Department Surface Waters - Research and Management

Hyperspectral retrieval of stratification in aquatic systems


Oceans and inland waters play a major role in global biogeochemical cycles. Therefore several polar-orbiting earth observation satellites are monitoring water quality parameters by means of measuring reflected sunlight.
However, vertical variations in water quality are neglected by current retrieval methods. This causes significant errors where the euphotic depth exceeds the depth of the mixed surface layer (Nouchi et al., 2018).

As members of NASA’s Science and Applications Team for the PACE satellite mission, we investigate how to overcome this limitation. Besides hyperspectral data as available from PACE in the future, we use an automated bio-optical profiler and hydrodynamic models. The Thetis profiler is moored next to the LéXPLORE research platform and acquires detailed absorption and scattering measurements several times a day. The operational model on the Meteolakes web page was developed by EPFL and Eawag, and allows the prediction of mixed layer depths.
These unique information sources for Lake Geneva open new opportunities for hyperspectral signal interpretation. Ultimately, such an integration of models and observations will improve our understanding of aquatic processes in time and space.

 

Publication

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      authors => protected'Nouchi, V.; Odermatt, D.; Wüest, A.; Bouffard, D.' (70 chars)
      title => protected'Effects of non-uniform vertical constituent profiles on remote sensing refle
         ctance of oligo- to mesotrophic lakes' (113 chars)
      journal => protected'European Journal of Remote Sensing' (34 chars)
      year => protected2018 (integer)
      volume => protected51 (integer)
      issue => protected'1' (1 chars)
      startpage => protected'808' (3 chars)
      otherpage => protected'821' (3 chars)
      categories => protected'inland waters; radiative transfer models; in field data acquisition; water q
         uality; non-uniformities; spectral reflectance' (122 chars)
      description => protected'We investigate the impact on remote sensing reflectance by the vertical non-
         uniformities of water constituents. Reflectance simulated for 210 pairs of i
         n situ measured chlorophyll-a and turbidity profiles (z = 0–20 m) from Lak
         e Geneva are compared to simulations for uniform constituent gradients and n
         on-uniform profiles approximated by Gaussian curves, orthogonal layers and s
         teady gradients. Relevant concentration ranges are between 0 and 17 mg m<sup
         >−3</sup> for chlorophyll-a and 0 and 4.6 g m<sup>−3</sup> for total sus
         pended matter within the photic layer. Our results show that mesotrophic lak
         es are specifically sensitive to non-uniformities with 20% of the 210 sample
         s used in this study showing deviations of the spectral angle > 5° between 
         a uniform assumption and observations which mostly occur for deeper-laying w
         ater constituents. By stressing the different use of blue and red parts of t
         he spectrum, we argue further that algorithms are affected by variable verti
         cal structures of algal and inorganic particles. Finally, we demonstrate tha
         t approximation models of the vertical structure of water constituents are a
          good solution to better account for non-uniformities in the development of 
         invertible bio-optical models.' (1246 chars)
      serialnumber => protected'' (0 chars)
      doi => protected'10.1080/22797254.2018.1493360' (29 chars)
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Effects of non-uniform vertical constituent profiles on remote sensing reflectance of oligo- to mesotrophic lakes

We investigate the impact on remote sensing reflectance by the vertical non-uniformities of water constituents. Reflectance simulated for 210 pairs of in situ measured chlorophyll-a and turbidity profiles (z = 0–20 m) from Lake Geneva are compared to simulations for uniform constituent gradients and non-uniform profiles approximated by Gaussian curves, orthogonal layers and steady gradients. Relevant concentration ranges are between 0 and 17 mg m−3 for chlorophyll-a and 0 and 4.6 g m−3 for total suspended matter within the photic layer. Our results show that mesotrophic lakes are specifically sensitive to non-uniformities with 20% of the 210 samples used in this study showing deviations of the spectral angle > 5° between a uniform assumption and observations which mostly occur for deeper-laying water constituents. By stressing the different use of blue and red parts of the spectrum, we argue further that algorithms are affected by variable vertical structures of algal and inorganic particles. Finally, we demonstrate that approximation models of the vertical structure of water constituents are a good solution to better account for non-uniformities in the development of invertible bio-optical models.
Nouchi, V.; Odermatt, D.; Wüest, A.; Bouffard, D. (2018) Effects of non-uniform vertical constituent profiles on remote sensing reflectance of oligo- to mesotrophic lakes, European Journal of Remote Sensing, 51(1), 808-821, doi:10.1080/22797254.2018.1493360, Institutional Repository

Contacts

Dr. Daniel Odermatt Tel. +41 58 765 6823 Send Mail
Dr. Abolfazl Irani Rahaghi Scientific collaborator Tel. +41 58 765 6753 Send Mail

Collaboration

Funding

Eawag