Ocean colour remote sensing of zooplankton swarms

Student thesis: Doctoral Thesis

Abstract

Zooplankton are keystone organisms in the marine environment, providing a crucial link between primary production and high order predators, as well as playing a critical role in biogeochemical cycling within the ocean. Many zooplankton groups also represent considerable economic interest, both by serving as a primary food source for many commercially harvested fish species and being directly harvested for the development of aquaculture feed and human health supplements. In this context, there is considerable interest in the accurate monitoring and characterisation of zooplankton populations, for the successful management of these organisms. Despite this interest, relatively little is known about wide-scale distributions of these organisms, largely due to their patchy population dynamics and the challenges associated with ship-based sampling. To help address this issue, this thesis explores the potential for the detection of surface swarms of zooplankton from satellite derived ocean colour data. This work presents the first attempt to remotely identify and characterise surface swarms of the copepod species Calanus finmarchicus using a novel enhanced RGB colour matching technique developed throughout this work. With this framework, surface concentration estimates of these copepods were determined from space for the first time. However, application of these methods to optically complex environments led to concerns regarding the quality of remote sensing reflectance data retrievals, resulting in the development of a novel per-pixel atmospheric correction optimisation method. This showed considerable improvement in data quality when compared to the NASA standard atmospheric correction scheme. With increased confidence in the spectral information, a spectral matching technique was developed as an alternative method to the colour matching approach for the detection of zooplankton, to allow for the inclusion of more spectral information. Whilst results were comparable, the spectral matching method provides more flexibility and can be consistently applied to both coastal and open water environments, making this methodology the most favourable. Finally, to explore the potential of remote detection of other key zooplankton groups, the spectral absorption properties of 7 groups of zooplankton were measured in a Point Source Integrating Cavity Absorption Meter (PSICAM). Results indicate that several different zooplankton groups have the potential to be identified and characterised through ocean colour if present in sufficient quantities. Further, intra-species variance was also preliminarily explored to determine the impact of life stage and seasonality on absorption properties, which provided evidence that considerable variance in absorption within organisms of the same species is possible.
Date of Award7 Oct 2024
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde & EPSRC (Engineering and Physical Sciences Research Council)
SupervisorDavid McKee (Supervisor) & Brian Patton (Supervisor)

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