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MTG LI L2: Hard coded the satellite position with the nominal vallues #3137

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MTG LI L2: Hard coded the satellite position with the nominal vallues #3137

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4d61d11
added a method to the reader to hardcode satpos with nominal position
May 16, 2025
18337e3
modified doc string
May 19, 2025
6bdfaf7
added a log info
May 19, 2025
d840efb
sync my fork with main
May 20, 2025
9449677
implemented suggested changes
May 20, 2025
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12 changes: 12 additions & 0 deletions satpy/readers/li_base_nc.py
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Original file line number Diff line number Diff line change
Expand Up @@ -737,6 +737,15 @@ def update_array_attributes(self, data_array, ds_info):

return data_array

def add_orbital_parameters(self, data_array):
"""Hard code the nominal position of the satellite in the orbital parameters attribute."""
logger.debug("Assuming nominal satellite position for LI L2. The exact position is available from FCI L1.")
data_array.attrs["orbital_parameters"] = {"satellite_nominal_longitude": 0.0,
"satellite_nominal_latitude": 0.0,
"satellite_nominal_altitude": 35786400.0
}
Comment on lines +743 to +746
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@gerritholl gerritholl May 19, 2025

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If at least the satellite number is known from the metadata (is it?) this hardcoded position could be sorted by satellite. MTG-I2 / Meteosat-14 will have a different position.

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@jequierz jequierz May 20, 2025

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Good point, I didn't think about the fact that other satellite's products would require the use of the LI reader... But it is true that in any case, it would be better to have a more general solution because apparently the same problem holds for any L2 product of the MTG.
However, I am not sure to understand, how does the satellite number can be used to for this application? By writing a dict of satellites containing a dict of nominal position for each satellite?

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@gerritholl gerritholl May 23, 2025

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Yes, I would have a dict of satellites. Those should rarely change, although if they do, it will cause more of a headache as we would need to cover old and new data.

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@ameraner ameraner May 23, 2025

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yeah, when we start moving the MTGs between the nominal, rapid scan , IODC position etc, we'll have a new headache. But maybe by then we can include the information in the file format... So for now a simple dict mapping the platform_name to the satellite_nominal_longitude should be good for a while. Note that the platform_name was added only recently in #2993

return data_array

def get_dataset(self, dataset_id, ds_info=None):
"""Get a dataset."""
# Retrieve default infos if missing:
Expand Down Expand Up @@ -770,5 +779,8 @@ def get_dataset(self, dataset_id, ds_info=None):
# Update the attributes in the final array:
data_array = self.update_array_attributes(data_array, ds_info)

# Add the nominal sat position in attrs orbital parameters
data_array = self.add_orbital_parameters(data_array)

# Return the resulting array:
return data_array
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