Functional Types (SynSenPFT): Algorithm Theoretical Base Document (ATBD). Technical report, Alfred Wegener Institute (AWI), Helmholtz Centre for Polar and Marine Research; Institute of Environmental Physics [...] investigate the sensitivity of the improved PhytoDOAS (version3.0) algorithm. Technical report, Alfred Wegener Institute (AWI), 212 Helmholtz Centre for Polar and Marine Research; Institute of Environmental Physics [...] support when in need. I thank all colleagues at the Institute of Environmental Physics and the Alfred-Wegener- Institute for the inspiring working environment and helping me with scientific questions. I would