The MapEO is a data processing service that converts optical aerial drone data into geo-referenced images. The camera sensors attached to drones collect RAW radiance and irradiance data together with GPS/IMU information. This information is then converted into geo-referenced water-leaving reflectance products, which provide information on parameters such as turbidity, total suspended sediments or chlorophyll concentrations.
Using drones as a tool to monitor water quality is especially useful as they can be deployed in all but the worst weather conditions, flying just tens of metres above the water surface, to look at centimeter scale features. In just one flight a single drone can cover several thousands of square metres!
Drone data products can help to fill the gaps in traditional water sampling and satellite remote sensing, as they have a high spatial resolution, are not hindered by cloud cover and can provide multiple surveys per day. Drones also allow collection of data in hard to reach areas.
Through MONOCLE the MapEO service has operationalized the processing workflow in the cloud and developed the processing of multispectral data along side RGB data.
The camera measures radiance over water bodies, expressed in Digital Numbers (DN). MapEO Water
converts these into physically meaningful values:
- Water leaving reflectance
- Total Suspended Matter
- Chlorophyll-a concentrations
In the development of the MapEO services some key challenges in application of image technology to characterize water columns had to be overcome, for example:
- Water bodies often look dark on images.
- The interaction of the light with the atmosphere just above the water surface plays a major role (sky glint). Luckily, this can be modelled through a modified version of VITO’s atmospheric correction algorithm iCOR (iCOR4Drones).
- The water surface acts as a mirror (sun glint). Therefore, a well-adapted flight protocol and hardware setup is indispensable.
- The water column is often a dynamic environment, variations in currents and tides can lead to a rapidly changing scene under investigation.
These challenges are addressed one by one in a clear processing workflow.
Diagram of MapEO workflow