Seadas aerindex

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disconomer
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Seadas aerindex

by disconomer » Wed Oct 26, 2022 12:06 am America/New_York

Hi,
I was wondering if there was a mechanism for SeaDAS to output the aerosol model it determines for a given atmospheric correction procedure (i.e. for aer_opt=-2,-3,-9). I was hoping this output would be available when I put the product aerindex into my L2Gen product list, however I just seem to get NaNs in that one. Perhaps i'm misunderstanding what aerindex is/was used for.

Furthermore, if one had access to an array of output aerindex (or whatever) values, then I was thinking it would be cool if the user could modify that array and then use it as an input to a subsequent L2Gen call to force the atmocor to choose the chosen aerosol model.
Cheers
Matt

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OB.DAAC - SeanBailey
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User Services
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Joined: Wed Sep 18, 2019 6:15 pm America/New_York
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Re: Seadas aerindex

by OB.DAAC - SeanBailey » Fri Oct 28, 2022 1:55 pm America/New_York

Matt,
With the original Gordon and Wang implementation with 12 aerosol models, it was pretty easy...just ask for:
aer_model_min
aer_model_max
aer_model_ratio

aer_model_min and max are the bounding models that encompassed measured epsilon value, ratio is the weighting between them.

Then we went to 80 models with a relative humidity selection and so we have:

aer_model_1
aer_model_2
aer_model_3
aer_model_4
aer_model_ratio_1_2
aer_model_ratio_3_4

Yeah, a bit complicated. Also, there is no mechanism within the code to read and apply model numbers from an input file. You can do so for a pair of models:

Code: Select all

aer_opt (int) (default=99) = aerosol mode option
...
       -4: Multi-scattering with fixed model pair
           (requires aermodmin, aermodmax, aermodrat specification)
       -5: Multi-scattering with fixed model pair
           and iterative NIR correction
           (requires aermodmin, aermodmax, aermodrat specification)

There is also a method that can take an input angstrom coefficient and use it for the model selection:

Code: Select all

       
 ...
       -6: Multi-scattering with fixed angstrom
           (requires aer_angstrom specification)
       -7: Multi-scattering with fixed angstrom
           and iterative NIR correction
           (requires aer_angstrom specification)
Both of these approaches apply the selected model(s) to the entire scene. Nothing exists to have the user pick the aerosol model on a per pixel basis.

BTW, aerindex is a very ancient attempt at flagging absorbing aerosol in the data (the aerosol models, even today, are non- or weakly absorbing). There is a convoluted polynomial that defines an absorbing aerosol index. I think it only worked for SeaWiFS and MODIS (if you can say what it ever did was "working"). One of those vestigial bits that never seems to get removed...you should ignore it ;)

Sean

disconomer
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Joined: Tue Oct 25, 2022 11:48 pm America/New_York
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Re: Seadas aerindex

by disconomer » Wed Nov 02, 2022 3:20 am America/New_York

Many thanks Sean,

Cheers
Matt
Last edited by disconomer on Wed Nov 02, 2022 5:08 am America/New_York, edited 1 time in total.

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