Red Slope Research Articles

Study on response characteristics of red clay slope under evaporation rainfall condition

Evaporation rainfall is one of the main causes of slope failure. Red clay belongs to special soil, and the failure mode of the slope is different from that of the general soil slope. In this paper, based on the theory of similarity simulation, a test model of red clay slope similar to the prototype is established in a certain proportion. Sensors are embedded in different positions of the slope to carry out the change rule of physical and mechanical indexes of the red clay slope under the condition of evaporation and rainfall. The results show that the water content of the slope increases during the rainfall period, the surface water content of the slope is obviously affected by the rainfall intensity, and the water content of the slope decreases in the drying period. Under the action of evaporation and rainfall, the internal temperature of slope is stable, and the surface temperature changes significantly. The pore water pressure of the top, shoulder and slope changes little with the times of evaporation and rainfall, and the pore water pressure at the foot of slope is obviously affected by evaporation and rainfall. Evaporation rainfall causes obvious horizontal displacement of red clay slope. The earth pressure increases in the rainfall period and decreases in the static and dry periods. With the increase of evaporation rainfall times, the earth pressure increases gradually.

Rigorous light-scattering simulations of nanophase iron space-weathering effects on reflectance spectra of olivine grains

We present a multi-scale light-scattering model that is capable of simulating the reflectance spectra of a regolith layer. In particular, the model can be applied to a case where the regolith grains have varying amounts of nanophase inclusions due to space weathering of the material. As different simulation tools are employed for different size scales of the target geometry (roughly, nano-, micro-, and millimeter scales), the particle size effects, the surface reflections, and the volume scattering can all be properly accounted for. Our results with olivine grains and nanophase iron inclusions verify the role of the nanoinclusions in the reflectance spectra of space-weathered materials. Together with the simulation results, we give simplified explanations for the space-weathering effects based on light scattering, namely the decrease of albedo, the general increase of the red spectral slope, and the dampening of the spectral bands. We also consider the so-called ultraviolet bluing effect, and show how the change in the spectral slope over the ultraviolet–visual wavelengths is due to the decrease of reflectance in the visual wavelengths rather than the increase of reflectance in the ultraviolet part.

Distribution Pattern of Anchorage Stress and Water Sensitivity Analysis of Red Clay

Red clay is a special soil layer with complex engineering properties distributed in tropical and subtropical regions. An anchor cable support is a common form of red clay slope support. The effectiveness of the anchor cable support is mainly determined by the anchoring force provided by the red clay stratum. Increase of the water content will lead to the rapid deterioration of the mechanical properties of red clay, which will lead to the reduction of the anchoring force of the slope anchor cable and lead to the failure of the support. Based on the classical Phillips and uniform anchorage shear stress distribution theory, this paper puts forward a uniform-exponential distribution pattern of anchorage shear stress according to the specific characteristics of red clay by using the characteristics of the peak shear strength and residual shear strength of the rock and soil mass. With increasing anchorage force, the dynamic evolution (single exponential distribution ⟶ double single exponential distribution ⟶ uniform index exponential complex distribution ⟶ uniform distribution) of the anchorage shear stress is analysed. Based on the peak and residual test of the cohesive force and internal friction angle, the relationship between the anchoring force and buried depth and water content is established by analysing the factors influencing the anchoring force. It can be found from the field test that, according to the relationship established, the limit anchorage force of the anchor cable in the red clay stratum can be calculated and the water sensitivity of the anchor cable’s limit anchorage force can be quantitatively analysed.

A long-term monitoring dataset of soil moisture content under different utilization modes of red soil slope land in Taoyuan Agro-ecology Research Station, 2004–2014

A long-term monitoring dataset of soil moisture content under different utilization modes of red soil slope land in Taoyuan Agro-ecology Research Station, 2004–2014

A conterminous United States analysis of the impact of Landsat 5 orbit drift on the temporal consistency of Landsat 5 Thematic Mapper data

The Landsat 5 orbit changed more than expected over its three-decade mission life. Previous modelling research indicated that the resulting Landsat 5 overpass time and so acquisition solar zenith differences will have caused non-negligible reflectance and normalized difference vegetation index (NDVI) temporal differences. Rather than use a modelling approach this paper presents the results of a comprehensive examination of the Landsat 5 Thematic Mapper (TM) data. Ten years of summer Landsat 5 TM Analysis Ready Data (ARD) sampled at >19.3 million 30 m pixel locations across the conterminous United States (CONUS) are considered. The acquisition solar zenith, red, near infrared (NIR), shortwave infrared (SWIR) (~2.1 μm) surface reflectance, and NDVI, are compared between five consecutive periods (1995 versus 2006, 1996 versus 2007, 1997 versus 2008, 1998 versus 2009, and 1999 versus 2010) that span years with very different Landsat 5 overpass times, and are also compared between 1998 and 1999 that have similar overpass times. The different years of Landsat 5 TM data are plotted against each other and reduced major axis (RMA) regressions passing though the origin are developed and compared with the acquisition solar geometry changes. The red, SWIR and NDVI RMA slopes are proportional to the magnitude of solar zenith change between years and are indicative of CONUS-wide differences due to orbit drift. The greatest differences occurred between 1995 and 2006, the years with the greatest solar zenith differences (median CONUS difference 8.43°) with RMA regression slopes quite far from unity (1.14 for the red and SWIR bands, 0.91 for NDVI). In years with smaller solar zenith differences the RMA slopes are closer to unity. As agricultural crops may be managed inconsistently through time, and as drought may have pronounced effects on reflectance, the analysis is also undertaken masking out crop pixels and considering locations that have similar precipitation and evapotranspiration conditions between years. These experiments indicate that, at CONUS scale, the cause of the changing RMA regression slopes between years is not due to agricultural changes or to the influence of above normal drought or wetness. The results confirm previous published modelling based findings but are based on direct examination of CONUS Landsat 5 TM data. They indicate that certain research and applications that require temporally consistent red, SWIR and NDVI data may need to take Landsat 5 orbit drift effects into account.

Effect of Fertilization on Soil Respiration and Its Temperature Sensitivity in a Sorghum Field

The characteristics of soil respiration under the condition of fertilization have not been fully understood,especially for a long-term fertilization condition. In this study we measured both soil respiration using an LI-COR-6400-09 soil chamber attached to LI-COR-6400 portable photosynthesis system, and the vegetation spectrum using an ASD FieldSpec HandHeld2, in five different fertilization treatment fields. The soil respiration (Rs) and vegetation spectrum were simultaneously measured with two samples per month in the growing season in 2016 and 2017. The soil temperature at 10 cm depth (T10) and moisture (Ws) for the surface of 10 cm were also measured simultaneously. The five different fertilization treatments included no fertilization (CK), inorganic fertilizer (INF), inorganic fertilizer+organic fertilizer (INF+M), inorganic fertilizer+organic fertilizer+straw turnover (INF+M+S) and organic fertilizer+straw turnover (M+S), and all treatments had been conducted since 2011. Based on those observation data, we made an analysis of Rs and its temperature sensitivity (Q10) in the five different fertilization treatments. The results showed that no significant temporal change in Rs among the five treatments was found. No significant difference was found in Rs between the CK and INF treatments. Compared with the values of Rs in CK and INF, the Rs values in INF+M, M+S, and INF+M+S treatments increased by 28.2%-39.1%, 47.9%-76.0%, and 46.2%-50.8%, respectively. This indicated that use of organic fertilization and straw application increased Rs. Both the Ts and Ws showed 14%-96% and 6%-37% in Rs seasonal variations, respectively. Among the treatments, the correlation coefficient of the fitted equations between Rsand Ts was higher in the INF+M, INF+M+S and M+S treatment than in CK and INF, but was not between Rsand Ws. For the relationship between Rs and vegetation indexes we found that the correlation coefficients between Rs and the difference vegetation index (DVI), ratio vegetation index (RVI), and enhanced vegetation index (EVI), respectively, were higher than that of Rs and the normalized differential vegetation index (NDVI); and that the correlation coefficients between Rsand the red edge slope (Dred) and red edge area (Sred) were higher than between Rs and the red edge position (λred). This indicated that the treatments in INF+M+S increased the correlation coefficient between Rs and the spectrum characteristics index. The determination coefficient of the fitted equations including the feature spectral parameters, T10, and Wsvariables was higher than that of the equations only including both T10 and Ws variables, or a single variable of T10 or Ws. Compared with CK, the Q10 value increased by 26%, 39%, 21%, and 37% for the INF, INF+M, INF+M+S, and M+S treatments, respectively. This indicated that temperature sensitivity Q10 increased under the condition of fertilization treatments. The Shannon diversity index, bulk density, and soil organic matter were the main factors causing the difference in Rs, Q10, and R10, i.e., Rs at a temperature of 10℃, in the different treatments, which could explain the 97.6%, 78.2%, and 92.8% variations in Rs, Q10, and R10, respectively.

The East African contribution to the formalisation of the soil catena concept

The concept of the soil catena was first explicitly formalised by Geoffrey Milne and his colleagues in East Africa in the 1930s. It has been widely adopted and applied in soil survey and continues to be of great value in soil and other field sciences The concept characterises widespread patterns in which distinctive associations of soils and vegetation are consistently located in specific slope positions. The formalisation of the concept in an area well outside the mainstream of soil research appears to have been due to the combination of highly visible recurrent patterns of red slope soils overlooking dark valley clays in East Africa’s extensive savannahs, together with a group of receptive and collaborative soil scientists working in a supportive institutional environment. The concept is often attributed to Geoffrey Milne, the group’s coordinator, but we show that several colleagues and friends also contributed. We summarise some of the early soil catenas characterised by Milne and his colleagues in Uganda, Kenya and Tanganyika Territory (now Tanzania). Even at the beginning, it was appreciated that the catena was not universally applicable and that heterogeneity of parent materials can override catenary patterns. The catena was quickly and widely adopted in soil science, and this diffusion has led to some broadening of the definition, and several types of soil pattern are now designated as catenas. The concept has also spread beyond soil science and is used by ecologists, geomorphologists and hydrologists amongst others. It continues to be a paradigm of great explicative and educational power in soil science and ecology.

Response of dust particle pollution and construction of a leaf dust deposition prediction model based on leaf reflection spectrum characteristics.

Urban plants can improve several environmental pollution problems in cities, especially dust prevention, noise reduction, purification of the atmosphere, etc. To explore the influence of dust deposition on the spectral characteristics of the leaf, a foliar dust deposition prediction model based on high-spectrum data was established. Taking Euonymus japonicus L., the common greening tree species in Beijing, as the research object, high (T1), medium (T2), and low (T3) dust pollution gradients were set and hyperspectral data were collected. Results showed that: (1) in the dust-contaminated environment with different concentrations, the trend of the reflectance curve of the leaves of Euonymus japonicus L. was generally consistent. The spectral reflectance of the leaf surface was positively correlated with the amount of leaf dust. (2) There were five obvious reflection peaks and five main absorption valleys with the same positions and ranges in the 350-2500 nm range. (3) The spectral reflectance of leaf flour dust particles of Euonymus japonicus L. was significantly different before and after dusting, and its size was generally clean leaves > dust-depositing leaves. The sensitive range of its spectral response was 695-1400 nm. (4) The overall trend of the first derivative spectrum was basically the same. The red edge slope and the blue edge slope appeared as T3 > T2 > T1, the red edge position and the blue edge position appeared as T1 < T2 < T3. The red edge position of the leaf surface after dust deposition had an obvious "blueshift", and the moving distance increases with the increase of dust retention on leaf surface. (5) The leaf water index (y = - 1.18x2 + 0.5424x + 0.9917, R2 = 0.8030, RMSE = 0.187) had the highest accuracy in the regression model of leaf surface dust deposition using spectral parameters. The test showed that the R2 reached 0.9019, which indicated that the model has a good fitting effect. This prediction model can effectively estimate the dust deposition of the leaf surface of Euonymus japonicus L.

Study on failure mechanism of red clay slope under dry and wet cycles

In order to study the failure characteristics and mechanism of red clay slope under dry-wet cycling conditions, a model slope similar to engineering slope was established. The test slope was monitored by testing elements, and the variation laws of moisture content, temperature, pore water pressure, soil pressure and displacement were analyzed respectively under the alternating conditions of dry-wet cycling. The failure characteristics and mechanism of slope are obtained. With the increase of dry-wet cycles, the overall water content of slope increases, pore water pressure decreases, lateral displacement increases, and vertical displacement remains unchanged to a certain extent. After five dry-wet cycles, the water content of the top and top of the slope is the largest, the water content of the bottom and foot of the slope is the smallest, the horizontal displacement of the slope is the largest, and the horizontal displacement of the top of the slope is the smallest. The range of temperature change increases with the number of dry-wet cycles, and tends to be stable after the third dry-wet cycle. The earth pressure is the largest at the top of the slope, followed by the foot of the slope and the smallest at the slope surface, and the first two dry-wet cycles have the greatest impact on the earth pressure. In the process of dry-wet cycling, the surface cracks of slope undergo the cyclic process of cracking, healing and re-cracking. The width and depth of cracks increase gradually. The surface failure characteristics represented by gully weathering and spalling gradually change into shallow failure characteristics represented by collapse and slump.

The last pieces of the primitive inner belt puzzle: Klio, Chaldaea, Chimaera, and Svea

Aims.Several primitive families in the inner region of the main asteroid belt were identified as potential sources for two near-Earth asteroids (NEAs), (101955) Bennu and (162173) Ryugu, targets of the sample-return missions OSIRIS-REx and Hayabusa2, respectively. Four of the families, located at high proper inclinations (i&gt; 10°), have not yet been compositionally studied: Klio, Chaldaea, Chimaera, and Svea. We want to characterize and analyze these families within the context of our PRIMitive Asteroid Spectroscopic Survey (PRIMASS), in order to complete the puzzle of the origins of the two NEAs.Methods.We obtained visible spectra (0.5–0.9μm) of a total of 73 asteroids within the Klio, Chaldaea, Chimaera, and Svea collisional families, using the instrument OSIRIS at the 10.4 m Gran Telescopio Canarias. We performed a taxonomical classification of these objects, and an analysis of the possible presence of absorption bands related to aqueous alterations, comparing the results with already studied primitive families in the inner main belt.Results.We present here reflectance spectra for 30 asteroids in the Klio family, 15 in Chaldaea, 20 in Chimaera, and 8 in Svea. We show that Klio, Chaldaea, and Chimaera members have moderately red spectral slopes, with aqueous alteration absorption bands centered around 0.7μm, characteristic of the group of primitive families known as Erigone-like. In contrast, Svea shows no 0.7μm features, and neutral and blue spectral slopes, and thus is a Polana-like family. While all four families might be related to (162173) Ryugu, the only family studied in this work that might be related to (101955) Bennu is Svea.

Reflectivity Characteristics of the Green and Golden Tides from the Yellow Sea and East China Sea

Min, S.H.; Hwang, J.D.; Oh, H., and Son, Y.B., 2019. Reflectivity characteristics of the green and golden tides from the Yellow Sea and East China Sea. In: Jung, H.-S.; Lee, S.; Ryu, J.-H., and Cui, T. (eds.), Advances in Remote Sensing and Geoscience Information Systems of Coastal Environments. Journal of Coastal Research, Special Issue No. 90, pp. 310-316. Coconut Creek (Florida), ISSN 0749-0208.The Yellow Sea (YS) and East China Sea (ECS) have the world's largest supply of floating algae. The green and golden tides appear mainly in the YS and ECS, respectively, but become entangled as they drift. The floating algae obstructs navigation and is a huge socioeconomic problem in the vicinity of coastal areas. To manage these floating algae more systematically, a method of distinguishing between the green and golden tides is required. In this study, the reflectivity characteristics of the green and golden tides appearing in the YS and ECS were investigated based on which a classification method was proposed and applied to satellite sensors. First, the reflectance of Ulva prolifera and Sargassum horneri was measured, which are the major causative species of the green and golden tides in the YS and ECS, respectively. Under visible light, the reflectance of U. prolifera increased at 555 nm, and that of S. horneri increased at 602 and 646 nm and decreased at 632 nm. To distinguish the two algae, slope of red-green (SRG) method was applied with the red and green reflectance slope. U. prolifera exhibited SRG that was always negative, whereas that of S. horneri was always positive. When SRG was applied to the difference in reflectance values between floating algae and nearby water detected in satellite imagery, the green tide was always negative, and the golden tide was always positive. Classification and detection of floating algae using multi-satellite sensors and SRG system can reduce the associated management cost and time.

Active Asteroid (6478) Gault: A Blue Q-type Surface below the Dust?

Abstract We present near-infrared spectroscopy of the sporadically active asteroid (6478) Gault collected on the 3 m NASA/Infrared Telescope Facility observatory in late 2019 March/early April. Long-exposure imaging with the 0.5 m Near Earth Environment Monitoring T05 telescope and previously published data simultaneously monitored the asteroid activity, providing context for our measurements. We confirm that Gault is a silicate-rich (Q- or S-type) object likely linked to the (25) Phocaea collisional family. The asteroid exhibits substantial spectral variability over the 0.75–2.45 μm wavelength range, from unusual blue (s′ = −13.5 ± 1.1% μm−1) to typical red (s′ = +9.1 ± 1.2% μm−1) spectral slope, that does not seem to correlate with activity. Spectral comparisons with samples of ordinary chondrite meteorites suggest that the blue color relates to the partial loss of the asteroid dust regolith, exposing a fresh, dust-free material at its surface. The existence of asteroids rotating close to rotational break-up limit and having similar spectral properties as Gault further supports this interpretation. Future spectroscopic observations of Gault, when the tails dissipate, will help further testing of our proposed hypothesis.

Near-infrared spectroscopy of the Klio primitive inner-belt asteroid family

The PRIMitive Asteroid Spectroscopic Survey (PRIMASS) aims to characterize primitive asteroids throughout the asteroid belt in the visible and near-infrared (NIR). There are eight primitive families in the inner main belt: Polana-Eulalia, Erigone, Sulamitis, Clarissa, Chaldaea, Klio, Svea and Chimaera. PRIMASS has already characterized all 8 families in the visible, and the Polana-Eulalia complex in the NIR. Results of our previous work show that low inclination inner belt family asteroids fall into at least two distinct compositional groups: Polana-like (anhydrous and spectrally homogeneous) or Erigone-like (hydrated and spectrally diverse). In the visible, the Klio family is spectrally diverse and 23% of the objects show evidence of hydration, but it is not Erigone-like.We observed 21 objects in the Kilo family using the NASA InfraRed Telescope Facility (IRTF) and the Telescopio Nazionale Galileo (TNG) between January 2017 and March 2019. Our survey shows that the Klio family is spectrally homogeneous in the NIR, i.e., the heterogeneity seen in the visible does not extend to the NIR. The Klio family NIR spectra have mostly convex shapes and have red slopes (average slope 1.052 ± 0.425%/1000 Å normalized at 1.0 μm). The average spectra of both families we have studied in the NIR (Polana-Eulalia and Klio) differ slightly in spectral shape and slope, consistent with space weathering effects, but not conclusively so. Based on our NIR spectral comparisons, the Klio family cannot be ruled out as a possible source for two near-Earth asteroids: (101955) Bennu and (162173) Ryugu.

Resolved UV and [C ii] Structures of Luminous Galaxies within the Epoch of Reionization

Abstract We present new deep ALMA and Hubble Space Telescope (HST)/WFC3 observations of MASOSA and VR7, two luminous Lyα emitters (LAEs) at z = 6.5, for which the UV continuum levels differ by a factor of four. No IR dust continuum emission is detected in either, indicating little amounts of obscured star formation and/or high dust temperatures. MASOSA, with a UV luminosity M 1500 = −20.9, compact size, and very high Lyα , is undetected in [C ii] to a limit of L [C ii] &lt; 2.2 × 107 L ⊙, implying a metallicity Z ≲ 0.07 Z ⊙. Intriguingly, our HST data indicate a red UV slope β = −1.1 ± 0.7, at odds with the low dust content. VR7, which is a bright (M 1500 = −22.4) galaxy with moderate color (β = −1.4 ± 0.3) and Lyα EW0 = 34 Å, is clearly detected in [C ii] emission (S/N = 15). VR7's rest-frame UV morphology can be described by two components separated by ≈1.5 kpc and is globally more compact than the [C ii] emission. The global [C ii]/UV ratio indicates Z ≈ 0.2 Z ⊙, but there are large variations in the UV/[C ii] ratio on kiloparsec scales. We also identify diffuse, possibly outflowing, [C ii]-emitting gas at ≈100 km s−1 with respect to the peak. VR7 appears to be assembling its components at a slightly more evolved stage than other luminous LAEs, with outflows already shaping its direct environment at z ∼ 7. Our results further indicate that the global [C ii]−UV relation steepens at SFR &lt; 30 M ⊙ yr−1, naturally explaining why the [C ii]/UV ratio is anticorrelated with Lyα EW in many, but not all, observed LAEs.

UV slope ofz∼ 3 bright (L&gt;L*) Lyman-break galaxies in the COSMOS field

Context. The analysis of the UV slopeβof Lyman-break galaxies (LBG) at different luminosities and redshifts is fundamental for understanding their physical properties, and in particular, their dust extinction.Aims. We analyse a unique sample of 517 bright (L &gt; L*) LBGs at redshiftz ∼ 3 in order to characterise the distribution of their UV slopesβand infer their dust extinction under standard assumptions.Methods. We exploited multi-band observations over 750 arcmin2of the COSMOS field that were acquired with three different ground-based facilities: the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT), the Suprime-Cam on the SUBARU telescope, and the VIRCAM on the VISTA telescope (ULTRAVISTA DR2). Our multi-band photometric catalogue is based on a new method that is designed to maximise the signal-to-noise ratio in the estimate of accurate galaxy colours from images with different point spread functions (PSF). We adopted an improved selection criterion based on deepY-band data to isolate a sample of galaxies atz ∼ 3 to minimise selection biases. We measured the UV slopes (β) of the objects in our sample and then recovered the intrinsic probability density function ofβvalues (PDF(β)), taking into account the effect of observational uncertainties through detailed simulations.Results.The galaxies in our sample are characterised by mildly red UV slopes with ⟨β⟩≃ − 1.70 throughout the enitre luminosity range that is probed by our data (−24 ≲ M1600 ≲ −21). The resulting dust-corrected star formation rate density (SFRD) is log(SFRD)≃ − 1.6 M⊙ yr−1 Mpc−3, corresponding to a contribution of about 25% to the total SFRD atz ∼ 3 under standard assumptions.Conclusions.Ultra-bright LBGs atz ∼ 3 match the known trends, with UV slopes being redder at decreasing redshifts, and brighter galaxies being more highly dust extinct and more frequently star-forming than fainter galaxies.

Analysis of Vegetation Red Edge with Different Illuminated/Shaded Canopy Proportions and to Construct Normalized Difference Canopy Shadow Index

Shadows exist universally in sunlight-source remotely sensed images, and can interfere with the spectral morphological features of green vegetations, resulting in imprecise mathematical algorithms for vegetation monitoring and physiological diagnoses; therefore, research on shadows resulting from forest canopy internal composition is very important. Red edge is an ideal indicator for green vegetation’s photosynthesis and biomass because of its strong connection with physicochemical parameters. In this study, red edge parameters (curve slope and reflectance) and the normalized difference vegetation index (NDVI) of two species of coniferous trees in Inner Mongolia, China, were studied using an unmanned aerial vehicle’s hyperspectral visible-to-near-infrared images. Positive correlations between vegetation red edge slope and reflectance with different illuminated/shaded canopy proportions were obtained, with all R2s beyond 0.850 (p &lt; 0.01). NDVI values performed steadily under changes of canopy shadow proportions. Therefore, we devised a new vegetation index named normalized difference canopy shadow index (NDCSI) using red edge’s reflectance and the NDVI. Positive correlations (R2 = 0.886, p &lt; 0.01) between measured brightness values and NDCSI of validation samples indicated that NDCSI could differentiate illumination/shadow circumstances of a vegetation canopy quantitatively. Combined with the bare soil index (BSI), NDCSI was applied for linear spectral mixture analysis (LSMA) using Sentinel-2 multispectral imaging. Positive correlations (R2 = 0.827, p &lt; 0.01) between measured brightness values and fractional illuminated vegetation cover (FIVC) demonstrate the capacity of NDCSI to accurately calculate the fractional cover of illuminated/shaded vegetation, which can be utilized to calculate and extract the illuminated vegetation canopy from satellite images.

Field Study on the Soil Water Characteristics of Shallow Layers on Red Clay Slopes and Its Application in Stability Analysis

Red clay is widely distributed in Zhejiang Province, China. Rain-induced shallow landslides easily occur on red clay slopes due to the reduction in shear strength caused by rainwater infiltration. The aim of this paper was to study the soil–water characteristic of red clay and its application on analyzing the stability of red clay slope. A series of field tests at different depths of red clay slope were carried out to monitor the variations of water content and matric suction under typical climate conditions. The results showed that the distribution of water content in red clay slope is complex because of long-term wetting–drying cycles. The water content within shallow layer is sensitive to external environment, and the response time of the water content is related to rainfall intensity. It is also observed that the soil water characteristic curve (SWCC) varies at different depths. The SWCCs of red clay can be fitted by linear function. The SWCCs from laboratory tests illustrated that saturated water content is more than 40%. Most of the SWCCs obtained at the depth of 90 cm are within the hysteresis loops of the SWCCs from laboratory test. The short-term rainfall has less effect on the stability of the slope, but the stability continuously decreases after the rain stops. The SWCCs obtained from laboratory were applied to analyze slope stability. Considering the influence of cracks, the computed results are close to field data. The study has a certain directive significance to the design of red clay slopes.

Regional Stability Analysis of Red Clay Slope Based on Different Failure Modes: A Case Study in Taizaifu Area, Fukuoka

Red clay slopes have different failure modes in different geological and climatic contexts. Underlying weak layers are frequently witnessed in integral failures because of the reverse consolidation characteristics. On the contrary, heavy rainfall often causes superficial sliding for a considerable infiltration through developed microfractures. Based on the Geographic Information System, regional stability of red clay slopes was evaluated with two failure modes, such as “integral sliding” and “planar sliding.” First, terrain and borehole data of the study area were used to construct the digital elevation model. Second, slope units were partitioned as research objects. For integral sliding, the slip surface was supposed to lie above the strata interface, and it was regarded as a lower part of an ellipsoid. After calculating safety factors of potential slip surfaces that were randomly generated by the Monte Carlo method, the minimum safety factor of the slope unit and the critical slip surface could be determined. For shallow landslides triggered by rainfall infiltration, the one‐dimensional infiltration model and infinite slope model were used. Moreover, the difference between the sliding direction of each column and the main aspect of entire slope unit was considered in safety factor calculation. Finally, regional slope stability characterized by the safety factor would be available; thus, it would be beneficial to sliding prevention and disaster treatment in this region.

MGS‐TES Spectra Suggest a Basaltic Component in the Regolith of Phobos

AbstractThe origins of the Martian moons Phobos and Deimos have been the subjects of considerable debate. Visible and near‐infrared spectra of these bodies are dark and nearly featureless, with red slopes of varying degrees. These spectra are generally consistent with those of carbonaceous asteroids, leading to the hypothesis that Phobos and Deimos are captured carbonaceous asteroids. The shapes and inclinations of the orbits of Phobos and Deimos present problems for the asteroid capture hypothesis. This had led researchers to suggest that Phobos and Deimos coaccreted with Mars or that they are the result of an impact with Mars or in the Mars vicinity. In this work, we reexamine Mars Global Surveyor Thermal Emission Spectrometer (MGS‐TES) data of Phobos and compare spectra of the Phobos surface to mid‐IR spectra of the ungrouped C2 meteorite Tagish Lake (a suggested analog for D‐class asteroids) and particulate basalt and phyllosilicate samples (mixed with carbon black to reduce their visible albedos) acquired in a simulated airless body environment. We find that Tagish Lake is a poor mid‐IR spectral analog to Phobos and that major spectral features in the Phobos spectrum are best matched by a silicate transparency feature similar to that found for finely particulate basalt. Other features in the spectrum are likely best explained by a phyllosilicate component. We suggest that these results indicate that at a portion of the Phobos surface regolith is derived from the Martian crust.

Spectral and chemical effects of simulated space weathering of the Murchison CM2 carbonaceous chondrite

We performed pulsed-laser irradiation of a chip of the CM2 Murchison carbonaceous chondrite meteorite to simulate micrometeorite impacts on carbonaceous asteroids. Optical reflectance spectroscopy and transmission electron microscopy were performed to characterize the unirradiated and irradiated samples and vapor and melt deposits collected on a glass slide ∼7 mm from the surface of the sample. The spectrum of the deposit on the glass slide shows a red slope between 0.35–2.5 µm, while the irradiated surface of the meteorite shows only slight darkening over the same spectral range. We identified predominant melt products and vesiculated textures in the glass slide deposit, in the fine-grained matrix of the meteorite, and in individual mineral phases of the meteorite chip. Extracted focused ion beam (FIB) sections from the matrix material, an olivine grain, a pentlandite grain, and from the glass slide deposit were analyzed by scanning transmission electron microscopy (STEM). Microstructural and chemical analyses based on the STEM observations show widespread melting and the formation of Fe-bearing nanoparticles (including prevalent Fe–Ni–sulfides) across the surface of the meteorite. The section extracted from the glass slide revealed nanoparticles embedded in a chemically and microstructurally complex deposit, which likely formed as a result of both melting and vaporization processes. These analyses reveal a significantly more compositionally diverse population of nanoparticles compared to what is observed in lunar or ordinary chondritic space weathered samples. We discuss the implications these results have for the space weathering of carbonaceous asteroids and their importance for understanding the surface processes on primitive bodies.