Earthdata Forum

Hi, everyone.
    I have two questions. One, I  confused about the A(?) and B(?) parameters setting in GIOP-DC. Are these two pamameters in Table 2 from Bricaud et al.(1995)?Are the values of A(?) and B(?) constant for different Chla between 0.03 to 10 mg m-3 or different area ? Two, GIOP-DC normalized the aphstar443 to 0.055 m2mg-1, however, we found that the value of aphstar443 in our study area is higher than default. We want to know if the values of A(?) and B(?) change with areas?  And if we can reset aphstar443 in our study areas?
Thanks
Deng

Hi Deng,

Yes, the default configuration for assigning aphstar is to use Bricaud et al. 1995, which is modulated by an input chlorophyll value (using the standard chlor_a product). Per that paper, yes, Bricaud's table values are used. Here's a glimpse at GIOP's parameter options for aphstar. You can display this by running l2gen from the command line without any inputs. You can also find these options in SeaDAS under the l2gen "IOP" tab:

   giop_aph_opt (int) (default=2) = GIOP model aph function type
        0: tabulated (supplied via giop_aph_file)
        2: Bricaud et al. 1995 (chlorophyll supplied via default empirical algorithm)
        3: Ciotti and Bricaud 2006 (size fraction supplied via giop_aph_s)
   giop_aph_file (ifile) (default=$OCDATAROOT/common/aph_default.txt) =
        GIOP model, tabulated aph spectra

From here, see that Bricaud is the default (giop_aph_opt=2).  If you'd like to input your own aphstar, set this to 0 "tabulated" and provide an input file using the giop_aph_file=<file> option. An example of how this file needs to be built is provided within OCSSW/SeaDAS, named "aph_default.txt" (see above).

See also the documents linked here:  https://oceancolor.gsfc.nasa.gov/atbd/giop/

Hope this helps.

Jeremy