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Sequoia Scientific

LISST-Holo2

Holographic Camera for Flocs and Plankton

UPDATED 07 JULY 2017

The LISST-Holo2 stores holograms for study of flocs, plankton, and other particles in water. It is an advanced successor to the original LISST-Holo.

This new version is the world’s fastest, capturing holograms at 20Hz, [vs.0.2Hz for the original LISST-Holo]. The same original housing now includes an 8-hr battery and 237GB of data memory. Processing speed per unit water volume imaged is faster than the competition. A unique new feature ranks thousands of holograms based on richness of imagery – a Sequoia innovation for fast overview of a collection of holograms.

The LISST-Holo2 will be available from August 2017. Contact us if you’d like to upgrade your original LISST-Holo.

Click here to watch a video on Sequoia’s updated fast hologram processing software.

Features

  • Submersible in-line holography
  • New: Up to 20Hz continuous hologram capture
  • New: Internal 237 GB data storage
  • New: Internal rechargeable battery, (or external power for lab use)
  • New: Faster processing, faster than the competition per unit volume imaged.
  • New: An algorithm that ranks holograms by the richness of imagery in them
  • Large volume viewed each image
  • Programmable data collection
  • Automated Batch or Detail hologram processing

The LISST-Holo2 advances the technology that was built into the original LISST-Holo. It can capture holograms 100X faster which makes it the fastest. A 237 GB internal memory stores upto 118,000 holograms. The high speed hologram capture permits study of phenomena such as thin layers. Users often wonder how to make a quick assessment of these 10’s of thousands of holograms. Sequoia has pioneered a ranking algorithm. You can now see your holograms ranked by the richness of imagery in them.

Unlike other submersible holography systems, we have now incorporated a powerful rechargeable NiMH battery within the same original housing. This instrument is self-contained, ready to be programmed and used.

The LISST-Holo2 views the largest volume per image of competing systems. Processing speed per unit volume imaged is faster than the competing system.

Data processing software is included. Holo-Batch processes a selected group of holograms, whereas Holo-Detail permits detailed manual study of individual holograms. Processed holograms produce crisp in-focus images on a plane. Computed size distribution of particles is also output.

The large open path of the LISST-Holo2 allows particles to freely pass through the sample volume with minimal disruption.

Figures below: (left) Watch the slider at bottom indicating the location of plane where image is focused; different particles come into focus at different distances from the optical window; axes are in microns, and (right) a collection of images, courtesy of Dr John Ryan, MBARI.

mbari-figure-2-550pxW

 

 

Specifications

(Specifications are subject to change)

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 1 cm 3 volume imaged, 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 1.5 cm 3
  • Volume sampled per second at 20Hz sample rate: 30 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
  • 237 GB internal solid state drive
  • Internal Battery life: 1.3M holograms for standard 14.4V, 15Ah NiMH rechargeable battery in continuous use.
  • External power input: 15VDC nominal, 12-16VDC
  • Power drain: 200µA / 700mA / 800mA / 800mA (sleeping / idling / laser on / laser + camera on)

Accessories

LISST-HOLO External Battery Case
Replacement Zscat Chamber
Replacement 2-meter Communications Cable
Clamps
Replacement Instrument Stands
Path Length Reduction Module
LISST-HOLO Replacement Battery

FAQ

How does the LISST-HOLO work?

The LISST-HOLO contains a red (658nm) laser that emits collimated light into the sample volume. The light is scattered by suspended particles. The scattered light then interferes with the unscattered portion of the beam. The resulting interference pattern is captured by an onboard camera. The image captured by the camera is known as a hologram.

The hologram can be digitally reconstructed to produce an in-focus picture of all the particles in the sample volume. Information about the particles size, shape, and position can all be extracted from the hologram.

How is the LISST-HOLO different from an in-situ microscope?

The LISST-HOLO is similar to a microscope in that it can produce in-focus images of small suspended particles. However, the benefit of using a holographic system is that you can have a large sample volume while still maintaining proper focus. In traditional microscopes, increasing the magnification decreases the depth of field. Thus, you can only image a thin slab of water. In holography the depth of field problem is eliminated, because each particle can be focused individually after the hologram has been captured.

The larger depth of field allows for a larger sample volume than is possible with a traditional microscope. This has two benefits. (1) It allows for more particles to be imaged, which will statistically improve the size distribution measurement. (2) It allows for a larger gap between the send and receive optics. The larger spacing is less likely to influence fluid flow and/or break apart aggregated particles.

How are holograms reconstructed?

Sequoia provides two pieces of software for hologram reconstruction. One is for batch processing of holograms and is used to generate a size distribution and output automatically focused particle images. The second is for qualitative viewing of holograms and allows for manually stepping through the focused planes of the hologram.

Both programs use the Fresnel transformation to reconstruct in-focus images throughout the sample volume. Particles are then extracted and characterized from these images.

See the following paper and references therein for more information about hologram reconstruction:

Owen, R.B., Zozulya, A.A. 2000. In-line digital holographic sensor for monitoring and characterizing marine particulates. Opt. Eng. 39(8): 2187-2197.

What do the particle reconstructions look like?

mbari-figure-2-550pxW