Turbidimeter Design and Analysis: A Review on Optical Fiber Sensors for the Measurement of Water Turbidity
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paper_title: Establishing the Relationship between Turbidity and Total Suspended Sediment Concentration

paper_content:

This laboratory work examines the relationship between turbidity (NTU) and total suspended sediment concentration (TSS, mg/L) for a Cecil Ap soil, a common Southeastern Piedmont soil type. We show a 1:1 correlation between NTU and TSS for the silt and clay fractions, but a smaller ratio for clay and bulk-soil samples. These results suggest that NTU measurements can be used to estimate sediment concentrations for fine soil fractions, but underestimates the total sediment concentration when sand-size fractions are present.
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paper_title: Definition of Clay and Clay Mineral: Joint Report of the AIPEA Nomenclature and CMS Nomenclature Committees

paper_content:

The definition of"clay" was first formalized in 1546 by Agricola. It has been revised many times since, although the fundamentals involving plasticity, particle size, and hardening on firing were retained by most. For an exhaustive account of the history of the definit ion to 1963, the reader is referred to Mackenzie (1963). More recent developments may be found in Weaver (1989). The definition of clay raises the important issue of clay constituents and, implicitly, the definition of "clay mineral." Mackenzie (1963, p. 15) noted the inappropriateness of defining clay mineral as "any mineral which occurs in clay" since, among several reasons, it would include many accessory minerals that are not characteristic of clay. Previous definitions of "clay mineral" (e.g., Bailey 1980) simply equated clay minerals to phyllosilicates, thus endorsing the use of a term without apparent justification. The term "clay mineral," however, is useful when applied in context to clay constituents. The approach of equating "clay mineral" to phyllosilicate fails to consider the relationship of the properties of the bulk clay with the properties of the constituents of clay. This inconsistency is addressed here in part, without making major changes to current usage. Weaver (1989, p. 5) noted an additional complication: the conceptual problem of combining particle size
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paper_title: High concentration suspended sediment measurements using a continuous fiber optic in-stream transmissometer

paper_content:

Suspended sediment loads mobilized during high flow periods in rivers and streams are largely uncharacterized. In smaller and intermittent streams, a large storm may transport a majority of the annual sediment budget. Therefore monitoring techniques that can measure high suspended sediment concentrations at semi-continuous time intervals are needed. A Fiber optic In-stream Transmissometer (FIT) is presented for continuous measurement of high concentration suspended sediment in storm runoff. FIT performance and precision were demonstrated to be reasonably good for suspended sediment concentrations up to 10g/L. The FIT was compared to two commercially available turbidity devices and provided better precision and accuracy at both high and low concentrations. Both turbidity devices were unable to collect measurements at concentrations greater than 4 g/L. The FIT and turbidity measurements were sensitive to sediment particle size. Particle size dependence of transmittance and turbidity measurement poses the greatest problem for calibration to suspended sediment concentration. While the FIT was demonstrated to provide acceptable measurements of high suspended sediment concentrations, approaches to real-time suspended sediment detection need to address the particle size dependence in concentration measurements.
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paper_title: Field and laboratory studies on the effect of particle size and composition on optical backscattering measurements in hydrothermal plumes

paper_content:

Abstract We describe the performance of an inexpensive but highly sensitive light backscattering sensor (LBSS) suitable for use in deep-sea waters, where particle concentrations are typically 10 μm. Field studies indicate that in hydrothermal plumes dominated by fine-grained metal precipitates the 95% confidence interval for predicting mass concentration with an LBSS ranges from ±0.004 mg/l for 0.03 mg/l suspensions to ±0.008 mg/l at 0.12 mg/l. Comparisons among a group of 19 LBSSs found between-instrument variability to reach 70%, but normalizing the raw data using a laboratory calibration procedure reduced the maximum variability to ∼8%.
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paper_title: Study of particle size effects on an optical fiber sensor response examined with Monte Carlo simulation

paper_content:

Optical fiber sensors based on the total light transmittance are widely used to measure the volume fraction of particles in suspensions. However, the sensor response depends not only on the volume fraction but also on the particle size. The particle size effect is studied for a sensor configuration consisting of two linear arrays of fibers on each of two blocks: the emitting and receiving blocks. These two linear arrays are arranged with three adjacent fibers (one fiber on the first array, two fibers on the second array) ::: forming a perfect triangle. The almost superimposition of the calculated sensor response versus the extinction factor for different particle sizes allows for the application of single- ::: curve models. Two single-curve models that describe the sensor response for all particle sizes ranging from 36 to ::: 200 μm are proposed. The models are validated by Monte Carlo simulation for different particle sizes and are valid within a detectable volume fraction. The single-curve models proposed provide an easier approach to creating a database for sensor calibration for suspended sediment concentration measurements.
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paper_title: Light attenuation and scattering by phytoplanktonic cells: a theoretical modeling.

paper_content:

A theoretical modeling is proposed to predict the efficiency factors for attenuation, total scattering, and backscattering for spherical and homogeneous phytoplanktonic cells in suspension. The input parameters of this modeling are the actual size distribution, the spectral values of absorption by the living cells, and an adjustable value of the real part of the refractive index. The variations in these parameters lead to very diverse spectral behavior of the efficiency factors. Theoretical predictions are compared to experimental results for some species to evaluate the reliability of the model for algal cells of various indices and morphologies.
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paper_title: Diffuse reflectance of oceanic waters: its dependence on Sun angle as influenced by the molecular scattering contribution.

paper_content:

A spectral model of the inherent optical properties (absorption and scattering coefficients a and b, respectively) of oceanic case 1 waters with varying chlorophyll concentrations C is operated. It provides the initial conditions for Monte Carlo simulations aimed at examining the diffuse reflectance directly beneath the surface R and its variations with the solar zenith angle zeta. In most oceanic waters, molecular scattering is not negligible, and molecular backscattering may largely exceed backscattering. The variable contributions (depending on C and wavelength) of water molecules and particles in the scattering process result in considerable variations in the shape of the volume-scattering function. R(zeta) is sensitive to this shape. From the simulations, R (which increases as zeta increases) appears to be linearly related to cos zeta, with a slope that is strongly dependent on eta(b), the ratio of molecular backscattering to particle backscattering. The value of the single-scattering albedo (?= b/a + b) has a negligible influence on the R(zeta) function provided that ? < 0.8, a condition that is always fulfilled when dealing with oceanic case 1 waters. Practical formulas for R(zeta) are proposed. They include the influence of the diffuse sky radiation. The history of each photon and the number of collisions it experiences before exiting have been recorded. These histories and also a probabilistic approach allow the variations of R with cos zeta, eta(b), and ? to be understood.
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paper_title: A model for estimating bulk refractive index from the optical backscattering ratio and the implications for understanding particle composition in case I and case II waters

paper_content:

A model based on Mie theory is described that estimates bulk participate refractive index n¯p from in situ optical measurements alone. Bulk refractive index is described in terms of the backscattering ratio and the hyperbolic slope of the particle size distribution (PSD). The PSD slope ξ is estimated from the hyperbolic slope of the particulate attenuation spectrum γ according to the relationship γ ≈ ξ − 3, verified with Mie theory. Thus the required in situ measurements are the particulate backscattering coefficient, the total particulate scattering coefficient, and the particulate attenuation coefficient. These parameters can be measured with commercially available instrumentation with rapid sampling rates and real-time data return. Application of the model to data from the Gulf of California yielded results that agreed with expectations, e.g., predicted n¯p was 1.04–1.05 in the chlorophyll maximum and 1.14–1.18 near sediments. Below the chlorophyll maximum in case I type waters, predicted n¯p values were between 1.10 and 1.12, suggesting the presence of a significant inorganic mineral component in the background or detrital organic particles with low water content.
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paper_title: An experiment to measure Mie and Rayleigh total scattering cross sections

paper_content:

We present an undergraduate-level experiment using a conventional absorption spectrophotometer to measure the wavelength dependence of light scattering from small dielectric spheres suspended in water. The experiment yielded total scattering cross-section values throughout the visible region that were in good agreement with theoretical values predicted by the Rayleigh and Mie theories.
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paper_title: Relationship of light scattering at an angle in the backward direction to the backscattering coefficient.

paper_content:

We revisit the problem of computing the backscattering coefficient based on the measurement of scattering at one angle in the back direction. Our approach uses theory and new observations of the volume scattering function (VSF) to evaluate the choice of angle used to estimate b(b). We add to previous studies by explicitly treating the molecular backscattering of water (b(bw)) and its contribution to the VSF shape and to b(b). We find that there are two reasons for the tight correlation between observed scattering near 120 degrees and the backscattering coefficient reported by Oishi [Appl. Opt. 29, 4658, (1990)], namely, that (1) the shape of the VSF of particles (normalized to the backscattering) does not vary much near that angle for particle assemblages of differing optical properties and size, and (2) the ratio of the VSF to the backscattering is not sensitive to the contribution by water near this angle. We provide a method to correct for the water contribution to backscattering when single-angle measurements are used in the back direction (for angles spanning from near 90 degrees to 160 degrees ) that should provide improved estimates of the backscattering coefficient.
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paper_title: Optical properties of the clearest natural waters ( 200-800 nm )

paper_content:

A new UV submersible spectroradiometer has been employed to determine the diffuse attenuation coefficient for irradiance in the clearest natural waters [K(w)(lambda)] with emphasis on the spectral region from 300 to 400 nm. K(w)(lambda) can be related to the inherent optical properties of pure water, in particular the total absorption coefficient a(w)(lambda) and the molecular scattering coefficient b(m)(lambda), by means of equations derived from radiative transfer theory. We present an analysis showing that limiting values of K(w)(lambda) can be estimated from a(w)(lambda) and vice versa. Published a(w)(lambda) data, which show discrepancies much larger than their estimated accuracies, are briefly reviewed and then compared, via our analysis, with K(w)(lambda) data (our own new and previously published data as well as relevant data of others). This comparative analysis and new data allow a consistent and accurate set of optical properties for the clearest natural waters and for pure fresh water and saltwater to be estimated from 300 to 800 nm.
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paper_title: Field and laboratory studies on the effect of particle size and composition on optical backscattering measurements in hydrothermal plumes

paper_content:

Abstract We describe the performance of an inexpensive but highly sensitive light backscattering sensor (LBSS) suitable for use in deep-sea waters, where particle concentrations are typically 10 μm. Field studies indicate that in hydrothermal plumes dominated by fine-grained metal precipitates the 95% confidence interval for predicting mass concentration with an LBSS ranges from ±0.004 mg/l for 0.03 mg/l suspensions to ±0.008 mg/l at 0.12 mg/l. Comparisons among a group of 19 LBSSs found between-instrument variability to reach 70%, but normalizing the raw data using a laboratory calibration procedure reduced the maximum variability to ∼8%.
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paper_title: Highly Sensitive Sensors Based on Photonic Crystal Fiber Modal Interferometers

paper_content:

We review the research on photonic crystal fiber modal interferometers with emphasis placed on the characteristics that make them attractive for different sensing applications. The fabrication of such interferometers is carried out with different post-processing techniques such as grating inscription, tapering or cleaving, and splicing. In general photonic crystal fiber interferometers exhibit low thermal sensitivity while their applications range from sensing strain or temperature to refractive index and volatile organic compounds.
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paper_title: Design and Fabrication of Slotted Multimode Interference Devices for Chemical and Biological Sensing

paper_content:

We present optical sensors based on slotted multimode interference waveguides. The sensor can be tuned to highest sensitivity in the refractive index ranges necessary to detect protein-based molecules or other water-soluble chemical or biological materials. The material of choice is low-loss silicon oxynitride (SiON) which is highly stable to the reactivity with biological agents and processing chemicals. Sensors made with this technology are suited to high volume manufacturing.
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paper_title: Comparability of suspended-sediment concentration and total suspended solids data

paper_content:

Introduction Field Techniques and Laboratory Methods Field Techniques Laboratory Methods Suspended-Sediment Concentration Analytical Method Total Suspended Solids Analytical Method Differences Between the Suspended-Sediment Concentration and Total Suspended Solids Analytical Methods Description of Data Used in the Evaluation Arizona Hawaii Illinois Kentucky Maryland Virginia Washington Wisconsin Quality-Control D a t a Comparability of Suspended-Sediment Concentration and Total Suspended Solids Data. Natural-Water Data Quality-Control D a t a Conclusions References Cited
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paper_title: Field techniques for suspended-sediment measurement

paper_content:

The measurement of suspended sediment, particularly in field settings, is important in the documentation of sediment transport and deposition. Many measurement techniques have been used with varying degrees of success. The techniques, including their operating principles, advantages, and disadvantages are discussed. The techniques discussed include acoustic, bottle, pump, focused beam reflectance, laser diffraction, nuclear, optical backscatter, optical transmission, and spectral reflectance. Emphasis is placed on instrumentation techniques, as this is the area of suspended-sediment measurement that has the greatest potential for improving sediment data. Acoustic technology (if further developed) emerges as a promising technology because of its ability to measure the concentration profile without intruding into the flow. This technology-transfer information will be valuable to practitioners and researchers needing to choose a means of measuring suspended sediment. The choice of a measurement technique has...
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paper_title: Comparison between ADCP and transmissometer measurements of suspended sediment concentration

paper_content:

Abstract For more than a decade, acoustic Doppler current profilers, ADCPs, have been in common use measuring current profiles. It has been recognised over this period that the backscattered ADCP signal could be used to not only evaluate the Doppler shift, but also offered the possibility to extract information on the scatterers. The present work reports on an analysis of opportunistic backscatter measurements collected using a 1 MHz ADCP system, to assess the potential of ADCPs to measure suspended sediment concentration quantitatively. The data were gathered during a water monitoring campaign which deployed ADCPs, near-bed and profiling transmissometers, and in situ bottle samplers. Although the original study was not specifically designed to test the capability of ADCPs to evaluate suspended sediment concentration, sufficient data were collected to examine the use of ADCPs for such measurements. The backscattered amplitude from one ADCP beam was recorded for quality control to assess the accuracy of velocity measurements. However, in this study these data have also been used to examine the potential of ADCPs for suspended sediment measurements. To investigate ADCPs in this role, the backscattered signals from one range cell has been calibrated against in situ bottle samples of the suspended material. Using this calibration, the backscattered signals have been inverted to give time series profiles of suspended particulate matter. To assess these profiles, comparisons have been made with in-situ calibrated profiling and moored transmissometers. The outcome from the present study shows ADCP results which are comparable with the transmissometer observations, and clearly demonstrate the potential of ADCPs for directly measuring suspended sediment profiles.
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paper_title: High concentration suspended sediment measurements using a continuous fiber optic in-stream transmissometer

paper_content:

Suspended sediment loads mobilized during high flow periods in rivers and streams are largely uncharacterized. In smaller and intermittent streams, a large storm may transport a majority of the annual sediment budget. Therefore monitoring techniques that can measure high suspended sediment concentrations at semi-continuous time intervals are needed. A Fiber optic In-stream Transmissometer (FIT) is presented for continuous measurement of high concentration suspended sediment in storm runoff. FIT performance and precision were demonstrated to be reasonably good for suspended sediment concentrations up to 10g/L. The FIT was compared to two commercially available turbidity devices and provided better precision and accuracy at both high and low concentrations. Both turbidity devices were unable to collect measurements at concentrations greater than 4 g/L. The FIT and turbidity measurements were sensitive to sediment particle size. Particle size dependence of transmittance and turbidity measurement poses the greatest problem for calibration to suspended sediment concentration. While the FIT was demonstrated to provide acceptable measurements of high suspended sediment concentrations, approaches to real-time suspended sediment detection need to address the particle size dependence in concentration measurements.
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paper_title: Study of particle size effects on an optical fiber sensor response examined with Monte Carlo simulation

paper_content:

Optical fiber sensors based on the total light transmittance are widely used to measure the volume fraction of particles in suspensions. However, the sensor response depends not only on the volume fraction but also on the particle size. The particle size effect is studied for a sensor configuration consisting of two linear arrays of fibers on each of two blocks: the emitting and receiving blocks. These two linear arrays are arranged with three adjacent fibers (one fiber on the first array, two fibers on the second array) ::: forming a perfect triangle. The almost superimposition of the calculated sensor response versus the extinction factor for different particle sizes allows for the application of single- ::: curve models. Two single-curve models that describe the sensor response for all particle sizes ranging from 36 to ::: 200 μm are proposed. The models are validated by Monte Carlo simulation for different particle sizes and are valid within a detectable volume fraction. The single-curve models proposed provide an easier approach to creating a database for sensor calibration for suspended sediment concentration measurements.
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paper_title: Fiber optic probes for biomedical optical spectroscopy

paper_content:

Optical spectroscopy has been well validated by the physical sciences as a method to characterize chemical compositions in biological material. It has also showed promising to detect atheroscleroti ...
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paper_title: Water Quality Measurement using Transmittance and 90° Scattering Techniques through Optical Fiber Sensor

paper_content:

This research is the continuance of the previous developed water quality fiber sensor by Omar et al (2007). The application of spectroscopy analysis is the major tasks established in the measurement of the capacity of total suspended solids (TSS) in water sample in the unit of mg/L. The interaction between the incident light and the turbid water sample will leads the light to be either transmitted through the water sample or absorbed and scattered by water molecules and TSS particles. The resultant light produced after the interaction will be collected by plastic optical fiber located at 180deg (transmittance measurement technique) and 90deg (90deg scattering measurement technique) from the incident light. The measurement is done through BLUE and RED Systems with peak response of emitter and detector at 470 nm and 635 nm respectively. Signal interpretation and data display is established through Basic Stamp 2 microcontroller. Transmittance measurement technique has a capability to sense the amount of solids suspended in water as low as 20 mg/L. 90deg measurement technique has a capability to sense the amount of solids suspended in water as low as 10 mg/L. Both measurement techniques recorded a very good linear correlation coefficient and low standard error.
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paper_title: Water Quality Measurement using Transmittance and 90° Scattering Techniques through Optical Fiber Sensor

paper_content:

This research is the continuance of the previous developed water quality fiber sensor by Omar et al (2007). The application of spectroscopy analysis is the major tasks established in the measurement of the capacity of total suspended solids (TSS) in water sample in the unit of mg/L. The interaction between the incident light and the turbid water sample will leads the light to be either transmitted through the water sample or absorbed and scattered by water molecules and TSS particles. The resultant light produced after the interaction will be collected by plastic optical fiber located at 180deg (transmittance measurement technique) and 90deg (90deg scattering measurement technique) from the incident light. The measurement is done through BLUE and RED Systems with peak response of emitter and detector at 470 nm and 635 nm respectively. Signal interpretation and data display is established through Basic Stamp 2 microcontroller. Transmittance measurement technique has a capability to sense the amount of solids suspended in water as low as 20 mg/L. 90deg measurement technique has a capability to sense the amount of solids suspended in water as low as 10 mg/L. Both measurement techniques recorded a very good linear correlation coefficient and low standard error.
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paper_title: Performance evaluation of fiber optic probes for tissue lifetime fluorescence spectroscopy

paper_content:

The design of fiber-optic probes plays an important role in optical spectroscopic studies, including fluorescence spectroscopy of biological tissues. It can affect the light delivery and propagation into the tissue, the collection efficiency (total number of photons collected vs. total number of photons launched) and the origin of collected light. This in turn affects the signal to noise ratio (SNR) and the extend of tissue interrogation, thus influencing the diagnostic value of such techniques. Three specific fiber-optic probe designs were tested both experimentally and computationally ::: via Monte Carlo simulations. In particular, the effects of probe architecture (single-fiber vs. two bifurcated multifiber probes), probe-to-target distance (PTD), and source-to-detector separation (SDS) were investigated on the collected diffuse reflectance of a Lambertian target and an agar-based tissue phantom. This study demonstrated that probe architecture, PTD, and SDS are closely intertwined and considerably affect the light collection efficiency, the extend of target illumination, and the origin of the collected reflected light. Our findings can be applied towards optimization of ::: fiber-optic probe designs for quantitative fluorescence spectroscopy of diseased tissues.
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Title: Turbidimeter Design and Analysis: A Review on Optical Fiber Sensors for the Measurement of Water Turbidity

Section 1: Introduction
Description 1: Introduce the concepts of turbidity, its causes, and the importance of measuring water turbidity. Discuss the different methods of turbidity measurement and the significance of optical fiber sensors.

Section 2: Relationship between Turbidity (NTU) and TSS (mg/L)
Description 2: Explain the correlation between turbidity and total suspended solids (TSS), the factors affecting these measurements, and their limitations.

Section 3: Light Scattering Phenomena
Description 3: Detail the interaction of light with suspended particles in water, including scattering and absorption effects, and their mathematical representation.

Section 4: Light Sources and Detectors
Description 4: Describe the types of light sources and detectors used in turbidimeters, their specifications, and the impact of these components on measurement accuracy.

Section 5: Tolerance in Design
Description 5: Discuss the variances in measurement results due to different instrument designs, and outline practices to ensure accurate turbidity measurements.

Section 6: Optical Fiber Sensor
Description 6: Provide an overview of optical fiber sensors, their working principles, advantages, and applications in measuring water turbidity.

Section 7: Relationship between TSS (mg/L) and SSC (mg/L)
Description 7: Discuss the distinctions and relationships between total suspended solids (TSS) and suspended sediment concentration (SSC), and the reliability of different measurement methods.

Section 8: Continuous Monitoring of Particle Concentration in Flowing Media
Description 8: Examine various technologies for real-time monitoring of suspended particles in flowing media, with a focus on optical and acoustic backscattering devices.

Section 9: Simple Turbidimeter Design
Description 9: Present a straightforward approach to constructing turbidimeters, suitable for educational purposes, and summarize experimental results.

Section 10: Water Quality Fiber Sensor
Description 10: Describe the development and testing of fiber optic water quality sensors, including their configuration, performance, and future improvements for field applications.

Section 11: Analysis
Description 11: Analyze the technical factors influencing the development of optical instruments for turbidity measurement, including the selection of optical components and measurement angles.

Section 12: Summary
Description 12: Summarize the key points discussed in the paper, emphasizing the considerations for developing reliable optical fiber sensors for water turbidity measurement.

Section 13: Conclusions
Description 13: Conclude the paper by highlighting the overall design concepts, experimental findings, and potential future advancements in the field of optical turbidity measurement.