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Spectral indexation of pixels of MODIS sea surface images for detecting inconstancy of phytopigment composition in water

Karabashev Genrik S.

Oceanologia

2021

No. 63 (4)

482--496

This paper presents the first results of a new way of using MODIS (Moderate Resolution Imaging Spectroradiometer) sensor data to visualize phytopigment inconstancy in the near-surface layer of water basins. Other sensors of this class alike, the MODIS spectral resolution is too low to reproduce the minimums of reflectance Rrs caused by phytopigments in water. However, MODIS is remarkable for the presence of a channel at 469 nm combined with channels at 412, 443, 488, 531, 547, and 555 nm. This makes it possible to distinguish the spectral limits of preferential light absorption by chlorophyll a (412-469 nm) and by accessory pigments (469-555 nm). These capabilities were realized thanks to spectral pixel indexation (SPI) of MODIS images of the sea surface. The SPI boils down to the fact that a user determines the presence of pigment minima in spectra of every image pixel, finds the sum of the wavelengths of these minima as a WRM code and assigns it to the image pixel as one of its attributes. WRM code = 100 is assigned to pixels free of the minima. Such indexation makes it possible to examine the inconstancy of phytopigments on the background of aquatic environment variability. Application of SPI approach to MODIS images of the Gulf of Mexico and the Baltic Sea made it possible to reveal new patterns of phytopigment dynamics during HABs events.

Phytoplankton distribution and variation along a freshwater-marine transition zone (Kızılırmak River) in the Black Sea

Baytut Ö., Gönülol A.

Oceanological and Hydrobiological Studies

2016

Vol. 45, No. 4

453--465

Both phytoplankton of the Kizilirmak River/Black Sea transition zone and their interactions with nutrients were investigated between July 2007 and December 2008. A total of 447 taxa belonging to the divisions: Cyanobacteria (24), Bacillariophyta (209), Bigyra (1), Cercozoa (1), Charophyta (11), Chlorophyta (32), Cryptophyta (11), Miozoa (119), Euglenozoa (14), Haptophyta (13), Ochrophyta (10) and Protozoa Incertae Sedis (2) were identified at 5 different sites in the study area. Seventy four taxa were recognized as new records for the Algal Flora of Turkey and 41 taxa were determined as HAB (Harmful Algal Bloom) organisms. According to the hierarchical clustering and MDS analyses, surface phytoplankton were distributed along the salinity gradient from freshwater to saline waters, and the early spring samples were separated from the other samples. However, in addition to the agglomerative hierarchical cluster analysis, the samples were divided into four groups – “Fresh”, “Brackish”, “Marine” and “Early spring-Marine” – as a result of MDS analysis. The results of this study revealed that the surface phytoplankton were influenced by the salinity and the Secchi Disc depth together with the seasonal water temperature dynamics and NO3-N concentrations throughout the research period.