Marine picophytoplankton, in particular cyanobacteria and prochlorophytes are ubiquitously distributed in the worlds oceans and are often especially in the more oligotrophic regions among the most important primary producers. The present work shows the results of in-situ measurements taken on meridional transects across the Atlantic Ocean. Data for phytoplankton pigment composition and particulate absorption give information about the functional groups found in the study area. Flow cytometry and an analysis of phycobilins were employed to encompass genera of prochlorophytes and cyanobacteria. These in situ measurements are used as ground-truth for the validation of hyper-spectral remote sensing data. High spectrally resolved satellite data from SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric Chartography) on ENVISAT and GOME-2 (Global Ozone Measurement Experiment 2) on Meteosat are analysed with Differential Optical Absorption Spectroscopy (DOAS) and combined with the in situ data to improve determinations of phytoplankton functional groups distribution. http://www.sgmeet.com/aslo/nice2009/viewabstract2.asp?AbstractID=5210