Subsurface Measurements Research Articles

Drone-based hyperspectral remote sensing of cyanobacteria using vertical cumulative pigment concentration in a deep reservoir

The remote sensing of algal pigments is essential for understanding the temporal and spatial distribution of harmful algal blooms (HABs). In particular, the vertical distribution of cyanobacterial pigment (e.g., phycocyanin (PC)) is critical factor in remote sensing because the diel vertical migration of cyanobacteria may affect the spectral signals according to observational time. Although numerous studies have been conducted on the remote sensing of algal bloom using pigments, few studies considered the vertical distribution of the pigments for the remote sensing of cyanobacteria in inland waters. In this regard, the objective of this study was to develop an improved bio-optical remote-sensing method using in-situ remote-sensing reflectance (Rrs) at different water depths and cumulative PC and Chlorophyll-a (Chl-a) concentrations, which was cumulated from the surface to a 5-m water depth. The results showed that the bio-optical algorithm using surface Rrs and surface pigment concentration was more accurate than that using the subsurface Rrs and surface pigments. The bio-optical algorithm using subsurface Rrs showed the highest R-squared (R2) values (0.87–0.94) in each regression with the cumulative PC concentration from surface to each depth. The regressions between drone-based surface reflectance and cumulative PC concentration for each depth indicated a better performance than those between the reflectance and surface PC concentration; the highest R2 value of 0.82 was obtained from a bio-optical algorithm using drone-based reflectance and a 1.0-m cumulative PC concentration, which was the best-performing algorithm. The PC maps developed using the best bio-optical algorithm accurately described the spatial and temporal distributions of the PC concentrations in the reservoir. This study demonstrates that the application of vertical cumulative pigment concentration and subsurface Rrs measurement in bio-optical algorithms can improve their performance in estimating pigments, and that drone-based hyperspectral imagery is an efficient tool for the remote sensing of cyanobacterial pigments over a wide area.

Sub-surface measurements of the austenite microstructure in response to martensitic phase transformation

In this work, we measure the microstructure response of the austenite phase during martensitic phase transformation tens of micrometers beneath the surface of a bulk single crystal nickel-titanium shape memory alloy. Using an emerging dark-field X-ray microscopy (DFXM) technique, the austenite phase fraction, relative misorientation, and elastic lattice plane strain are measured in the interior of the microstructure with a spatial resolution of 108 nm. The results show that some defects consistently induce forward transformation and delay reverse transformation, while other defects consistently impede the propagation of both forward and reverse transformation fronts. We also show that the austenite undergoes an orientation splitting wherein the austenite near the transformation front is constrained from rotating and the austenite far from the transformation front is free to rotate. Finally, we measure interfacial strain fields at the transformation front that extend tens of micrometers into the material. We use an analytical model to show how these strain fields can be explained by a lack of kinematic compatibility between the austenite and martensite phases at the austenite-martensite interface.

Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements

Abstract. Accurate description of snow and firn processes is necessary for estimating the fraction of glacier surface melt that contributes to runoff. Most processes in snow and firn are to a great extent controlled by the temperature therein and in the absence of liquid water, the temperature evolution is dominated by the conductive heat exchange. The latter is controlled by the effective thermal conductivity k. Here we reconstruct the effective thermal conductivity of firn at Lomonosovfonna, Svalbard, using an optimization routine minimizing the misfit between simulated and measured subsurface temperatures and densities. The optimized k* values in the range from 0.2 to 1.6 W (m K)−1 increase downwards and over time. The results are supported by uncertainty quantification experiments, according to which k* is most sensitive to systematic errors in empirical temperature values and their estimated depths, particularly in the lower part of the vertical profile. Compared to commonly used density-based parameterizations, our k values are consistently larger, suggesting a faster conductive heat exchange in firn.

Evaluation of Unbound Aggregate Base Layers using Moisture Monitoring Data

The behaviors of unbound aggregate base (UAB) and subgrade layers are considerably affected by seasonal moisture fluctuations which ultimately affect both their load-bearing capacity and the overall performance of the pavement structure. As part of an effort towards designing optimal performing pavements, this study was undertaken to evaluate, characterize, and quantify the effects of moisture and temperature variations on UAB and subgrade materials commonly used in Minnesota. The scope included analyses of subsurface moisture and temperature measurements and characterization of moisture variation in multiple instrumented pavement sections. Key findings indicated that dense-graded aggregate base materials with high quality crushed aggregates and lower fine particles were more resistant to seasonal moisture variations. By contrast, the subbase and subgrade materials exhibited considerable sensitivity to seasonal moisture variations. The subgrade layers, in particular, were found to operate in fully saturated conditions for more than half of their service life. Overall, the study results are a valuable contribution to establishing guidelines for laboratory testing and designing optimal performing pavement structures.

The present-day state of tectonic stress in the offshore Kutch-Saurashtra Basin, India

Abstract Exploration activity in the Kutch-Saurashtra area has drawn major attention and because of the recent hydrocarbon discoveries offshore Kutch-Saurashtra basin is now moved from category III to II. Accurate understanding of the full present-day stress tensor and pore pressure is critical for field development. In this study, pore pressure, stress magnitudes and horizontal stress direction have been estimated from high resolution geophysical logs and various direct downhole measurements recorded in the studied offshore exploratory wells. Extensive availability of subsurface pressure measurements confirms hydrostatic pore pressure in the tertiary sediments. Magnitudes of vertical, minimum and maximum horizontal stresses indicate a strike slip tectonic stress regime. Wellbore breakouts of A-C qualities have been identified in density image logs and four arm caliper logs, indicating a NNE trend (N10°E to N20°E) of SHMax (maximum horizontal stress). The same has been confirmed from Shear wave anisotropy analysis as well. The interpreted stress direction is in good agreement with the World Stress map data available from the adjacent area. This study is significant in understanding the subsurface behavior during drilling, reservoir modeling, future well stimulation and production optimization.

Retrieval of water quality parameters of South Andaman coral Islands using remotely operated underwater vehicle

ABSTRACT Remotely operated underwater vehicle (ROV)-based spectral irradiance measurements at South Andaman coral reef islands are used to derive water quality parameters (chlorophyll-a, total-suspended sediments, turbidity, salinity, Secchi disk depth, diffuse attenuation coefficient) at different depths of the water column. Different combination of standard formula is used to extract the water quality information from the sub-surface reflectance measurement and compared with the data derived from satellite images and conventional water sample analyses. Water quality data derived from ROV-based irradiance measurement and satellite sensor (Landsat data) correlate well to the extent of 0.85 (R2). Results from spectral irradiance measurements up to 20 m water depth using the ROV along with high-definition images of coral reef biodiversity can be effectively used to understand the habitats' diversity and also to derive different water quality parameters in spatio-temporal scale.

Heat and Mass Transport in a Vapor‐Dominated Hydrothermal Area in Yellowstone National Park, USA: Inferences From Magnetic, Electrical, Electromagnetic, Subsurface Temperature, and Diffuse CO2 Flux Measurements

AbstractVapor‐dominated hydrothermal systems are characterized by localized and elevated heat and gas flux. In these systems, steam and gas ascend from a boiling water reservoir, steam condenses beneath a low‐permeability cap layer, and liquid water descends, driven by gravity (“heat pipe” model). We combine magnetic, electromagnetic, and geoelectrical methods and CO2 flux and subsurface temperature measurements in the Solfatara Plateau Thermal Area in the Yellowstone Caldera to address several fundamental questions: (1) What are the structural and/or lithological controls on heat and mass transport in vapor‐dominated areas? (2) What is the geometry and size of convecting multiphase thermal plumes? (3) Are thermal plumes associated with subsurface rock alteration and demagnetization? Magnetic and electromagnetic data inversions suggest an asymmetric 50‐ to 100‐m thick basin of glacial deposits with the thickest part adjacent to the margin of a rhyolite flow. The 3‐D electrical conductivity model in the glacial basin reveals a narrow vertical conductor interpreted as a focused multiphase plume, which coincides at the ground surface with the heat and CO2 flux maxima. The magnetic data suggest that destruction of magnetic minerals due to rock alteration associated with the hydrothermal plume occurs mainly near the ground surface. We propose a model where the buoyant multiphase plume forms in response to decompression, boiling, and phase separation of pressurized thermal groundwater that discharges from the brecciated base of a rhyolite flow into the basin of glacial deposits. Results from multiphase groundwater flow and heat transport numerical simulations corroborate the first‐order characteristics of this model.

Cliff retreat of permafrost coast in south‐west Baydaratskaya Bay, Kara Sea, during 2005–2016

AbstractRecent years of increasing air temperature in the Arctic have led to a significant increase in the rate of retreat of permafrost coast, which has threatened livelihoods and infrastructure in these areas. The Kara Sea hosts more than 25% of the total Arctic coastline. However, little is known about how coastal erosion in the Kara Sea may have changed through time, and the climatic and environmental drivers remain unclear. Here we study coastal dynamics along a 4‐km stretch of permafrost and sea‐ice‐affected coastline in south‐west Baydaratskaya Bay of the Kara Sea, western Siberia, between 2005 and 2016, by using handheld differential GPS mapping and satellite imagery. We identified temporal and spatial variations in the retreat rates, ranging between 1.0 (+0.1/−0.6) and 1.9 (+0.7/−1.3) m/yr over the studied coastline during 2005–2016. We also made ground temperature measurements, subsurface resistivity measurements and estimates of wave energy flux of wind‐driven ocean waves, to investigate the dominant climatic factors influencing the observed retreat rates through time. We found that wind‐driven wave activity during sea‐ice‐free days influences the magnitude of coastal retreat in the study area, while recent temperature rise has contributed less to enhancing coastal retreat during the study period. This suggests that the amount of eroded sediment and the associated release of nutrient to the nearshore zone are controlled by the magnitude of wave activity, which may influence infrastructure along the permafrost coast and marine ecosystems in the proximal ocean.

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

AbstractWe use more than 10 years of the Martian topside ionospheric data measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft to derive an empirical model of electron densities from the peak altitude up to 325 km. Altogether, 16,044 electron density profiles obtained at spacecraft altitudes lower than 425 km and at solar zenith angles lower than 80° are included in the analysis. Each of the measured electron density profiles is accurately characterized by the peak electron density, peak altitude, and three additional parameters describing the profile shape above the peak: (i) steepness at high altitudes, (ii) main layer thickness, and (iii) transition altitude. The dependence of these parameters on relevant controlling factors (solar zenith angle, solar irradiance, crustal magnetic field magnitude, and Sun‐Mars distance) is evaluated, allowing for a formulation of a simple empirical model. Mars Atmosphere and Volatile EvolutioN Extreme Ultraviolet monitor data are used to show that the solar ionizing flux can be accurately approximated by the F10.7 index when taking into account the solar rotation. Electron densities predicted by the resulting empirical model are compared with electron densities locally evaluated based on the Mars Advanced Radar for Subsurface and Ionosphere Sounding measurements, with the Langmuir Probe and Waves electron density measurements on board the Mars Atmosphere and Volatile EvolutioN spacecraft, and with electron densities obtained by radio occultation measurements. Although the electron densities measured by the Langmuir Probe and Waves instrument are systematically somewhat lower than the model electron densities, consistent with former findings, the model performs reasonably well.

Sub-Surface Measurements of the Austenite Microstructure in Response to Martensitic Phase Transformation

Sub-Surface Measurements of the Austenite Microstructure in Response to Martensitic Phase Transformation

Occurrence and fate of methane leakage from cut and buried abandoned gas wells in the Netherlands

Methane leakage caused by well integrity failure was assessed at 28 abandoned gas wells and 1 oil well in the Netherlands, which have been plugged, cut and buried to below the ground surface (≥3 mbgl). At each location, methane concentrations were thoroughly scanned at the surface. A static chamber setup was used to measure methane flow rates from the surface as well as from 1 m deep holes drilled using a hand auger. An anomalously high flow rate from 1 m depth combined with isotopic confirmation of a thermogenic origin revealed ongoing leakage at 1 of the 29 wells (3.4%), that had gone undetected by surficial measurements. Gas fluxes at the other sites were due to shallow production of biogenic methane. Detailed investigation at the leaking well (MON-02), consisting of 28 flux measurements conducted in a 2 × 2 m grid from holes drilled to 1 and 2 m depth, showed that flux magnitude was spatially heterogeneous and consistently larger at 2 m depth compared to 1 m. Isotopic evidence revealed oxidation accounted for roughly 25% of the decrease in flux towards the surface. The estimated total flux from the well (443 g CH4 hr−1) was calculated by extrapolation of the individual flow rate measurements at 2 m depth and should be considered an indicative value as the validity of the estimate using our approach requires confirmation by modelling and/or experimental studies. Together, our findings show that total methane emissions from leaking gas wells in the Netherlands are likely negligible compared to other sources of anthropogenic methane emissions (e.g. <1% of emissions from the Dutch energy sector). Furthermore, subsurface measurements greatly improve the likelihood of detecting leakage at buried abandoned wells and are therefore essential to accurately assess their greenhouse gas emissions and explosion hazards.

Measurement of CTOD along a surface crack by means of digital image correlation

The experimental measurement of fracture toughness and crack driving force are the main steps for the application of fracture mechanics methods in structural integrity assessment. Crack Tip Opening Displacement (CTOD), defined as the opening of a defect at its crack front upon loading a test specimen or structure, is one of the most important crack driving force parameters. However, due to its subsurface nature direct measurement of CTOD is very cumbersome. CTOD is commonly measured using single or double clip gauge techniques and applying a plastic hinge model. However, clip gauge CTOD calculations merely provide information related to the center of the defect. For the case of a finite-length surface breaking defect, where CTOD is variable along the defect front, exact knowledge of CTOD over the entire front is not possible by the clip gauge measurement techniques. In the present paper a novel technique is proposed based on full field three-dimensional profile measurement of the notched surface by means of stereoscopic Digital Image Correlation (3D-DIC) to measure the CTOD over the entire crack front. The proposed method is verified by measurement of silicone replicas cast inside the notch in addition to a supporting Finite Element (FE) investigation.

Contact Resonance Force Microscopy for Viscoelastic Property Measurements: From Fundamentals to State-of-the-Art Applications

Contact resonance force microscopy (CRFM) is an atomic force microscopy (AFM) method that evolved from a curiosity about the detection of ultrasonic vibrations with an AFM cantilever and an unaddressed need to characterize the mechanical properties of stiffer materials (elastic modulus >50 GPa). The method has matured to allow near-surface and subsurface elastic property measurements of single crystals, thin films, nanomaterials, composites, and other advanced materials. More recently, CRFM has been extended to viscoelastic property measurements, where the CR frequency and CR quality factor are utilized to quantitatively assess properties such as storage modulus, loss modulus, and loss tangent. In this Perspective, we trace the evolution of CRFM from initial discovery to elastic property measurements to viscoelastic property measurements. The techniques for extending single-point property measurements to two-dimensional property maps are then described in terms of their operational characteristics, demons...

Thermal Regime and Properties of Soils and Ice‐Rich Permafrost in Beacon Valley, Antarctica

AbstractSubsurface temperatures in polar environments control geomorphic, hydrologic, and biologic processes and ground ice stability. Most studies of the thermal regime in permafrost areas have been developed for the Arctic where interest and concern focus on permafrost thawing. In contrast, this study focuses on soils in the McMurdo Dry Valleys of Antarctica where conditions are much colder and drier, and long‐term persistence of ground ice is of interest including as an analog site for Mars. The soil temperature in Beacon Valley, one of the McMurdo Dry Valleys, has been modeled using the surface temperature, measured heat capacity, and temperature‐dependent thermal conductivity and compared to continuous, high‐resolution measurements of temperatures for a decade down to 19.6‐m depth. For the temperature range of −47.9 to 7.5 °C at our study site, the heat capacity of the dry soil ranges from 580 to 690 J · kg−1 · K−1, thermal conductivity from 0.22 to 0.27 W · m−1 · K−1, and the calculated thermal diffusivity from 0.23 to 0.25 mm2/s. Both the finite difference method and the finite volume method are used to solve the 1‐D heat diffusion equation; the finite volume method‐modeled temperature most closely approximates the measured temperature at all depths with average differences ranging from 0.01 to 0.03 °C. The latent heat contribution of documented episodic snowmelt events and of modeled changes in ice content due to condensation or sublimation is negligible. This study can be applied readily to thermal regimes of similar systems where subsurface temperature measurements are not available such as on Mars.

Micro-slotting technique for reliable measurement of sub-surface residual stress in Ti-6Al-4V

Micro-slotting, a relaxation residual stress measurement technique, has recently been shown to be an effective method for measuring local residual stresses in a variety of materials. The micro-slotting method relies on a scanning electron microscope–focused ion beam system for milling and imaging, digital image correlation software to track displacements due to residual stress relaxation after milling, and finite element analysis for displacement–stress correlation and calculation of the original stress state in the imaged region. The high spatial resolution of the micro-slotting method makes it a promising technique for obtaining near-surface residual stress data in Ti-6Al-4V components for input into fatigue life models and crack growth simulations. However, use of the micro-slotting method on this alloy has yet to be evaluated against more established measurement techniques. In this study, spatially resolved sub-surface residual stress measurements were obtained on shot peened and low-stress surface-machined Ti-6Al-4V planar coupons using the micro-slotting method and were compared to measurements obtained using the conventional X-ray diffraction depth profiling technique. The sub-surface measurements were in good agreement for the shot peened sample. Observed differences in the measured near-surface residual stresses on the surface-machined sample were attributed to the larger measurement volume of the X-ray diffraction method, suggesting that the micron-sized measurement volume of the micro-slotting method may be more suitable for capturing shallow stress profiles and steep stress gradients. Prior to performing the micro-slotting measurements, finite element modeled displacements were used to verify the measurement procedure and to address uncertainties in the milled slot geometries. The results of this study demonstrated the validity of the micro-slotting procedure and established the technique as a reliable method for measuring sub-surface residual stresses in Ti-6Al-4V.

Integrating real-time subsurface hydrologic monitoring with empirical rainfall thresholds to improve landslide early warning

Early warning for rainfall-induced shallow landsliding can help reduce fatalities and economic losses. Although these commonly occurring landslides are typically triggered by subsurface hydrological processes, most early warning criteria rely exclusively on empirical rainfall thresholds and other indirect proxies for subsurface wetness. We explore the utility of explicitly accounting for antecedent wetness by integrating real-time subsurface hydrologic measurements into landslide early warning criteria. Our efforts build on previous progress with rainfall thresholds, monitoring, and numerical modeling along the landslide-prone railway corridor between Everett and Seattle, Washington, USA. We propose a modification to a previously established recent versus antecedent (RA) cumulative rainfall thresholds by replacing the antecedent 15-day rainfall component with an average saturation observed over the same timeframe. We calculate this antecedent saturation with real-time telemetered measurements from five volumetric water content probes installed in the shallow subsurface within a steep vegetated hillslope. Our hybrid rainfall versus saturation (RS) threshold still relies on the same recent 3-day rainfall component as the existing RA thresholds, to facilitate ready integration with quantitative precipitation forecasts. During the 2015–2017 monitoring period, this RS hybrid approach has an increase of true positives and a decrease of false positives and false negatives relative to the previous RA rainfall-only thresholds. We also demonstrate that alternative hybrid threshold formats could be even more accurate, which suggests that further development and testing during future landslide seasons is needed. The positive results confirm that accounting for antecedent wetness conditions with direct subsurface hydrologic measurements can improve thresholds for alert systems and early warning of rainfall-induced shallow landsliding.

Farm field monitoring and irrigation automation using IOT

The Agricultural farming crops are produced in low qualitydue to lack of knowledge of farmers and crops destroyed by insects. To overcome that, many implemented factors are used. The factors can be temperature,soil,humidity,etc.,In biotechnology,some techniques are used withthe help of IoT. It is mainly used to increase the crops productivity in good quality.Existing related research works on sensor cloud have primarily focused on the challenges that wireless sensor network (WSN)-based applications. A direct estimate of water use by subsurface measurements of soil water content has been limited by the high cost of reliable soil moisture sensors. Using some sensors and techniques water can be irrigated automatically.IOT plays a vital role in smart farming.By using set of specified sensors,the irrigation man-agement can be done properly.The sensed data from the sensors and the irrigation controller are interfaced with Wi-Fi connection. In naive Bayes, by using decision making process the farmer can decide when and where to irrigate with the help of mobile application. An algo-rithm was developed with threshold values of temperature and soil moisture that was programmed into a microcontroller-based gateway to control water quantity.

Subsurface temperature measurements for detecting tectonic dislocations

An example of characterization of a tectonic zone by using underground temperature measurements is presented. A tectonic discontinuity, located in NW Italy, was investigated by precision temperature measurements by means of the analysis of thermal data recorded in a monitoring well along the northern part of Torrente Traversola Deformation Zone. Moreover, we investigated the lateral extension of the deformed zone by means of the analysis of thermal logs recorded in three control wells located at some distance from the tectonic structure. The monitoring well and the three control wells show completely different thermal pattern. The former exhibits advection and a thermal profile that can be well matched with a model of fluid flow within a sub-vertical fracture. The control wells instead reveal prevailing conductive thermal regime. This might be evidence that the deformation zone has little lateral extension. Our study showed that high-precision temperature logs can be a valuable tool for detecting fractured zones and delimit their lateral extent.

Late Pleistocene acceleration of deformation across the northern Tianshan piedmont (China) evidenced from the morpho-tectonic evolution of the Dushanzi anticline

We document the temporal evolution of deformation in the northern Tianshan piedmont where the deformation is partitioned across several thrusts and folds. We focus on the Dushanzi anticline, where abandoned terraces and growth strata allow us to constrain the history of folding since the Miocene. Based on subsurface seismic imaging, structural measurements and morphological analysis, we show that this anticline is associated with two decollement levels. We use kink band migration in growth strata dated by paleomagnetism to constrain the shortening from the Mio-Pliocene to the Holocene. Our results show that the Dushanzi anticline has been active since at least 8 Ma and that the fold grew at a steady shortening rate of 0.6 ± 0.1 mm/yr from 8 to ~1.5 Ma with possible variations from 2.5 to 1.5 Ma. Then it accelerated rapidly to a rate of 4.3 ± 1.0 mm/yr over at least the last 100 ka. These results, together with similar temporal shortening evolutions across other structures, suggest that the deformation rate across the eastern Tianshan piedmont increased relatively recently. This may reflect either a redistribution of the deformation from the internal structures toward the borders or a general acceleration of the deformation across the entire range.

Impact of soil surface and subsurface properties on soil saturated hydraulic conductivity in the semi-arid Walnut Gulch Experimental Watershed, Arizona, USA

The estimation of saturated hydraulic conductivity (Ks) is of high relevance to correctly reproduce water fluxes, such as infiltration rates or surface runoff in hydrological simulations. Yet, estimation of Ks is challenging especially in semi-arid regions with particular soil surface characteristics like crusting and sealing. This study presents results of a field campaign in the semi-arid Walnut Gulch Experimental Watershed, Arizona (US), where surface and subsurface Ks measurements were undertaken across the watershed. Data of saturated hydraulic conductivity on crust covered and crust-free surfaces was collected and compared to results of commonly used methods to retrieve spatially distributed Ks data. Results reveal that methods typically used for estimating Ks, such as exponential decay functions or pedo-transfer functions (PTFs), can be inadequate in such regions. The analysis shows that in our study area the presence of surface crust is the dominating factor for determining the spatial distribution of Ks. Furthermore, the results reveal that remote sensing data can provide useful information for estimating surface Ks values as it could be successfully applied for the spatial detection of surface crust characteristics.