Assessment of remotely sensed chlorophyll- a concentration in Guanabara Bay, Brazil

Massive Blooms of Chattonella subsalsa Biecheler (Raphidophyceae) in a Hypereutrophic, Tropical Estuary—Guanabara Bay, Brazil

“…A recent and exhaustive review on the occurrence of HABs along the Brazilian coast from 2006 to 2016 (Castro et al, 2016) did not report blooms in Guanabara Bay, despite the extremely high chlorophyll biomass normally found in its waters (Mayr et al, 1989;Kjerfve et al, 1997;Oliveira et al, 2016). Our monitoring focusing on a single HAB species unveiled several blooms over a relatively short period of time.…”

“…Guanabara Bay's poor water quality and high pollution levels, especially due to high loads of untreated urban waste from its drainage basin is well-known and acknowledged as one of the main environmental issues in the highly populated metropolitan area of Rio de Janeiro city (Paranhos et al, 1998;Fistarol et al, 2015). High chlorophyll levels normally found in the bay are evidence of its high primary productivity and the occurrence of algal blooms (Fistarol et al, 2015;Oliveira et al, 2016). During our survey of series B (five stations), chlorophyll concentrations in excess of 100 µgL −1 were registered several times.…”

Selecting the Best Band Ratio to Estimate Chlorophyll-a Concentration in a Tropical Freshwater Lake Using Sentinel 2A Images from a Case Study of Lake Ba Be (Northern Vietnam)

“…Among the many band-reflectance ratio algorithms that have been proposed for Chla estimation in lake waters, algorithms based on spectral band ratios are the more preferred because they help reduce the irradiance, atmospheric and air-water surface effects on reflectance [14,34]. Three commonly-used algorithms are based on the ratios of: (1) reflectances within the first peak of strong absorption at the blue region between 440 and 510 nm, to reflectances at the minimum absorption at the green region between 550 and 555 nm [35,36]; (2) reflectances at the minimum absorption at the NIR region between 685 and 710 nm, to reflectances at the second peak of absorption at the red region between 670 and 675 nm [16,18]; and (3) reflectances at the minimum absorption at the green region between 550 and 555 nm, to reflectances at the second peak absorption at the red region between 670 and 675 nm [33,37]. In addition to two-band ratio algorithms, three-band ratio algorithms also have been widely used to estimate Chla in turbid productive waters using two reflectances in the NIR region (720 and 750 nm) and one at near-670 nm [38], particularly when based on MERIS data using the ratio of the two NIR bands at 708 nm and 748 nm [17].…”

“…A small reflectance peak appeared weakly near 690 nm (within 685 to 695 nm, that corresponded to a natural fluorescence signal) indicating the low Chla contained in the lake water [41]. 550 and 555 nm, to reflectances at the second peak absorption at the red region between 670 and 675 nm [33,37]. In addition to two-band ratio algorithms, three-band ratio algorithms also have been widely used to estimate Chla in turbid productive waters using two reflectances in the NIR region (720 and 750 nm) and one at near-670 nm [38], particularly when based on MERIS data using the ratio of the two NIR bands at 708 nm and 748 nm [17].…”

“…As previously mentioned, a wide range of band ratios has been developed for retrieving Chla [16][17][18][34][35][36][37][38]. The successful selection of these ratios depends largely on the biogeochemical characteristics of the water body, clearly shown by the water reflectance spectrum.…”