Establishing the extent and proportion of live biomass and dead shell in estuary mussel beds has been carried out on foot typically during intertidal periods at low water springs (LWS). Clearly, such periods are of short duration and estimations of biomass vs shell have necessarily to be done on a sampling basis to cover sufficient ground. Given the limited time available and patchy and non-uniform nature of the ground, there is potential for significant error. For larger beds, such foot mapping may need to extend over several tides, extending the project both in terms of time and cost.
Typical lightly populated mussel bed
Traditional sampling on foot using a 1M Quadrat part of the;ground truthing of biomass and live vs. dead shell. The mapping is carried out by walking a regular pattern back and forth across the survey site i.e. at spaced intervals. As this is done the presence or absence of mussels is noted at regular intervals thus building up a picture with each pass across the site.
A 'Quadrat' in use to assess mussel volume and quality
An area of about 100m x 300m (3 Ha) was chosen, it being the site of a depleted mussel bed recently surveyed on foot. The mission was flown autonomously, the UAV being pre-programmed with a series of waypoints at each of which a photograph was taken. At the end of the mission the digital images were downloaded and processed.
The surveyed area
A typical down-looking image colour enhanced for clarity
An example of image stitching (4 images)
After a considerable amount of planning, the entire 3 Ha aerial survey was carried out in less than 10 minutes on-site without manual intervention. Around 40 images were acquired, which, when processed and put together with ground truthing data represented a considerable improvement in accuracy and reduction of time on site than would have been possible by conventional means.