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IOCS• Rüdiger Röttgers • 21.05.2013 1
Light absorption in turbid waters
Rüdiger Röttgers, Kerstin Heymann,
Hajo Krasemann
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 2
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 3
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 4
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 5
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 6
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 7
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean 0.5 mg (n=150)
IOCS• Rüdiger Röttgers • 21.05.2013 8
-0.5 mg
0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30 35 40
rel.
err
or
[%]
mass on filter [mg]
Determination of suspended matter concentration
problematic issues:
- offset problems especially with glass fiber filters by salt retention in the rim of the filter (Banse et al. 1963;
Stavn et al. 2009) and loss of filter material
- methodology in sea water:
1) rinsing of the rim after filtration
2) collection of high sample masses to reduce the rel. effect of the offset
3) Stavn et al. 2009: prepare process filters with particle-free sample water to determine the offset
- problem: process filter offset highly variable: -0.1 – 1 mg, mean: 0.5 mg (n=150)
- real sample filter offset varies even more: -4 – +7 mg, mean: 1 mg (n=380), inducing error of >100 %
to reach error of <15%, >20 mg have to be collected
IOCS• Rüdiger Röttgers • 21.05.2013 9
Light absorption in turbid waters
- what are the dominating absorbing water constituents in turbid waters?
- how large is the absorption in the NIR/SWIR region?
- what absorbs light in the NIR/SWIR region?
IOCS• Rüdiger Röttgers • 21.05.2013 10
mass-specific particulate absorption, ap
IOCS• Rüdiger Röttgers • 21.05.2013 13
y = 0,0109x - 0,023 R² = 0,980
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
0 20 40 60 80 100 120 140 160 180
a8
50
nm [1
/m]
TSM [mg/L]
River Elbe
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 14
Absorption of dried matter
To reduce influence by water absorption filter pad samples were dried at ca. 60 °C.
German Bight, dried samples
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 15
Absorption of dried non-algal matter
German Bight, dried samples
from Graham R. Hunt, 1977
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 17
NIR/SWIR Absorption of Minerals
from Graham R. Hunt, 1977
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 18
NIR/SWIR Absorption of Minerals
from Graham R. Hunt, 1977
reflectance studies
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 19
NIR/SWIR Absorption of Minerals vs. Particle Size
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 20
NIR/SWIR Absorption of Minerals vs. Particle Size
Barcelona October 2012 • Rüdiger Röttgers • 21.05.2013 21
Summary / Conclusions
•absorption in turbid water is dominated by non-algal matter
•NIR/SWIR absorption is substantial in natural samples, a800nm >1 - 25 % of the a442nm and can be
measured exactly
• absorption in NIR/SWIR is dominated by minerals, mainly from water structures in the mineral
• absorption by organic detritus has still to be determined, as separation of inorganic and organic
part remains difficult
• NIR/SWIR absorption might be used for identification of mineral types in suspended matter
• dependencies of absorption on particle size can be determined → imaginary part of the complex
refractive index