1. A study of hyperspectral reflectance and fluorescence imaging as alternative methods for assessing coral health
- Author
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Teague, Jonathan, Day, John, and Scott, Tom
- Subjects
coral reef ,coral ,Hyperspectral ,reflectance ,fluorescence - Abstract
Coral reefs are facing a point of historic and critical vulnerability. With rising oceanic temperatures, more frequent coral bleaching events are occurring worldwide. As such there is a need for rapid, non-destructive survey techniques to gather greater and higher definition information than that currently offered by traditional image-based systems. The symbiotic partnership of corals with photosynthetic algae, Symbiodiniaceae, can be exploited as these algae are primarily responsible for coral colour. Consequently by using spectral based approaches, colour can be used as a marker for coral health. Distinguishing healthy from impacted or diseased coral is important for colony health monitoring. Stressed or diseased corals are frequently characterised by abnormal or diminished pigmentation in compromised tissue, compared to healthy counterparts. Hence, spectral imaging techniques offer a highly sensitive method for quantifying relative health. As such, these techniques could allow for quantifying coral health non-destructively offering low-cost, high resolution data capture whilst also providing data that can help to verify and validate spectral data sets that encompass far greater spatial scales i.e. satellite imagery. This project demonstrated the technique of using hyperspectral imagers to monitor wavelengths associated to key pigments (or markers) found within coral symbionts, which deteriorate or are expelled as part of the bleaching process. Thermically and chemically induced bleaching studies were conducted to understand the mechanisms of coral bleaching and the effect on pigment concentrations. It was concluded that reflectance signals were more appropriate as 'health' markers in comparison to their fluorescent counterparts. This was largely due to the difficulty in measurement when obtaining fluorescent data in-situ. To best suit hyperspectral imaging in the marine environment, a low-cost imager was designed, built, tested and refined. Low-cost imagers enable the use of underwater hyperspectral imagers without the high financial risk of submerging expensive electronics. The process of making underwater imagers more affordable allows for a bridge to be established between high spatial scale data sets able to be obtained by airbourne imaging, that require ground truthing, and high resolution in situ data. Current advances in hyperspectral imaging technologies, specifically linear variable filters (LVF), allow for off-the-shelf imagers such as digital single-lens reflex (DSLR) cameras to be converted into hyperspectral imagers, which can reduce the cost of spectral imagers by up to 80%. A hyperspectral imager was designed and built utilising a DSLR and LVF; the 'Bi-Frost DLSR'. The imager performed well in tests to assess its spectral performance both above and below the water's surface.
- Published
- 2022