fields attributes - MODIS: MYD021KM data set - can't find radiance scales to convert SI to radiances

I would like to convert the scaled integers (SI) to radiances for all my SDS MYD021Km thermal emissive bands.

In the MODIS Level 1B Product user guide on page 36 in section 5.5.1 it says:

The values of radiance_scales and radiance_offsets are computed inside Level 1B and written as attributes to the Science data sets. Thus, radiance may be simply recovered from SI by reading these two attributes and applying Equation 5.8.

where Equation 5.8 states the relation between radiance, radiance_scales and radiance_offsets. However, I can't find those attributes in my hdf file. Even though, I downloaded the whole package without any post-processing choices on LAADS DAAC.

Where can i find them?

Answer

The numbers you are asking for are stored in the HDF-EOS v2 file as attributes. The way to extract attributes depends on the choice of tools available to you.

If you have command-line programs for HDF4, you could use a version of ncdump utility built with HDF4 support. It may be called ncdump or hncdump depending on your distribution.

hncdump -h MOD021KM.A2018150.0020.005.2018151073854.hdf | grep -E \
'(band_names|radiance_(scales|offsets)|reflectance_(scales|offsets))'

Would output the following list:

    EV_1KM_RefSB:band_names = "8,9,10,11,12,13lo,13hi,14lo,14hi,15,16,17,18,19,26" ;
    EV_1KM_RefSB:radiance_scales = 0.013427167f, 0.0084019899f, 0.0054145837f, 0.0036830753f, 0.0034992441f, 0.0011288056f, 0.00084021641f, 0.0015078289f, 0.00083084067f, 0.0010439196f, 0.00093331479f, 0.00810323f, 0.0091102663f, 0.0075753126f, 0.0032291501f ;
    EV_1KM_RefSB:radiance_offsets = 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f ;
    EV_1KM_RefSB:reflectance_scales = 2.4827241e-05f, 1.4246029e-05f, 8.8230718e-06f, 6.3097509e-06f, 5.9693111e-06f, 2.3535526e-06f, 1.7518461e-06f, 3.2272799e-06f, 1.7782888e-06f, 2.6024989e-06f, 3.096286e-06f, 2.7981168e-05f, 3.3658562e-05f, 2.8003564e-05f, 2.856155e-05f ;
    EV_1KM_RefSB:reflectance_offsets = 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f, 316.9722f ;

    EV_1KM_Emissive:band_names = "20,21,22,23,24,25,27,28,29,30,31,32,33,34,35,36" ;
    EV_1KM_Emissive:radiance_scales = 6.2623985e-05f, 0.0031495101f, 6.9215974e-05f, 7.9103978e-05f, 3.1556141e-05f, 5.6398207e-05f, 0.0001175573f, 0.00019244973f, 0.00053248694f, 0.00040632344f, 0.000840022f, 0.00072969758f, 0.00026226387f, 0.00020069582f, 0.00017670827f, 0.00011833857f ;
    EV_1KM_Emissive:radiance_offsets = 2730.5835f, 2730.5835f, 2730.5835f, 2730.5835f, 1077.4448f, 1560.3334f, 2730.5833f, 2317.4883f, 2730.5835f, 1560.3333f, 1577.3397f, 1658.2213f, 2501.2976f, 2501.2976f, 2501.2979f, 2501.2979f ;
    EV_250_Aggr1km_RefSB:band_names = "1,2" ;
    EV_250_Aggr1km_RefSB:radiance_scales = 0.02789869f, 0.010482604f ;
    EV_250_Aggr1km_RefSB:radiance_offsets = -0.f, -0.f ;
    EV_250_Aggr1km_RefSB:reflectance_scales = 5.6068438e-05f, 3.4103123e-05f ;
    EV_250_Aggr1km_RefSB:reflectance_offsets = -0.f, -0.f ;
    EV_500_Aggr1km_RefSB:band_names = "3,4,5,6,7" ;
    EV_500_Aggr1km_RefSB:radiance_scales = 0.034588818f, 0.025763946f, 0.0062726424f, 0.0027750582f, 0.00086950249f ;

    EV_500_Aggr1km_RefSB:radiance_offsets = -0.f, -0.f, -0.f, -0.f, -0.f ;
    EV_500_Aggr1km_RefSB:reflectance_scales = 5.3474156e-05f, 4.456985e-05f, 4.2685773e-05f, 3.7288173e-05f, 3.1073403e-05f ;
    EV_500_Aggr1km_RefSB:reflectance_offsets = -0.f, -0.f, -0.f, -0.f, -0.f ;
    EV_Band26:radiance_scales = 0.0032291501f ;
    EV_Band26:radiance_offsets = 316.9722f ;
    EV_Band26:reflectance_scales = 2.856155e-05f ;
    EV_Band26:reflectance_offsets = 316.9722f ;

So you can get radiance_scales and radiance_offsets for each MODIS band.

Note that the scales for band 26 are stored twice, first in the array EV_1KM_RefSB:radiance_scales and in EV_Band26:radiance_scales. The same is true for radiance offsets, reflectance scales and reflectance offsets for Band 26.