Sequoia Scientific LISST-SL - Laser Diffraction System
The LISST-SL (for StreamLine) is a laser diffraction system for measuring sediment properties in freshwater rivers and streams. It is not designed for use in brackish or saltwater environments. 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.
- Small-angle forward laser light scattering (laser diffraction) – compliant with ISO-13320-1 standard.
- Isokinetic, self-contained operation.
- 2-wire special communication protocol consistent with USGS B-reel use.
- Real-time display of multi-parameter measurements: Current speed, temperature, concentration, depth, mean sediment grain size.
- Streamlined shape for low drag (CD <0.2) in fast streams.
- Twin stabilizer fins facilitate rapid re-orientation into flow on insertion and maintain accurate orientation.
- 4.3” graphics display, 480 x 272 pixels (3.75” W x?2.12” H), 16-bit color allows for easy programming and display of data without a PC.
- Switch between ft and ft/s or m and m/s for depth and velocity units.
- Data processing performed on board and stored in ASCII-format
- Raw binary data can be post-processed to obtain full size distribution.
A major difference between the LISST-SL and other LISST instruments is that the LISST-SL is only a sensor. It cannot operate autonomously and no data can be stored on the instrument itself. The LISST-SL must be constantly connected using a USGS B-Reel to a Topside Control Box (TCB), 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.
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.
Sediment Concentration Range
- Range: 15 – 13,500 mg l-1 for standard 3.2 mm optical path. NOTE: THE ACTUAL CONCENTRATION RANGE IS VERY HEAVILY GRAIN-SIZE DEPENDENT.
- Resolution: < 10 mg l-1.
- 2.5-500 µm in 32 log-spaced size classes.
- 0.15-30 m @ 0.02 m resolution.
Current Speed Range
- 0-8 m/s @ 0.03 m/s resolution.
Water Temperature Range
- 0-25C @ 0.1 C resolution.
Sample Acquisition Time
- 3 seconds for a 16 sample average
- Average value subsequently transmitted to the topside control box for immediate display
Mechanical and Electrical
- Dimensions (SL): 13 cm (5.1”) maximum Ø × 75 cm (29.5”) L
- Topside Box: 40.6 cm (16”) × ?31.8 cm (12.5”) ×? 16.5 cm (6.5”)
- Weight in air / submerged (SL): 16 kg (35 lbs) / 7 kg (15.4 lbs)
- Topside Box: 8.6 kg (19 lbs)
- Rechargeable battery life: 6 hours (nominal; longer available)