Suspended Sediment

Sequoia Scientific LISST-Deep

The LISST-Deep extends operating depth range beyond the LISST-100X or LISST-200X instruments allowing measurements of particle size to be made at 1 hz with minimal disturbance to the particles.

  • 4,000 meter depth rating (as of 2020)
  • Small angle forward scattering laser diffraction technology
  • Self contained with internal datalogger
  • Externally powered
  • RS232 connection to PC for programming, offloading and real-time size distribution displays
  • Programmable, autonomous data collection
  • Integrated depth and temperature sensor
  • 32 size classes
  • Optional external battery pack, rated to 4,000 m depth
  • Optional 80% path reduction module for higher concentrations
  • Sea-Bird cable for powering from Sea-Bird CTD


Using a red 670nm diode laser and a custom silicon detector, small-angle scattering from suspended particles is sensed at 32 specific log-spaced angle ranges. This primary measurement is post-processed to obtain sediment size distribution, volume concentration, optical transmission, and VSF. The LISST-Deep is based on the now discontinued LISST-100X, and is operated just like a LISST-100X. The LISST-Deep has a size range covering 1.25 µm to 250 µm OR 2.5 µm to 500 µm.

If you study the design of the LISST-Deep and compare it with the LISST-100X  it is clear that the mechanical design is very different from that of the LISST-100X. The optical path is more or less in the middle of the instrument, not at the end. This means that no accessories available for the LISST-100X will work with the LISST-Deep, with the exception of communication cables and instrument stands. No BioBlock, mixing chambers or path reduction modules are available for the LISST-Deep.

Also, because of the much thicker wall of the pressure housing, there is no room for internal battery packs as for the LISST-100X. The LISST-Deep must be powered externally at all times. This is typically achieved by connecting it to a CTD, getting power from the CTD. A cable for connecting to a CTD will be included, if the customer supplies Sequoia with the pin-out of the CTD upon ordering.

The table below illustrates the main differences between the LISST-Deep and the LISST-100X instruments.

Standard optical path length of 5 cm
Two size ranges; type B (1.25 µm to 250µm) or type C (2.5 µm to 500 µm) available
Use standard LISST-SOP Windows software for programming and offload of data
Measures particle size distribution in 32 size classes, volume concentration, optical transmission, and volume scattering function
Depth rating 4,000 m
SeaBird CTD connector for external power from SeaBird CTD
Optical path reduction modules (PRM’s) available
Internal Battery for power
External Digital Input for start/stop of sampling
External Analog port for logging data from OBS3+, Turner Designs Cyclops 7 fluorometer or SeaBird MicroCat C-T sensor
Accessories for laboratory work (e.g. Full Path Mix Chamber, Small Volume Flow Through Chamber, Full Path Flow Through Chamber, Large Test Chamber)
BioBlock option to slow down fouling and extend deployments in productive waters

The LISST-Deep and the LISST-100X was used after the Deepwater Horizon accident in April 2010 to detect oil droplets and their size in the deep waters of the Gulf of Mexico.

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