The effects of cyanobacterial blooms on MODIS-L2 data products in the southern Caspian Sea

Abstract

MODIS satellite imageries with minimal cloud cover (<25%) were used to extract cyanobacteria index, floating algea index, fluorescence line height, chlorophyll-a and sea surface temperature products, for seven days concurrent with blooms. The results showed a positive correlation between cyanobacteria index and chlorophyll-a (R = 0.74, p ≤ 0.05 and R = 0.75, p ≤ 0.05 for 2005 and 2010 respectively), and a negative correlation between the cyanobacteria index and fluorescence line height (R = −0.74, p ≤ 0.05 and R = −0.93, p ≤ 0.005 for 2005 and 2010 respectively). Further analysis showed that considering Fluorescence Line Height is not sufficient to detect the cyanobacterial blooms in the offshore area. However, the results indicated a weak correlation between cyanobacteria index and floating algae index (R = −0.42, p = 0.34 and R = −0.47, p = 0.29 for 2005 and 2010 respectively). The results also indicated that the irregular increases in the cyanobacteria index and chlorophyll-a in the study region was an operational index for the incidence of cyanobacterial bloom, where the surface wind speed and temperature conditions were <4 m s−1 and ≥30°C, respectively. Finally, a linear model was defined for monitoring, which determines occurrence or non-occurrence of cyanobacteria bloom based on daily monitoring of the changes of products. In order to evaluate the proposed model, its efficiency was tested on datasets at different times and locations, and the results were consistent with field reports, as expected.