[Academic] Fwd: Abstract

[David McKee]

Dear Colleagues

The Institute of Biophotonics is hosting a seminar on holographic 
imaging next week (7th June, 12-1pm, HW113-114).  I know the speaker 
well and expect it will be a good talk!  More info below.




Seeing is believing: holographic imaging of marine suspended particles

Alex Nimmo Smith

School of Marine Science & Engineering, Plymouth University, UK
alex.nimmo.smith at plymouth.ac.uk

Abstract

Particles suspended in the sea play a significant role in many of the 
biogeochemical processes of central importance to our changing world. 
They may be of biological or mineral origin, and hence occur in a myriad 
complex forms. In addition to their fundamental nature, key 
characteristics of suspended particles are their size (which may vary 
from submicron to millimeter scales) and effective density. For example, 
small particles tend to be better scatterers of light, while large 
particles tend to settle more quickly and so are important to mass 
transport. Added complexity arises from the flocculation and 
disaggregation of particles as they interact within the varying 
turbulence of the natural environment, leading to changes in the size 
distribution and settling characteristics of the particle population.

In situ measurements of particle parameters are often performed with 
laser scattering (LISST) instruments, but these assume the particles are 
(nearly) spherical and provide no information on their nature. 
Floc-cameras have also been utilised to image particles in situ, but 
usually suffer from limited resolution or a small depth-of-field, so 
restricting sample volume size.

Here we discuss the application of holography to the characterisation of 
suspended particles, and how these measurements enable clearer 
understanding of the particle populations and associated optical 
scattering characteristics in waters around the UK. A variety of digital 
in-line holographic systems have been developed and deployed that allow 
the in situ imaging of all particles O(micron to mm) within relatively 
large sample volumes O(ml). Digital reconstruction of the recorded 
holograms allows the automatic extraction of in-focus images of each 
particle, from which key characteristics (size, shape, nature) may then 
be derived.


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