Examining the obs_seq.final file
If you are testing with a single observation, just look in the file. If this file is in binary format, edit the
&obs_sequence_nmlnamelist in input.nml so the output observation sequence file will be written in ASCII:
&obs_sequence_nml write_binary_obs_sequence = .false. /
Then rerun filter to regenerate an obs_seq.final file in ASCII. For an explanation of the contents of your obs_seq.final file, see Detailed structure of an obs_seq file.
If you are using many observations, run the obs_diag program appropriate for your model. The MATLAB observation space diagnostics will help to summarize your output and to explore what is going on.
If there are no changes in the model state after assimilation and a visual examination of obs_seq.final was not informative, convert the obs_seq.final file to netCDF with obs_seq_to_netcdf and either use the Matlab tools distributed with DART or something of your own. Actually, obs_seq_to_netcdf works on all observation sequence files, not just obs_seq.final files.