@article{fdi:010070009,
  title = {{V}ariability of apparent and inherent optical properties of sediment-laden waters in large river basins - lessons from in situ measurements and bio-optical modeling},
  author = {{P}inet, {S}. and {M}artinez, {J}ean-{M}ichel and {O}uillon, {S}ylvain and {L}artiges, {B}. and {V}illar, {R}. {E}.},
  editor = {},
  language = {{ENG}},
  abstract = {{W}e investigated the relationships between inherent and apparent optical properties ({IOP} and {AOP}, respectively) and suspended sediment concentrations ({SSC}) in the main {A}mazonian river waters. {I}n situ measurements of {SSC}, remote sensing reflectance ({R}-rs), the diffuse light attenuation coefficient ({K}-d) and the total and non-algal particle ({NAP}) absorption coefficients (a({TOT}) and a({NAP}), respectively) were conducted during three sampling trips along different streams of the {A}mazon {R}iver catchment (104 stations). {T}he size distribution and chemical characteristics of the suspended sediment were also determined for 85 stations. {W}e show that the particle size distribution ({PSD}) in the river water is best described by a segmented {J}unge power law distribution with a smaller slope value for the smallest particles ({J}(1) = 2.4) and a larger slope value ({J}(2) = 4.1) for the largest particles (> 10 mu m). {A} strong relationship was found between {AOP}s and {IOP}s and {SSC} when the entire data set was considered. {H}owever, for the {M}adeira {R}iver, the primary {A}mazon {R}iver tributary in terms of suspended sediment discharge, a significant dispersion was detected for the {R}-rs - {SSC} relationship but not for the d {K}-d - {SSC} relationship. {T}his dispersion has been shown by a previous study, using {MODIS} data, to display a seasonal pattern, which we investigated in this study using {M}ie modeling calibrated with suspended sediment characteristics. {I}n the {M}adeira {R}iver, suspended sediment had a finer distribution size and a different mineralogy (e.g., a greater smectite content and a lower kaolinite content) during the rising water stage. {S}pectral variations of the imaginary part n' (lambda) of the refraction index also showed significant differences during the rising water stage. {I}n contrast, other streams of the {A}mazon basin had very stable properties with respect to granulometry and mineralogy. {M}odel simulations made possible to reproduce both field and satellite observations, showing that the {R}-rs hysteresis observed in the {M}adeira {R}iver in the near infrared was mainly due to n' (lambda) seasonal variations, leading to a decrease of absorption during the rising water stage. {K}-d was shown to remain stable because of its strong dependency on scattering processes. {T}he model was used to further understand how suspended sediment size distribution and refraction index drive the {IOP}s in large rivers: n' (lambda) variations were shown to control primarily the reflectance variability; {R}-rs (850) presented limited variations as a function of {PSD} in the range typical of large rivers ({J}(1) < 3) although it remained sensitive to particle mineralogical composition; {R}-rs (670) showed the opposite behavior with a higher sensitivity to {PSD} variation for coarser {PSD}. {F}inally, we demonstrate that the use of the {R}-rs ratio between the red and infrared channels allowed a reduction of the {R}-rs sensitivity in all cases, by an average of 50% with respect to changes in the mineral composition or size distribution of suspended sediment. {I}n particular, the {R}-rs ratio varied by less than 5% for {PSD} representative of surface river waters.},
  keywords = {},
  booktitle = {},
  journal = {{O}ptics {E}xpress},
  volume = {25},
  numero = {8},
  pages = {{A}283--{A}310},
  ISSN = {1094-4087},
  year = {2017},
  DOI = {10.1364/oe.25.00a283},
  URL = {https://www.documentation.ird.fr/hor/fdi:010070009},
}