SIMBIOS IOP Workshop
Questions raised concerning a possible species specify absorption. Others asserted it is rather a size distribution (synechococcus below 1 micron may less than the wavelength of light)
- On filter issue: Errors may be spectrally dependent -or- different cells may act differently on different filters -or- both may occur.
- GF/C filters may have a smaller porosity than GF/F.
- G. Mitchell: "Increased detritus may lead to increased absorption at 750 (Italians reported)
- Report on TR method: measure transmission and reflectance, solve for correction of absorption from filter scattering (may not be needed in case I waters)
- Report on FTF (freeze transfer technique) of Bricaud et al., appears to agree well w/ integrated sphere data, difficult procedure
The index of refraction is seen to exhibit a larger value between fresh and saltwater at larger wavelengths, this leads to need to 'zero' scan data by the null wavelength
- Group suggests 850 nm as the null wavelength for CDOM scans (and a 350-850 scanning range) but not all instruments may go to 850
- Group suggest reporting the raw optical density (OD) scans along with needed processing info
- Glenn Cota suggested the use of a power law curve to pre-smooth low absorbing CDOM (as) scans, re-attachment at a UV wavelength (325nm), then null wavelength correction
- Heidi Sosik has performed extensive tests to examine the effects of long term storage of samples. Report status unknown.
Beta and bb:
- Balch addressed de-bubbling techniques
- Pope & Fry data available at
- Protocols to follow at Wetlabs: www.wetlabs.com, under news or instruments
- Use Pope & Fry pure water std.
- To submit, first apply the temp and sal correction to both 'a' and 'c' and provide raw and fully processed data
- Submitters should document scattering correction method used. Three primary types:
- subtract null wavelength (at 715nm)
- assume Epsilon(Cb(lambda) - aTS(lambda)) <-- useful if not good temp & sal correction available
- Epsilon = a(715)/c(715)-a(715)
must be: 0.08 < Epsilon < 0.5 should be: 0.1 < Epsilon < .3 - small errors in 'c' & 'a' strongly affect this value.
** If scan has 670 > 650, assume phytoplankton main component, if slowly decreasing w/ wavelength, assume sediment
- Definitions:ar - absorption raw cr - beam attenuation raw Submit: ar, cr, temp, sal
- Calibrate instrument on its frame due to torquing problem w/ AC-9 (new meters have better design and don't suffer from this problem)
- Use clean DI water under pressurized flow w/ a valve for back pressure when calibrating
- Filters on AC-9 for 'as' determination may need null wavelength correction applied
- Scott Pegau uses tygon tubing (saw no difference w/ teflon coated, except possibly in bluest waters)
- Outstanding IOP issues:
- aph & ad techniques vary by investigator
- length of storage of samples may or may not be a problem
San Diego Absorption Workshop
Information on the absorption workshop held at Scripps during December 9-13, 1996
- All San Diego absorption workshop instruments compared well except the HP spectrophotometer.
- Workshop resulted in some convergence in Beta and null wavelength, more work needed
- Dave Karl suggested GF/F absorbs CDOM (per G. Mitchell)
- "For SIMBIOS purposes, people should specify their measurement methods" -G. Mitchell