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[Datastream #XNQ-246736]: Re: [ldm-users] 20220622: 2nd Notice: upcoming product addition to the IDD NIMAGE feed



Hi,

re:
> I have a question about the Vlab Level 2 GLM product described in an email
> titled: "[ldm-users] 20220622: 2nd Notice: upcoming product addition to the
> IDD NIMAGE feed", sent on Wed, 22 Jun 2022 11:24:52 -0600
> 
> I am looking at an example of this data, specifically
> 20220924/OR_GLM-L2-GLMF-M6_G16_s20222672353000_e20222672354000_c20222672353300.nc,
> and am wondering what the units are for Flash_extent_density.  Using
> ncdump, I see:
> 
> 
> short Flash_extent_density(y, x) ;
> Flash_extent_density:_FillValue = 0s ;
> Flash_extent_density:standard_name = "Flash Extent Density"
> ;
> Flash_extent_density:long_name = "GLM Flash Extent Density"
> ;
> Flash_extent_density:grid_mapping =
> "goes_imager_projection" ;
> Flash_extent_density:_Unsigned = "true" ;
> Flash_extent_density:coordinates = "time y x" ;
> 
> which does not mention units.  

Evidently, the NOAA group that is creating the Vlab GLM composites did not
think including the units for the various parameters was important!

re:
> Apparently it is not just number of flashes
> in that grid point, as I think the total number of flashes would be
> "nmeas", which in this case is 1568 (nmeas = UNLIMITED ; // (1568
> currently)), yet if I sum up Flash_extent_density over all grid points, I
> get 229994 (way more!)
> 
> Thanks for any clarification you can offer.

Since the Vlab code was reportedly based on the code that created the composites
that were being produced at Texas Tech University (TTU), I would assume that 
the units
for the parameters are the same as for the TTU products.  A quick 'ncdump'
of one of the TTU FullDisk files shows:

netcdf OR_GLM-L2-GLMF-M3_G16_s20212242021000_e20212242022000_c20212242022510 {
dimensions:
        x = 5424 ;
        y = 5424 ;
        dim_0 = 1 ;
variables:

 ...
        short flash_extent_density(y, x) ;
                flash_extent_density:_FillValue = 0s ;
                flash_extent_density:standard_name = "flash_extent_density" ;
                flash_extent_density:long_name = "Flash extent density" ;
                flash_extent_density:units = "Count per nominal    3136 
microradian^2 pixel per 1.0 min" ;
                flash_extent_density:grid_mapping = "goes_imager_projection" ;
                flash_extent_density:add_offset = 0. ;
                flash_extent_density:scale_factor = 0.0625 ;
                flash_extent_density:_Unsigned = "true" ;

If the supposition that the Vlab code is doing the same things as the TTU
code, the unit for Flash Extent Density should be:

Count per nominal    3136 microradian^2 pixel per 1.0 min

I can not guarantee this, however.

In case it may be helpful, here are the units of the parameters in the TTU GLM
products:

        short flash_extent_density(y, x) ;
                flash_extent_density:_FillValue = 0s ;
                flash_extent_density:standard_name = "flash_extent_density" ;
                flash_extent_density:long_name = "Flash extent density" ;
                flash_extent_density:units = "Count per nominal    3136 
microradian^2 pixel per 1.0 min" ;
                flash_extent_density:grid_mapping = "goes_imager_projection" ;
                flash_extent_density:add_offset = 0. ;
                flash_extent_density:scale_factor = 0.0625 ;
                flash_extent_density:_Unsigned = "true" ;
        short flash_centroid_density(y, x) ;
                flash_centroid_density:_FillValue = 0s ;
                flash_centroid_density:standard_name = "flash_centroid_density" 
;
                flash_centroid_density:long_name = "Flash centroid density" ;
                flash_centroid_density:units = "Count per nominal    3136 
microradian^2 pixel per 1.0 min" ;
                flash_centroid_density:grid_mapping = "goes_imager_projection" ;
                flash_centroid_density:add_offset = 0. ;
                flash_centroid_density:scale_factor = 1. ;
                flash_centroid_density:_Unsigned = "true" ;
        short average_flash_area(y, x) ;
                average_flash_area:_FillValue = 0s ;
                average_flash_area:standard_name = "average_flash_area" ;
                average_flash_area:long_name = "Average flash area" ;
                average_flash_area:units = "km^2 per flash" ;
                average_flash_area:grid_mapping = "goes_imager_projection" ;
                average_flash_area:add_offset = 0. ;
                average_flash_area:scale_factor = 10. ;
                average_flash_area:_Unsigned = "true" ;
        short total_energy(y, x) ;
                total_energy:_FillValue = 0s ;
                total_energy:standard_name = "total_energy" ;
                total_energy:long_name = "Total radiant energy" ;
                total_energy:units = "nJ" ;
                total_energy:grid_mapping = "goes_imager_projection" ;
                total_energy:add_offset = 0. ;
                total_energy:scale_factor = 1.52597e-06 ;
                total_energy:_Unsigned = "true" ;
        short group_extent_density(y, x) ;
                group_extent_density:_FillValue = 0s ;
                group_extent_density:standard_name = "group_extent_density" ;
                group_extent_density:long_name = "Group extent density" ;
                group_extent_density:units = "Count per nominal    3136 
microradian^2 pixel per 1.0 min" ;
                group_extent_density:grid_mapping = "goes_imager_projection" ;
                group_extent_density:add_offset = 0. ;
                group_extent_density:scale_factor = 0.25 ;
                group_extent_density:_Unsigned = "true" ;
        short group_centroid_density(y, x) ;
                group_centroid_density:_FillValue = 0s ;
                group_centroid_density:standard_name = "group_centroid_density" 
;
                group_centroid_density:long_name = "Group centroid density" ;
                group_centroid_density:units = "Count per nominal    3136 
microradian^2 pixel per 1.0 min" ;
                group_centroid_density:grid_mapping = "goes_imager_projection" ;
                group_centroid_density:add_offset = 0. ;
                group_centroid_density:scale_factor = 1. ;
                group_centroid_density:_Unsigned = "true" ;
        short average_group_area(y, x) ;
                average_group_area:_FillValue = 0s ;
                average_group_area:standard_name = "average_group_area" ;
                average_group_area:long_name = "Average group area" ;
                average_group_area:units = "km^2 per group" ;
                average_group_area:grid_mapping = "goes_imager_projection" ;
                average_group_area:add_offset = 0. ;
                average_group_area:scale_factor = 1. ;
                average_group_area:_Unsigned = "true" ;
        short minimum_flash_area(y, x) ;
                minimum_flash_area:_FillValue = 0s ;
                minimum_flash_area:standard_name = "minimum_flash_area" ;
                minimum_flash_area:long_name = "Minimum flash area" ;
                minimum_flash_area:units = "km^2" ;
                minimum_flash_area:grid_mapping = "goes_imager_projection" ;
                minimum_flash_area:add_offset = 0. ;
                minimum_flash_area:scale_factor = 10. ;
                minimum_flash_area:_Unsigned = "true" ;

Cheers,

Tom
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Ticket Details
===================
Ticket ID: XNQ-246736
Department: Support Datastream
Priority: Normal
Status: Closed
===================
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