A laboratory evaluation of the laser in situ scattering and transmissometery instrument using natural sediments (original) (raw)
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Journal of Atmospheric and Oceanic Technology
Suspended particle size and concentration are critical parameters necessary to understand water quality, sediment dynamics, carbon flux, and ecosystem dynamics among other ocean processes. In this study we detail the integration of a Sequoia Scientific, Inc., Laser In situ Scattering and Transmissometry (LISST) sensor into a Teledyne Webb Research Slocum autonomous underwater glider. These sensors are capable of measuring particle size, concentration, and beam attenuation by particles in size ranges from 1.00 to 500 μm at a resolution of 1 Hz. The combination of these two technologies provides the unique opportunity to measure particle characteristics persistently at specific locations, or survey regional domains from a single profiling sensor. In this study we present the sensor integration framework, detail quality assurance and control (QAQC) procedures, as well as provide a case study of storm driven sediment resuspension and transport. Specifically, Rutgers glider RU28 was depl...
Marine Geology, 2001
Advances in technology have resulted in a new instrument that is designed for in-situ determination of particle size spectra. Such an instrument that can measure undisturbed particle size distributions is much needed for sediment transport studies. The LISST-100 (Laser In-Situ Scattering and Transmissometry) uses the principle of laser diffraction to obtain the size distribution and volume concentration of suspended material in 32 size classes logarithmically spaced between 1.25 and 250 mm. This paper describes a laboratory evaluation of the ability of LISST-100 to determine particle sizes using suspensions of single size, arti®cial particles. Findings show the instrument is able to determine particle size to within about 10% with increasing error as particle size increases. The instrument determines volume (or mass) concentration using a volume conversion factor C v. This volume conversion factor is theoretically a constant. In the laboratory evaluation C v is found to vary by a factor of about three over the particle size range between 5 and 200 mm. Results from ®eld studies in South San Francisco Bay show that values of mass concentration of suspended marine sediments estimated by LISST-100 agree favorably with estimates from optical backscatterance sensors if an appropriate value of C v , according to mean size, is used and the assumed average particle (aggregate) density is carefully chosen. Analyses of size distribution of suspended materials in South San Francisco Bay over multiple tide cycles suggest the likelihood of different sources of sediment because of different size characteristics durinḡ ood and ebb cycles.
The Use of a Laser Light-Scattering Technique in Fluvial Sediment Measurement
1982
Kertas ini melapurkan pengukuran yang dibuat ke atas kepadatan enapan dengan menggunakan teknik penyerakan-cahaya laser. Dalam bentuk yang sedia ada, teknik ini mengalami beberapa masalah praktik, tetapi sifat yang mudah dan cepat membuatkan teknik ini lebih berguna. Cara-cara untuk mengatasi masalah-masalah yang timbul turut dibincangkan.
Continental Shelf Research, 2006
The Laser In Situ Scattering Transmissometry (LISST) instruments produced by Sequoia Scientific Inc. use light scattering to measure concentration and size distributions of sediment suspensions. In this article, the capabilities of the LISST-ST instrument are studied. The instrument reports the suspended sediment concentration and the settling velocity for eight different size classes by measuring the sediment concentration at the bottom of a small settling column. The size resolution of the LISST-100 and LISST-ST instruments is studied. This study utilizes a new inversion algorithm to obtain the size distribution from the scattered light pattern. In addition, attention is directed to observed deviations in laboratory measurements that may affect the relative concentrations and the settling velocity estimations. These deviations are analyzed in terms of: sample mixing problems; deviations on the settling of a suspension from its ideal behavior; and the effect of the shape of natural particles on laser scattering compared to that of spheres. Results suggests, of these three points the difference in the light scattering by irregular particles compared to the scattering by spheres is the main source of deviation on the settling velocity estimations. Finally, practical recommendations are given in order to gain confidence in the instrument results.
Water Resources Research, 2015
Laser-diffraction technology, recently adapted for in-stream measurement of fluvial suspended-sediment concentrations (SSCs) and particle-size distributions (PSDs), was tested with a streamlined (SL), isokinetic version of the Laser In Situ Scattering and Transmissometry (LISST) for measuring volumetric SSCs and PSDs ranging from 1.8 to 415 lm in 32 log-spaced size classes. Measured SSCs and PSDs from the LISST-SL were compared to a suite of 22 data sets (262 samples in all) of concurrent suspendedsediment and streamflow measurements using a physical sampler and acoustic Doppler current profiler collected during 2010-2012 at 16 U.S. Geological Survey streamflow-gaging stations in Illinois and Washington (basin areas: 38-69,264 km 2 ). An unrealistically low computed effective density (mass SSC/volumetric SSC) of 1.24 g/mL (95% confidence interval: 1.05-1.45 g/mL) provided the best-fit value (R 2 5 0.95; RMSE 5 143 mg/L) for converting volumetric SSC to mass SSC for over two orders of magnitude of SSC (12-2,170 mg/L; covering a substantial range of SSC that can be measured by the LISST-SL) despite being substantially lower than the sediment particle density of 2.67 g/mL (range: 2.56-2.87 g/mL, 23 samples). The PSDs measured by the LISST-SL were in good agreement with those derived from physical samples over the LISST-SL's measureable size range. Technical and operational limitations of the LISST-SL are provided to facilitate the collection of more accurate data in the future. Additionally, the spatial and temporal variability of SSC and PSD measured by the LISST-SL is briefly described to motivate its potential for advancing our understanding of suspended-sediment transport by rivers.
1] We present new observational data on small-angle light scattering properties of natural, random shaped particles, as contrasted with spherical particles. The interest in this ''shape effect'' on scattering arises from the need for a suitable kernel matrix for use in the laser diffraction method (LD) of particle sizing. LD is now used broadly for measuring size distribution of suspended marine particles. LD involves the measurement of small-angle forward scattering at multiple angles. This data is inverted using the kernel matrix to produce size distribution. In the absence of a suitable matrix for random shaped particles, past practice has been to use a model based on Mie theory, applicable strictly only to homogeneous spheres. The present work replaces Mie theory with empirical data. The work was motivated in part by anomalous field observations of size distribution and settling velocity distributions reported in literature. We show that a kernel matrix for random shaped particles results in improved interpretation of field multiangle scattering observations. In particular, a rising edge at the fine particle end of the size spectrum is shown to be associated with shape effects. Citation: Agrawal, Y. C., A. Whitmire, O. A. Mikkelsen, and H. C. Pottsmith (2008), Light scattering by random shaped particles and consequences on measuring suspended sediments by laser diffraction,
Optics Express, 2018
High spatial and temporal resolution estimates of the particle size distribution (PSD) in the surface ocean can enable improved understanding of biogeochemistry and ecosystem dynamics. Oceanic PSD measurements remain rare due to the time-consuming, manual sampling methods of common particle sizing instruments. Here, we evaluate the utility of measuring particle size data at high spatial resolution with a commercially-available submersible laser diffraction particle sizer (LISST-100X, Sequoia Scientific), operating in an automated mode with continuously flowing seawater. The LISST PSD agreed reasonably well with discrete PSD measurements obtained with a Coulter Counter and data from the flow-through sampling Imaging Flow-Cytobot, validating our methodology. Total particulate area and Volume derived from the LISST PSD agreed well with beam-attenuation and particulate organic carbon respectively, further validating the LISST PSD. Furthermore, When compared to the measured spectral characteristics of particulate beam attenuation, we find a significant correlation. However, no significant relationship between the PSD and spectral particulate backscattering was found.
Evaluation of a wide range laser diffraction grain size analyser for use with sediments
Sedimentology, 1994
The qualities of a laser diffraction grain size analyser, the Coulter LS-100 (range claimed by the manufacturer: 0+900 pm in a single measurement), are evaluated on sediments of fluvial and lacustrine origin. Accuracy and resolution of measurement on standard latex spheres are excellent. Reproducibility of the results on natural sediments appears to be satisfactory, but the method underestimates the fraction of clay particles with an efficiency of detection (3670%) proportional to the clay content determined from pipette analysis. This efficiency is somewhat higher than those reported from other instruments of the same Comparison of the Coulter LS-100 with other sizing techniques shows good agreement with the sieving method but some differences appear with the electroresistance particle technique: median and mean size values measured by the Coulter Counter TAl are systematically lower than those obtained by the Coulter LS-100. Analyses show good correlation with those of a Malvern Laser particle analyser but a discrepancy appears with very fine silt and clay sized sediments. The Coulter LS-100 detects a higher clay content than that measured with the Malvern Laser Sizer 2600. Except when precise measurements of clay content are needed, the Coulter LS-100 produces precise and accurate results in size ranges required for geological and environmental studies. generation.. .
Sedimentary Geology, 2000
Surface and deep-sea core sediments and two sets of standards were measured by three different techniques -Galai Cis-1 laser system, Coulter Counter TA II, and Micromeritics SediGraph 5000D -in order to compare the Galai results with the other two. The differences between the three types of measuring device turned out to be greater in sediments than in standards, and were attributed to the physical properties, shape, density and composition of the particles (complexity of the matrix). Comparison of moment statistics showed that the Galai determines coarser grain sizes than the Coulter and finer than the SediGraph, particularly as regards analysis of surface sediments. The relationships between Galai and SediGraph were estimated using analysis of variation=residuals within individual intervals. The analysis showed a higher variability of residuals for the coarser fractions (8-16 µm and 16-32 µm) with respect to the finer (2-4 µm and 4-8 µm) fractions. The <2 µm SediGraph fraction, with a cut-off at 0.49 µm, showed good correspondence with the <2.5 µm Galai analysis.
Field test of the accuracy of laser particle counters to measure aeolian sediment flux
Aeolian Research, 2021
In this study we tested to what extent grain count data from a laser particle counter, when enriched with granulometric data, can lead to accurate measurements of aeolian sediment fluxes in the field. Field experiments were conducted at Koksijde beach (Belgium) with a vertical array of five Wenglor fork sensors and co-located vertically stacked mesh sand traps. Sand collected in the traps was used to both obtain the reference values for sediment flux as well as to obtain granulometric data at the five Wenglor sensor elevations. Grain counts were transformed to sediment fluxes by combining the granulometric data with the grain size dependent, effective detection width concept. It was found that the limitation of the Wenglor sensor to have a minimum detectable grain size, well within the diameter range of sand grains in transport, could easily be corrected for through a linear relation of Wenglor detectable sediment flux with total sediment flux. However, we found that the Wenglor derived fluxes deviated from the sand trap derived fluxes in an inconsistent manner, both in the vertical and over time, which made us conclude that there is no uniform calibration possible to match the Wenglor data with the trap data. This suggests that further studies using optical aeolian transport sensors should focus on analysing the raw photoelectric signal rather than on internally processed count data.