Sequoia Scientific


Deep Ocean Laser Diffraction Particle Size Analyzer

The LISST-Deep instrument obtains in-situ measurements of particle size distribution, optical transmission, and the optical volume scattering function(VSF) at depths down to 3,000 meters.

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




  • 3000 meter depth rating
  • 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 3000 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 programmed and operated like a LISST-100X. The LISST-Deep can be ordered as a type B (1.25-250µm) or type C (2.5-500µm) size range.

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. Upon request, Sequoia can furnish a quote for a LISST-Deep external battery pack with cable for connecting to the LISST-Deep.

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 – 250µm) or type C (2.5-500µm) 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 3000 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.

Questions about the LISST-Deep? Email us!


Parameters measured

  • Particle size distribution from 1.25-250µm or 2.5-500µm
  • Depth (3000 m max depth @ 0.8 m resolution)
  • Optical transmission @ 0.1 % resolution
  • Volume concentration @ 0.1 µl/l resolution
  • Volume concentration @ 0.1 µl/l resolution
  • Volume concentration @ 0.1 µl/l resolution
  • Volume scattering function (VSF)

Operating concentration range

  • Optical transmission from  0.3-0.985 (30-98.5%)
  • Concentration range 1-800 mg/l (grain-size dependent)


  • Small-angle forward scattering
  • 32-ring custom photodiode ring detector for small-angle VSF
  • 50 mm optical path (10 mm with optional 80% PRM)

Mechanical and electrical

  • Dimensions 12.57 cm (4.95”) dia. by 80.3 cm (31.6”) L
  • Weight: 17/8 kg (38/18 lbs) in air/water
  • 3000 m depth rating
  • External power input: 9VDC nominal, 6-24VDC
  • Sampling rate: Up to 1 Hz
  • 670 nm solid state diode laser
  • Power drain: 145 mA / 8mA (measuring / quiescent)
  • Data storage: 1 GB (~12,500,000 size distributions)

LISST-Deep drawing with dimensions


  • 2-meter Communications Cable (included as standard for new instruments)
  • Clamps (included as standard for new instruments)
  • Instrument Stands (included as standard for new instruments)
  • 80% Optical Path Reduction module (PRM) for LISST-Deep
  • External 12V Battery Pack
  • Path Reduction Module for LISST-Deep
  • FAQ