a
 Absorption coefficient,
${\mathrm{m}}^{1}$

${b}_{\mathrm{b}}$
 Backscattering coefficient,
${\mathrm{m}}^{1}$

${b}_{\mathrm{bd}}$
 Diffuse backscattering coefficient,
${\mathrm{m}}^{1}$

C
 Pigment concentration,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008C{\u3009}_{\mathrm{e}}$
 Mean pigment concentration within the euphotic layer,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008C{\u3009}_{\mathrm{p}}$
 Mean pigment concentration within the penetration layer,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008C{\u3009}_{\text{rs}}$
 Weighted mean pigment concentration within the whole water column, detectable by remote sensors,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

Chl  Chlorophyll a concentration,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{0\u20131\text{\hspace{0.17em}}\mathrm{m}}$
 Mean Chl concentration within the first
$1\text{\hspace{0.17em}}\mathrm{m}$
depth,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\mathrm{b}}$
 Mean Chl concentration within the whole water column,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\mathrm{max}}$
 Chlorophyll a concentration at the deep chlorophyll maximum,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\mathrm{e}}$
 Mean Chl concentration within the euphotic layer,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\mathrm{p}}$
 Mean Chl concentration within the penetration layer,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\text{pr}}$
 Mean Chl concentration within the productive layer,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

$\u3008\text{Chl}{\u3009}_{\text{rs}}$
 Weighted mean Chl concentration within the whole water column, detectable by remote sensors,
$\mathrm{mg}\text{\hspace{0.17em}}{\mathrm{m}}^{3}$

CV  Coefficient of variation (
$\mathrm{CV}=\mathrm{SD}/\text{Mean}$
), % 
DCM  Deep chlorophyll maximum 
$\mathrm{d}{E}_{\mathrm{u}}(Z,0)$
 Optical contribution to the upwelling irradiance at the surface that originates from a layer of thickness
$dz$
at depth z. 
${E}_{\mathrm{d}}$
 Downwelling irradiance,
$\mathrm{W}\text{\hspace{0.17em}}{\mathrm{m}}^{2}$

${E}_{\mathrm{u}}$
 Upwelling irradiance,
$\mathrm{W}\text{\hspace{0.17em}}{\mathrm{m}}^{2}$

${K}_{\mathrm{d}}(z)$
 Attenuation coefficient for downwelling irradiance at the depth z,
${\mathrm{m}}^{1}$

${\overline{K}}_{\mathrm{d}}(0\to z)$
 Average attenuation coefficient for downwelling irradiance
${E}_{d}$
within the depth interval from
$0$
to z

${K}_{\mathrm{u}}(z)$
 Attenuation coefficient for upwelling irradiance
${E}_{u}$
at the depth z,
${\mathrm{m}}^{1}$

MAPE  Mean absolute percentage error, % 
n
 Sample size 
NRMSE  Normalized (to the mean value) rootmeansquare error, % 
p
 Significance level 
PAR  Photosynthetically Available Radiation (
$400\u2013700\text{\hspace{0.17em}}\mathrm{nm}$
),
$\mathrm{W}\text{\hspace{0.17em}}{\mathrm{m}}^{2}$

${R}^{2}$
 Determination coefficient 
s
 Shape factor 
SD  Standard deviation 
z
 Current depth, m 
${Z}_{\mathrm{b}}$
 Bottom depth, m 
${\mathrm{Z}}_{\mathrm{e}}=(\mathrm{ln}100)/{\overline{K}}_{\mathrm{d}}(\mathrm{PAR},0\to {Z}_{\mathrm{e}})$
 Euphotic depth, m 
${\mathrm{Z}}_{\mathrm{m}}=(\mathrm{ln}10)/{\overline{K}}_{\mathrm{d}}(\mathrm{PAR},0\to {Z}_{\mathrm{m}})$
 Middle of the euphotic zone, m 
${Z}_{\mathrm{max}}$
 Depth of maximum Chl, m 
${\mathrm{Z}}_{\mathrm{p}}=1/{\overline{K}}_{\mathrm{d}}(\mathrm{PAR},0\to {Z}_{\mathrm{p}})$
 Penetration depth, m 
${\mathrm{Z}}_{\text{pr}}=(\mathrm{ln}1000)/{\overline{K}}_{\mathrm{d}}(\mathrm{PAR},0\to {Z}_{\text{pr}})$
 Productive depth, m 
$\kappa (z)$
 Attenuation coefficient for upwelling irradiance
$\mathrm{d}{E}_{\mathrm{u}}(z)$
at the depth z,
${\mathrm{m}}^{1}$

$\overline{\kappa}(z\to 0)$
 Average attenuation coefficient for upwelling irradiance
$\mathrm{d}{E}_{\mathrm{u}}(z)$
within the depth interval from z to
$0$
,
${\mathrm{m}}^{1}$

λ
 Wavelength, nm 
${\overline{\mu}}_{\mathrm{d}}$
 Mean cosine for the downwelling irradiance 
${\overline{\mu}}_{\mathrm{u}}$
 Mean cosine for the upwelling irradiance 
${\tau}_{k}(z)=z{\overline{K}}_{\mathrm{d}}(\mathrm{PAR},0\to z)$
 Optical thickness for the downwelling attenuation coefficient 