I have found in some journals that some researchers predict AOD value for 355nm using AERONET AOD data from 340nm and 380nm. By doing so they can minimize error when doing Klett inversion to obtain the backscatter coefficient from Lidar data. Can anyone teach me how to do it?
The Angstrom exponent is a quotient of two AODs (in this case, at 340 and 440 nm). I think you'll find the definition under the Wikipedia link cited by Peggy.
Actually, the AOD at 355 will almost certainly deviate only very little from the one at 340; I'm guessing less than 5% for small aerosols...
I have used the OMAERUV-OMI product which can be largely useful for the AOD and AAOD measurements. Because we were researching on dust storms in desert where the regions appear very bright in visible and near-IR, UV-radiance made a great contribution for the research. You find the details of the algorithm for the OMAEURV-OMI just by googling "OMAEURV OMI readme"
You may find this paper useful.
http://onlinelibrary.wiley.com/doi/10.1029/2008JD011024/abstract
(Let me know if you need the pdf version of the paper)
The most simple way is to get the Angstrom exponent from spectral optical depth and use it to find AOD at the specified wavelength.
One must calculate the Angstrom exponent between the two AODs and wavelengths (340 and 380 nm). Use the formula given here http://en.wikipedia.org/wiki/Angstrom_exponent and substitute the available AODs and wavelengths accordingly. Then convert to 355 nm.
I agree with the two answers given above, but watch out: depending on aerosol type (or mix) the Angstrom coefficient itself may be wavelength dependent. So taking the Angstrom coefficient from the 340/380 nm intensities (like Peggy suggests) is probably quite reliable, whereas taking it from a more distant wavelength pair (e.g. 340/870) may not be!
Sorry I meant "from the 340/380 nm AODs", not intensities...
I see. The Angstrom Exponent I can get from AERONET that is closest to my lidar wavelength is 340-440 Angstrom. (My lidar is at 355nm) So what is mean by 340-440 Angstrom? The average of the Angstrom Exponent from 340 to 440?
The Angstrom exponent is a quotient of two AODs (in this case, at 340 and 440 nm). I think you'll find the definition under the Wikipedia link cited by Peggy.
Actually, the AOD at 355 will almost certainly deviate only very little from the one at 340; I'm guessing less than 5% for small aerosols...
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