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.
| LISST-100X | LISST-Deep | |
| 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.