Hi all,
The "Geostationary projection" section of Appendix F "Grid Mappings" says
The x (abscissa) and y (ordinate) rectangular coordinates are identified by
the standard_name attribute values projection_x_coordinate and
projection_y_coordinate respectively. In the case of this projection, the
projection coordinates in this projection are directly related to the
scanning angle of the satellite instrument, and their units are radians.
To more explicitly fit CF expectations for units of variables with a
standard_name attribute, I believe the last bit should read:
... and their *canonical* units are radians.
This came up because the GOES-16 Full Disk data (example below [1]) is
stored with the projection_{x|y}_coordinate values in microradians and, it
turns out, the netCDF-Java code didn't like that as it expected radians.
(Oops!)
Unless anyone disagrees, I will open a CF Trac ticket for this change later
this week.
Thanks,
Ethan
[1]
http://thredds-test.unidata.ucar.edu/thredds/dodsC/satellite/goes16/GOES16/FullDisk/Channel08/20180406/GOES16_FullDisk_20180406_201540_6.19_6km_0.0S_75.0W.nc4.html
netcdf GOES16_FullDisk_20180406_201540_6.19_6km_0.0S_75.0W {
dimensions:
x = 1808 ;
y = 1808 ;
variables:
int time ;
time:units = "seconds since 2017-01-01" ;
time:standard_name = "time" ;
time:long_name = "The start date / time that the satellite began capturing
the scene" ;
time:axis = "T" ;
time:calendar = "standard" ;
short y(y) ;
y:standard_name = "projection_y_coordinate" ;
y:units = "microradian" ;
y:scale_factor = -167.999999999971 ;
y:add_offset = 151788. ;
short x(x) ;
x:standard_name = "projection_x_coordinate" ;
x:units = "microradian" ;
x:scale_factor = 167.999999999971 ;
x:add_offset = -151788. ;
int fixedgrid_projection ;
fixedgrid_projection:grid_mapping_name = "geostationary" ;
fixedgrid_projection:latitude_of_projection_origin = 0. ;
fixedgrid_projection:longitude_of_projection_origin = -75. ;
fixedgrid_projection:semi_major = 6378137. ;
fixedgrid_projection:semi_major_axis = 6378137. ;
fixedgrid_projection:semi_minor = 6356752.31414 ;
fixedgrid_projection:semi_minor_axis = 6356752.31414 ;
fixedgrid_projection:perspective_point_height = 35785831. ;
fixedgrid_projection:sweep_angle_axis = "x" ;
short Sectorized_CMI(y, x) ;
Sectorized_CMI:_FillValue = 0s ;
Sectorized_CMI:standard_name = "brightness_temperature" ;
Sectorized_CMI:units = "kelvin" ;
Sectorized_CMI:grid_mapping = "fixedgrid_projection" ;
Sectorized_CMI:add_offset = 138.05f ;
Sectorized_CMI:scale_factor = 0.04224986f ;
Sectorized_CMI:valid_min = 0s ;
Sectorized_CMI:valid_max = 4095s ;
Sectorized_CMI:coordinates = "time y x" ;
// global attributes:
:title = "Sectorized Cloud and Moisture Imagery for the EFD region." ;
:ICD_version = "GROUND SEGMENT (GS) TO ADVANCED WEATHER INTERACTIVE
PROCESSING SYSTEM (AWIPS) INTERFACE CONTROL DOCUMENT (ICD) Revision B" ;
:Conventions = "CF-1.6" ;
:channel_id = 8 ;
:central_wavelength = 6.19f ;
:abi_mode = 3 ;
:source_scene = "FullDisk" ;
:periodicity = 15.f ;
:production_location = "RBU" ;
:product_name = "EFD-060-B12-M3C08" ;
:satellite_id = "GOES-16" ;
:product_center_latitude = 0. ;
:product_center_longitude = -75. ;
:projection = "Fixed Grid" ;
:bit_depth = 12 ;
:source_spatial_resolution = 2.f ;
:request_spatial_resolution = 6.f ;
:start_date_time = "2018096201540" ;
:number_product_tiles = 4 ;
:product_tile_width = 1024 ;
:product_tile_height = 1024 ;
:product_rows = 1808 ;
:product_columns = 1808 ;
:pixel_x_size = 6. ;
:pixel_y_size = 6. ;
:satellite_latitude = 0. ;
:satellite_longitude = -75. ;
:satellite_altitude = 35785831. ;
:created_by = "ldm-alchemy" ;
:product_tiles_received = 4 ;
}
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