High Temporal Resolution Monitoring Research Articles

Assessment of annual physico-chemical variability via high-temporal resolution monitoring in an Antarctic shallow coastal site (Terra Nova Bay, Ross Sea)

Assessment of annual physico-chemical variability via high-temporal resolution monitoring in an Antarctic shallow coastal site (Terra Nova Bay, Ross Sea)

Assessment of annual physico-chemical variability via high-temporal resolution monitoring in an Antarctic shallow coastal site (Terra Nova Bay, Ross Sea)

Assessment of annual physico-chemical variability via high-temporal resolution monitoring in an Antarctic shallow coastal site (Terra Nova Bay, Ross Sea)

Enteromorpha Coverage Information Extraction by 1D-CNN and Bi-LSTM Networks Considering Sample Balance From GOCI Images

Remote sensing technology is widely used for the dynamic monitoring of Enteromorpha prolifera (EP) blooms due to its high temporal resolution and large scale monitoring. Recently, deep learning(DL) methods have been applied to EP analysis due to their excellent feature representation. However, EP information extraction methods based on DL from low-spatial-resolution satellite images are still immature. The main problems with such methods include the insufficiency of spectral and spatial feature learning in low-resolution satellite images, as well as the sample imbalance that DL-based neural networks face in EP information extraction. To solve the above problems, a neural network-based EP extraction method considering sample balance is proposed in this article and named EP rough-then-accurate extraction network. The method consists of two components: EP rough extraction, a strategy that attends to sample balance, and EP accurate extraction, a deep neural network based on one-dimensional convolutional neural network and bidirectional long short-term memory (Bi-LSTM), which fully considers the learned spectral information of each pixel and interpixel contextual dependencies. Geostationary Ocean Color Imager images with 500-m resolution were applied as the LR images in the experiments. The experimental results show that the proposed method has the capability to enhance adaptability in areas with different EP densities (achieving stable and excellent performance) and exhibits at least a 10% gain in F1-score and at least a 6% gain in IoU in extracting EP coverage information over other representative and traditional EP extraction methods in the Yellow Sea region.

Spatial and Temporal Variability of Diffusive CO2 and CH4 Fluxes From the Amazonian Reservoir Petit‐Saut (French Guiana) Reveals the Importance of Allochthonous Inputs for Long‐Term C Emissions

AbstractVariability in greenhouse gas emissions from reservoirs creates uncertainty in global estimates of C emissions from reservoirs. This study examines the temporal and spatial variability in CO2 and CH4 surface water concentrations and diffusive fluxes from an Amazonian reservoir using an original data set combining both a high temporal (1 central site × 22 years) and spatial (44 sites × 1 season) resolution monitoring. The gas concentrations at the central site decreased over time and suggested reduced bioavailability of C in the initial flooded soil but exhibited strong seasonal variation. Not accounting for this variability may result in uncertainties in estimates of annual concentrations (ranging from −68.9% to +260% for CH4 and from −71.5% to +156% for CO2) and thus in estimates of diffusive gas emissions. Gas concentrations and diffusive fluxes exhibited high spatial variability in the reservoir, 24 years after impoundment. In particular, diffusive fluxes were higher in littoral and transitional areas than in open areas, suggesting a large contribution of allochthonous C to current gaseous emissions. Not accounting for this spatial variability in diffusive fluxes may underestimate the total emissions expressed in CO2 equivalents from the whole reservoir by 50.7%. Our study stresses the importance of well‐resolved temporal and spatial monitoring to provide reliable estimated of C emissions and a comprehensive understanding of the processes involved; both of these inputs are needed to support decision‐making for developing energy strategies.

Hydromechanical insight of fracture opening and closure during in-situ hydraulic fracturing in crystalline rock

Six hydraulic fracturing (HF) experiments were conducted in situ at the Grimsel Test Site (GTS), Switzerland, using two boreholes drilled in sparsely fractured crystalline rock. High spatial and temporal resolution monitoring of fracture fluid pressure and strain improve our understanding of fracturing dynamics during and directly following high-pressure fluid injection. In three out of the six experiments, a shear-thinning fluid with an initial static viscosity approximately 30 times higher than water was used to understand the importance of fracture leak-off better. Diagnostic analyses of the shut-in phases were used to determine the minimum principal stress magnitude for the fracture closure cycles, yielding an estimate of the effective instantaneous shut-in pressure (effective ISIP) 4.49±0.22 MPa. The jacking pressure of the hydraulic fracture was measured during the pressure-controlled step-test. A new method was developed using the uniaxial Fibre-Bragg Grating strain signals to estimate the jacking pressure, which agrees with the traditional flow versus pressure method. The technique has the advantage of observing the behavior of natural fractures next to the injection interval. The experiments can be divided into two groups depending on the injection location (i.e., South or North to a brittle-ductile S3 shear zone). The experiments executed South of this zone have a jacking pressure above the effective ISIP. The proximity to the S3 shear zone and the complex geological structure led to near-wellbore tortuosity and heterogeneous stress effects masking the jacking pressure. In comparison, the experiments North of the S3 shear zone has a jacking pressure below the effective ISIP. This is an effect related to shear dislocation and fracture opening. Both processes can occur almost synchronously and provide new insights into the complicated mixed-mode deformation processes triggered by high-pressure injection.

UAV-based high spatial and temporal resolution monitoring and mapping of surface moisture status in a vineyard

Drone-based RGB and thermal infrared remote sensing are rapidly becoming useful tools for monitoring crop and soil status for precision farming. The objectives of this study are as follows: (1) flying UAV or drone to collect large spatial scale RGB and infrared aerial images during the growing season and (2) producing high spatial–temporal resolution digital surface models and imagery mosaics to help farmers monitor surface moisture status in the study vineyard. A total of four field aerial surveys were conducted during the growing season of 2018 from May to August. A surface moisture mapping index (SMMI) model was proposed based on modified normalized difference water index and topographic wetness index. This model combines the factors of both radiant reflection properties by moisture bearing surfaces of a farming field, and the slope gradient and micro-topographic positions in the field. The results indicate that the spatial pattern of SMMI, or the relative quantities of surface moisture contents, across the vineyard was maintained the same during the entire growing season. This might be impacted by localized factors of surface slope gradient and topographic positions. Meanwhile, temporal variations of surface moisture status are mainly influenced by frequency and intensity of the precipitations.

Functional trade-off of hydration strategies in old forest epiphytic cephalolichens

Although water is essential for photosynthetic activation in lichens, rates of vapor uptake and activation in humid air, which likely influence their niche preferences and distribution ranges, are insufficiently known. This study simultaneously quantifies rehydration kinetics and PSII reactivation in sympatric, yet morphologically and functionally distinct cephalolichens (Lobaria amplissima, Lobaria pulmonaria, Lobaria virens). High-temporal resolution monitoring of rehydrating thalli by automatic weighing combined with chlorophyll fluorescence imaging of maximal PSII efficiency (FV/FM) was applied to determine species-specific rates of vapor uptake and photosynthetic activation. The thin and loosely attached growth form of L. pulmonaria rehydrates and reactivates faster in humid air than the thick L. amplissima, with L. virens in between. This flexible hydration strategy is consistent with L. pulmonaria’s wide geographical distribution stretching from rainforests to continental forests. By contrast, the thick and resupinate L. amplissima reactivates slowly in humid air but stores much water when provided in abundance. This prolongs active periods after rain, which could represent an advantage where abundant rain and stem flow alternates with long-lasting drying. Understanding links between morphological traits and functional responses, and their ecological implications for species at risk, is crucial to conservation planning and for modelling populations under various climate scenarios.

Monitoring Freeze-Thaw State by Means of GNSS Reflectometry: An Analysis of TechDemoSat-1 Data

The article of the freeze/thaw dynamic of high-latitude Earth surfaces is extremely important and informative for monitoring the carbon cycle, the climate change, and the security of infrastructures. Current methodologies mainly rely on the use of active and passive microwave sensors, while very few efforts have been devoted to the assessment of the potential of observations based on signals of opportunity. This article aims at assessing the performance of spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) for high-spatial and high-temporal resolution monitoring of the Earth-surface freeze/thaw state. To this aim, reflectivity values derived from the TechDemoSat-1 (TDS-1) data have been collected and elaborated, and thus compared against the soil moisture active passive (SMAP) freeze/thaw information. Shallow subsurface soil temperature values recorded by a network of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> stations have been considered as well. Even if an extensive and timeliness cross availability of both types of experimental data is limited by the spatial coverage and density of TDS-1 observations, the proposed analysis clearly indicates a significant seasonal cycle in the calibrated reflectivity. This opens new perspectives for the bistatic L-band high-resolution satellite monitoring of the freeze/thaw state, as well as to support the development of next-generation of GNSS-R satellite missions designed to provide enhanced performance and improved temporal and spatial coverage over high latitude areas.

Exploring extreme rainfall impacts on flow and turbidity dynamics in a steep, pristine and tropical volcanic catchment

Tropical volcanic landscapes are important because of the short timescales (< years) over which they transform. Sediment sources, availability and transport can be highly dynamic, but our understanding of these is limited by a lack of data in these complex environments, especially with regards to extreme events. To investigate the responses to extreme rainfall events in particular, we conducted extensive monitoring in a pristine tropical rainforest catchment (3.2 km2), located in the Volcanic Cordillera of Tilarán, Costa Rica. We established high temporal resolution hydro-meteorological and turbidity monitoring from June 2015 to July 2016. This included a record convective rainfall event in August 2015 which resulted in an estimated >50 yr return period flood event. We also surveyed hillslope soils, landslides, and sediments of the river network, to characterize sediments before and after the extreme event. Our results suggested that rainfall events activated surface flow pathways with associated mobilization of material. However, erosion processes were mostly linked to finer material (sand, silt) properties of the soils that developed on more highly weathered bedrock. The single extreme event (return period >50 years) had an overriding impact on the general sediment dynamics. Recovery in the form of fine material transport and associated hysteresis took only about three months. We conclude that the combined use of high-temporal resolution monitoring with spatially distributed surveys provided new insights for the initial assessment into the fluvial geomorphology and transport dynamics of steep, volcanic headwater catchments in the humid tropics with potential to establish more complete time scales of land-forming processes. This work can build the foundation for more complete monitoring using radioisotopes as a tool to fingerprint the sediment origin and composition.

High Temporal Resolution Monitoring of Suspended Matter Changes from GOCI Measurements in Lake Taihu

The Tiaoxi River is the main source of water for Lake Taihu and can result in plumes in the lake after heavy precipitation events. These plumes have played a crucial role in the water quality changes within the lake. High temporal resolution GOCI (Geostationary Ocean Color Imager) data were used to study the spatial distribution of the total suspended matter concentration in Lake Taihu after heavy precipitation events in the Tiaoxi River Basin via an empirical model. The plumes were analyzed after two heavy precipitation events in 2011 and 2013 using 16 GOCI images, which indicated that the Tiaoxi River had a great influence on the spatial distributions of total suspended matter and algal blooms. It was concluded that the main factors affecting the plumes in the Tiaoxi River were precipitation intensity, runoff, and total suspended matter concentration. Human activity, such as sand excavation also played a crucial role in sediment discharge. The results of this study demonstrate that the visualization of GOCI data makes it possible to use remote sensing technology to continuously monitor an inland water environment on an hourly scale, which is of great significance for studying the diffusion and evolution of river plumes.

High Temporal Resolution Monitoring of Small Variations in Crustal Strain by Dense Seismic Arrays

AbstractWe demonstrate the feasibility of detecting very weak deformation in the shallow crust with high temporal resolution by monitoring the relative changes in seismic wave velocity (dv/v) using dense arrays of seismometers. We show that the dv/v variations are consistent between independent measurements from two seismic arrays. Dominant peaks in the observed dv/v spectrum suggest that tides and temperature changes are the major causes of daily and subdaily velocity changes, in accordance with theoretical strain modeling. Our analysis illustrates that dv/v perturbations of the order of 10−4, corresponding to crustal strain changes of the order of 10−8, can be measured from ambient seismic noise with a temporal resolution of 1 hr. This represents a low‐cost technique for high precision and high time‐resolution monitoring of crustal deformation that is complementary to existing geodetic measurements and is instrumental in both the detection and understanding of low‐amplitude precursory processes of natural catastrophic events.

Single photon ionization time-of-flight mass spectrometry with a windowless RF-discharge lamp for high temporal resolution monitoring of the initial stage of methanol-to-olefins reaction

Methanol-to-olefins (MTO) is a very important industrial catalysis technique for the production of light olefins, which is of great economic value and strategic significance. However, it is a great challenge for the traditional analytical methods to obtain the real-time information of product variation during MTO reaction process, which is vital for the conversion process research and mechanism explanation. In this study, a single photon ionization time-of-flight mass spectrometry (SPI-TOFMS) based on a windowless RF-discharge (WLRF) lamp was developed for real-time measurement of catalytic product during the initial stage of MTO reaction. The vacuum ultraviolet (VUV) photon energy was easily adjusted by changing the discharge gas. Argon (Ar) gas was eventually adopted as the discharge gas, since it produces photons with appropriate energy of 11.6 eV and 11.8 eV for ionization of light olefin molecules. The detection sensitivities of ethylene and propylene were largely improved to a substantially similar level with limits of detection (LODs) down to 16.98 and 9.64 ppbv, respectively. The initial stage of MTO reaction was real-time monitored with a high temporal resolution of 0.5 s, revealing that ethylene was the first olefin product followed by propylene. The successful application of WLRF-SPI-TOFMS in the monitoring of MTO catalytic process indicated broad application prospects of this instrument in the industrial reaction process monitoring.

Seasonal Cycles, Hypoxia, and Renewal in a Coastal Fjord (Barkley Sound, British Columbia)

ABSTRACTThe west coast of Vancouver Island (WCVI) is an important marine ecosystem in which concentrations of dissolved oxygen can reach hypoxic levels at certain times of the year. Although the general features of its oceanography are well understood, little is known in particular about the seasonal cycle of oxygen in shelf areas and its interannual variability. It is possible that high temporal resolution monitoring efforts could be carried out relatively easily in sheltered fjords adjacent to the shelf, but the linkages between conditions in these fjords and those on the shelf are also not known. Here a 10-year time series of monthly hydrographic stations in Barkley Sound, British Columbia, is used to identify the seasonal cycle of temperature, salinity, density, dissolved oxygen, and chlorophyll fluorescence in a WCVI fjord. Analysis suggests that there is a standard estuarine circulation in surface and near-surface waters of the Sound, as well as a deep renewal cycle in intermediate and deep waters, and that the two are largely independent. The deep basin in the Sound undergoes annual summer renewals in response to wind-driven upwelling on the shelf, separated by stagnation and hypoxia during fall, winter, and spring downwelling periods. Other than for the stagnant deep waters in winter, residence times in different parts of the Sound are only a few weeks. Barkley Sound characteristics thus adjust rapidly to shelf conditions, and inshore measurements can be used with care as a proxy for some shelf properties. However, phytoplankton biomass does not appear to be affected by the onset of deep renewal and the associated reversal of along-shore winds and instead responds to local factors. Finally, once the seasonal cycle has been accounted for, interannual variations in temperature, density, and dissolved oxygen are uncoupled, possibly in response to longer-term changes in the characteristics of source waters offshore and/or to changes in shelf processes.

Long-term monitoring of streambed sedimentation and scour in a dynamic stream based on streambed temperature time series

This study presented the monitoring and quantification of streambed sedimentation and scour in a stream with dynamically changing streambed based on measured phase and amplitude of the diurnal signal of sediment temperature time series. With the applied method, changes in streambed elevation were estimated on a sub-daily scale with 2-h intervals without continuous maintenance of the measurement system, thus making both high temporal resolution and long-term monitoring of streambed elevations possible. Estimates of streambed elevation showed that during base flow conditions streambed elevation fluctuates by 2-3cm. Following high stream stages, scouring of 2-5cm can be observed even at areas with low stream flow and weak currents. Our results demonstrate that weather variability can induce significant changes in the stream water and consequently sediment temperatures influencing the diurnal temperature signal in such an extent that the sediment thickness between paired temperature sensors were overestimated by up to 8cm. These observations have significant consequences on the design of vertical sensor spacing in high-flux environments and in climates with reduced diurnal variations in air temperature.

The environmental legacy of historic Pb-Zn-Ag-Au mining in river basins of the southern edge of the Massif Central (France).

The main rivers (Aude, Orb, Herault) that discharge into the Gulf of Lions and the west bank tributaries of the Rhone River including the Gardon have former non-ferrous metal mines in their upper drainage basin. Using unpublished data and data from the literature, this study provides an integrated overview of the contamination of water and sediment along the continent-sea continuum and of its impacts on the biota and on human health. In the upper part of these basins, water and stream sediments are enriched in metal(-loids) compared to median European concentrations. Arsenic is the main contaminant in the rivers Aude and Gardon d'Anduze, Sb in the Orb and Gardon d'Alès, and Tl in the Herault river. A rapid reduction in dissolved and particulate concentrations was systematically observed along the river due to dilution and precipitation. The high concentrations of metal(-loid)s observed suggest that the former mining activity still represents a potential threat for the environment, but the lack of high temporal resolution monitoring, especially during Mediterranean floods, prevents accurate assessment of metal fluxes from these rivers to the Mediterranean Sea. Studies dedicated to the impacts on human health are too rare, given that studies have shown a higher rate of arsenic-specific cancer near Salsigne mine in the Aude River basin and cases of saturnism in children in the upper Herault River basin. These studies underline the need to take environmental health issues into consideration not only in these watersheds but around the entire Mediterranean basin, which harbors numerous metalliferous ores that have been mined for millennia.

Effects of climate change on bioaccumulation and biomagnification of polycyclic aromatic hydrocarbons in the planktonic food web of a subtropical shallow eutrophic lake in China

To date effects of climate change on bioaccumulation and biomagnification of chemical pollutants in planktonic food webs have rarely been studied. Recruitments of plankton have shifted earlier due to global warming. Global warming and precipitation patterns are projected to shift seasonally. Whether and how the shifts in plankton phenology induced by climate change will impact bioaccumulation and biomagnification of chemical pollutants, and how they will respond to climate change are largely unknown. Here, we combine data analysis of the past seven decades, high temporal resolution monitoring and model development to test this hypothesis with nine polycyclic aromatic hydrocarbons (PAHs) in the planktonic food web of a subtropical shallow eutrophic lake in China. We find biphasic correlations between both bioconcentration factors and bioaccumulation factors of the PAHs and the mean temperature, which depend on the recruitment temperatures of cyanobacteria, and copepods and cladocerans. The positive correlations between bioconcentration factors, bioaccumulation factors and the mean temperature will be observed less than approximately 13–18 days by 2050–2060 due to the shifts in plankton phenology. The PAHs and their bioaccumulation and biomagnification will respond seasonally and differently to climate change. Bioaccumulation of most of the PAHs will decrease with global warming, with higher decreasing rates appearing in winter and spring. Biomagnification of most of the PAHs from phytoplankton to zooplankton will increase with global warming, with higher increasing rates appearing in winter and spring. Our study provides novel insights into bioaccumulation and biomagnification of chemical pollutants in eutrophic waters under climate change scenarios.

Alpine glacier-fed turbid lakes are discontinuous cold polymictic rather than dimictic

Glacier retreat as a consequence of climate change influences freshwater ecosystems in manifold ways, yet the physical and chemical bases of these effects are poorly studied. Here, we characterize how water temperature differs between alpine lakes with and without direct glacier influence on seasonal and diurnal timescales. Using high temporal resolution monitoring of temperature in 4 lakes located in a catchment influenced by glacier retreat, we reported unexpectedly high surface temperatures, even in proglacial lakes located 2600 m a.s.l. Cold glacier meltwater and low nighttime air temperatures caused a distinct diurnal pattern of water temperature in the water column of glacier-influenced lakes. Precipitation onto glacier surfaces apparently leads to rapid cooling of the glacier-fed lakes and disrupts the thermal stratification with several mixing events during the summer. Taken together, these mechanisms contribute to the unique seasonal and diurnal dynamics of glacier-influenced lakes that contrast with the typical dimictic pattern of clear alpine lakes and represent an example of discontinuous cold polymictic lake type. This work contributes to the basic description of how climate and meteorology affect the physical properties of an increasingly common lake type.

Constructed Wetlands as Urban Water Constructed Wetlands as Urban Water Quality Control Ponds - Studies on Reliability and Effectiveness

Constructed wetlands have come into widespread use as water quality control systems in urban areas. However Published research into their water quality improvement performance has, been sporadic and often contradictory. In order to address this situation, a cooperative study was initiated in 2009 by Wollongong City Council and the University of Wollongong to investigate the pollutant reduction performance of an existing water quality control pond. The pond was monitored for a period between 2009 and 2010 and a unique method for estimating constructed wetland performance was developed to address limitations found in other studies. This method incorporated automated sampling, high temporal resolution monitoring and standard least squares procedures to fit multivariate statistical models to estimate the pollutant reduction performance. The monitoring results were used to calibrate and validate a model which is able to quantitatively assess uncertainty. Results from this study suggest the method applied could be used as a standard method for estimating the pollutant reduction performance of other similar water quality improvement systems.

Inorganic carbon flux and its source in the karst catchment of Maocun, Guilin, China

New findings have shown that the contribution of carbonate weathering to the atmospheric CO2 sink is far greater than previous estimates, through the combined action of carbonate dissolution, the global water cycle, and photosynthetic uptake of dissolved inorganic carbon (DIC). However, in order for calculations to be accurate, any carbon source effect should be deducted from the overall carbon sink. In this study, we carried out high temporal resolution monitoring of flow and hydrochemistry within the Xiaolongbei (XLB) silicate catchment and Beidiping (BDP) carbonate catchment for 1 year. We found the dissolved inorganic carbon concentrations to be higher in BDP than in XLB, and the annual inorganic carbon fluxes in BDP are roughly 23.8 times higher than those in XLB. Similarly, the rate of carbonate rock dissolution is much higher than the rate of silicate rock dissolution. We find carbonate rock dissolution to respond rapidly to rainfall events, and it is sensitive to rainfall changes on hourly, diurnal, and seasonal scales. The high rate of carbonate rock dissolution gives rise to the high concentrations of DIC, Ca, Mg, and to the high inorganic carbon flux in this basin. Differences between the theoretical and calculated contributions of atmospheric and soil CO2 to the DIC are possibly due to CO2 outgassing.

Validation of the SO2 camera for high temporal and spatial resolution monitoring of SO2 emissions

Ground-based measurements of sulfur dioxide (SO2) are a key part of monitoring networks at many volcanic centers. SO2 camera systems represent an attractive addition to conventional spectroscopic methods such as COSPEC or DOAS, because they offer higher sampling rates (up to 1Hz) and two-dimensional concentration mapping which provides additional contextual information for emission rate calculation and interpretation. Here we present the results of an SO2 camera development project and corresponding validation experiment conducted at a coal-burning power plant in Arizona (USA), where the emissions are independently measured. Emissions of SO2 and other acid gases are regulated in the United States, and hourly data are publicly reported by the US Environmental Protection Agency (EPA). We measured the emissions from two exhaust stacks that had an average combined rate of 8.2±2.1×10−2kgs−1 (7±1.8td−1) over a period of 3h. Masses integrated from our dataset are within 10–20% of the emissions reported by the EPA. The contextual information contained in the images allowed the identification and measurement of the individual plumes from each stack. Measured emission rates decrease with increasing distance from the source, pointing to an apparent loss of SO2 primarily by gas dilution processes, with SO2 concentrations dropping below the detection limit at the edge of the plume at distances>200m from the source. Cross-sections very close to the vent (within 50m; ~2 vent diameters), through the optically thick condensing part of the plume, yielded emission rates lower than those reported to the EPA. This near-vent discrepancy is interpreted to be the result of light dilution effects due to attenuation and reflections off the surface of the condensing plume. This work is the first reported validation of emission rate measurements produced by an SO2 camera in a volcano-like geometry, and demonstrates that reliable emission rates can be measured, but also emphasizes the importance of the selection of the cross-section locations.