Mapping Live Coral: Comparing Spaceborne to Airborne Imaging Spectroscopy

Highlights: What are the main findings? Spaceborne imaging spectroscopy from the Tanager-1 satellite provided verifiable estimates of live coral cover on a Hawaiian reef. Airborne and spaceborne imaging spectrometers produced comparable geospatial distributions of live coral cover, macroalgal cover, and their ratio. What are the implications of the main findings? Live coral cover can be mapped with high-fidelity imaging spectroscopy from Earth orbit. The findings support repeatable mapping of coral and macroalgae in reef compositional monitoring at a global scale. Live coral cover is a key indicator of coral reef composition, health, and functioning. Airborne imaging spectroscopy provides verifiably accurate estimates of live coral cover to seawater depths of 25 m, yet satellite-based approaches have not achieved the same level of performance. The new Tanager-1 satellite carries a high-fidelity imaging spectrometer in sun-synchronous Earth orbit, providing an opportunity to transition from airborne to spaceborne imaging of live corals and other benthic constituents. We coordinated overpasses of Tanager-1 and Global Airborne Observatory (GAO) imaging spectrometer measurements of coral reef to a depth of 25 m in Hawaiʻi. Tanager-1 has a spatial resolution of 30 m, while the GAO data were collected at 2 m resolution, requiring detailed modeling to simulate 30 m data for subsequent comparison to the satellite data. At 30 m resolution, the two sensors generated similar geographic patterns of live coral, macroalgal, and sand cover. Field validation indicated similar precision and accuracy of live coral cover estimates, and the ratio of live coral to macroalgal cover proved similar between sensors. Overall results indicate that live coral cover can be mapped with high-fidelity imaging spectroscopy from Earth orbit. With the advent of more spaceborne imaging spectrometers, a new era of live coral monitoring will be possible, filling a critical gap for repeated assessments of reef compositional change at a global level.