Martin Ligi defended his doctoral thesis "Application of close range remote sensing for monitoring aquatic environment"

Tiia Lillemaa | 28.03.2017

Martin Ligi defended his doctoral thesis titled "Application of close range remote sensing for monitoring aquatic environment" on 28 March 2017.

Martin Ligi kaitsmine 2017.jpg

Lead Research Fellow Tiit Kutser, PhD (Estonian Marine Institute);
Tartu Observatory Director Anu Reinart, PhD

Lead Research Fellow Vittorio Ernesto Brando, PhD (Institute of Atmospheric Sciences and Climate (CNR-ISAC), Italy)

Knowing the quality of different waterbodies has been essential for human kind for thousands of years. There are two main European Union’s documents guiding the status assessment of water bodies: Water Framework Directive and Marine Strategy Framework Directive. Both of these documents state that all waterbodies in the European Union have to achieve “good” status by the year 2020. In order to fulfil this requirement, water bodies have to be monitored in regular bases. It is impossible to collect laboratory samples from every waterbody as it would be too expensive and would require many workers and still wouldn’t provide information about the spatial distribution of water quality parameters within each waterbody. Optical instruments can provide data fast and over larger areas and therefore have to be included in the monitoring programs. In addition to devices used at the in situ measurements are several satellite products that are available through Copernicus program for the coming decades. These products must, however, be constantly validated with in situ measurements. Additionally, new calculation methods have to be developed to improve the results precision. During this thesis, the variability of optical properties (like absorption and scattering) was assessed in the Baltic Sea. It was studied how much this variability influences the reflectance signal that reaches water remote sensing instruments. The performance of different set-ups and protocols of field spectrometers to collect reflectance data was assessed. The possibility to use near-infrared part of the spectrum in water remote sensing was investigated. In extreme absorbing lakes this is the only part of radiation providing us information about the water properties, but it proved to be useful also in other waterbodies. The performance of many remote sensing algorithms in retrieving water quality parameters in the Baltic Sea was tested. The possible applications for hand-held spectrometers were investigated.