Deep Blue and Polynesian Black Pearls

Airbus has developed an advanced satellite image processing algorithm for creating detailed bathymetry maps of coastal areas and coral reef cartography. In this example, we apply it to a Pléiades Neo image captured on September 6, 2022, over the Arutua atoll.

The resulting map delivers depth readings of up to 25m with a resolution of 1.2m, all achieved without the need for external reference data.

The process begins with atmospheric correction and the creation of a clear, haze-free image. Next, water depth is estimated using sophisticated physical or reflectance modelling techniques. 

While all six spectral bands of Pléiades Neo contribute to the algorithm, the Deep Blue band plays a pivotal role. This valuable information is visually represented using a colour scale.

The Deep Blue band spans between 400 and 450 nanometers, sitting right on the cusp of the visible light spectrum. With minimal water absorption, it enables us to see further into the depths.

The water around this atoll provides an ideal environment for both oysters and fish to flourish. As a result, it's essential to safeguard the pearl oysters by housing them in wire mesh baskets suspended on lines.

These lines, visible in the blue band, appear as long, parallel streaks near the pearl farms. Comparing them to the bathymetry map, these oyster lines are typically found at depths ranging from 8 to 10 meters.