Remote sensing chlorophyll a of optically complex waters ( rias Baixas, NW Spain): Application of a regionally specific chlorophyll a algorithm for MERIS full resolution data during an upwelling cycle

• Published in: Remote sensing of environment Vol. 115; no. 10; pp. 2471 - 2485
• Main Authors: Spyrakos, Evangelos, González Vilas, Luis, Torres Palenzuela, Jesus M., Barton, Eric Desmond
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 17.10.2011; Elsevier
• Subjects: Algorithms; Animal, plant and microbial ecology; Applied geophysics; Biological and medical sciences; Biomass; Chlorophyll a; Chlorophylls; Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Galician rias; General aspects. Techniques; Internal geophysics; Marine; MERIS; Neural networks; Remote sensing; Teledetection and vegetation maps; Upwelling; Iberian Peninsula; Southern Europe; Europe; Spain; ANE, Spain, Galicia, Pontevedra, Ria de Vigo; MERIS; Upwelling; Galician rias; Algorithms; Chlorophyll a; experimental studies; Site; algorithms; data; Mussel breeding; neural networks; cycles; Image; coastal zone; upwelling; Coastal water; performances; maps; Algae; remote sensing; concentration; in situ; quality; Northwest; Geographical division; Advantage; Characteristics; techniques; Parameter; Harmful alga; Comparative study
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2011.05.008

This study takes advantage of a regionally specific algorithm and the characteristics of Medium Resolution Imaging Spectrometer (MERIS) in order to deliver more accurate, detailed chlorophyll a (chl a) maps of optically complex coastal waters during an upwelling cycle. MERIS full resolution chl a concentrations and in situ data were obtained on the Galician (NW Spain) shelf and in three adjacent rias (embayments), sites of extensive mussel culture that experience frequent harmful algal events. Regionally focused algorithms (Regional neural network for rias Baixas or NNRB) for the retrieval of chl a in the Galician rias optically complex waters were tested in comparison to sea-truth data. The one that showed the best performance was applied to a series of six MERIS (FR) images during a summer upwelling cycle to test its performance. The best performance parameters were given for the NN trained with high-quality data using the most abundant cluster found in the rias after the application of fuzzy c-mean clustering techniques (FCM). July 2008 was characterized by three periods of different meteorological and oceanographic states. The main changes in chl a concentration and distribution were clearly captured in the images. After a period of strong upwelling favorable winds a high biomass algal event was recorded in the study area. However, MERIS missed the high chlorophyll upwelled water that was detected below surface in the ria de Vigo by the chl a profiles, proving the necessity of in situ observations. Relatively high biomass “patches” were mapped in detail inside the rias. There was a significant variation in the timing and the extent of the maximum chl a areas. The maps confirmed that the complex spatial structure of the phytoplankton distribution in the rias Baixas is affected by the surface currents and winds on the adjacent continental shelf. This study showed that a regionally specific algorithm for an ocean color sensor with the characteristics of MERIS in combination with in situ data can be of great help in chl a monitoring, detection and study of high biomass algal events in an area affected by coastal upwelling such as the rias Baixas. ►We apply regionally and cluster specific chlorophyll a algorithms for MERIS data. ►We produce more accurate chlorophyll a maps of optically complex waters. ►We describe an upwelling cycle using in situ and satellite data. ►MERIS images capture the development and decay of a phytoplankton bloom.