Accurately assessing coral reef health is fundamental to conservation and restoration efforts. The Reef Restoration and Adaptation Program (RRAP), managed by the Australian Institute of Marine Science (AIMS), is revolutionising coral reef monitoring through 4D photogrammetry. This cutting-edge approach enhances traditional 3D mapping by integrating temporal changes, allowing scientists to track reef dynamics over time with millimetre-level precision.
What is 4D Photogrammetry?
4D photogrammetry is an advanced monitoring technique that reconstructs high-resolution 3D models and 2D orthomosaics of coral reefs. These models are generated using Structure from Motion (SfM) algorithms, which analyse overlapping images to create digital representations of reef surfaces. Unlike conventional methods, 4D photogrammetry enables precise spatial alignment of multiple time points, making it possible to detect changes in coral structure, growth, and degradation.
How It Works: A Field-to-Model Workflow
The EcoRRAP photogrammetry workflow, outlined in the AIMS Standard Operational Procedures (SOPs), consists of three key steps:
- Field Data Collection
- Divers use a specialised rig equipped with to capture detailed images of reef sites.
- These images provide coverage at different resolutions, from 0.3 mm per pixel (high resolution for small areas) to 5 mm per pixel (medium resolution for large-scale surveys).
- Strategic placement of reference markers ensures that images can be accurately co-registered across different survey periods.
- Model Processing and Co-Registration
- Images are processed using specific software to generate 3D digital surface models (DSMs) and 2D orthomosaics.
- A crucial step is temporal co-registration, where different time-point models are precisely aligned, allowing for long-term monitoring of reef changes.
- Data Extraction and Analysis
- Final models enable scientists to measure coral growth, habitat complexity, and changes in reef structure.
- Key metrics include curvature, range of heights, slope, coral recruitment, growth, and mortality among others
Why 4D Photogrammetry Matters for Coral Reef Conservation
Traditional coral reef monitoring methods often rely on visual surveys or 2D imagery, which can miss subtle structural changes. The introduction of 4D photogrammetry provides a highly detailed, repeatable, and scalable method to track reef health. This technology can:
- Assess reef resilience – Identify areas of natural recovery or vulnerability.
- Detect early signs of degradation – Monitor coral loss from bleaching, storms, and disease.
- Evaluate restoration success – Measure the impact of interventions such as coral planting.
The integration of 4D photogrammetry into global coral reef monitoring evidences the continued drive for innovation in coral reef monitoring. By ensuring that monitoring methods remain scalable, and high-resolution, policy makers and governments are better equipped to guide effective reef management and policy decisions.
Both SOPs are available to download below, alongside all of AIMS’ SOPs which are accessible here.
Header photo credit: Ocean Image Bank / The Ocean Agency
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