Anomalous Light Scattering by Pure Seawater

The latest model for light scattering by pure seawater was used to investigate the anomalous behavior of pure water. The results showed that water exhibits a minimum scattering at 24.6 °C, as compared to the previously reported values of minimum scattering at 22 °C or maximum scattering at 15 °C. The temperature corresponding to the minimum scattering also increases with the salinity, reaching 27.5 °C for S = 40 ps

Laboratory Characterization of Reservoir Stimulation and Heat Extraction with Application to EGS

Enhanced or engineered geothermal systems (EGS) could enable extraction of significant geothermal energy from hot relatively dry rock reservoirs. However, issues related to reservoir creation in different type of rocks and stress conditions, reservoir monitoring during reservoir creation and consequent production, better knowledge of the fluid/heat flow in the induced fracture, field management and optimization need be addressed before successful commercial development. As an effort to help solve these essential questions, a novel lab-scale EGS test system was developed to perform EGS simulation experiments on rock blocks under high pore pressure/elevated temperature and representative in-situ stress regimes while simultaneously recording Acoustic Emission (AE), self-potential (SP), temperature/pressure and tracers to characterize the reservoir creation, heating mining and flow characteristics of the system. The tests were performed on the 330 mm × 330 mm ×330 mm cubic igneous rock blocks. Two kinds of igneous rocks with different texture and permeability were tested with one injection hole and four producers (five-spot pattern). The great potential of EGS was demonstrated by the fact that about 50 watts of power was obtained by fluid flowing through the induced fracture with length of 8.9 cm and rock temperature less than 80oC. Analysis of the test results sheds light on the use of acoustic emission for better understanding of hydraulic fracturing. Also, self-potential analysis indicates SP response was mainly controlled by electrokinetic coupling and the impact of thermoelectric coupling on recorded SP is negligible as demonstrated in some field observations and modeling while the fluid concentration (salinity) has a great influence on the SP response compared with temperature gradient when the concentration contrast between the injection fluid and the pore fluid is large due to the streaming potential coefficient reduction by the high concentration liquid. The heat circulation test shows that it is the effective fracture area instead of the total fracture area that controls the heat mining in EGS and thus the distance between injection/production wells or the location of the producer(s) and flow path tortuosity need be optimized to increase the effective heat exchange area in reservoir stimulation practice and the heat mining should be operated in a proper way to avoid well competition when multiple producers are connected to the same injection well by natural/man-made fractures. Excessive fracture propagation and high injection pressure was avoided during circulation tests by increasing the injection rate step by step. The cooling effect of the rock matrix i.e., increased fracture conductivity and lowering of the injection pressure is clearly manifested in the circulation experiments. As the first lab-scale tracer test on EGS, the obtained result was promising. The existing of two linear tracer tail was observed in Sierra White granite test and tracer result does show a good correlation between hydraulic conductivity and the tracer concentration response. The impact of rock texture was observed. What’s more, the test result could provide some useful guide for future lab-scale tracer test deign. Low permeability rock is recommended for tracer test to minimize leakage of tracer fluid into the rock matrix and also improve the fluid recovery. Low injection rate will increase the tracer time the in the fracture while proper tracer candidate with low-concentration detectability is required. Since the in-situ permeability of most of the dry hot rocks is not high enough to support the water injection with sufficient rate, reservoir stimulation by hydraulic fracture is usually applied. Considering the comment presence of natural fractures in the underground rocks, it is of importance to analyze the interaction between the hydraulic fracture and natural fracture. Analog experiments were conducted to investigate the interaction between a natural fracture and a hydraulic fracture with focus on slippage on the natural fracture or a bedding plane discontinuity due to an approaching hydraulic fracture. The tests were conducted on 101.6 mm diameter cylinder samples with a horizontal wellbore. The test materials included PMMA, shales, and Sierra White granite. Injection pressure, deviator stress, acoustic emission and the sample deformation are monitored during the test. In all the reported tests, the displacement calculated from the measured strain across the joint clearly shows a jump subsequent to pressure breakdown, and is accompanied by increased AE activity and decreased deviator stress. The displacement jump (slippage) across the joint with decreased deviatoric stress and AE activities on the joint from show that the hydraulic fracture caused slip of the saw-cut fractures even before reaching them. Analysis of the data clearly shows the occurrence of slippage on the joint in response to an approaching hydraulic fracture. The slippage due to the increased pore pressure on the natural fracture was also observed. Before the induced fracture reached the natural fracture, different degree of slippage (0.085mm ~ 0.11 mm) was obtained from these tests with various amount of deviator stress drop (0.14 MPa~ 0.6 MPa). Expectedly, the degree of shear slip varies with natural fracture dip, and friction angle and the differential stress. It is also observed that the pore pressure increase on the natural fracture by the encroaching hydraulic fracturing triggered larger slip on the natural fracture

Light Scattering by Pure Seawater: Effect of Pressure

The Zhang et al. model [Optics Express,17, 5698-5710 (2009)] for calculating light scattering by seawater doesnot account for pressure, which should, theoretically, affect molecular scattering. While negligible in nearsurface waters, the error associated with this approximation could be significant when backscattering is mea-sured directly in the deep ocean, by deep CTD casts or biogeochemical-Argo floats, for example. We updated theparameterization in the Zhang et al. model using (1) the Millard and Seaver equation for the refractive index ofseawater [Deep Sea Research Part A,37, 1909-1926 (1990)] and (2) the Feistel equation for Gibbs free energyfor seawater thermodynamics [Deep-Sea Research I,55, 1639-1671 (2008)]. As these equations include theeffect of pressure as well as salinity and temperature, our new parameterization allows us to investigate thepotential effect of pressure on scattering. Increasing pressure suppresses the random motion of molecules, re-ducing the fluctuations in both density and concentration, which in turn causes an overall decrease in lightscattering by seawater. For pure water and seawater with a salinity of 34 PSU, the decreases are approximately13% and 12%, respectively, with a 100-MPa (approximately the pressure of seawater at 10000 m) increase inpressure. Below the thermocline and/or halocline where temperature and salinity change slowly, the steadyincrease of pressure is the dominant factor affecting the light scattering by seawater. At depths where back-scattering is typically dominated by molecular scattering by seawater, particulate backscattering would beunderestimated if the effect of pressure on molecular scattering were not considered

Calibration of the LISST-VSF to Derive the Volume Scattering Functions In Clear Waters

The recently commercialized LISST-VSF instrument measures the volume scattering function (VSF) from 0.1° to 15° with a traditional laser diffraction unit (LISST) and from 15° to 155° with an eyeball component. Between these two optical components, only the LISST unit is calibrated. The eyeball measurements are scaled using the VSFs at 15° that are measured by both components. As this relative calibration relies on a valid measurement at 15° by the LISST, it might fail in clear oceanic waters, where the forward scattering is relative weak either due to a lack of large particles or an overall low concentration of all particles. In this study, we calibrated the LISST-VSF eyeball component through a series of lab experiments using standard polystyrene beads. Validation with the beads of two different sizes showed a median difference of 11.1% between theoretical and calibrated values. Further evaluations with in situ data collected by the LISST-VSF and an ECO-BB3 meter indicated that the new calibration worked well in both turbid and clear waters, while the relative calibration method tended to overestimate VSFs in clear waters

Multispecies Coevolution Particle Swarm Optimization Based on Previous Search History

A hybrid coevolution particle swarm optimization algorithm with dynamic multispecies strategy based on K-means clustering and nonrevisit strategy based on Binary Space Partitioning fitness tree (called MCPSO-PSH) is proposed. Previous search history memorized into the Binary Space Partitioning fitness tree can effectively restrain the individuals’ revisit phenomenon. The whole population is partitioned into several subspecies and cooperative coevolution is realized by an information communication mechanism between subspecies, which can enhance the global search ability of particles and avoid premature convergence to local optimum. To demonstrate the power of the method, comparisons between the proposed algorithm and state-of-the-art algorithms are grouped into two categories: 10 basic benchmark functions (10-dimensional and 30-dimensional), 10 CEC2005 benchmark functions (30-dimensional), and a real-world problem (multilevel image segmentation problems). Experimental results show that MCPSO-PSH displays a competitive performance compared to the other swarm-based or evolutionary algorithms in terms of solution accuracy and statistical tests

A Novel Plant Root Foraging Algorithm for Image Segmentation Problems

This paper presents a new type of biologically-inspired global optimization methodology for image segmentation based on plant root foraging behavior, namely, artificial root foraging algorithm (ARFO). The essential motive of ARFO is to imitate the significant characteristics of plant root foraging behavior including branching, regrowing, and tropisms for constructing a heuristic algorithm for multidimensional and multimodal problems. A mathematical model is firstly designed to abstract various plant root foraging patterns. Then, the basic process of ARFO algorithm derived in the model is described in details. When tested against ten benchmark functions, ARFO shows the superiority to other state-of-the-art algorithms on several benchmark functions. Further, we employed the ARFO algorithm to deal with multilevel threshold image segmentation problem. Experimental results of the new algorithm on a variety of images demonstrated the suitability of the proposed method for solving such problem

Discrete and Continuous Optimization Based on Hierarchical Artificial Bee Colony Optimizer

This paper presents a novel optimization algorithm, namely, hierarchical artificial bee colony optimization (HABC), to tackle complex high-dimensional problems. In the proposed multilevel model, the higher-level species can be aggregated by the subpopulations from lower level. In the bottom level, each subpopulation employing the canonical ABC method searches the part-dimensional optimum in parallel, which can be constructed into a complete solution for the upper level. At the same time, the comprehensive learning method with crossover and mutation operator is applied to enhance the global search ability between species. Experiments are conducted on a set of 20 continuous and discrete benchmark problems. The experimental results demonstrate remarkable performance of the HABC algorithm when compared with other six evolutionary algorithms

A closure study of ocean inherent optical properties using flow cytometry measurements

Flow cytometry and inherent optical property measurements of UK coastal waters were used to evaluate optical closure of different combinations of models for particle size, refractive index and shape. The particle size and refractive index distributions were derived from flow cytometry measurements and subsequently simplified through averaging down to the simplest model consisting of a Junge size distribution with a single bulk refractive index. Models for particle shapes included homogeneous spheres, coated spheres, and hexahedra. The simplest particle model, based on a Junge size distribution and a single bulk refractive index, gave the poorest quality of closure, suggesting that it underestimates particle complexity in the sampled waters. Other particle models using more detailed combinations of size and refractive index distributions gave broadly equivalent results for absorption and scattering. Backscattering was better represented by the most complex particle size and refractive index model, indicating that backscattering is sensitive to those factors. The homogeneous spherical model gave relatively good results, which is expected because the inversion of size and refractive index distributions from flow cytometry is based on the homogeneous spherical model using forward and side scattering signals. Lorenz-Mie theory, assuming homogeneous spheres, provided optical closure that was generally as accurate as models with more complex particle shape and structure. Cumulative contribution simulations revealed that particles between 0.5 and 20 µm substantially contributed to attenuation, scattering and backscattering, while particles larger than 20 µm mainly contributed to absorption and small particles (< 0.5 µm) contribute to 30–40% of backscattering

Alignment of Optical Backscatter Measurements From the EXPORTS Northeast Pacific Field Deployment

Backscattering of light is commonly measured by ocean observing systems, including ships and autonomous platforms, and is used as a proxy for the concentration of water column constituents such as phytoplankton and particulate carbon. Multiple on-going projects involve large numbers of independent measurements of backscatter, as well as other biologically relevant parameters, to understand how biology is changing in time and space throughout the global ocean. Rarely are there sufficient measurements to test how well these instruments are inter-calibrated in real-world deployment conditions. This paper develops a procedure to align multiple independently calibrated backscatter instruments to each other using nearby profiling casts and applies this method to nine instruments deployed during a recent field campaign in the North Pacific during August–September of 2018. This process revealed several incorrect calibrations; post-alignment, all nine instruments aligned extremely well with each other. We also tested an alignment to a deep-water reference and found that this method is generally sufficient but has significant limitations; this procedure lacks the ability to correct instruments measuring only shallow profiles and can only account for additive offsets, not multiplicative changes. These findings highlight the utility of process studies involving several independent measurements of similar parameters in the same area