1 / 24

Lab 3 Particulate Absorption

Lab 3 Particulate Absorption. Collin Roesler 5 July 2007. Particulate absorption. Spectrophotometer Quantitative Filter Technique Corrections Kishino method Ac9 Calibration dependent method Calibration independent method. Absorption: Filtration method.

gianna
Télécharger la présentation

Lab 3 Particulate Absorption

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Lab 3 Particulate Absorption Collin Roesler 5 July 2007

  2. Particulate absorption • Spectrophotometer • Quantitative Filter Technique • Corrections • Kishino method • Ac9 • Calibration dependent method • Calibration independent method

  3. Absorption: Filtration method • Separates particles from dissolved • Concentrates particles from dilute medium

  4. Measure in Spectrophotometer • Reference • Match optical density of filter pad • No variability • Baseline • Blank filter pad in sample compartment (what is ODblankfilter:ODsample?)

  5. A h Compute absorption a (m-1) = 2.303 OD . L (m) What is L? Vfiltered = Aeff h L = h = V (m3) A (m2)

  6. What about the scattering by the filter?Path length amplification a (m-1) = 2.303 OD . V(m3) A(m2) • Filter pad • Creates nearly isotropic light field • Increases optical path length • Increases absorption signal • How to correct for it?

  7. b correction: path length amplification • Approach • Thick cultures • Measure absorption in cuvette • Measure absorption on filter pad • Determine ratio, b = ODfilt = optical . ODcuv geometric

  8. = ODf ODc OD filter pad cuvette Filter pad Issue: scattering in cuvette? Determining b Kiefer and SooHoo ’82, Mitchell and Kiefer ’85, ‘88 • For low loadings • Very variable • For high loadings • Approaches 2

  9. What about the scattering by the filter?Path length amplification, empirical approach a (m-1) = 2.303 ODf corrected V(m3) A(m2) • Filter pad creates multiple scattering environment • The relationship between ODf and ODc is non linear of the form: • ODf corrected = C1 * ODf + C2 * ODf2 C1 = 0.29 to 0.48 C2 = 0.05 to 0.75 Mitchell 1990, Cleveland and Weidemann 1993; Moore et al. 1995; Arbones et al. 1996 among others

  10. What about the scattering by the filter?Path length amplification, theoretical approach a (m-1) = 2.303 OD . V(m3) A(m2) • The geometric path length is t the thickness of the pad • The optical path length is r , • t /r = cos q where cos q is the average cosine of the light field • If the filter pad creates an isotropic light field, cos q = 0.5 • The optical path length is 2 * geometric path length a (m-1) = 2.303 ODfilt . 2V(m3) A(m2) Roesler 1998

  11. Partitioning of particulate absorption • First scan is total particles, ap • Extract with methanol and scan again, anap • aphyt = ap – anap • Other issues • Phytoplankton “parts” • Detrital pigments • Phycobilipigments • Inorganics

  12. Kishino et al. 1985

  13. Summary Filter pad technique • Filter sample, want high loading to overcome the variability in the blank filter pad absorption itself, but not muddy • Reference? • Extraction to separate particulates, nap • Computation • Offset correction, Stramski and Babin 2002 • Beta correction, try all models • Absorption calculation, ap and anap • Phytoplankton calculation, aphyt = ap - anap

  14. Unfiltered water samples Pure water calibration T/S correction Scattering correction Particulate absorption method apart = atotal – afilt Calibration independent method ac9 approach

  15. But spectra are problematic water calibration applied 1. Pure water calibration Absorption from AC9

  16. 2. Temperature and salinity correction Absorption from AC9 c am • 500 600 700 • Wavelength

  17. Subtract am(715 nm) • “b not a function of l” • spectrophotometric approach Absorption from AC9 am • 500 600 700 • Wavelength 3. Scattering correction Stramski and Babin 2002

  18. b’(l) = c(l) – am(l) Absorption from AC9 c am • 500 600 700 • Wavelength 3. Scattering correction b. Subtract fraction of b(l) am(715) * b’(l) . b’(715) a(l) =am(l)-

  19. Pure water calibration Temperature/Salinity correction Scattering correction Calculate scattering spectrum Absorption from AC9 c b a • 500 600 700 • Wavelength

  20. Particulate Absorption AC9 method • Measure sample absorption, at • Apply water cal, T/S, scattering corrections • Measure sample filtrate absorpion, af • Apply water cal, T/S, (scattering corrections?) • Compute particulate absorption, ap = at – af • Configurations • Single profiling instrument, multiple casts • Automated filtering on single instrument • Dual profiling instruments, sensor intercalibration

  21. Particulate Absorption AC9 methodCalibration Independent • Measure sample absorption, at • T/S, scattering corrections • Measure sample filtrate absorpion, af • T/S, (scattering corrections?) • Compute particulate absorption, ap = at – af • Configurations • Single profiling instrument, multiple casts • Automated filtering on single instrument

  22. Automated shipboard flow-through method, calibration-independent atotal a<0.2mm Slade et al., 2006

  23. Automated shipboard flow-through method 0.04 0.03 0.02 ap(440) (m-1) 0.015 0.010 0.005 0.000 Slade et al., 2006

  24. ac9 Summary • Pure water calibrations • Whole sample measurement • Filtered sample measurement • Data analysis • Apply water cals • Apply Temperature/Salinity corrections • Compute ap = at – afilt, cp = ct - cfilt • Apply scattering correction to ap

More Related