PROGRAM MIDAS_to_obs

Overview

MIDAS netCDF file to DART observation converter

Alex Chartier (University of Bath, UK) contributed the code.

“MIDAS runs in Matlab. The raw observations come from GPS receivers as RINEX files, but we can’t use them directly just yet … Currently, the ‘slant’ (satellite-to-receiver path) observations are inverted by MIDAS to make vertical, column-integrated ‘observations’ of plasma density.”

Data sources

The original files have been converted to netCDF files that are then converted to DART observation sequence files. The netCDF files have a pretty simple format:

netcdf Test {
dimensions:
        latitude = 5 ;
        longitude = 6 ;
        height = 30 ;
        time = UNLIMITED ; // (1 currently)
variables:
        double latitude(latitude) ;
                latitude:units = "degrees_north" ;
                latitude:long_name = "latitude" ;
                latitude:standard_name = "latitude" ;
        double longitude(longitude) ;
                longitude:units = "degrees_east" ;
                longitude:long_name = "longitude" ;
                longitude:standard_name = "longitude" ;
        double height(height) ;
                height:units = "metres" ;
                height:long_name = "height" ;
                height:standard_name = "height" ;
        double time(time) ;
                time:units = "Days since 1601-01-01" ;
                time:long_name = "Time (UT)" ;
                time:standard_name = "Time" ;
        double Ne(height, latitude, longitude) ;
                Ne:grid_mapping = "standard" ;
                Ne:units = "1E11 e/m^3" ;
                Ne:long_name = "electron density" ;
                Ne:coordinates = "latitude longitude" ;
        double TEC(time, latitude, longitude) ;
                TEC:grid_mapping = "standard" ;
                TEC:units = "1E16 e/m^2" ;
                TEC:long_name = "total electron content" ;
                TEC:coordinates = "latitude longitude" ;
        double Variance(time, latitude, longitude) ;
                Variance:grid_mapping = "standard" ;
                Variance:units = "1E16 e/m^2" ;
                Variance:long_name = "Variance of total electron content" ;
                Variance:coordinates = "latitude longitude" ;
                Variance:standard_name = "TEC variance" ;
// global attributes:
                :Conventions = "CF-1.5" ;
}

Programs

The MIDAS_to_obs.f90 file is the source code for the main converter program.

To compile and test, go into the MIDAS/work subdirectory and run the quickbuild.sh script to build the converter and a couple of general purpose utilities. The program obs_sequence_tool manipulates (i.e. combines, subsets) DART observation files once they have been created. The default observations supported are those defined in observations/forward_operators/obs_def_upper_atm_mod.f90. If you need additional observation types, you will have to add the appropriate obs_def_XXX_mod.f90 file to the input.nml &preprocess_nml:input_files variable and run quickbuild.sh again. It rebuilds the table of supported observation types before compiling the source code.

Namelist

This namelist is read from the file input.nml. Namelists start with an ampersand ‘&’ and terminate with a slash ‘/’. Character strings that contain a ‘/’ must be enclosed in quotes to prevent them from prematurely terminating the namelist.

&MIDAS_to_obs_nml
   input_file    = 'infile.nc'
   obs_out_file  = 'obs_seq.out',
   verbose       = .false.
   /

Item	Type	Description
input_file	character(len=256)	Name of the input netCDF MIDAS file to read.
obs_out_file	character(len=256)	Name of the output observation sequence file that is created.
verbose	logical	Controls how much informational output is printed during a conversion. .true. the most amount of output. .false. the least amount of output.

Example

&MIDAS_to_obs_nml
   input_file    = '../data/Test.nc',
   obs_out_file  = 'obs_seq.out',
   verbose       = .TRUE.,

References