CDO

The CTX file contains coordinates with units in radians, therefore you need a gridfile for the CTX input file like

gridfile.txt

#
# gridID 1
#
gridtype  = projection
gridsize  = 13778944
xsize     = 3712
ysize     = 3712
xname     = x
xlongname = "x coordinate of projection" 
xunits    = "radian" 
yname     = y
ylongname = "y coordinate of projection" 
yunits    = "radian" 
xfirst    = -0.155613222592103
xinc      = 8.38433311379864e-05
yfirst    = 0.155613222592103
yinc      = -8.38433311379864e-05
grid_mapping = projection
grid_mapping_name = geostationary
long_name = "projection information" 
perspective_point_height = 35785831.
latitude_of_projection_origin = 0.
longitude_of_projection_origin = 0.
sweep_angle_axis = "y" 
semi_minor_axis = 6356583.8
semi_major_axis = 6378169.
proj_params = "+proj=geos +h=35785831.0 +lon_0=0.r +lat_0=0.r +a=6378169. +b=6356583.8 +sweep=y +no_defs" 
#
# gridID 2
#
gridtype  = generic
gridsize  = 1

Then try (this takes a long time):

cdo -P 8 -remapnn,claas3_level3_aux_data_005deg.nc -setgrid,g.txt CTXin20240420234500405SVMSGI1MD.nc outfile.nc

I tried with your suggestion. But now it's showing

cdo(1) setgrid (Abort): xsize undefined

Apologies. Its on the run. It was showing that because of one of my typo.

Another follow up query!
I literally have around 100 such files which I need to remap in such way. Is it possible to make a loop over here? Any tips for quicker processing?

I have been trying for about 6 years to get this issue resolved. Best fix so far is to use gdal.It only works on one parameter at a time and you need to reset all attributes. here is some test code I use that you are welcome to adapt.

#!/bin/bash

# Reproject data
echo "Starting reprojection of data..." 
for f in dX_2019121000_B*.nc; do
    base=$(basename "$f" .nc)
    echo "Reprojecting $base..." 
    gdalwarp -t_srs EPSG:4326 -te 85 -45 160 50 -tr 0.02 0.02 -r cubic "$f" wgs_${base}.nc &
done
wait
echo "Reprojection complete." 

# Translate to NetCDF
echo "Translating reprojected files to NetCDF..." 
for f in wgs_dX_2019121000_B*.nc; do
    base=$(basename "$f" .nc | sed 's/^wgs_//')
    gdal_translate -of netCDF -a_srs EPSG:4326 wgs_${base}.nc "${base}.nc" 
done
wait
echo "Translation complete." 

# Rename variable names and set properties
echo "Setting variable names and time for reprojected files..." 
for f in dX_2019121000_B*.nc; do
    base=$(basename "$f" .nc)
    param_name=$(echo $base | cut -d'_' -f3) # Extracts B07, BTD14_15, etc.
    echo "Setting variable name for $base to $param_name..." 
    ncrename -v Band1,$param_name "${base}.nc" 
    time_val=$(date -d "2019-12-10 00:00:00" +%s)
    ncap2 -O -s "defdim(\"time\",1); time[time]=$time_val" "${base}.nc" "${base}.nc" 
    ncatted -O -a units,time,o,c,"seconds since 1970-01-01 00:00:00" -a reftime,time,o,c,"2019-12-10 00:00:00" "${base}.nc" 
done
echo "Variable names and properties set." 

thx for posting your workaround, Miles ;-)

cheers
ralf