Sequoia Scientific - Model LISST-Holo2 -Flocs and Plankton Holographic Camera

• In-situ digital holography
• Particle Imagery
• Self-contained with internal datalogger
• Ethernet connection to PC for programmable data collection
• Power via external battery pack (accessory) or external power source
• Automated hologram processing

The LISST-HOLO differs from other LISST instruments in that it uses holography instead of laser diffraction to measure particle size. The other key difference is the LISST-HOLO is able to provide images of suspended particles. This allows for particle identification and recording of shape characteristics in addition to size. The LISST-HOLO is Sequoia’s only imaging particle size analyzer. Having the ability to view particles is especially important for those interested in biological particles or complex aggregates.

The optics end of the LISST-HOLO consists of a 50 mm optical path. A red (658 nm) laser beam traverses the optical path, overfilling a 7 × 4 mm CCD array. A hologram is formed when particles in the sample volume scatter the laser light which then creates an interference pattern on the CCD.

The holographic method used by the LISST-HOLO eliminates the typical depth of field issues common with submersible microscopes and camera systems.  The LISST-HOLO has the ability to bring all the particles across the 50 mm spacing between the windows in to focus after the image is collected.  The large open path of the LISST-HOLO allows particles to freely pass through the sample volume with minimal disturbance and therefore capture the true nature of the particles.

Sequoia provides state of the art software that can digitally reconstruct the hologram to provide crisp particle images. The software then automatically extracts particle characteristics and size from the reconstructed images.

The LISST-HOLO has onboard memory for storage of ~15,000 holograms. An additional external memory module can extend the data logging ability of the LISST-HOLO even further. The LISST-HOLO is configured through an Ethernet connection and a simple web browser interface.

Parameters Measured

• 2MB Hologram containing the interference pattern of all particles in the laser beam
• Depth
• Temperature
• Time-stamp on each hologram

Parameters derived upon hologram processing

• Reconstructed in-focus images of particles in laser beam.
• Particle Size Distribution (PSD)
• Standard Deviation of PSD
• Particle Area Concentration
• Mean and Median particle size
• 5 seconds processing time per hologram in MATLAB (typical, @ 2.2 GHz PC)

Particle Size Distribution and concentration range

• ~25-2500µm size range
• Beam attenuation values between 0 and 4 m^-1
• Maximum concentration between 0 and 50 mg/l, depending on grain size. 

Technology

• Solid state laser diode @ 658 nm, 8 mW
• 4.4µm pixel size digital camera, 1600 x 1200 pixels
• 2 MB hologram size
• Hologram capture rate programmable up to 20 Hz continuous;
• Optical path length 50 mm standard; Path reduction modules available for high-concentration environments.
• All particles in focus in optical path.
• Sampling volume per hologram 1.86 cm ³
• Volume sampled per second at 20Hz sample rate: 37.2 cm ³
• Maximum current velocity/CTD speed during deployment: 2 m s ^-1 

Software

• Holo Batch: Automated image reconstruction and particle segmentation
• Holo Detail: Hologram sorting by richness of information content, and detailed reconstructed image examination.

Mechanical and Electrical

• Dimensions: 13.3 cm × 76.7 cm (5.25″ × 30.21″) [Ø × L]
• Weight: 7.2 kg (15.8 lbs) in air; 1.0 kg (2.2 lbs) in water
• 600 m depth rating
• 50 GB internal solid state drive
• Internal Battery life: **** holograms for standard 14.4V, 15Ah NiMH rechargeable battery
• External power input: 15VDC nominal, 12-16VDC
• Power drain: *********200µA / 500mA / 600mA / 880mA******* (sleeping / idling / laser on / laser + camera on)