Local algorithms using SeaWiFS data for the retrieval of phytoplankton, pigments, suspended sediment, and yellow substance in coastal waters

S. Tassan

doi:10.1364/AO.33.002369

Applied Optics
Vol. 33,
Issue 12,
pp. 2369-2378
(1994)
•https://doi.org/10.1364/AO.33.002369

Local algorithms using SeaWiFS data for the retrieval of phytoplankton, pigments, suspended sediment, and yellow substance in coastal waters

S. Tassan

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S. Tassan, "Local algorithms using SeaWiFS data for the retrieval of phytoplankton, pigments, suspended sediment, and yellow substance in coastal waters," Appl. Opt. 33, 2369-2378 (1994)

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Abstract

Algorithms that use the SeaWiFS radiometer band reflectance data for the retrieval of phytoplankton pigment concentration, suspended sediment concentration, and yellow substance absorption in coastal water are set up by a computation based on a three-component model of sea color. The varying coastal environment is characterized by a site-specific correlation among the three parameters, subjected to large spatial and temporal fluctuations. The computation is performed with respect to the summer situation of the Gulf of Naples (Mediterranean Sea). The sensitivity of the retrieval of each parameter to variations in the concentration of the two other quantities is investigated by numerical simulations. The sensitivity to the variability of the absorption and scattering properties of phytoplankton and suspended sediment is analyzed, as well as the error induced by the uncertainty of the remote-sensing data. The algorithms’s performance is satisfactorily tested on sets of SeaWiFS band reflectances randomly generated within wide water composition ranges. Although the results obtained cannot be generalized and require experimental validation, the series of tests performed suggests that the proposed algorithms, with numerical constants adjusted to the local conditions, can be effectively applied to several types of coastal environment.

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Spectral Region	SeaWiFS			Band Center (nm)	CZCS
Spectral Region	Band	NER ^a	Width (nm)	Band Center (nm)	Width (nm)	NER ^a	Band
Violet	1	0.0182	20	412	—	—	—
Blue	2	0.0125	20	443	20	0.0445	1
Green	3	0.0098	20	490	—	—	—
Green	4	0.0088	20	510	20	0.0310	2
Yellow	—	—	—	550	20	0.0248	3
Yellow	5	0.0077	20	555	—	—	—
Red	6	0.0056	20	670	20	0.0248	4
Far red	—	—	—	750	100	0.0114	5
Far red	7	0.0035	29	765	—	—	—
Near infrared	8	0.0023	40	865	—	—	—
Digitization		10 bits				8 bits

Synopsis of formulas
R(λ) = 0.33B _b (λ)/A(λ)
B _b (λ) = r _w B _w (λ) + r _c B _c (λ) + r _s B _s (λ)
$B_{w} (λ) = B_{w} (550) {(λ / 550)}^{n_{w}}$
B _c (λ) = 0.12C ^0.63 a _c (550)/a _c (λ)
$B_{s} (λ) = b_{s} (550) {(λ / 550)}^{n_{s}} S$
A(λ) = A _w (λ) + a _c (λ)C + a _s (λ)S + A _y (λ)
A _y (λ) = A _y (440)exp[−0.014(λ − 440)]
Notation
R	Subsurface reflectance, i.e., ratio of upwelling to downwelling irradiance just below the sea surface
B _b	Backscattering coefficient (m⁻¹)(Ref. 2)
A	Absorption coefficient (m⁻¹)
r	Backscattering ratio (Ref. 2)
B	Volume scattering coefficient (m⁻¹)
b	Specific volume scattering coefficient (m⁻¹ per unit concentration)
n	Exponent of wavelength dependence of scattering
a	Specific absorption coefficient (m⁻¹ per unit concentration)
λ	Wavelength (nm)
C	Chlorophyll a + phaeophytin a concentration (mg m⁻³)
S	Suspended sediment concentration (g m⁻³)
A _y	Yellow substance absorption (m⁻¹)
w, c, s, y	Water, chlorophyll, sediment, and yellow substance (subscripts)
Input data
Scattering
r _w = 0.5
r _c = 0.005
r _s = 0.015
B _w (550) = 0.0020 m⁻¹
b _s (550) = 1 m² g⁻¹
n _w = −4.3
n _s = −1
Absorption
A _w (440) = 0.015 m⁻¹
a _c (443) = 0.07 m² mg⁻¹ if C ≤ 1 mg m⁻³
a _c (443) = 0.018 m² mg⁻¹ if C > 1 mg m⁻³
a _s (443) = 0.034 m² g⁻¹
Absorption spectra (relative units):
	SeaWiFS Band
	1	2	3	4	5	6
Wavelength (nm)	412	443	490	510	555	670
A _w	1.13	1	1.33	3.20	5.05	28
a _c	0.88	1	0.75	0.53	0.27	0.53
a _s	1.35	1	0.75	0.65	0.55	0.35
A _υ	1.54	1	0.52	0.39	0.21	0.042

C(mg m⁻³) Range	Retrieved Parameter	Retrieval Error Limit (%)	R(λ _i ) Error Bound (%)
0.025–1.0	C	±40	6
	S	±15	7.5
	A _y (440)	±20	6.5
1–40	C	±50	5.5
	S	±15	8.1
1–10	A _y (440)	±40	4

Spectral Region	SeaWiFS			Band Center (nm)	CZCS
Spectral Region	Band	NER ^a	Width (nm)	Band Center (nm)	Width (nm)	NER ^a	Band
Violet	1	0.0182	20	412	—	—	—
Blue	2	0.0125	20	443	20	0.0445	1
Green	3	0.0098	20	490	—	—	—
Green	4	0.0088	20	510	20	0.0310	2
Yellow	—	—	—	550	20	0.0248	3
Yellow	5	0.0077	20	555	—	—	—
Red	6	0.0056	20	670	20	0.0248	4
Far red	—	—	—	750	100	0.0114	5
Far red	7	0.0035	29	765	—	—	—
Near infrared	8	0.0023	40	865	—	—	—
Digitization		10 bits				8 bits

Synopsis of formulas
R(λ) = 0.33B _b (λ)/A(λ)
B _b (λ) = r _w B _w (λ) + r _c B _c (λ) + r _s B _s (λ)
$B_{w} (λ) = B_{w} (550) {(λ / 550)}^{n_{w}}$
B _c (λ) = 0.12C ^0.63 a _c (550)/a _c (λ)
$B_{s} (λ) = b_{s} (550) {(λ / 550)}^{n_{s}} S$
A(λ) = A _w (λ) + a _c (λ)C + a _s (λ)S + A _y (λ)
A _y (λ) = A _y (440)exp[−0.014(λ − 440)]
Notation
R	Subsurface reflectance, i.e., ratio of upwelling to downwelling irradiance just below the sea surface
B _b	Backscattering coefficient (m⁻¹)(Ref. 2)
A	Absorption coefficient (m⁻¹)
r	Backscattering ratio (Ref. 2)
B	Volume scattering coefficient (m⁻¹)
b	Specific volume scattering coefficient (m⁻¹ per unit concentration)
n	Exponent of wavelength dependence of scattering
a	Specific absorption coefficient (m⁻¹ per unit concentration)
λ	Wavelength (nm)
C	Chlorophyll a + phaeophytin a concentration (mg m⁻³)
S	Suspended sediment concentration (g m⁻³)
A _y	Yellow substance absorption (m⁻¹)
w, c, s, y	Water, chlorophyll, sediment, and yellow substance (subscripts)
Input data
Scattering
r _w = 0.5
r _c = 0.005
r _s = 0.015
B _w (550) = 0.0020 m⁻¹
b _s (550) = 1 m² g⁻¹
n _w = −4.3
n _s = −1
Absorption
A _w (440) = 0.015 m⁻¹
a _c (443) = 0.07 m² mg⁻¹ if C ≤ 1 mg m⁻³
a _c (443) = 0.018 m² mg⁻¹ if C > 1 mg m⁻³
a _s (443) = 0.034 m² g⁻¹
Absorption spectra (relative units):
	SeaWiFS Band
	1	2	3	4	5	6
Wavelength (nm)	412	443	490	510	555	670
A _w	1.13	1	1.33	3.20	5.05	28
a _c	0.88	1	0.75	0.53	0.27	0.53
a _s	1.35	1	0.75	0.65	0.55	0.35
A _υ	1.54	1	0.52	0.39	0.21	0.042

Abstract

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Applied Optics