Optical Teledetection of Chlorophyll a in Turbid Inland Waters

Abstract

Determination of subsurface spectral irradiance reflectance by use of a hand-held spectroradiometer and then estimation of chlorophyll a (Chl-a) concentration facilitate assessment of ecological change in turbid lakes, rivers, and estuaries. The method was applied under widely varying solar elevation and weather. Noise due to reflected sky light was evaluated by theory on surface waves and by field data. A strong relationship was established for the shallow and eutrophic freshwater IJssel Lagoon including the River IJssel (The Netherlands) between corrected Chl-a concentrations (3-185 mg m -3 ) and the reflectance ratio for 704 and 672 nm with backscattering derived from the reflectance at 776 nm (R 2 > 0.95; N ) 114; standard error of estimate <9 mg m -3 ). This relationship adequately predicted Chl-a concentrations in well-mixed and optically deep water in lakes in The Netherlands, the Scheldt Estuary in Belgium and The Netherlands, and Lake Tai in China (N ) 40; standard error of estimate <9 mg m -3 ). Floating layers of the cyanobacterium Microcystis in Lake Chao in China were distinguished from homogeneously distributed phytoplankton by reflectance in the violet, blue, and nearinfrared wavebands.

Shellfish Aquaculture from Space: Potential of Sentinel2 to Monitor Tide-Driven Changes in Turbidity, Chlorophyll Concentration and Oyster Physiological Response at the Scale of an Oyster Farm

“…For our study site, an intercomparison exercise based on in situ measurements demonstrates that the chlorophyll-retrieval algorithm of Gons et al (2005) provided the most satisfactory results (see Supplementary Information for more details). This algorithm was originally developed for the Medium Resolution Imaging Spectrometer (MERIS) using the bands at 665, 705, and 775 nm (Gons, 1999;Gons et al, 2002Gons et al, , 2005. It was applied here to Sentinel2/MSI using bands B4 (665 nm), B5 (705 nm), and B7 (783 nm).…”

“…The parameters a * phy (665) and p were initially estimated using a large dataset of field measurements from diverse inland, estuarine and coastal waters (Gons, 1999;Gons et al, 2002Gons et al, , 2005. For our study site in Bourgneuf Bay, a * phy (665) was recalibrated to 0.133 m 2 (mg chl a) −1 (standard error is 0.002 m 2 (mg chl a) −1 ) and p to 1.02.…”

“…In the initial algorithm of Gons et al (2005), the chlorophyll-retrieval parameters were originally set to p = 1.05 and a * phy (665) = 0.014 m 2 (mg Chl a) −1 using observations performed in a variety of inland, estuarine and coastal waters over a range of chl a concentration from 1 to 181 mg m −3 (Gons, 1999;Gons et al, 2002). For the present study p was recalibrated to 1.02.…”

Developments in Earth observation for the assessment and monitoring of inland, transitional, coastal and shelf-sea waters

“…Many inland and near-shore waters are sporadically dominated by material of biological origin and during such phases these environments typically exhibit phytoplankton absorption spectra similar to the phytoplankton-dominated reservoir shown in Figure 1. In this situation, the Chl-a absorption features near 430 nm and 675 nm and a phycocyanin absorption feature at 620 nm are clearly apparent (Gons et al, 1999;Babin et al, 2003;Hunter et al, 2008;Mishra & Mishra 2014). …”

Estimation of chlorophyll-a concentration in turbid productive waters using airborne hyperspectral data

“…Algorithms that use reflectances in the red and near infrared (NIR) regions are preferable for turbid productive waters because the absorption by suspended solids and CDOM are very low in these regions (Gitelson and Kondratyev, 1991;Gitelson, 1992;Dekker, 1993;Han and Rundquist, 1997;Gons, 1999;Gower et al, 1999;Ruddick et al, 2001;. NIR-red algorithms take advantage of a local minimum in reflectance around 670 nm due to absorption by chl-a and a local maximum of reflectance around 700 nm, which is due to the combination of diminishing absorption by chl-a and increasing absorption by water (Vasilkov and Kopelevich, 1982;Gitelson, 1992;Han et al, 1994).…”