The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal

Simple item page
dc.contributor.advisorReason, Christopheren_ZA
dc.contributor.authorRobertson Lain, Elisabethen_ZA
dc.date.accessioned2018-04-24T14:02:16Z
dc.date.available2018-04-24T14:02:16Z
dc.date.issued2018en_ZA
dc.description.abstractThere is increasing interdisciplinary interest in phytoplankton community dynamics as the growing environmental problems of water quality (particularly eutrophication) and climate change demand attention. This has led to a pressing need for improved biophysical and causal understanding of Phytoplankton Functional Type (PFT) optical signals, in order that satellite radiometry may be used to detect ecologically relevant phytoplankton assemblage changes. This understanding can best be achieved with biophysically and biogeochemically consistent phytoplankton Inherent Optical Property (IOP) models, as it is only via modelling that phytoplankton assemblage characteristics can be examined systematically in relation to the bulk optical water-leaving signal. Harmful Algal Bloom (HAB) conditions in the Southern Benguela and various inland waters of Southern Africa require continuous observation by satellite due to the potential for significant negative environmental impacts. Current oceanic bio-optical models do not perform well in elevated Chlorophyll a conditions, but the high biomass conditions of Southern African inland and coastal waters lend themselves extremely well to the development of phytoplankton IOP models as the water-leaving signal is overwhelmingly phytoplankton-dominated. An initial validation of a new model of Equivalent Algal Populations (EAP) is presented here, and comparison is made with two prominent phytoplankton IOP models. The EAP model places emphasis on explicit biophysical modelling of the phytoplankton population as a holistic determinant of IOPs. By necessity due to its origins in highly scattering waters, a distinctive attribute of the EAP model is its comprehensive handling of the spectral and angular character of phytoplankton scattering. This emphasis is shown to have an impact on the ability to retrieve the detailed phytoplankton spectral scattering information necessary for PFT applications and to successfully simulate waterleaving reflectance across wide ranges of physical environments, biomass, and assemblage characteristics. The accurate description of a water body's Volume Scattering Function (VSF), and hence its phase functions, is critical to the determination of the constituent IOPs, the associated spectral water-leaving reflectance, and consequently the retrieval of PFT information. The EAP model offers the ability to provide phytoplankton population-specific phase functions, unveiling an opportunity to gain further insight into the causality of the PFT signal. This is a new modelling capability, and its application in case studies and sensitivity analyses has resulted in improved understanding of the PFT/assemblage-related signal, in particular the discovery that phytoplankton spectral scattering is the primary driver of the PFT-related signal. The required thresholds of PFT detection with respect to biomass, IOP budget and assemblage effective diameter are quantified. Key findings are that the backscattering-driven signal in the 520 to 600 nm region is the critical PFT identifier at marginal biomass, and that while PFT information does appear at blue and red wavelengths, it is compromised by biomass/gelbstoff ambiguity in the blue and low signal in the red, due primarily to absorption by water. The key findings and recommendations are hoped to provide considerable insight into PFT approaches with regard to in situ observation, sensor development and algorithm optimisation for the next generation of PFT investigations.en_ZA
dc.identifier.apacitationRobertson Lain, E. (2018). <i>The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Oceanography. Retrieved from http://hdl.handle.net/11427/27856en_ZA
dc.identifier.chicagocitationRobertson Lain, Elisabeth. <i>"The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Oceanography, 2018. http://hdl.handle.net/11427/27856en_ZA
dc.identifier.citationRobertson Lain, E. 2018. The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Robertson Lain, Elisabeth AB - There is increasing interdisciplinary interest in phytoplankton community dynamics as the growing environmental problems of water quality (particularly eutrophication) and climate change demand attention. This has led to a pressing need for improved biophysical and causal understanding of Phytoplankton Functional Type (PFT) optical signals, in order that satellite radiometry may be used to detect ecologically relevant phytoplankton assemblage changes. This understanding can best be achieved with biophysically and biogeochemically consistent phytoplankton Inherent Optical Property (IOP) models, as it is only via modelling that phytoplankton assemblage characteristics can be examined systematically in relation to the bulk optical water-leaving signal. Harmful Algal Bloom (HAB) conditions in the Southern Benguela and various inland waters of Southern Africa require continuous observation by satellite due to the potential for significant negative environmental impacts. Current oceanic bio-optical models do not perform well in elevated Chlorophyll a conditions, but the high biomass conditions of Southern African inland and coastal waters lend themselves extremely well to the development of phytoplankton IOP models as the water-leaving signal is overwhelmingly phytoplankton-dominated. An initial validation of a new model of Equivalent Algal Populations (EAP) is presented here, and comparison is made with two prominent phytoplankton IOP models. The EAP model places emphasis on explicit biophysical modelling of the phytoplankton population as a holistic determinant of IOPs. By necessity due to its origins in highly scattering waters, a distinctive attribute of the EAP model is its comprehensive handling of the spectral and angular character of phytoplankton scattering. This emphasis is shown to have an impact on the ability to retrieve the detailed phytoplankton spectral scattering information necessary for PFT applications and to successfully simulate waterleaving reflectance across wide ranges of physical environments, biomass, and assemblage characteristics. The accurate description of a water body's Volume Scattering Function (VSF), and hence its phase functions, is critical to the determination of the constituent IOPs, the associated spectral water-leaving reflectance, and consequently the retrieval of PFT information. The EAP model offers the ability to provide phytoplankton population-specific phase functions, unveiling an opportunity to gain further insight into the causality of the PFT signal. This is a new modelling capability, and its application in case studies and sensitivity analyses has resulted in improved understanding of the PFT/assemblage-related signal, in particular the discovery that phytoplankton spectral scattering is the primary driver of the PFT-related signal. The required thresholds of PFT detection with respect to biomass, IOP budget and assemblage effective diameter are quantified. Key findings are that the backscattering-driven signal in the 520 to 600 nm region is the critical PFT identifier at marginal biomass, and that while PFT information does appear at blue and red wavelengths, it is compromised by biomass/gelbstoff ambiguity in the blue and low signal in the red, due primarily to absorption by water. The key findings and recommendations are hoped to provide considerable insight into PFT approaches with regard to in situ observation, sensor development and algorithm optimisation for the next generation of PFT investigations. DA - 2018 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 2018 T1 - The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal TI - The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal UR - http://hdl.handle.net/11427/27856 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/27856
dc.identifier.vancouvercitationRobertson Lain E. The fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signal. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Oceanography, 2018 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/27856en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Oceanographyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherOceanographyen_ZA
dc.titleThe fundamental role of spectral scattering in the ocean colour Phytoplankton Functional Type signalen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
Files
Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
thesis_sci_2018_robertson_lain_elisabeth.pdf
Size:
4.02 MB
Format:
Adobe Portable Document Format
Description:
Download
Collections
PhD / Doctoral