Incorrect nominal_satellite_subpoint_lon attribute in Goes East output files

[LeviDPC]

Goes East Gridded GLM output netcdf files (For this write up I Created them with make_GLM_grids.py example) seem to have incorrect nominal_satellite_subpoint_lon values.

Example:

Generate file:

LeviDPC$ python make_GLM_grids.py --fixed_grid --split_events --goes_position east --goes_sector conus --dx=2.0 --dy=2.0 goes16/OR_GLM-L2-LCFA_G16_s20223141900000_e20223141900200_c20223141900224.nc goes16/OR_GLM-L2-LCFA_G16_s20223141900200_e20223141900400_c20223141900423.nc goes16/OR_GLM-L2-LCFA_G16_s20223141900400_e20223141901000_c20223141901028.nc

This produces an output file which we can check the nominal_satellite_subpoint_lon of with ncdump:

LeviDPC$ ncdump OR_GLM-L2-GLMC-M3_G16_s20223141900000_e20223141901000_c20250281711250.nc | grep "subpoint_lon"
(extraneous output omitted)
 nominal_satellite_subpoint_lon = -75 ;

Compare that output value of -75 to the -75.2 value in a G16 ABI file for subpoint_lon :

LeviDPC$ ncdump OR_ABI-L1b-RadM2-M6C13_G16_s20240931939549_e20240931940019_c20240931940043.nc | grep "subpoint_lon"
(extraneous output omitted)
 nominal_satellite_subpoint_lon = -75.2 ;

I believe that this is happening because here subpoint_lon is set equal to nadir_lon and while these two values do seem to be equal for Goes-West and Goes-Test they appear to not be equal for Goes-Test.

(In an ABI file) Goes West subpoint_lon is the same value as nadir_lon:

LeviDPC$ ncdump OR_ABI-L1b-RadM2-M6C11_G18_s20242661030557_e20242661031014_c20242661031052.nc | grep "subpoint_lon"
(extraneous output omitted)
 nominal_satellite_subpoint_lon = -137 ;

LeviDPC$ncdump OR_ABI-L1b-RadM2-M6C11_G18_s20242661030557_e20242661031014_c20242661031052.nc | grep "lon_nadir"
		geospatial_lat_lon_extent:geospatial_lon_nadir = -137.f ;

(In an ABI file) But for Goes West the two values are (slightly) different:

LeviDPC$ ncdump OR_ABI-L1b-RadM2-M6C13_G16_s20240931939549_e20240931940019_c20240931940043.nc | grep "subpoint_lon"
(extraneous output omitted)
 nominal_satellite_subpoint_lon = -75.2 ;

LeviDPC$ncdump OR_ABI-L1b-RadM2-M6C13_G16_s20240931939549_e20240931940019_c20240931940043.nc | grep "lon_nadir"
		geospatial_lat_lon_extent:geospatial_lon_nadir = -75.f ;

[graemely]

For GOES-West I think the value in the ABI L1B file is wrong. The GLM L2+ files show the correct value.

ncdump -v nominal_satellite_subpoint_lon OR_GLM-L2-LCFA_G18_s20223141900000_e20223141900200_c20223141900209.nc | grep "nominal_satellite_subpoint_lon ="
 nominal_satellite_subpoint_lon = -137.2 ;

I'll report the issue to the PRO Team and see what response I get.

[graemely]

OK, I think I was wrong. A newer GOES-18 (GOES-West) GLM file shows the sub-point lon value of -137, consistent with the ABI value you posted. So apparently the satellite was moved at some point.

ncdump -v nominal_satellite_subpoint_lon OR_GLM-L2-LCFA_G18_s20250342154200_e20250342154400_c20250342154418.nc | grep "nominal_satellite_subpoint_lon ="
 nominal_satellite_subpoint_lon = -137 ;

Sorry for the misdirect.