…Wherein we’ll learn about the LISST-Infinite, LISST-StreamSide, and the LISST-SL.
(Part VI can be found here: https://www.sequoiasci.com/article/the-history-of-sequoia-part-vi/ )
Remember from Part VI that Dr. Gray from USGS had proposed the LISST-25? Around the same time, he and FISP also proposed a streamlined LISST. The idea was to deploy the LISST in fast flowing rivers and measure the size and concentration of suspended sediment in profiles across a transect. Then the laborious and expensive sampling with point- and depth integrated samplers could be reduced. However, a standard LISST was difficult to deploy in a river because it would orient itself somewhat randomly in the flow. Furthermore, the USGS was (and is) very keen on isokinetic measuring and sampling to reduce sampling bias. This led to the development of the original LISST-SL in the first half of the 2000’s. Housed in a streamlined, low-drag body it was lowered into the river using a standard B-reel. When submerged, a pitot tube would measure the in-water flow speed and an internal pump would then pump water through the instrument at the same speed as water flowing around the instrument, thus ensuring an isokinetic measurement. The latest iteration of the LISST-SL2, released in 2018, transmits 1 Hz data in real-time via the B-reel cable to a topside computer where the current speed, particle size, concentration, depth, and temperature is instantly displayed and saved. Multiple papers have been published using the LISST-SL and LISST-SL2.
Simultaneously with the original LISST-SL development, Sequoia had eyed a new market: Hydropower. In hydropower plants, high sediment concentrations can lead to turbine abrasion. A warning system that could help operators figure out if concentrations were too high seemed like a good idea. The main issue was that concentrations could reach several tens of thousands of mg/l – far beyond what any LISST could measure. The LISST-Infinite, with a dilution chamber that could dilute a sample up to a factor of 100 was invented. It would output sediment concentration in size classes (fine, medium, coarse) every 5-10 minutes depending on the number of dilutions needed. The market never took to this, preferring cheaper sensors that measured just the concentration (or a surrogate for concentration). Sequoia now offers the LISST-ABS (for coarse particles) and the LISST-AOBS (for coarse and fine particles) for hydropower applications with great success; particularly in South America where they are seeing extensive use for hydropower monitoring.
A derivative of the LISST-Infinite was the LISST-StreamSide, designed for long-term autonomous monitoring of size and concentration in rivers. The instrument itself would be mounted on the riverbank, and a submersible pump would pump water through the instrument to make a measurement. The LISST-StreamSide had potential, but the market was (still) more interested in the submersible instruments, so the LISST-StreamSide was discontinued in 2016 with the introduction of the LISST-200X and the LISST-ABS.
In Part VIII we’ll learn about the LISST-Portable, the first Particles in Europe (PiE) conference and the LISST-Holo.