I am searching for a robust method for measuring Remote Sensing Reflectance from relatively low volumes (< 50L) of sample, in this case, mixed algal cultures. Warner and Fan (2013) used a black can filled with sample and an above water radiometer outdoors. Wondering if I'm overlooking some other methodology, or maybe unpublished work that seems to work well. Thanks for any advice!
Ryan
Not possible, unless the boundary conditions could be sufficiently accounted for.
Hi Ryan,
I recently conducted a study to measure the reflectances/emissivities of dry and wet soils in a petridish (60 mm diameter by 20 mm height) for 1.4 µm to 16 µm wavelength range. Although I do not have experience with algal cultures, nevertheless I think you may draw some parallels from spectral measurements of low volume soils. Since you know that the In situ measurements you take with a radiometer may be usually limited to the top few millimeters of the sample, the challenge therefore is to keep the top surface of the sample representative of the bottom sample volume which is not exposed to the radiometer. I found with wet soil reflectance measurements that the top few micrometers of the soil samples dry out quickly when exposed to the air. Are you taking In situ measurements of the sample or are you conducting an experimental setup outdoor by disturbing the mixed algal cultures? How do the algal cultures look when they are completely dry and completely wet? I have attached the links to two papers related to spectral measurements of soil that might give you some ideas.
http://www.sciencedirect.com/science/article/pii/S0034425710000611
http://onlinelibrary.wiley.com/doi/10.1029/2007JF000749/abstract
While in a general situation I agree with the above comment by Jianwei Wei, if the concentration of algae is high enough so that no photons get to the boundary (or, better yet, to a boundary and back to the sensor), then it may be possible to measure the Rrs as you describe. I suspect, however, that the concentration would need to be very high.
If that isn't the case throughout the spectral range you are interested in, then I agree with JianWei Wei. If any photons at all can interact with the container, and still scatter back to the sensor, then you will have problems which can cause problems in interpretation.
Aren't there flow-through sensors you can use to measure the absorption (a) and scattering (b), (an AC-9, or a hyperspectral version?) and then numerically calculate the Rrs for the case of an infinitely deep water body? Yes, I know, you'll need some assumption about the particulate phase-function, but it's a start.
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