Krista Alikas will defend her doctoral thesis titled “From research to applications–monitoring optically-complex waters with MERIS/ENVISAT data”
on 15. June 2016 at 10.15 at W. Ostwaldi 1, room B103.
Anu Reinart, Tartu Observatory
Marko Vana, Institute of Physics, University of Tartu
Sampsa Koponen, Finnish Environment Institute, Finland
Lakes and seas provide a wide range of essential ecosystem services. European Union has created various directives and regional conventions to ensure the monitoring and assessment of the ecological status of these ecosystems. Since water quality can have rapid changes in temporal and spatial scale, remote sensing can provide a cost-effective approach to assess the current and derive historic water quality information and also for waterbodies that have not been part of conventional monitoring programmes. This thesis presents research about applications for MERIS/ENVISAT data in order to monitor optically-complex aquatic environment such as inland and coastal waters on the basis of bio-optical data from five North European lakes and two coastal sites.
The validation of MERIS standard water quality products indicated their unsuitability for waters with high amounts of chlorophyll a and humic substances. To map the phytoplankton parameters (CHL, cyanobacterial biomass, phytoplankton biomass) a spectral index which operates on red and near-infrared bands was used and calibrated to local conditions. As the index is applicable on L1b images, the water quality parameters can be derived quantitatively in case of highly scattering cyanobacterial blooms, which is not possible with standard algorithms. To estimate underwater light field via transparency, an empirical combined band ratio algorithm was developed which switches from 490/709 to 560/709 in case of less transparent waters and determines the diffuse attenuation coefficient Kd(490) with high accuracy. Additionally Secchi depth can be estimated reliably via satellite derived inputs of diffuse and total beam attenuation coefficients and reflectance over visible wavelengths.
The developed algorithms were applied on the MERIS archive from 2002 to 2011 to estimate the ecological status in lakes as required by the EU water framework directive which showed that remote sensing products could be used as an additional source of information for assessment and reporting purposes. The research done in this thesis was based on the MERIS/ENVISAT data, but the developed methods can be applied on S3a/OLCI data which will be accompanied probably in 2017 with Sentinel-3B to provide EO data over optically complex waters at least until 2029.