Data processing and correction algorithms

Use this Forum to find information on, or ask a question about, NASA Earth Science data.
Post Reply
madhusmita
Posts: 13
Joined: Mon Jul 17, 2017 8:39 am America/New_York
Answers: 0

Data processing and correction algorithms

by madhusmita » Fri Oct 02, 2020 4:35 am America/New_York

Hello all
I am doing MODIES - Aqua multilevel data processing from level 1 to level 3 using all the 11 atmospheric correction algorithms.
I processed the data  successfully from level 1 to level 2.

From level 2 to level 3 i am getting the following problems:

While processing, when i am using chlorophyll as a product , i am getting chl-a data for 8 correction algorithms  (-99, 0, -1, -2, -3, -8, -9, -10,)  only. for the remaining four algorithms i am not getting any data.
And except chlorophyll, when i am changing the product to Rrs indifferent wavelengths like Rrs_412, Rrs_443, Rrs_469  of aot_869, angstrom. them i am getting the data for only four correction algorithms (-2, -3, -9, -10).

Here i am proving the code details, can any one please rectify and suggest what is missing exactly.

  /bin/bash -c "l2gen ifile=$L1bFile par=$L1bFile.anc geofile=$GeoFile \
        ofile1=$L2File1 l2prod1='chlor_a, Rrs_412, Rrs_443, Rrs_469, Rrs_488, Rrs_531, Rrs_547, Rrs_555, Rrs_645, Rrs_667, Rrs_678, Rrs_748, Rrs_859, Rrs_869, angstrom, aot_869'
        aer_opt=${AeroMod[$Indx_AeroMod]}"
      
      L2inFileOC="L2Bin-OC-4km."${NameAeroMod[$Indx_AeroMod]}".txt";
      l2binFileOC="A"$Yyear$Yday"-4KM-SpaceBin-OC-L2BIN."${NameAeroMod[$Indx_AeroMod]};
      ls -1 A*_OC.${NameAeroMod[$Indx_AeroMod]}.L2_LAC > $L2inFileOC;

      l2bin infile=$L2inFileOC ofile=$l2binFileOC.L3_GAC sday=$Yyear$Yday eday=$Yyear$Yday resolve=4 \
      flaguse=LAND,CLDICE,HIGLINT \
      l3bprod=chlor_a,Rrs_412,Rrs_443,Rrs_469,Rrs_488,Rrs_531,Rrs_547,Rrs_555,Rrs_645,Rrs_667,Rrs_678,Rrs_748,Rrs_859,Rrs_869,angstrom,aot_869 prodtype='regional' noext=1
      oformat=netCDF4 verbose=1

      L3inFileOC=$l2binFileOC.L3_GAC;
      l3binFileOC="A"$Yyear$Yday"-4KM-SpaceBin-OC-L3BIN."${NameAeroMod[$Indx_AeroMod]};
      OpMapFileOC="A-"$Ymonth$Yyear"-d"$Ydom"-4KM-Entire-OC."${NameAeroMod[$Indx_AeroMod]};

      l3bin in=$L3inFileOC out=$l3binFileOC.nc
      out_parm=chlor_a,Rrs_412,Rrs_443,Rrs_469,Rrs_488,Rrs_531,Rrs_547,Rrs_555,Rrs_645,Rrs_667,Rrs_678,Rrs_748,Rrs_859,Rrs_869,angstrom,aot_869 latnorth=20.0 latsouth=18.0
      loneast=89.0 lonwest=87.0 sday=$Yyear$Yday eday=$Yyear$Yday noext=1

Thank you in advance :smile:

Filters:

OB.DAAC - SeanBailey
User Services
User Services
Posts: 1485
Joined: Wed Sep 18, 2019 6:15 pm America/New_York
Answers: 1
Been thanked: 5 times

Data processing and correction algorithms

by OB.DAAC - SeanBailey » Sat Oct 03, 2020 9:34 am America/New_York

The aer_opt parameter selects the aerosol correction method (it is not the full atmospheric correction).  Not all aerosol correction (or lack thereof in the case of aer_opt=-99) will be appropriate to the conditions.    You should not have the expectation that every option will work for every condition.

1) aer_opt=-99 : no aerosol subtraction.  If there are aerosols (likely) in the atmosphere over the scene, choosing this can case failures for retrievals if the aerosol load is indeed high
2) aer_opt=0:  white aerosol.  Assumes the black pixel assumption is valid and the aerosol reflectance is spectrally flat.  If the   black pixel assumption is not valid, an excessive aerosol subtraction will occur resulting in retrieval failures
3) aer_opt=-1: Multi-scattering with 2-band model selection.  Like aer_opt=0, this assumes the black pixel assumption is valid.  Failures due to excessive aerosol subtraction, or a wildly incorrect model selection can occur if the assumption is violated.
4) aer_opt=-2 is effectively the same as aer_opt=-3 as we no longer distribute aerosol tables that do not have  the relative humidity based selection.  This is the default option and uses the NIR-correction approach to adjust the selection for non-zero NIR water-leaving radiance
5) aer_opt=-8 requires that the user supply the aerosol optical thickness values for each band.  If those values are not correct (or at least reasonable) failures can result
6) aer_opt=-9 will produce the same result as aer_opt=-2 unless the estimated turbidity is above a threshold, at which point the SWIR bands are used to select the aerosol model for subtraction
7) aer_opt=-10 requires   mumm_alpha , mumm_gamma and mumm_epsilon to be appropriate for the scene.  The defaults may work, but users should evaluate this for their conditions.

Regards,
Sean

madhusmita
Posts: 13
Joined: Mon Jul 17, 2017 8:39 am America/New_York
Answers: 0

Data processing and correction algorithms

by madhusmita » Sat Oct 03, 2020 10:11 am America/New_York

Thanks Sean for your well explained reply:smile:
My question is about the correction algorithms -4, -5, -6, and -7.
I am not getting data in those correction algorithms. so what could be the reason? could you please tell  details about of these correction algorithms.

And when i am changing the product from chlorophyll to any other like aot_869, angstrom, Rrs_412, Rrs_443 etc i am getting data for only four correction algorithms (-2, -3, -9 and -10).

However, earlier i have tried to export the data in same way from level 1 to level 3 using all correction algorithms. and i have chosen different products (e.g chl, Rrs , Es, Lu   Lw and nLw in all visible and near infra red bands and aot, angstrom), i got the data for 8 ACs except -4, -5, -6, -7.

Is there any specific criteria, i mean whether we need to change any specific variables value from the default value for different correction algorithms.

Regards
Madhusmita

OB.DAAC - SeanBailey
User Services
User Services
Posts: 1485
Joined: Wed Sep 18, 2019 6:15 pm America/New_York
Answers: 1
Been thanked: 5 times

Data processing and correction algorithms

by OB.DAAC - SeanBailey » Sat Oct 03, 2020 10:55 am America/New_York

The l2gen usage statement explains what is required for those:

      -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)
       -6: Multi-scattering with fixed angstrom
           (requires aer_angstrom specification)
       -7: Multi-scattering with fixed angstrom
           and iterative NIR correction
           (requires aer_angstrom specification)


aer_opt=-4 and aer_opt=-5 both require the user to supply the two aerosol models and the mixing ratio.
aer_opt=-6 and aer_opt=-7 both require the user to supply an angstrom (which is used to select the closest matching model)

There should be no need to take a shotgun approach to the aer_opt selection.  If the default aer_opt=-2 does not produce desirable results, you could examine the conditions for the scene in question and choose an alternative selection method.  Keep in mind, however, if you do not have the information to supply to the code (e.g. aerosol angstrom value for aer_opt=-6 or -7), choosing that option will not help get better retrievals.

Sean

madhusmita
Posts: 13
Joined: Mon Jul 17, 2017 8:39 am America/New_York
Answers: 0

Data processing and correction algorithms

by madhusmita » Mon Oct 05, 2020 1:58 am America/New_York

Thanks Sean:smile:

Post Reply