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LISST Instruments >
LISST-SL
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The LISST-SL (for StreamLine) is a laser diffraction system for measuring sediment properties in rivers and streams. The streamlined body is a minimum drag shape. Twin fins below the body orient the LISST-SL facing upstream before insertion. A pitot static tube on top of the body measures river velocity.
The system employs active control of the intake pump that matches river velocity to intake velocity making the sample acquisition isokinetic. Diffracted light is measured in an enclosed electro-optics section.
A major difference between the LISST-SL and other LISST instruments is that the LISST-SL is only a sensor. No data are stored on the instrument itself. The LISST-SL must be constantly connected to a topside control box, which contains a rechargeable battery, and which receives the raw scattering data from the LISST-SL itself.
Depth, velocity, and temperature are stored with each sample. With the included depth data, the system is capable of delivering sediment flux in the river. Not only is it possible to measure the total flux; since the LISST-SL measures the concentration in each of 32 size bins it is possible to measure the size-dependent flux of suspended sediment across the entire transect.
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Data are transmitted up the USGS B-reel to the ‘topside’ Control Box, equipped with a touch panel display showing depth, temperature, river current velocity, mean grain size and total concentration in real-time. These data are stored together with date and time in an ASCII file, which can be offloaded and immediately displayed in EXCEL or any other spreadsheet.
In order to obtain the detailed size distribution and volume concentration in 32 size classes, the raw scattering data are also stored on the topside box. The raw data can subsequently be offloaded and processed into the standard 32-size class volume distribution.
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The USGS B-reel is seen in the background. The B-reel is a NECESSARY ACCESSORY to the LISST-SL, which serves multiple purposes:
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It is used for suspending the LISST-SL in the river from the deployment location.
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It supplies power from the topside box to the LISST-SL.
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It transmits data from the LISST-SL to the topside box for real-time processing on the topside box.
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Upon startup the touch panel display will initialize the instrument and load instrument-specific calibration files.
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On the Main Menu there are three options: Calibrate (in order to acquire a zscat measurement), Measure (starts a profile), and Setup.
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A step-by-step instruction on how to obtain a zscat with the LISST-SL is displayed. The user must check all three boxes before the 'Collect Background' button appears.
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As soon as the 'Measure' button is pressed the LISST-SL will start sending data to the topside control box. The data are partially processed in order to show total volume concentration and mean grain-size, together with depth, velocity and temperature. The units displayed can be changed from English to Metric in the Setup Menu.
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The Setup Menu allows the user to set the instrument clock, change units, list files and delete files.
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Setting the clock is done via the keypad.
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Units for depth and velocity are changed by pressing the button. The data from the instrument are saved in an ASCII file, ready for import into Excel. The units in the ASCII file will change according to which button was selected when a profile was started.
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A list of the files that have been saved can be accessed from the Setup Menu.
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Related Links
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Updated 3/25/2011
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|  | | Sequoia visit to Colombia and Ecuador! |  | | Sequoia's Yogi Agrawal and Ole Mikkelsen visited C'Particulas, Sequoia's Colombian distributor 28-30 November 2011. See the pictures on our facebook page! | |  | |  | |
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