Abteilung Oberflächengewässer

Hyperspektrale Untersuchung der Schichtung in aquatischen Systemen


Ozeane und Binnengewässer haben eine tragende Rolle in globalen biogeochemischen Kreisläufen. Mehrere polar umlaufende Erdbeobachtungssatelliten überwachen deshalb die Wasserqualität, indem sie reflektiertes Sonnenlicht messen.
Heutige Methoden vernachlässigen allerdings vertikale Unterschiede in der Wasserqualität. Dadurch entstehen erhebliche Fehler, sobald Licht bis unter die durchmischte Oberflächenschicht eindringt (Nouchi et al., 2018).

Als Teil des Science and Applications Teams für die PACE Satellitenmission der NASA versuchen wir diese Einschränkung zu beheben. Neben verbesserten hyperspektralen Messungen, wie sie in Zukunft auch von PACE aufgezeichnet werden, verwenden wir eine automatische, bio-optische Sonde und hydrodynamische Modelle. Die Thetis Sonde ist neben der LéXPLORE Forschungsplattform im Genfersee verankert. Sie erhebt mehrmals täglich detaillierte Messungen von Absorption und Streuung. Das operationelle Modell auf der Website Meteolakes wurde von der EPFL und der Eawag entwickelt. Es ermöglicht die Voraussage der Tiefe der durchmischten Oberflächenschicht.
Diese beiden einzigartigen Informationsquellen für den Genfersee eröffnen neue Möglichkeiten bei der Interpretation von hyperspektralen Daten. Eine solche Integration von Modellen und Umweltbeobachtungen verbessert letztlich unser Verständnis von aquatischen Prozessen in Raum und Zeit.

Publikation

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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)
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      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

Kontakte

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

Zusammenarbeit

Finanzierung

Eawag