Satellite Spectroscopy Matches Airborne Accuracy in Coral Reef Mapping, Study Finds

Researchers at Arizona State University, led by ecologist Gregory Asner, have demonstrated for the first time that a spaceborne imaging spectrometer can produce verified, high-fidelity maps of live coral cover to depths of 25 meters.¹ This is a capability previously limited to costly and logistically complex airborne missions. Analyzing live coral cover is important in tracking the health of the sea and its ecosystem, and through the use of Planet Labs’ Tanager-1 satellite and Arizona State University’s Global Airborne Observatory (GAO), the researchers demonstrated how spectroscopy can play a key role in reef science and management.

What is live coral cover?

Live coral cover is the proportion of living coral tissue occupying the sea floor.¹ This metric is used to evaluate the health of coral reefs in the sea over time. Given that coral bleaching (the disappearance and decay of live coral tissue) events are growing in number, monitoring live coral cover has become paramount, as it indicates the health of the underwater ecosystem.¹

What tools have been used to study live coral cover in the past?

Multispectral satellite sensors have been the methods in the past used to study live coral cover. For example, satellites Landsat, Sentinel-2, IKONOS, and Planet Dove were used to map coral bleaching events and the benthic habitats.^2–7 Despite the successful deployment of these satellites, none of these satellite platform demonstrated the spectral fidelity needed to reliably distinguish live coral from macroalgae and sand at depth. In this study, which was published in the journal Remote Sensing, Asner and his team sought to remedy this issue.

What did the researchers do in their study?

As part of the experimental procedure, the research team coordinated simultaneous overflights of the GAO aircraft and Tanager-1 along 50.3 kilometers of coastline off the island of Hawaii. This island is known for having significant biodiversity, making it an ideal location to conduct geological and ecological studies.⁸ The GAO collected data at 2-meter spatial resolution; Tanager-1 operated at 30 meters.¹ To enable a valid comparison, the team applied detailed instrument and atmospheric modeling to simulate 30-meter GAO data, then compared both data sets against field-collected quadrat samples.¹

The researchers found in their results that both sensors produced similar geographic distributions of live coral, macroalgal, and sand cover. Field validation yielded an R² of 0.65 and a root mean square error of 0.09 for both the modeled GAO data and Tanager-1 at 30-meter resolution.¹ The ratio of live coral to macroalgal cover was also consistent between sensors, a metric critical for assessing competitive dynamics on degraded reefs.

What are the key takeaways from this study?

There are several important takeaways from this study. For one, the researchers demonstrated how airborne and spaceborne imaging spectroscopy was able to deliver accurate estimates of live coral cover.¹ Previous satellite reef assessments have largely relied on multispectral sensors, which lack the spectral resolution needed to discriminate between benthic constituents in optically shallow, low-reflectance water.¹ Tanager-1's hyperspectral spectrometer overcame that constraint.

The findings of the study also show that live coral cover can be mapped from Earth’s orbit, and that repeatable mapping of coral and microalgae is indeed possible.¹

“The advent of the Tanager satellite, equipped with a high-fidelity imaging spectrometer in low Earth orbit, presents a potential transition from airborne to spaceborne imaging spectroscopy for regional live coral detection and mapping,” the authors wrote in their study.¹

References

1. Asner, G. P.; Vaughn, N. R.; Heckler, J.; et al. Mapping Live Coral: Comparing Spaceborne to Airborne Imaging Spectroscopy. Remote Sens. 2026, 18 (3), 435. DOI: 10.3390/rs18030435
2. Andréfouët, S.; Muller-Karger, F.E.; Hochberg, E.J.; Hu, C.; Carder, K.L. Change Detection in Shallow Coral Reef Environments Using Landsat 7 ETM+ Data. Remote Sens. Environ. 2001, 78, 150–162. DOI: 10.1016/S0034-4257(01)00256-5
3. Hedley, J.; Roelfsema, C.; Koetz, B.; Phinn, S. Capability of the Sentinel 2 Mission for Tropical Coral Reef Mapping and Coral Bleaching Detection. Remote Sens. Environ. 2012, 120, 145–155. DOI: 10.1016/j.rse.2011.06.028
4. Xu, J.; Zhao, J.; Wang, F.; Chen, Y.; Lee, Z. Detection of Coral Reef Bleaching Based on Sentinel-2 Multi-Temporal Imagery: Simulation and Case Study. Front. Mar. Sci. 2021, 8, 584263. DOI: 10.2112/SI93-061.1
5. Mumby, P.J.; Edwards, A.J. Mapping Marine Environments with IKONOS Imagery: Enhanced Spatial Resolution Can Deliver Greater Thematic Accuracy. Remote Sens. Environ. 2002, 82, 248–257. DOI: 10.1016/S0034-4257(02)00041-X
6. Asner, G.P.; Martin, R.E.; Mascaro, J. Coral Reef Atoll Assessment in the South China Sea Using Planet Dove Satellites. Remote Sens. Ecol. Conserv. 2017, 3, 57–65. DOI: 10.1002/rse2.42
7. Lyons, M.B.; Murray, N.J.; Kennedy, E.V.; Kovacs, E.M.; Castro-Sanguino, C.; Phinn, S.R.; Acevedo, R.B.; Alvarez, A.O.; Say, C.; Tudman, P.; et al. New Global Area Estimates for Coral Reefs from High-Resolution Mapping. Cell Rep. Sustain. 2024, 1, 100015. DOI: 10.1016/j.crsus.2024.100015
8. Wetzel, W. Analyzing Hawaii’s PTA-2 Drill Core With LWIR and SWIR Spectroscopy. Spectroscopy. Available at: https://www.spectroscopyonline.com/view/analyzing-hawaii-s-pta-2-drill-core-with-lwir-and-swir-spectroscopy (accessed 2026-04-24).