I have Pyrgeometer and Pyranometer's data coincident with the MODIS (Terra and Aqua) overpass. Can these instruments (Pyrgeometer and Pyranometer) be used for the atmospheric correction of the MODIS imagery? Any suggestions of how can we employ these instruments for this purpose.
P.S:
Pyrgeometer is an instrument used for the measurement of the far-infrared energy at wavelengths from 4.5 um to 40 um; and
Pyranometer is an instrument used for the measurement of the shortwave radiations at wavelengths from 0.3 um to 3.0 um.
You cannot use them as your only sorce of data, since pyranometers give an integrated value in the whole range while MODIS (or other optical remote sensing instrumens) measure in several subsets in that region. It might be used to constrain the atmospheric correction, but you can never resolve how much energy corresponds to each band (even if you had continuos channels in the whole range, so you can calculate an equivalent integrated value, there is the uncertainty of hich channel contribute more, i.e. hoe was the energy distributed through the spectrum, that is, depending on the atmospheric conditions a given day it might be that there is more energy in the blue channels and less in the NIR ones (clear day), but another day there are aerosols and the blue is weaker and NIR stronger, and in both cases the total energy is the same so the pyranopmeter would report the same value.
So, in brief, pyranometers cannot give you the information on how is the enegry distributed spectrally (and you need to correct all channels individually), but might provide a constrain to the total energy available that day. But wihtout any other source of information you cannot proceed further.
There are atmospheric correction algorithms that estimate the parameters from the image itself, but they are all complex approaches. Please look at L. Guanter publications.
Cheers
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