The Use of Photogrammetry
in Coral Reef Restoration, Maldives
Quantifying coral structure is essential for assessing changes in the health of coral reefs under rapidly changing climatic conditions. Reefs provide key services to humans including fishing, coastal protection, and tourism. Many of these services are attributed to the 3D structure of reefs, as their structure plays a major role in the reef biodiversity they are able to support, and the overall complex functionality of the ecosystem.
Photogrammetry is the science of making measurements from photographs. To do this, we take a series of photographs of an object from multiple angles, then specialist software is used to match points across these images to construct 3D models. From these models, accurate measurements of the object can be made. Photogrammetry can be used to depict a coral’s 3D structure and measure a colony’s growth – a useful tool to aid coral reef restoration efforts both here in the Maldives and worldwide.
Reefscapers restore coral reefs by propagating corals. We start with small coral fragments harvested from large, healthy donor colonies, and transplant them onto supporting frame structures. These fragments then grow over time to form large coral colonies, which encourage and support a high diversity of marine life in the lagoons that surround our partner Maldivian island resorts.
Amelia taking raw data photographs of our coral frames …
… to generate 3D photogrammetric images of the growing coral colonies.
Interactive 3D Photogrammetry MODELS
Each coral fragment is manually attached to the frame with a tie; after several weeks, the fragment has encrusted over the tie and starts to fuse onto the supporting frame. Slowly, the fragment grows into a large mature coral colony. To construct a model that depicts the growth of a single fragment over time, we took a series of underwater photos of this fragment from every angle, every 6 months. These pictures were then uploaded to software that matched points across images, and built a depth-map to depict how these points were distributed in 3D space. From this map, a textured mesh is overlayed to form the resulting 3D model of the coral fragment, and later of the growing colony.
Photogrammetry can be used as an interactive learning tool to show how restored coral fragments grow over time, and in the future this technique can be applied to quantify the growth of restored colonies under changing climatic conditions, in the Maldives and globally.
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First model: Fragments from donor colonies are attached to coral frames using cable ties
Second model: Within 6 months, the fragment “self attaches” to the coral frame, and grows over the cable tie.
The fragment grows into a small colony that is now firmly attached to the frame.
Third model: The colony continues to grow larger and form more branches over time.