Submersible Holographic Particle Imaging System
Imaging and measuring the size of particles and organisms in the water is not easy. This is especially true when the object being measured is fragile and non-spherical such as flocculated particles or fragile colonies. The LISST-Holo2 was developed to provide measurements of objects that can not be pumped or sampled easily and are few in number. The holographic method used by the LISST-Holo2 eliminates the typical depth of field issues common with submersible microscopes and camera systems. The LISST-Holo2 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-Holo2 allows particles to freely pass through the sample volume with minimal disturbance and therefore capture the true nature of the particles.
For more details on the LISST-Holo2 please visit the LISST-Holo2 product page.
The LISST-Holo2 is the second generation of Sequoias’s submersible holographic sensor. The LISST-Holo2 is able to image particles significantly faster than Sequoia’s original LISST-Holo. At 20 holograms per second, the LISST-Holo2 is the fastest holographic sensor currently available. The maximum depth has also been increased from 300 meters in the original LISST-Holo to 600 meters in the LISST-Holo2. The LISST-Holo2 also contains an internal rechargeable battery pack allowing for several hours of autonomous operation.
Holography has applications anywhere complex particle are found. One example that demonstrates the utility of holography is tracking of harmful algal blooms in Monterey Bay, California. The Monterey Bay Aquarium Research Institute (MBARI) in Moss Landing,CA uses large autonomous underwater vehicles to study the Monterey Bay. They have used the LISST-100X particle size analyzer on their AUVs for many years to measure the size of the particles in the water column. However, they needed additional information to better understand the details of the harmful algal blooms that were occurring in Monterey Bay. The addition of the LISST-Holo provided the additional information that they were looking for. Below is a composite of some the images they obtained during some early testing in 2011. A more detailed discussion of this testing can be found here.
The LISST-Holo2 is also useful for other applications such as flocculated sediment studies, oil droplet size and shape studies, entrained air bubble studies, measuring frazil ice and even snow flakes.
How Does it work?
The holographic method used by the LISST-Holo2 gives the ability to capture in-focus images of particles as large as 2.5mm but still capture features as small as 25 microns. All particles across the 50 mm path can be imaged. This is done by using what is called in-line digital holography. The LISST-Holo2 shines a collimated red (658nm) laser beam through the water. The laser light illuminates the particles in the water. The scattered light from the particles interferes with the unscattered light to form interference patterns at the receiving digital camera sensor. These images of interference patterns (holograms) are stored on the internal disk of the instrument. The instrument is self-contained and does not need to be cabled to a computer.
The holograms are post-processed to obtain the in focus images of the particles. Software is provided that will find the ideal focus depth for each particle individually. The in focus particle are then extracted from the reconstructed image and saved individually or in a composite image. Using image processing tools the software outputs measurements of particle size, shape and volume concentration. The images below show how different particles come into focus at different image planes.
For more information, including pricing, please contact us at info@SequoiaSci.com.