiments, it makes sense to first analyze the signals reflected from smooth areas, then from the area in which a three-dimensional digital model of lunar surface reveals the presence of depressions, and then areas with mountain ranges.

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

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.

Signal enhancement for planetary radar sounders

Orbital radar sounders are a useful tool to investigate planetary bodies. The sounding signal lies in the high frequency or very high frequency band, allowing a good ground penetration but limiting the system's resolution. Moreover, electromagnetic interference (EMI) may affect the system, increasing the noise in the radar products. In this Letter, a method to enhance the resolution and to suppress the EMI is presented. The method's performance and the parameters setting are investigated. Finally, some results for the Mars Advanced Radar for Subsurface and Ionosphere Sounding and for the Shallow Radar sounders are presented.

Undistorted reception of impulse carrier-free signals using a ferrite antenna

Relevance. In recent decades, a new direction of radar has emerged. Temporarily and spatially limited signals with different types of envelope and the wide width of the spectrum have found their application here. The use of such ultra-wideband (UWB) electromagnetic pulses in subsurface sounding requires changes in the principles of designing of equipment for radar systems, including receiving antenna systems. The urgent task remains to build compact pulsed UWB receiving antennas that have high sensitivity and do not distort the shape of the received signal. As such antennas, ferrite loop antennas can be used. The use of ferrite rods in receiving antennas allows to increase their sensitivity, leaving the dimensions small. Methods of designing UWB pulsed ferrite antennas are still in the initial stage of their development and require comprehensive fundamental and applied research. The purpose of work is to investigate the shape of the induced current in the receiving antenna consisting of a ferrite rod with a loop of a conductor when the antenna is excited by a pulsed electromagnetic field of the form of the most common carrier-free signals. Methods. To calculate the currents induced in a conductor that encloses a ferrite rod, the finite difference time domain method (FDTD) was used. Results. There were revealed the relationships between optimal from the point of view of effective undistorted signal reception, the electrodynamic parameters of the ferrite element of the antenna, and the time-frequency parameters of the exciting pulse field in the form of the most common carrier-free functions, namely, the Gaussian functions, the 1st and 2nd derivatives in time of the Gauss function. Conclusions. The parameters of the ferrite element of the pulsed receiving antenna and the carrier-free exciting pulsed electromagnetic field, at which the receiving antenna in the form of a ferrite rod with a loop of conductor provides sensitive undistorted reception of the pulse signals were determined.

Improved estimation of Mars ionosphere total electron content

We describe an improved method to estimate the Total Electron Content (TEC) of the Mars ionosphere from the echoes recorded by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) (Picardi et al., 2005; Orosei et al., 2015) onboard Mars Express in its subsurface sounding mode. In particular, we demonstrate that this method solves the issue of the former algorithm described at (Cartacci et al., 2013), which produced an overestimation of TEC estimates on the day side.The MARSIS signal is affected by a phase distortion introduced by the Mars ionosphere that produces a variation of the signal shape and a delay in its travel time. The new TEC estimation is achieved correlating the parameters obtained through the correction of the aforementioned effects.In detail, the knowledge of the quadratic term of the phase distortion estimated by the Contrast Method (Cartacci et al., 2013), together with the linear term (i.e. the extra time delay), estimated through a radar signal simulator, allows to develop a new algorithm particularly well suited to estimate the TEC for solar zenith angles (SZA) lower than 95° The new algorithm for the dayside has been validated with independent data from MARSIS in its Active Ionospheric Sounding (AIS) operational mode, with comparisons with other previous algorithms based on MARSIS subsurface data, with modeling and with modeling ionospheric distortion TEC reconstruction.

Global permittivity mapping of the Martian surface from SHARAD

SHARAD is a subsurface sounding radar aboard NASA's Mars Reconnaissance Orbiter, capable of detecting dielectric discontinuities in the subsurface caused by compositional and/or structural changes. Echoes coming from the surface contain information on geometric properties at metre scale and on the permittivity of the upper layers of the Martian crust. A model has been developed to estimate the effect of surface roughness on echo power, depending on statistical parameters such as RMS height and topothesy. Such model is based on the assumption that topography can be characterized as a self-affine fractal, and its use allows the estimation of the dielectric properties of the first few metres of the Martian soil. A permittivity map of the surface of Mars is obtained, covering several large regions across the planet surface. The most significant correspondence with geology is observed at the dichotomy boundary, with high dielectric constant on the highlands side (7 to over 10) and lower on the lowlands side (3 to 7). Other geological correlations are discussed.

3-D Imaging of Mars' Polar Ice Caps Using Orbital Radar Data.

Since its arrival in early 2006, various instruments aboard NASA's Mars Reconnaissance Orbiter (MRO) have been collecting a variety of scientific and engineering data from orbit around Mars. Among these is the SHAllow RADar (SHARAD) instrument, supplied by Agenzia Spaziale Italiana (ASI) and designed for subsurface sounding in the 15-25 MHz frequency band. As of this writing, MRO has completed over 46,000 nearly polar orbits of Mars, 30% of which have included active SHARAD data collection. By 2009, a sufficient density of SHARAD coverage had been obtained over the polar regions to support 3-D processing and analysis of the data. Using tools and techniques commonly employed in terrestrial seismic data processing, we have processed subsets of the resulting collection of SHARAD observations covering the north and south polar regions as SHARAD 3-D volumes, imaging the interiors of the north and south polar ice caps known, respectively, as Planum Boreum and Planum Australe. After overcoming a series of challenges revealed during the 3-D processing and analysis, a completed Planum Boreum 3-D volume is currently being used for scientific research. Lessons learned in the northern work fed forward into our 3-D processing and analysis of the Planum Australe 3-D volume, currently under way. We discuss our experiences with these projects and present results and scientific insights stemming from these efforts.