We have just completed a two year programme of aerial (drone) surveys in Christchurch Harbour, looking at the seasonal distribution of algal mats.

Drone surveys were undertaken each month from June to September in both 2023 and 2024 using a combined RGB and Near Infra-Red (NIR) sensor. Combining the RGB and NIR spectrums allows us to use image analysis to classify the aerial image outputs to determine the extent of both green algae and the invasive red algae (Gracilaria vermiculophylla), which has become established in the harbour.
The above image is taken from the RGB camera sensor, whilst the image below is the same frame taken with the NIR sensor.

In order to ground-truth the aerial imagery and facilitate training the image analysis software, ground surveys were undertaken using quadrats to determine the species composition and abundance of both red and green algae at known locations.

This project, funded by South West Water, is part of ongoing work in Christchurch Harbour to understand the impacts of both red and green algae on wading bird feeding and distribution.
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