program obs_selection

Overview

This specialized tool selects a subset of input observations from an observation sequence file. For a more general purpose observation sequence file tool, see the program obs_sequence_tool. This tool takes a selected list of observation types, times, and locations, and extracts only the matching observations out of one or more obs_sequence files. The tool which creates the input selection file is usually program obs_seq_coverage. Alternatively, the selection file can be a full observation sequence file, in which case the types, times, and locations of those observations are used as the selection criteria.

This tool processes each observation sequence file listed in the input namelist filename_seq or filename_seq_list. If the observation type, time and location matches an entry in the selection file, it is copied through to the output. Otherwise it is ignored.

The actions of the obs_selection program are controlled by a Fortran namelist, read from a file named input.nml in the current directory. A detailed description of each namelist item is described in the namelist section of this document. The names used in this discussion refer to these namelist items.

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.

&obs_selection_nml
   filename_seq          = ''
   filename_seq_list     = ''
   filename_out          = 'obs_seq.processed'
   num_input_files       = 0
   selections_file       = 'obsdef_mask.txt'
   selections_is_obs_seq = .false.
   latlon_tolerance      = 0.000001
   match_vertical        = .false.
   surface_tolerance     = 0.0001
   pressure_tolerance    = 0.001
   height_tolerance      = 0.0001
   scaleheight_tolerance = 0.001
   level_tolerance       = 0.00001
   print_only            = .false.
   partial_write         = .false.
   print_timestamps      = .false.
   calendar              = 'Gregorian'
  /

Item

Type

Description

filename_seq

character(len=256), dimension(500)

The array of names of the observation sequence files to process, up to a max count of 500 files. (Specify only the actual number of input files. It is not necessary to specify 500 entries.)

filename_seq_list

character(len=256)

An alternative way to specify the list of input files. The name of a text file which contains, one per line, the names of the observation sequence files to process. You can only specify one of filename_seq OR filename_seq_list, not both.

num_input_files

integer

Optional. The number of observation sequence files to process. Maximum of 500. If 0, the length is set by the number of input files given. If non-zero, must match the given input file list length. (Can be used to verify the right number of input files were processed.)

filename_out

character(len=256)

The name of the resulting output observation sequence file. There is only a single output file from this tool. If the input specifies multiple obs_seq input files, the results are concatinated into a single output file.

selections_file

character(len=256)

The name of the input file containing the mask of observation definitions (the textfile output of program obs_seq_coverage). Alternatively, this can be the name of a full observation sequence file. In this case, the types, times, and locations are extracted from this file and then used in the same manner as a mask file from the coverage tool.

selections_is_obs_seq

logical

If .TRUE. the filename given for the “selections_file” is a full obs_sequence file and not a text file from the coverage tool.

latlon_tolerance

real(r8)

Specified in degrees. For observations to match in the horizontal the difference in degrees for each of latitude and longitude must be less than this threshold. If less than or equal to 0, the values must match exactly.

match_vertical

logical

If .TRUE. the locations of the observations in the input files have to match the selection list not only the horizontal but also in the vertical.

surface_tolerance

real(r8)

Specified in meters. If “match_vertical” is .FALSE. this value is ignored. If “match_vertical” is .TRUE., this applies to observations with a vertical type of VERTISSURFACE. For observations which match in the horizontal, the vertical surface elevation difference must be less than this to be considered the same.

pressure_tolerance

real(r8)

Specified in pascals. If “match_vertical” is .FALSE. this value is ignored. If “match_vertical” is .TRUE., this applies to observations with a vertical type of VERTISPRESSURE. For observations which match in the horizontal, the vertical difference must be less than this to be considered the same.

height_tolerance

real(r8)

Specified in meters. If “match_vertical” is .FALSE. this value is ignored. If “match_vertical” is .TRUE., this applies to observations with a vertical type of VERTISHEIGHT. For observations which match in the horizontal, the vertical difference must be less than this to be considered the same.

scaleheight_tolerance

real(r8)

Specified in unitless values. If “match_vertical” is .FALSE. this value is ignored. If “match_vertical” is .TRUE., this applies to observations with a vertical type of VERTISSCALEHEIGHT. For observations which match in the horizontal, the vertical difference must be less than this to be considered the same.

level_tolerance

real(r8)

Specified in fractional model levels. If “match_vertical” is .FALSE. this value is ignored. If “match_vertical” is .TRUE., this applies to observations with a vertical type of VERTISLEVEL. For observations which match in the horizontal, the vertical difference must be less than this to be considered the same. Note that some models only support integer level values, but others support fractional levels. The vertical value in an observation is a floating point/real value, so fractional levels are possible to specify for an observation.

print_only

logical

If .TRUE. do not create an output file, but print a summary of the number and types of each observation in each input file, and then the number of observations and types which would have been created in an output file.

partial_write

logical

Generally only used for debugging problems. After each input obs_seq file is processed, this flag, if .TRUE., causes the code to write out the partial results to the output file. The default is to process all input files (if more than a single file is specified) and write the output file only at the end of the processing.

print_timestamps

logical

Generally only used for debugging very slow execution runs. This flag, if .TRUE., causes the code to output timestamps (wall clock time) at various locations during the processing phases. It may help isolate where particularly slow execution times are occurring. For very large input files, or long lists of input files, it can also help to estimate what the eventual run time of the job will be.

calendar

character(len=32)

Set to the name of the calendar; only controls the printed output for the dates of the first and last observations in the file. Set this to “no_calendar” if the observations are not using any calendar.

Building

Most $DART/models/*/work directories contain files needed to build this tool along with the other executable programs. It is also possible to build this tool in the $DART/observations/utilities directory. In either case the preprocess program must be built and run first to define what set of observation types will be supported. See the PROGRAM preprocess for more details on how to define the list and run it. The &preprocess_nml namelist in the input.nml file must contain files with definitions for the combined set of all observation types which will be encountered over all input obs_seq files.

Usually the directories where executables are built will include a quickbuild.sh script which builds and runs preprocess and then builds the rest of the executables.

Modules used

types_mod
utilities_mod
time_manager_mod
obs_def_mod
obs_sequence_mod

Files

  • input.nml

  • The input files specified in the filename_seq namelist variable.

  • The output file specified in the filename_out namelist variable.

References

  • none