Rayleigh optical thickness in msl12_sensor_info.dat

[fsteinmetz]

Dear SeaDAS team,

I am relying on Rayleigh optical thickness values provided in msl12_sensor_info.dat, as Tau_r (for VIIRS, SeaWiFS and MODIS).
However after recalculating these values using the SRF as provided in https://oceancolor.gsfc.nasa.gov/docs/rsr/ and using [Bodhaine, 99], and I am finding large discrepancies, for example for VIIRS from +2% at 410nm, to nearly -2% at 671nm - with differences of similar order of magnitudes for MODIS and SeaWiFS.
Could you clarify how these Tau_r values have been generated, and how they are used ?

Thanks,
François

[OB.DAACx - SeanBailey]

François,

The method we used is described here: https://oceancolor.gsfc.nasa.gov/reprocessing/r2009/sources/

To make sure I could replicate the numbers following the description given, I whipped up a quick python script...and turned it into an example which I've added to the above webpage.

BTW, this is NOT the actual code we used (that was in IDL), but it was nice to see I could match the numbers independently :grin:

I hope this helps.

Sean

[fsteinmetz]

Hi Sean,

Many thanks for your detailed answer !
Now I understand why I have found different values. The first thing I did when looking at the spectral response (semilogy(rsr.index, rsr.M1)) was to filter out the values lower than 2% (rsr.M1[rsr.M1 < 0.02] = 0).
So apparently I should not do that, but I am a bit worried by the look of the RSR and by the uncertainty that these out-of-band responses (>1% around 800nm for M1) introduce in the ROD calculation.

François

[OB.DAACx - SeanBailey]

François,

Yes, it can be a little disconcerting to see  significant out-of-band responses - but that is what was measured and needs to be included.

Regards,
Sean