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A LIDAR-compatible approach to remote sensing of water temperature using Raman spectroscopy

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posted on 28.03.2022, 18:30 authored by Andréa De Lima Ribeiro
The measurement of water temperature provides essential information for the understanding of the water column dynamics, being important for research fields including oceanography, climate change, marine ecology, fisheries and coastal management. Traditional in situ measurements provide accurate depth-resolved information at limited spatial and temporal scales. As an alternative suitable for large scales studies, researchers may rely on remote sensing tools such as passive satellite sensors and active LIDAR (Light Detection and Ranging) methods. However, satellite-derived sea surface data are restricted to the first micrometres of the water column, not providing information regarding vertical structure and stratification. LIDAR methods employ active excitation and fast time-resolved detectors, allowing for depth-resolved measurements performed from airborne or ship-based platforms and, when coupled to spectroscopic measurements, have the potential to assess subsurface water temperature. The aim of this research work is to develop LIDAR-compatible spectroscopic methods for monitoring water temperature based on the inelastic Raman scattering of photons in water. Raman scattering in water exhibits a temperature-dependent behaviour, which can be used to estimate temperature markers for remote sensing predictions. The analysis of Raman spectra from natural water samples, which were acquired by using a commercial Raman spectrometer (532 nm excitation) indicated that the presence of other optical signals in natural waters, such as fluorescence, may compromise the accuracy of Raman temperature sensing. In order to circumvent this issue, I proposed methods for spectral correction which resulted in temperature determination with improved accuracy. I designed and assembled multichannel LIDAR-compatible Raman spectrometers integrated to excitation lasers having green and blue wavelengths. The design allowed for simultaneous collection of unpolarised and polarised Raman signals, enabling the calculation of four temperature markers carrying different types of temperature information.Each marker was analysed in terms of accuracy of temperature predictions, sensitivities and percentage errors associated with signal-to-noise ratios. A novel linear combination method was employed to use all four temperature markers and was effective in enabling enhanced temperature predictions. The relative merits of using green and blue excitation were considered in the context of laboratory studies and proposed field implementation. The work presented in this thesis represents a major step forward in the quest for a LIDAR-based optical system to measure subsurface water temperature with an accuracy of ±0.5°C and depth resolution of 0.5 m in near real-time.

History

Table of Contents

Chapter 1. Introduction -- Chapter 2. Experimental and analysis methods -- Chapter 3. Raman spectroscopy as a technique for natural water temperature determination -- Chapter 4. LIDAR-compatible multichannel Raman spectrometer using green (532 nm) excitation light 97 -- Chapter 5. LIDAR-compatible multichannel Raman spectrometer using blue (473 nm) excitation light 132 -- Chapter 6. Conclusions and future outlook -- Bibliography -- Appendices.

Notes

Bibliography: pages 193-203 Empirical thesis.

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Degree

PhD, Macquarie University, Faculty of Science and Engineering, Department of Physics and Astronomy

Department, Centre or School

Department of Physics and Astronomy

Year of Award

2019

Principal Supervisor

Helen Pask

Additional Supervisor 1

David Spence

Rights

Copyright Andréa de Lima Ribeiro 2018. Copyright disclaimer: http://mq.edu.au/library/copyright

Language

English

Extent

1 online resource (243 pages) graphs, tables

Former Identifiers

mq:71004 http://hdl.handle.net/1959.14/1269881