Assessing the Potential of Remotely-Sensed Drone Spectroscopy to Determine Live Coral Cover on Heron Reef

Valerie J Cornet,Karen E Joyce

doi:10.3390/drones5020029

Abstract

Coral reefs, as biologically diverse ecosystems, hold significant ecological and economic value. With increased threats imposed on them, it is increasingly important to monitor reef health by developing accessible methods to quantify coral cover. Discriminating between substrate types has previously been achieved with in situ spectroscopy but has not been tested using drones. In this study, we test the ability of using point-based drone spectroscopy to determine substrate cover through spectral unmixing on a portion of Heron Reef, Australia. A spectral mixture analysis was conducted to separate the components contributing to spectral signatures obtained across the reef. The pure spectra used to unmix measured data include live coral, algae, sand, and rock, obtained from a public spectral library. These were able to account for over 82% of the spectral mixing captured in each spectroscopy measurement, highlighting the benefits of using a public database. The unmixing results were then compared to a categorical classification on an overlapping mosaicked drone image but yielded inconclusive results due to challenges in co-registration. This study uniquely showcases the potential of using commercial-grade drones and point spectroscopy in mapping complex environments. This can pave the way for future research, by increasing access to repeatable, effective, and affordable technology.

Highlights

Coral reefs are some of the most biologically diverse ecosystems on the planet, providing key ecosystem services to coastal communities through tourism, food security, and coastal protection [1]
By combining drone spectroscopy data and a public spectral library, linear unmixing of the spectroscopy points collected on the drone flight was achieved
Over 82% of the spectral variance seen in the drone spectroscopy dataset was explained by the chosen endmembers

Summary

Introduction

Coral reefs are some of the most biologically diverse ecosystems on the planet, providing key ecosystem services to coastal communities through tourism, food security, and coastal protection [1]. Reefs around the world are currently experiencing decline, through mass coral bleaching, ocean acidification, and water quality reduction [2] Due to both their ecological and economic importance, more accessible and cost-effective methods to map and monitor the decline of coral reefs are needed. By developing more affordable and repeatable methods in remote sensing, research can be made more accessible and efficient This is useful in locations that are hard to access as the improved capacity to survey remote areas can facilitate repeated monitoring [6]. This can be achieved at broad spatial and temporal scales, using platforms such as drones, aircrafts, or satellites

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