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Laboratory Evaluation of Acoustic Backscatter and LISST Methods for Measurements of Suspended Sediments

View Article: PubMed Central - PubMed

ABSTRACT

The limitation of traditional sampling method to provide detailed spatial and temporal profiles of suspended sediment concentration has led to an interest in alternative devices and methods based on scattering of underwater sound and light. In the present work, acoustic backscatter and LISST (the Laser In Situ Scattering Transmissometry) devices, and methodologies were given. Besides a laboratory study was conducted to compare pumping methods for different sediment radiuses at the same concentration. The glass spheres (ballotini) of three different radiuses of 115, 137 and 163 μm were used to obtain suspension in the sediment tower at laboratory. A quite good agreement was obtained between these methods and pumping results with the range at 60.6-94.2% for sediment concentration and 91.3-100% for radius measurements. These results and the other studies show that these methods have potential for research tools for sediment studies. In addition further studies are needed to determine the ability of these methods for sediment measurement under different water and sediment material conditions.

No MeSH data available.


Related in: MedlinePlus

The LISST devices elements: (a) laser diode source, (b) companion focusing optics, (c) and (e) two pressure windows, (d) sample volume, (f) receiving lens, (g) concentric photodetector rings, (h) transmission detector
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f1-sensors-08-00979: The LISST devices elements: (a) laser diode source, (b) companion focusing optics, (c) and (e) two pressure windows, (d) sample volume, (f) receiving lens, (g) concentric photodetector rings, (h) transmission detector

Mentions: The LISST-100, with diameter of 13 cm and length of 81 cm, is a laser particle size analyser and consists of a diode laser operating at 670 μm which is collimated to form a parallel beam of light (figure 1). The beam passes through a 5 cm sample cell of water where particles produce scattering. The forward diffracted beam is collected by a set of 32 ring detectors that are logarithmically spaced and located in the focal plane of the laser receiving lens. Each ring detector measures scattering over a sub-range of angles. The ring radius and focal plane length of the receiving lens determine the range of the angles. A photo-diode is placed behind the ring detector which detects the main laser beam. This supplies the optical transmissometer function [5].


Laboratory Evaluation of Acoustic Backscatter and LISST Methods for Measurements of Suspended Sediments
The LISST devices elements: (a) laser diode source, (b) companion focusing optics, (c) and (e) two pressure windows, (d) sample volume, (f) receiving lens, (g) concentric photodetector rings, (h) transmission detector
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3927532&req=5

f1-sensors-08-00979: The LISST devices elements: (a) laser diode source, (b) companion focusing optics, (c) and (e) two pressure windows, (d) sample volume, (f) receiving lens, (g) concentric photodetector rings, (h) transmission detector
Mentions: The LISST-100, with diameter of 13 cm and length of 81 cm, is a laser particle size analyser and consists of a diode laser operating at 670 μm which is collimated to form a parallel beam of light (figure 1). The beam passes through a 5 cm sample cell of water where particles produce scattering. The forward diffracted beam is collected by a set of 32 ring detectors that are logarithmically spaced and located in the focal plane of the laser receiving lens. Each ring detector measures scattering over a sub-range of angles. The ring radius and focal plane length of the receiving lens determine the range of the angles. A photo-diode is placed behind the ring detector which detects the main laser beam. This supplies the optical transmissometer function [5].

View Article: PubMed Central - PubMed

ABSTRACT

The limitation of traditional sampling method to provide detailed spatial and temporal profiles of suspended sediment concentration has led to an interest in alternative devices and methods based on scattering of underwater sound and light. In the present work, acoustic backscatter and LISST (the Laser In Situ Scattering Transmissometry) devices, and methodologies were given. Besides a laboratory study was conducted to compare pumping methods for different sediment radiuses at the same concentration. The glass spheres (ballotini) of three different radiuses of 115, 137 and 163 μm were used to obtain suspension in the sediment tower at laboratory. A quite good agreement was obtained between these methods and pumping results with the range at 60.6-94.2% for sediment concentration and 91.3-100% for radius measurements. These results and the other studies show that these methods have potential for research tools for sediment studies. In addition further studies are needed to determine the ability of these methods for sediment measurement under different water and sediment material conditions.

No MeSH data available.


Related in: MedlinePlus