Smooth Terrain Research Articles

Turbulence length scales in a low-roughness near-neutral atmospheric surface layer

This paper investigated the integral length scales of turbulence in a low-roughness atmospheric surface layer (ASL), characterised by very smooth terrain in the Utah desert during near-neutral conditions, and evaluated the Engineering Sciences Data Unit (ESDU) 85020 and 86010 predictions for the turbulence length scales in a low-roughness ASL. The correlation integral method was used to estimate the integral length scales of the velocity components with longitudinal, lateral and vertical separations from sonic measurements on a vertical tower and spanwise array in the Surface Layer Turbulence and Environmental Science Test (SLTEST) field experiment. It was found that the longitudinal integral length scales calculated using near-neutral SLTEST data followed a logarithmic relationship with height proportional to the mean velocity profile with approximately constant integral time scale, however the sizes of the longitudinal components of the energy-containing eddies in the low-roughness flat terrain were 2–3 times smaller than those previously measured during field experiments in open country terrains. The calculated length scales with longitudinal separations over the very smooth terrain characteristics of the salt flats at Dugway were not consistent with those predicted by ESDU 85020. In contrast, the scaling of the lateral and vertical components of the three-dimensional turbulence structure with respect to the longitudinal component in the low-roughness ASL were consistent with similarity theory predictions in ESDU 86010 that the scaling ratios are independent of terrain roughness. Furthermore, this confirms the large dependence of the longitudinal turbulence length scales on the upstream terrain roughness and highlights the large variation of turbulence length scales observed at different low-roughness sites in the literature.

DYNAMICS AND ENVIRONMENTAL STATE OF VEGETABLE COVERAGE AND LAND USE IN LANDSCAPE REGIONS OF THE SOUTHWESTERN PORTION OF THE BRAZILIAN STATE OF MATO GROSSO

The objective of this article is to investigate the space-time dynamics of vegetation cover and land use and the Environmental State of the landscape regions of the southwestern portion of the Brazilian state of Mato Grosso.The vegetation cover and land use maps were generated from the Landsat 5 satellite images from 1984, and Landsat 8 from 2013 in the SPRING software. Map quantifications and layouts were elaborated withArcGis. The regionalization and analysis of the environmental state of the landscape were made through a regional geoecological matrix. From the results obtained, it was verified that the anthropic uses in the period of study were expanded by 134.08% while the vegetal coverings were reduced by 21.66% and the water bodies by 39%. Pasture is the predominant land use in the region, 24.09% (31,335.86 km²), mainly occupying the flat and smooth wavy terrain. Forest cover totaled 66.36% (84,967.12 km2), being found mainly in forest fragments, in which the larger territorial dimensions are either protected by environmental legislation or located in indigenous lands. Eight landscape regions were delimited in the southwest portion of Mato Grosso, including the Paraguay River Depression, which presents the landscape with the highest percentage of anthropic uses, predominantly the Degraded Environmental State. It was concluded that there is a need to adopt land use practices that minimize the environmental degradation of landscape regions, considering that during the period under investigation, the expansion of anthropic uses, mainly Livestock, directly influenced the suppression of vegetation cover.

Evaluation of Peak Transmission Line Conductor Reactions Under Downburst Winds Using Optimization and Simplified Approaches

Transmission line structures, though designed per code provisions, suffered several failures worldwide in the past. As reported in the body of the available literature, more than 90% of those failures are due to sever localized wind events such as downbursts. Several recent studies emphasised on the importance of the conductor loads and how their forces contribute to the failure of the towers. The velocity profile and loads associated with a downburst wind field vary significantly with the change in its configuration. Previous studies, focused on identifying the critical transmission tower members that are likely to fail during a downburst event and the associated critical downburst configurations. In all these studies, a smooth terrain was assumed where the effect of terrain roughness is not considered. In the current study, an evolutionary optimization algorithm is coupled with a semi-closed form solution technique to predict the maximum conductor’s reactions under downburst wind field and the associated critical downburst configurations. A Large Eddy Simulation (LES) model of downbursts impinging on various exposure conditions, developed in a previous study, has been incorporated to predict wind forces acting on the conductor line. It is believed that the current study is the first of its kind to provide critical downburst configurations that lead to maximum conductors’ reactions while considering the effect of terrain exposure (open, countryside, suburban, and urban). Based on the optimal downburst configuration identified for each type of terrain roughness, a simple and practical approach in the form of simple equations and a set of charts to evaluate maximum reactions has been developed and validated. The simplified approach is suitable for practitioner engineers to accurately and rapidly evaluate maximum conductor reactions under downburst events considering multiple terrain conditions.

Upper-plate deformation of Late Pleistocene marine terraces in the Trinidad, California, coastal area, southern Cascadia subduction zone

Abstract Forming at sea level, uplifted shore platforms serve as long-term geodetic markers. The spatial distribution and elevation of marine terrace sequences offer insight into regional tectonics. In the Trinidad coastal area (California, USA), active tectonic processes reflect upper-plate deformation above the southern extent of the Cascadia subduction megathrust. A set of five uplifted and deformed Late Pleistocene marine terraces is preserved in the Trinidad region and provides an opportunity to analyze regional uplift, folding, and faulting. Using lidar imagery embedded within a GIS, we employ a surface classification model (SCM) that identifies uplifted marine terraces on the basis of their micro-topographical characteristics, i.e., low slope and low roughness. The SCM-based identification of marine terraces both supplements and verifies existing field mapping. We demonstrate the utility of the SCM, which can be applied to a variety of surface terrain analysis investigations that seek to identify smooth and/or rough terrain features, e.g., terraces and fault scarps. Age assignments for the five marine terraces, which range from 80 ka to <500 ka, are based on paleo–sea cliff geomorphology and soil development trends. Specifically, the steepest, highest, and most prominent paleo–sea cliff, which is associated with terrace number 3, is correlated to the long-duration sea-level highstand centered at 125 ka (marine isotope stage 5e), exemplifying a novel method in relative age assignment for Pleistocene geomorphic features. Based on these age assignments, the average maximum uplift rates in the Trinidad coastal area are ∼1.0 m/k.y., and the average long-term uplift rate diminishes westward to ∼0.4 – 0.5 m/k.y. on the downthrown side of the Trinidad fault. Based on analysis of deformation using the high-resolution lidar imagery of the marine terraces, the Trinidad hanging-wall anticline represents a fault propagation fold that ceased to be active when the associated reverse fault, the Trinidad fault, daylighted to the surface ca. 80–100 ka. Based on deformation tilts of a marine terrace with an assigned age of 200 ka, the Trinidad anticline has accommodated at least 1 km of shortening in the last 200 k.y., which represents at least 2% of the convergence of the Juan de Fuca plate relative to North America over the same time period. Overall, both the hanging wall and the footwall of the Trinidad fault show long-term positive rock uplift, which implies that the Trinidad anticline and fault are contained within the hanging wall of a deeper structure. Therefore, the Trinidad fault likely splays off of the Cascadia subduction zone megathrust or off of a deeper thrust fault that splays off of the megathrust.

A Hybrid Tracked-Wheeled Multi-Directional Mobile Robot

Abstract This paper presents the novel design and integration of a mobile robot with multi-directional mobility capabilities enabled via a hybrid combination of tracks and wheels. Tracked and wheeled locomotion modes are independent from one another, and are cascaded along two orthogonal axes to provide multi-directional mobility. An actuated mechanism toggles between these two modes for optimal mobility under different surface-traction conditions, and further adds an additional translational axis of mobility. That is, the robot can move in the longitudinal direction via the tracks on rugged terrain for high traction, in the lateral direction via the wheels on smooth terrain for high-speed locomotion, and along the vertical axis via the translational joint. Additionally, the robot is capable of yaw axis mobility using differential drives in both tracked and wheeled modes of operation. The paper presents design and analysis of the proposed robot along with a dynamic stabilization algorithm to prevent the robot from tipping over while carrying an external payload on inclined surfaces. Experimental results using an integrated prototype demonstrate multi-directional capabilities of the mobile platform and the dynamic stability algorithm to stabilize the robot while carrying various external payloads on inclined surfaces measuring up to 2.5 kg and 10 deg, respectively.

Density distribution of asteroid 25143 Itokawa based on smooth terrain shape

The shape and internal structure of an asteroid is a result of its violent collisional history, and Asteroid 25143 Itokawa is an important target for investigating the internal structure and formation processes associated with rubble pile asteroids. The surface of Itokawa contains numerous boulders and is very rough, but 20% of the surface is covered with centimeter-sized gravels that are called ”smooth terrain”. These flat areas are associated with low areas of the gravitational potential and are considered to be formed by down-slope migration and accumulation of pebbles. We propose a method to constrain the interior density distribution of an asteroid by modeling the gravity field and fitting the smooth terrains to equi-potential surfaces. Density models that are composed of two distinct lobes best explain the data if the ”head” and ”body” have different densities of 2,450 kg/m3 and 1,930 kg/m3, respectively. Alternatively, the two lobes could have comparable densities if there was a compressed ”neck” of higher density between the two. Three layer models that treat the densities of the head, neck and body separately are largely unconstrained. However, when using an independent estimate of the center-of-mass/center-of-figure offset as determined from modeling the YORP spin-up of Itokawa, our models require the density of the head to be larger than the global average.

Comparing the accuracy of estimated terrain elevations across spatial resolution

ABSTRACTTerrain is modelled in Geographic Information Science on a grid, assuming that elevation values are constant within any single pixel of a Digital Elevation Model (DEM). Pixels are considered flat and rigid, for computational simplicity (a ‘rigid pixel’ paradigm). This paradigm does not account for the slope and curvature of terrain within each pixel, generating imprecise measurements, particularly as pixel size increases or in uneven terrain. This paper relaxes the rigid pixel assumption, allowing for possible sub-pixel variations in slope and curvature (a ‘surface-adjusted’ paradigm). This paper compares different interpolation methods to investigate sub-pixel variations for estimating elevation of arbitrary points given a regular grid. Tests interpolating elevation values for 20,000 georeferenced off-centroid random points from a regular grid DEM are presented, using a variety of exact and inexact local deterministic interpolation methods within contiguity configurations incorporating first and second order neighbours. The paper examines the accuracy of surface-adjusted estimations across a progression of spatial resolutions (10 m, 30 m, 100 m, and 1,000 m DEMs) and a suite of terrain types varying in latitude, altitude, slope, and roughness, validating off-centre estimates against direct elevation measurements on 3 m resolution lidar DEM. Results illustrate that the Bi-quadratic and Bi-cubic interpolation methods outperform Weighted Average, Linear, and Bi-linear methods at coarse resolutions and in rough or non-uniform terrain. In smooth or flat terrain and at finest resolutions, the interpolation method impacts estimation accuracy less or not at all. The type of contiguity configuration appears to play a role in estimation errors as well, with tighter neighbourhoods exhibiting higher accuracy. The analysis also examined regularized mathematical surfaces, adding autocorrelated randomly distributed noise to simulate terrain. The results of experiments based on regularized smooth mathematical surfaces do not translate directly to terrain modelling. The analysis also considers the balance between the increased computation times needed to measure surface-adjusted elevation against improvements in accuracy.

Effects of ground roughness on near-surface flow field of a tornado-like vortex

Roughness of a terrain is an important parameter that influences the near-ground flow field of tornadoes. In this study, both stationary and translating tornado-like vortices were simulated in a laboratory to investigate the influence of ground roughness on their flow fields. The near-ground flow fields, over the smooth and rough terrains, were studied using a mini version (1:3-scale) of the ISU tornado simulator and a 2D-PIV system for a stationary tornado and using the ISU tornado simulator and a pressure-based anemometer for a translating tornado. Main goal of this study is to examine the influence of ground roughness on tornado flow field. The results show that, for the stationary tornado, the flow regime transitioned from a multi-celled core structure over a smooth terrain at a higher swirl ratio to a single or dual-celled core structure over the rough terrain. A significant decrease in tangential velocity and core radius, and an increase in vertical and radial velocities and turbulent kinetic energy near the center of the tornado were also observed. For the translating tornado, ground roughness reduced the core radius, increased the radial velocity toward the center of rotation, and moved the location of the maximum horizontal velocity toward the front side of the tornado center close to the ground. There was a decrease in local or corner-flow swirl ratio in both stationary and translating tornadoes for the rough terrains compared with the smooth one.

Numerical Study of Turbulent Flow Fields Over Steep Terrain by Using Modified Delayed Detached-Eddy Simulations

Turbulent flow fields over a two-dimensional steep ridge and three-dimensional steep hill with rough and smooth surfaces are investigated by using a delayed detached-eddy simulation (DDES) with the specified height as a new control parameter. The applicability of typical turbulence models in previous studies is evaluated by using validation metrics. While all turbulence models simulate the turbulent flow fields over the steep rough terrain well, the k − e model overestimates the mean wind speed and underestimates the turbulent kinetic energy over steep, smooth terrain. The large-eddy simulation captures the large-scale vortices and improves the mean wind speed, but overestimates the turbulent kinetic energy due to the inaccurate specification of the surface roughness. The detached-eddy simulation considering the surface roughness shows further improvement, but still overestimates the turbulent kinetic energy, since the region using the Reynolds-averaged Navier–Stokes model is too thin. The modified DDES model with a new control parameter is suitable for the prediction of the mean wind speed and turbulence as demonstrated by the visualization of instantaneous flow fields through vortex cores, and a quadrant analysis to examine the organized motion, with strong organized motions identified in the wake region of smooth terrain. Roller vortices are significant on the lee side of the two-dimensional smooth ridge, while horseshoe vortices appear in the wake region of the three-dimensional smooth hill.

Thermal inertia and roughness of the nucleus of comet 67P/Churyumov–Gerasimenko from MIRO and VIRTIS observations

Aims.Using data from the Rosetta mission to comet 67P/Churyumov–Gerasimenko, we evaluate the physical properties of the surface and subsurface of the nucleus and derive estimates for the thermal inertia (TI) and roughness in several regions on the largest lobe of the nucleus.Methods.We have developed a thermal model to compute the temperature on the surface and in the uppermost subsurface layers of the nucleus. The model takes heat conduction, self-heating, and shadowing effects into account. To reproduce the brightness temperatures measured by the MIRO instrument, the thermal model is coupled to a radiative transfer model to derive the TI. To reproduce the spatially resolved infrared measurements of the VIRTIS instrument, the thermal model is coupled to a radiance model to derive the TI and surface roughness. These methods are applied to Rosetta data from September 2014.Results.The resulting TI values from both instruments are broadly consistent with each other. From the millimetre channel on MIRO, we determine the TI in the subsurface to be <80 JK−1m−2s−0.5for the Seth, Ash, and Aten regions. The submillimetre channel implies similar results but also suggests that higher values could be possible. A low TI is consistent with other MIRO measurements and in situ data from the MUPUS instrument at the final landing site of Philae. The VIRTIS results give a best-fitting value of 80 JK−1m−2s−0.5and values in the range 40–160 JK−1m−2s−0.5in the same areas. These observations also allow the subpixel scale surface roughness to be estimated and compared to images from the OSIRIS camera. The VIRTIS data imply that there is significant roughness on the infrared scale below the resolution of the available shape model and that, counter-intuitively, visually smooth terrain (centimetre scale) can be rough at small (micrometre–millimetre) scales, and visually rough terrain can be smooth at small scales.

The mineralogy of Ceres’ Nawish quadrangle

Quadrangle Ac-H-08 Nawish is located in the equatorial region of Ceres (Lat 22°S-22°N, Lon 144°E- 216°E), and it has variable mineralogy and geology. Here, we report on the mineralogy using spectra from the Visible and InfraRed (VIR) mapping spectrometer onboard the NASA Dawn mission. This quadrangle has two generally different regions: the cratered highlands of the central and eastern sector, and the eastern lowlands. We find this dichotomy is also associated with differences in the NH4-phyllosilicates distribution. The highlands, in the eastern part of the quadrangle, appear depleted in NH4-phyllosilicates, conversely to the lowlands, in the north-western side. The Mg-phyllosilicates distribution is quite homogeneous across Nawish quadrangle, except for few areas. The 2.7 µm band depth is lower in the south-eastern part, e.g. in the Azacca ejecta and Consus crater ejecta, and the band depth is greatest for the Nawish crater ejecta, and indicates the highest content of Mg-phyllosilicates of the entire quadrangle. Our analysis finds an interesting relationship between geology, mineralogy, topography, and the age in this quadrangle. The cratered terrains in the highlands, poor in NH4 phyllosilicates, are older (̴2 Ga). Conversely, the smooth terrain, such as with Vindimia Planitia, is richer in ammonia-bearing phyllosilicates and is younger (̴1 Ga). At the local scale, Ac-H-8 Nawish, displays several interesting mineralogical features, such as at Nawish crater, Consus crater, Dantu and Azzacca ejecta, which exhibit localized Na-carbonates deposits. This material is superimposed on the cratered terrains and smooth terrains and shows the typical depletion of phyllosilicates, already observed on Ceres in the presence of Na-carbonates.

A Gravity Wave Drag Matrix for Complex Terrain

Abstract We propose a simplified scheme to predict mountain wave drag over complex terrain using only the regional-average low-level wind components U and V. The scheme is tuned and tested on data from the South Island of New Zealand, a rough and highly anisotropic terrain. The effect of terrain anisotropy is captured with a hydrostatically computed, 2 × 2 positive-definite wave drag matrix. The wave drag vector is the product of the wind vector and the drag matrix. The nonlinearity in wave generation is captured using a Gaussian terrain smoothing inversely proportional to wind speed. Wind speeds of |U| = 10, 20, and 30 m s−1 give smoothing scales of L = 54, 27, and 18 km, respectively. This smoothing treatment of nonlinearity is consistent with recent aircraft data and high-resolution numerical modeling of waves over New Zealand, indicating that the momentum flux spectra shift to shorter waves during high-drag conditions. The drag matrix model is tested against a 3-month time series of realistic full-physics wave-resolving flow calculations. Correlation coefficients approach 0.9 for both zonal and meridional drag components.

Exposed bright features on the comet 67P/Churyumov–Gerasimenko: distribution and evolution

Context. Since its arrival at the comet 67P/Churyumov–Gerasimenko in August 2014, the Rosetta spacecraft followed the comet as it went past the perihelion and beyond until September 2016. During this time there were many scientific instruments operating on board Rosetta to study the comet and its evolution in unprecedented detail. In this context, our study focusses on the distribution and evolution of exposed bright features that have been observed by OSIRIS, which is the scientific imaging instrument aboard Rosetta. Aims. We envisage investigating various morphologies of exposed bright features and the mechanisms that triggered their appearance. Methods. We co-registered multi-filter observations of OSIRIS images that are available in reflectance. The Lommel–Seeliger disk function was used to correct for the illumination conditions and the resulting colour cubes were used to perform spectrophotometric analyses on regions of interest. Results. We present a catalogue of 57 exposed bright features observed on the nucleus of the comet, all of which are attributed to the presence of H2O ice on the comet. Furthermore, we categorise these patches under four different morphologies and present geometric albedos for each category. Conclusions. Although the nucleus of 67P/Churyumov–Gerasimenko appears to be dark in general, there are localised H2O ice sources on the comet. Cometary activity escalates towards the perihelion passage and reveals such volatile ices. We propose that isolated H2O ice patches found in smooth terrains in regions, such as Imhotep, Bes, and Hapi, result from frost as an aftermath of the cessation of the diurnal water cycle on the comet as it recedes from perihelion. Upon the comet’s return to perihelion, such patches are revealed when sublimation-driven erosion removes the thin dust layers that got deposited earlier. More powerful activity sources such as cometary outbursts are capable of revealing much fresher, less contaminated H2O ice that is preserved with consolidated cometary material, as observed on exposed patches resting on boulders. This is corroborated by our albedo calculations that attribute higher albedos for bright features with formations related to outbursts.

Investigation into an efficient numerical modelling approach for estimating path-loss over variable terrain

Different studies have been conducted for radio wave propagation in troposphere using different numerical modelling approaches. The most reliable approach is based on parabolic wave equation (PWE). The modelling of PWE is approached using different numerical schemes that include Split-step Fourier Transform Method (SSFM), Finite Element/Difference method and Wavelet based numerical method. The conventional Finite Element/Difference method are less accurate and/or computationally more expensive. While in comparison, split-step wavelet method (SSWM) is highly accurate and computationally very efficient. The SSWM has been previously used for modelling of PWE with smooth terrain. However, the real conditions are completely different as they contain variable terrain. The irregularities in surface of terrain have considerable influence because of reflection and diffraction on radio-wave propagation. In order to develop an effective communication system, a model that properly incorporates the reflection parameters from the variable terrain. In this research work, the SSWM is proposed for modelling of PWE for radio wave propagation over variable terrain. In SSWM, compactly supported wavelet of Daubechies 6 are used as bases. Obtained results accurately accounts the reflection from rough terrain surface and shows good agreement with SSFM.

Hybrid Locomotion Evaluation for a Novel Amphibious Spherical Robot

We describe the novel, multiply gaited, vectored water-jet, hybrid locomotion-capable, amphibious spherical robot III (termed ASR-III) featuring a wheel-legged, water-jet composite driving system incorporating a lifting and supporting wheel mechanism (LSWM) and mechanical legs with a water-jet thruster. The LSWM allows the ASR-III to support the body and slide flexibly on smooth (flat) terrain. The composite driving system facilitates two on-land locomotion modes (sliding and walking) and underwater locomotion mode with vectored thrusters, improving adaptability to the amphibious environment. Sliding locomotion improves the stability and maneuverability of ASR-III on smooth flat terrain, whereas walking locomotion allows ASR-III to conquer rough terrain. We used both forward and reverse kinematic models to evaluate the walking and sliding gait efficiency. The robot can also realize underwater locomotion with four vectored water-jet thrusters, and is capable of forward motion, heading angle control and depth control. We evaluated LSWM efficiency and the sliding velocities associated with varying extensions of the LSWM. To explore gait stability and mobility, we performed on-land experiments on smooth flat terrain to define the optimal stride length and frequency. We also evaluated the efficacy of waypoint tracking when the sliding gait was employed, using a closed-loop proportional-integral-derivative (PID) control mechanism. Moreover, experiments of forward locomotion, heading angle control and depth control were conducted to verify the underwater performance of ASR-III. Comparison of the previous robot and ASR-III demonstrated the ASR-III had better amphibious motion performance.

Study on the strength loss of Multi-hop HF Radio Propagation

The reflections of high frequency (HF) radio waves between ionosphere and earth’s surface make long-distance information transmission possible. In this paper, the propagation process of radio signals was analyzed and the ionosphere was simplified. Considering the strength loss of signals that occurs in the travelling process and at the reflection points, two pairs of differential equations and integral equations were established to simulate the strength variations of HF radio waves and noises. A different equation of SNR was also developed, which utilized the failure threshold of signal-noise-ratio (SNR) as a criterion to evaluate the effectiveness of signals. Meanwhile, the pace of SNR attenuation was simulated when reflections happens on calm ocean, turbulent ocean, smooth terrain and rugged terrain.

IMPROVING RUNWAY STRIP PERFORMANCE TO FULFILL INTERNATIONAL REQUIREMENTS THROUGH ECO-EFFICIENT SOIL TREATMENTS: CASE STUDY OF A MAJOR ITALIAN AIRPORT

The paper presents a case study of a significant intervention conducted on a major Italian airport for improving the structural and functional properties of the runway safety STRIP in order to fulfill specific national and international standards. The STRIP had to accomplish strict requirements in terms of the maximum longitudinal and transversal terrain slope and minimum values of bearing capacity; in particular, soil bearing capacity was identified as the main lack and thus the most urgent action to be carried out in the airport. However, the STRIP itself is located in a very critical area due to its closeness to the runway and several constraints were therefore identified during the design stage. The optimal strategy was identified as the one that minimized the intervention timing and costs, reducing the handling of construction material to/from the airport, avoiding delays to the air traffic, and maximizing the performance of the treated soils in terms of bearing capacity. In this framework, an energy-controlled stabilization technique of in-situ soils was developed. Several measurements, in both laboratory and field environment, were also conducted at different stages: i) before the intervention took place, ii) during the construction stage, and iii) at the conclusion of the work to monitor and validate the expected results. The intervention was able to provide the STRIP areas with a smooth surface presenting terrain slopes and bearing capacity in accordance with the standards. The illustrated methodology could also be applied to other airports saving time, costs, materials, and limiting air traffic delays.

Viscous relaxation as a prerequisite for tectonic resurfacing on Ganymede: Insights from numerical models of lithospheric extension

Ganymede’s bright terrain formed during a near-global resurfacing event (or events) that produced both heavily tectonized and relatively smooth terrains. The mechanism(s) by which resurfacing occurred on Ganymede (e.g., cryovolcanic or tectonic), and the relationship between the older, dark and the younger, bright terrain are fundamental to understanding the geological evolution of the satellite. Using a two-dimensional numerical model of lithospheric extension that has previously been used to successfully simulate surface deformation consistent with grooved terrain morphologies, we investigate whether large-amplitude preexisting topography can be resurfaced (erased) by extension (i.e., tectonic resurfacing). Using synthetically produced initial topography, we show that when the total relief of the initial topography is larger than 25–50 m, periodic groove-like structures fail to form. Instead, extension is localized in a few individual, isolated troughs. These results pose a challenge to the tectonic resurfacing hypothesis. We further investigate the effects of preexisting topography by performing suites of simulations initialized with topography derived from digital terrain models of Ganymede’s surface. These include dark terrain, fresh (relatively deep) impact craters, smooth bright terrain, and a viscously relaxed impact crater. The simulations using dark terrain and fresh impact craters are consistent with our simulations using synthetic topography: periodic groove-like deformation fails to form. In contrast, when simulations were initialized with bright smooth terrain topography, groove-like deformation results from a wide variety of heat flow and surface temperature conditions. Similarly, when a viscously relaxed impact crater was used, groove-like structures were able to form during extension. These results suggest that tectonic resurfacing may require that the amplitude of the initial topography be reduced before extension begins. We emphasize that viscous relaxation may be the key to enabling tectonic resurfacing, as the heat fluxes associated with groove terrain formation are also capable of reducing crater topography through viscous relaxation. For long-wavelength topography (large craters) viscous relaxation is unavoidable. We propose that the resurfacing of Ganymede occurred through a combination of viscous relaxation, tectonic resurfacing, cryovolcanism and, at least in a few cases, band formation. Variations in heat flow and strain magnitudes across Ganymede likely produced the complex variety of terrain types currently observed.

Meteorological and environmental variables affect flight behaviour and decision‐making of an obligate soaring bird, the California Condor Gymnogyps californianus

The movements of animals are limited by evolutionary constraints and ecological processes and are strongly influenced by the medium through which they travel. For flying animals, variation in atmospheric conditions is critically influential in movement. Obligate soaring birds depend on external sources of updraft more than do other flying species, as without that updraft they are unable to sustain flight for extended periods. These species are therefore good models for understanding how the environment can influence decisions about movement. We used meteorological and topographic variables to understand the environmental influences on the decision to engage in flight by obligate soaring and critically endangered California Condors Gymnogyps californianus. Condors were more likely to fly, soared at higher altitudes and flew over smoother terrain when weather conditions promoted either thermal or orographic updrafts, for example when turbulence and solar radiation were higher and when winds from the east and north were stronger. However, increased atmospheric stability, which is inconsistent with thermal development but may be associated with orographic updrafts, was correlated with a somewhat higher probability of being in flight at lower altitudes and over rougher terrain. The close and previously undescribed linkages between Condor flight and conditions that support development of thermal and orographic updrafts provide important insight into the behaviour of obligate soaring birds and into the environmental parameters that may define the currently expanding distribution of Condors within and outside the state of California.

Characteristics of small young lunar impact craters focusing on current production and degradation on the Moon

Analysing the size-frequency distribution of very small lunar craters (sized below 100 m including ones below 10 m) using LROC images, spatial density and related age estimations were calculated for mare and terra terrains. Altogether 1.55 km2 area was surveyed composed of 0.1–0.2 km2 units, counting 2784 craters. The maximal areal density was present at the 4–8 m diameter range at every analysed terrain suggesting the bombardment is areally relatively homogeneous.Analysing the similarities and differences between various areas, the mare terrains look about two times older than the terra terrains using <100 m diameter craters. The calculated ages ranged between 13 and 20 Ma for mare, 4–6 Ma for terra terrains. Substantial fluctuation (min: 936 craters/km2, max: 2495 craters/km2) was observed without obvious source of nearby secondaries or fresh ejecta blanket produced fresh crater. Randomness analysis and visual inspection also suggested no secondary craters or ejecta blanket from fresh impact could contribute substantially in the observed heterogeneity of the areal distribution of small craters – thus distant secondaries or even other, poorly known resurfacing processes should be considered in the future. The difference between the terra/mare ages might come only partly from the easier identification of small craters on smooth mare terrains, as the differences were observed for larger (30–60 m diameter) craters too. Difference in the target hardness could more contribute in this effect.It was possible to separate two groups of small craters based on their appearance: a rimmed thus less eroded, and a rimless thus more eroded one. As the separate usage of different morphology groups of craters for age estimation at the same area is not justifiable, this was used only for comparison. The SFD curves of these two groups showed characteristic differences: the steepness of the fresh craters' SFD curves are similar to each other and were larger than the isochrones. The eroded craters’ SFD curves also resemble to each other, which are less steep than the isochrones. These observations confirm the expectation that as the time passes by, rims are erased and depressions became shallower, presenting such observations for the first time in this small crater size range.