Technical note: Algal Pigment Index 2 in the Atlantic off the southwest Iberian Peninsula: standard and regional algorithms
- 1Centre for Marine and Environmental Research, FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
- 2Sagremarisco Lda., Apartado 21, 8650-999 Vila do Bispo, Portugal
- 3FCT, University of Algarve, Campus de Gambelas, 8005-139 Faro, Portugal
- 4Bio-Optika, Crofters, Gunnislake, PL18 NQ, UK
- 5Norwegian Institute for Air Research-IMPEC, Box 100, 2027 Kjeller, Norway
Abstract. In this study, Algal Pigment Index 2 (API2) is investigated in Sagres, an area located in the Atlantic off the southwestern Iberian Peninsula. Standard results provided by the MEdium Resolution Image Spectrometer (MERIS) ocean colour sensor were compared with alternative data products, determined through a regional inversion scheme, using both MERIS and in situ remote sensing reflectances (Rrs) as input data. The reference quantity for performance assessment is in situ total chlorophyll a (TChl a) concentration estimated through a phytoplankton absorption coefficient (i.e. equivalent to API2). Additional comparison of data products has also been addressed for TChl a concentration determined by high-performance liquid chromatography. The MERIS matchup analysis revealed a systematic underestimation of TChl a, which was confirmed with an independent comparison of product map analysis. The study demonstrates the importance of regional algorithms for the study area that could complement upcoming standard results of the current Sentinel-3/OLCI space mission.