Thesis
Development of a coherence-based transmissometer for the removal of scattering bias
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18045
- Person Identifier (Local)
- 202163439
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The measurement of the beam attenuation coefficient by transmissometers has long been negatively affected by the presence of errors due to the collection of light scattered at small forward angles. The magnitude of these errors is difficult to predict and account for, relying on characteristics of the transmissometer, such as the path length and collection angle, and also on the parameters describing the particle population, like the particle size distribution and refractive index, among other terms. This makes accounting for the errors in beam attenuation associated with scattered light very challenging. Researchers have focused on developing corrections for the beam attenuation coefficient after measurement. However, these approaches require further knowledge about the water sample, such as the volume scattering function. This thesis introduces the design of a novel, coherence transmissometer that utilizes the loss of spatial coherence associated with particle scattering to measure an increased beam attenuation coefficient compared to that measured by a standard transmissometer design that uses only a lens and pinhole. After optimization of the coherence transmissometer for sensitivity to various noise sources, it is found that combining the lens–pinhole arrangement with a coherence filter produces consistently higher attenuations values than a transmissometer that only uses a lens–pinhole arrangement for a range of polystyrene microspheres and spherical phytoplankton from approximately 1 to 50 μm. The difference in beam attenuation measurements between the two transmissometers increases with increasing particle size, as expected due to changes in the volume scattering function, and is reasonably consistent with expectations of the scattering errors from Mie scattering simulations at low particle sizes. These results suggest that the use of a coherence filter should be further explored for inclusion in future transmissometer designs, to substantially reduce the effect of scattering errors on beam attenuation measurements.
- Advisor / supervisor
- McKee, David
- Griffin, Paul
- Resource Type
- DOI
Relations
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PDF of thesis T18045 | 2026-06-09 | Public | Download |