Radar Sounding Research Articles

Sedimentation waves on the Martian North Polar Cap: Analogy with megadunes in Antarctica

Complex interactions between katabatic winds and the cryosphere may lead to the formation of sedimentation waves at the surface of ice sheets. These have been first described and named snow megadunes in Antarctica. Here we use topographic data, optical images, subsurface radar soundings and spectroscopic data acquired by Mars orbiters, to show that the surface of the Martian North Polar Cap displays two superimposed sets of sedimentation waves with differing wavelengths. These sedimentation waves have similarities with Antarctic snow megadunes regarding their surface morphology, texture, grain size asymmetry, and internal stratigraphic architecture. Both sets of Martian sedimentation waves present young ice and occasional sastrugi fields, indicative of net accumulation, on their shallow-dipping upwind sides, their tops and the intervening troughs. Old layers of dusty ice, indicative of net ablation, are exhumed on the steep-dipping downwind sides of the larger waves. Smooth surfaces of coarse-grained ice, indicative of reduced accumulation associated with sublimation metamorphism, cover the steep-dipping downwind sides of the smaller waves. These surface characteristics and the internal stratigraphy revealed by radar soundings are consistent with the interpretation that both sets of Martian sedimentation waves grow and migrate upwind in response to the development of periodic accumulation/ablation patterns controlled by katabatic winds. The recognition of these sedimentation waves provides the basis for the development of a common model of ice/wind interaction at the surface of Martian and terrestrial glaciers. Martian smaller waves, characterized by reduced net accumulation on their downwind sides, are analogous to Antarctic snow megadunes that have been described so far. A terrestrial equivalent remains to be discovered for the larger Martian waves, characterized by net ablation on their downwind sides.

Simulation of radar echoes from Mars' surface/subsurface and inversion of surface media parameters

A two-layer model of Mars' regolith/bedrock media with a cratered rough surface/subsurface is presented for radar echo simulation of planetary exploration research. The numerical approach of geometric ray tracing for the scattering of rough surfaces, which is digitized by the triangulated network, is applied to the calculation of the scattering and imaging simulation of radar range echoes. Numerical simulations of a cratered rough surface generated by the Monte Carlo method are used to analyze the functional dependence of radar range echoes at 1–50 MHz center frequencies upon the surface/subsurface feature and the parameters of the layering media, that is, layer depth and dielectric properties. The radar range echoes from two areas of the real Mars surface, which is described by digital elevation model data with a resolution of 1 m × 1 m and a vertical error of less than 1 m, are also simulated and analyzed. Based on these simulations, this study presents a numerical imaging test of radar sounder at center frequencies 1–50 MHz for exploration of different dielectric regolith and bedrock media. The channel 50 MHz with high resolution might be an optimal frequency. Finally, inversion of the dielectric constants of the two-layer media and the regolith layer thickness are developed.

Bottom-up restructuring of ice

Water at the base of ice sheets can lead to faster ice flow. Radar sounding of the Greenland ice sheet reveals that refreezing of this water can also induce large changes in ice flow and structure.

Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet

Heterogeneous hydrologic, lithologic, and geologic basal boundary conditions can exert strong control on the evolution, stability, and sea level contribution of marine ice sheets. Geothermal flux is one of the most dynamically critical ice sheet boundary conditions but is extremely difficult to constrain at the scale required to understand and predict the behavior of rapidly changing glaciers. This lack of observational constraint on geothermal flux is particularly problematic for the glacier catchments of the West Antarctic Ice Sheet within the low topography of the West Antarctic Rift System where geothermal fluxes are expected to be high, heterogeneous, and possibly transient. We use airborne radar sounding data with a subglacial water routing model to estimate the distribution of basal melting and geothermal flux beneath Thwaites Glacier, West Antarctica. We show that the Thwaites Glacier catchment has a minimum average geothermal flux of ∼ 114 ± 10 mW/m(2) with areas of high flux exceeding 200 mW/m(2) consistent with hypothesized rift-associated magmatic migration and volcanism. These areas of highest geothermal flux include the westernmost tributary of Thwaites Glacier adjacent to the subaerial Mount Takahe volcano and the upper reaches of the central tributary near the West Antarctic Ice Sheet Divide ice core drilling site.

Dayside episodic ion outflow from Martian magnetic cusps and/or magnetosheath boundary motion associated with plasma oscillations

AbstractThe radar sounder on the Mars Express Spacecraft is able to make measurements of electron densities in the Martian ionosphere from both local electron plasma oscillations and remote soundings. A study of thousands of orbits shows that in some cases the electron plasma oscillations disappear and reappear abruptly near the upper boundary of the dayside ionosphere. In some cases, the Analyzer of Space Plasmas and Energetic Atoms (ASPERA‐3) data show clear evidence of upwardly accelerated ionospheric ions, on interconnected magnetic field lines. In other cases, ASPERA‐3 data show that when the plasma oscillations disappear, the spacecraft is in the magnetosheath and when they return, the ionospheric plasma reappears. These intermittent appearances of plasma suggest the multiple crossings of the magnetosheath boundary. The motion of the boundary or plasma clouds and ionospheric streamers (a relatively narrow strip of plasma attached to the ionosphere) can cause these multiple crossings.

Deeply incised submarine glacial valleys beneath the Greenland ice sheet

The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. A combination of sparse radar soundings of ice thickness and high-resolution ice motion data suggest that many submarine ice-covered valleys extend significantly deeper below sea level and farther inland than thought.

Mare volcanism: Reinterpretation based on Kaguya Lunar Radar Sounder data

The Lunar Radar Sounder (LRS) onboard Kaguya (SELENE) detected widespread horizontal reflectors under some nearside maria. Previous studies estimated that the depths of the subsurface reflectors were up to several hundreds of meters and suggested that the reflectors were interfaces between mare basalt units. The comparison between the reflectors detected in the LRS data and surface age maps indicating the formation age of each basalt unit allows us to discuss the lower limit volume of each basalt unit and its space and time variation. We estimated volumes of basalt units in the ages of 2.7 Ga to 3.8 Ga in the nearside maria including Mare Crisium, Mare Humorum, Mare Imbrium, Mare Nectaris, Mare Serenitatis, Mare Smythii, and Oceanus Procellarum. The lower limit volumes of the geologic units estimated in this study were on the order of 103 to 104 km3. This volume range is consistent with the total amount of erupted lava flows derived from numerical simulations of thermal erosion models of lunar sinuous rille formation and is also comparable to the average flow volumes of continental flood basalt units formed after the Paleozoic and calculated flow volumes of Archean komatiite flows on the Earth. The lower limits of average eruption rates estimated from the unit volumes were on the order of 10−5 to 10−3 km3/yr. The estimated volumes of the geologic mare units and average eruption rate showed clear positive correlations with their ages within the same mare basin, while they vary among different maria compared within the same age range.

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.

A radar map of Titan Seas: Tidal dissipation and ocean mixing through the throat of Kraken

We present a radar map of the Titan’s seas, with bathymetry estimated as proportional to distance from the nearest shore. This naïve analytic bathymetry, scaled to a recent radar sounding of Ligeia Mare, suggests a total liquid volume of ∼32,000km3, at the low end of estimates made in 2008 when mapping coverage was incomplete. We note that Kraken Mare has two principal basins, separated by a narrow (∼17km wide, ∼40km long) strait we refer to as the ‘throat’. Tidal currents in this strait may be dramatic (∼0.5m/s), generating observable effects such as dynamic topography, whirlpools, and acoustic noise, much like tidal races on Earth such as the Corryvreckan off Scotland. If tidal flow through this strait is the dominant mixing process, the two basins take ∼20 Earth years to exchange their liquid inventory. Thus compositional differences over seasonal timescales may exist, but the composition of solutes (and thus evaporites) over Croll–Milankovich timescales should be homogenized.

UAS-Based Radar Sounding of the Polar Ice Sheets

Both the Greenland and Antarctic ice sheets are currently losing mass and contributing to global sea level rise. To predict the response of these ice sheets to a warming climate, ice-sheet models must be improved by incorporating information on the bed topography and basal conditions of fast-flowing glaciers near their grounding lines. High-sensitivity, low-frequency radars with 2-D aperture synthesis capability are needed to sound and image fast-flowing glaciers with very rough surfaces and ice that contains inclusions. In response to this need, CReSIS developed an Unmanned Aircraft System (UAS) equipped with a dual-frequency radar that operates at approximately 14 and 35 MHz. The radar transmits 100-W peak power at a pulse repetition frequency of 10 kHz, operates from 20 W of DC power, and weighs approximately 2 kg. The UAS has a take-off weight of about 38.5 kg and a range of approximately 100 km per gallon of fuel. We recently completed several successful test flights of the UAS equipped with the dual-frequency radar at a field camp in Antarctica. The radar measurements performed as a part of these test flights represent the first-ever successful sounding of glacial ice with a UAS-based radar. We also collected data for synthesizing a 2-D aperture, which is required to prevent off-vertical scatter, caused by the rough surfaces of fast-flowing glaciers, from masking bed echoes. In this article, we provide a brief overview of the need for radar soundings of fast-flowing glaciers at low-frequencies and a brief description of the UAS and radar. We also discuss our field operations and provide sample results from data collected in Antarctica. Finally, we present our future plans, which include miniaturizing the radar and collecting measurements in Greenland.

Enhanced ionization of the Martian nightside ionosphere during solar energetic particle events

Electron densities in the Martian nightside ionosphere are more than 90% of time too low to be detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft. However, the relative number of ionograms with peak electron density high enough to be detected represents a good statistical proxy of the ionospheric density. We focus on solar energetic particle (SEP) events, and we analyze their effects on ionospheric formation. SEP time intervals were identified in situ using the background counts recorded by the ion sensor of the ASPERA‐3 instrument on board Mars Express. We show that peak electron densities during the SEP events are large enough to be detected in more than 30% of measurements, and, moreover, the reflections of the sounding signal from the ground almost entirely disappear. Nightside electron densities during SEP events are thus substantially increased as compared to normal nightside conditions.

Validation of FORMOSAT-3/COSMIC radio occultation electron density profiles by incoherent scatter radar data

Low Earth Orbiting satellites carrying a dual frequency GPS receiver onboard offer a unique opportunity to remote sensing of the global ionosphere on a continuous basis. No other profiling technique unifies profiling through the entire F2-layer with global coverage. The FORMOSAT-3/COSMIC data can make a positive impact on the global ionosphere study providing essential information about the height electron density distribution and particularly over regions that are not accessible with ground-based measuring instruments such as ionosondes and GPS dual frequency receivers. Therefore, it is important to verify occultation profiles with other techniques and to obtain experience in the reliability of their derivation. In the given study we present results of comparison of the electron density profiles derived from radio occultation measurements on-board FS-3/COSMIC and from the Kharkov incoherent scatter radar sounding.

Subsurface radar location of the putative ocean on Ganymede: Numerical simulation of the surface terrain impact

Exploration of subsurface oceans on Jupiter׳s icy moons is a key issue of the icy moons׳ geology. Radar is in fact the only sounding technique which is able to penetrate their icy mantles, which can be many kilometers thick.Surface clutter, i.e. scattering of the radio waves on the rough surface, is known to be one of the most important problems of subsurface radar probing. Adequate numerical modeling of this scattering is required on all stages of subsurface radar experiment, including design of an instrument, operational strategy planning and data interpretation.In the present paper, a computer simulation technique for numerical simulations of radar sounding of rough surfaces is formulated in general form. Subsurface radar location of the ocean beneath Ganymedian ice with chirp radar signals has been simulated.

High-resolution ice-thickness mapping in South Greenland

AbstractAirborne radar sounding is difficult in South Greenland because of the presence of englacial water, which prevents the signal from reaching the bed. Data coverage remains suboptimal for traditional methods of ice-thickness and bed mapping that rely on geostatistical techniques, such as kriging, because important features are missing. Here we apply two alternative approaches of high-resolution (~300m) ice-thickness mapping, that are based on the conservation of mass, to two regions of South Greenland: (1) Qooqqup Sermia and Kiattuut Sermiat, and (2) Ikertivaq. These two algorithms solve optimization problems, for which the conservation of mass is either enforced as a hard constraint, or as a soft constraint. For the first region, very few measurements are available but there is no gap in ice motion data, whereas for Ikertivaq, more ice-thickness measurements are available, but there are gaps in ice motion data. We show that mass-conservation algorithms can be used as validation tools for radar sounding. We also show that it is preferable to apply mass conservation as a hard constraint, rather than a soft constraint, as it better preserves elongated features, such as glacial valleys and ridges.

Radiological Monitoring of Borehole in Dei-Dei, Abuja, North Central Nigeria

Inhabitants in Dei-Dei area of Abuja consume groundwater that recharges from different lithologic units of subsurface structures due to inadequate public water supply.The water is consumed untreated and during drilling, it cuts across so many rock formations, to extents constitute radioactive elements which are to be evaluated. Vertical Electric Sounding and Shuttle Radar Topography mission was used to determine the structure of electric conductivity and map lineaments.Hydrogeologically motivated borehole with geophysical log data was drilled. Activity concentrations were analysed using high resolution co-axial HPGe gamma spectrometer system. The activity concentrations ranges from 45± 2 to 98 ± 6 Bq kg-1 for 232Th, 18 ± 2 to 37 ± 4 Bq kg-1 for 238U and 236 ± 32 Bq kg-1 to 1195±151 Bq kg-1 for 40K. Structurally, fractured interconnectivity attributed to low levels in some layers. Activity levels are within the limits, requires research within groundwater activity levels and rock geochemistry.

Reply to “Comments on “An Inversion of Planetary Rough Surface Permittivity From Radar Sounder Observations””

Presented is the reply to the comments on “An Inversion of Planetary Rough Surface Permittivity From Radar Sounder Observations”. We proved that in KA integral and in nadir direction and isotropic rough surface with zero slope, the surface reflection coefficient Ro can be moved out from the KA integral. We further proved that the received echo power and inversion of are also related with the area topography. Therefore, the simulated echoes based on rough surface model can now be applied to inversion of , as the simulated power with a proposed can iteratively approaches the real measurement at the same location.

Low-frequency radar sounding of ice in East Antarctica and southern Greenland

AbstractWe discuss a decameter-wavelength airborne radar sounder, the Warm Ice Sounding Explorer (WISE), that provides ice thickness in areas where radar signal penetration at higher frequencies is expected to be limited. Here we report results for three campaigns conducted in Greenland (2008, 2009, 2010) and two in Antarctica (2009, 2010). Comparisons with higher-frequency radar data indicate an accuracy of ±55 m for ice-thickness measurements in Greenland and ±25 m in Antarctica. We also estimate ice thickness of the Qassimiut lobe in southwest Greenland, where few ice-thickness measurements have been made, demonstrating that WISE penetrates in strongly scattering environments.

Comments on “An Inversion of Planetary Rough Surface Permittivity From Radar Sounder Observations”

Ye and Jin presented a method to derive the soil dielectric permittivity from radar surface echoes when a Digital Elevation Model of the observed region is known. However, this method has been already extensively applied on Mars, and the scientific protocol to demonstrate its efficiency only derives the numerical uncertainties inherent to the simulation tool used by the authors.

Variability of temperature and thickness of permafrost active layer at coastal sites of Svalbard

Abstract We present the variability of the thermal state and thickness of permafrost active layer at the raised marine beaches in Svalbard. The investigations were carried out using direct probing, thaw tube, ground temperature and radar soundings at Holocene strand plains 10-20 m a.s.l. in Fuglebergsletta (SW Spitsbergen) and at the shore of Kinnvika Bay (Nordaustlandet). Their results were compared to those obtained at other coastal sites in Svalbard. The ground temperature measurements were conducted in 2009 on August, recognized as the standard month for the maximum thawing during the last decade. The studied sites are typical for close to extreme active layer conditions on Svalbard. In Hornsund, the thawing depth exceeded 2 m, while in Kinnvika the active layer was thinner than 1 m. In Svalbard, the depth of thawing decreases generally from south to north and from the open sea coast to the central parts of islands. These differences are the consequence of diverse climatic conditions strongly determined by the radiation balance modified by a number of regional (e.g. ocean circulation) and local (e.g. duration of snow deposition) conditions.

The influence of the ionosphere in subsurface Martian soil sounding experiments and a method of its correction

The problem of radar sounding of the Martian soil from an orbiting spacecraft is analyzed. The influence of the ionosphere on the results of remote sounding is revealed through the results of numerical modeling and actual subsurface soil sounding experiments carried out using the MARSIS radar sounder aboard the MarsExpress spacecraft. A method of corr ection of the dispersion distortion is proposed and tested through radiolocation of the polar cap on Mars.