Ave Ansper-Toomsalu defended her Doctoral Thesis "Synergy of Earth Observation data to advance monitoring of optically complex waters"

On 29 May at 10:15 Ave Ansper-Toomsalu defended her doctoral thesis in Environmental Technology "Synergy of Earth Observation data to advance monitoring of optically complex waters".

Supervisor:
Associate Professor Krista Alikas (University of Tartu, Tartu Observatory)

Opponent:
Carmen Cillero Castro, PhD (Head of R&D Area of 3edata)

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Summary
Lakes and coastal areas are very important parts of the aquatic ecosystem, therefore consistent monitoring is essential. They are influenced by antrophogenic factors, but also natural factors should be taken into account, such as daily and seasonal dynamics. Copernicus programme satellites Sentinel-2 and Sentinel-3 have great potential to complement current water quality monitoring under European Union Water Framework Directive. However, using satellite data for monitoring waterbodies is challenging because of atmospheric composition, different amount of optically active substances in water and influence from the vicinity of the land. For developing satellite-based applications, the whole Earth Observation processing chain is crucial. Minimizing uncertainties in each processing chain is essential, starting from the reference data for validating the satellite data until the final application development. The study found that satellite data processing has to consider the parameter of interest, optical water type and the vicinity of land of the target waterbody. As Chlorophyll a is the key parameter for estimating the ecological status of water, Chlorophyll a algorithms were tested and developed for Sentinel-2 satellite, which has suitable resolution for monitoring small lakes. The inclusion of both in situ and satellite data could improve the ecological status assessment in terms of data availability showing more dynamics and trends. It was found that the suitability of Chlorophyll a algorithms was dependent on optical water types and most suitable algorithms were found. To improve the assessment of ecological status, the synergy between optical and altimetry data was created to remove water level influence from water quality parameters. This approach will advance monitoring in terms of assessment of ecological status under the Water Framework Directive derived by Earth Observation data.