WOD Observations

Overview

The World Ocean Database (WOD) is a collection of data from various sources, combined into a single format with uniform treatment. WOD is created by the National Centers for Environmental Information (NCEI) of the National Oceanic and Atmospheric Administration (NOAA).

An updated version of the dataset is released approximately every four years. It was first produced in 1994 and has been released in 1998, 2001, 2005, 2009, 2013 and 2018.

The WOD website has detailed information about the repository, observations, and datasets. The programs in this directory convert from the packed ASCII files found in the repository into DART observation sequence (obs_seq) file format.

There are two sets of available files: the raw observations and the observations binned onto standard levels.

Note

DAReS staff recommend using the datasets on standard levels for assimilation. The raw data can be very dense in the vertical and are not truly independent observations. The correlation between nearby observations leads to too much certainty in the updated values during the assimilation.

Data sources

Use already existing obs_seq files

NSF NCAR staff have prepared datasets already converted to DART’s obs_seq file format for the World Ocean Database 2013 (WOD13) and the World Ocean Database 2009 (WOD09).

Warning

The WOD data is in PSU, the dart observation converter wod_to_obs converts the observations to MSU.

PSU = g/kg

MSU = PSU/1000 = kg/kg

The WOD observation sequence files availiable from NSF NCAR’s RDA are in MSU.

WOD13

The already-converted WOD13 dataset comprises data from 2005-01-01 to 2016-12-31 and was created by Fred Castruccio. Thanks Fred! The files are stored in the following directory on GLADE:

/glade/p/cisl/dares/Observations/WOD13

The subdirectories are formatted in YYYYMM order and contain the following observation types:

FLOAT_SALINITY	FLOAT_TEMPERATURE
DRIFTER_SALINITY	DRIFTER_TEMPERATURE
GLIDER_SALINITY	GLIDER_TEMPERATURE
MOORING_SALINITY	MOORING_TEMPERATURE
BOTTLE_SALINITY	BOTTLE_TEMPERATURE
CTD_SALINITY	CTD_TEMPERATURE
XCTD_SALINITY	XCTD_TEMPERATURE
APB_SALINITY	APB_TEMPERATURE
XBT_TEMPERATURE

If you use WOD13, please cite Boyer et al. (2013). [1]

WOD09

The already-converted WOD09 dataset, which comprises data from 1960-01-01 to 2008-12-31, is stored in the following directory on GLADE:

/glade/p/cisl/dares/Observations/WOD09

If you use WOD09, please cite Johnson et al. (2009). [2]

Download WOD from NCEI

Data from each of the WOD releases can be downloaded interactively from the WOD website.

Download WOD from NSF NCAR

WOD09 can also be downloaded from NSF NCAR’s research data archive (RDA) dataset 285.0.

Programs

The data is distributed in a specialized packed ASCII format. In this directory is a program called wodFOR.f which is an example reader program to print out data values from the files. The program wod_to_obs converts these packed ASCII files into DART obs_sequence files.

As with most other DART directories, the work directory contains a quickbuild.sh script to build all necessary executables.

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.

&wod_to_obs_nml
   wod_input_file       =  'XBTS2005',
   wod_input_filelist   =  '',
   wod_out_file         =  'obs_seq.wod',
   avg_obs_per_file     =  500000,
   debug                =  .false.,
   timedebug            =  .false.,
   print_qc_summary     =  .true.,
   max_casts            =  -1,
   no_output_file       =  .false.,
   print_every_nth_cast =  -1,
   temperature_error    =  0.5,
   salinity_error       =  0.5,
 /
! temperature error is in degrees C, salinity error in g/kg.

Item	Type	Description
wod_input_file	character(len=128)	The input filename when converting a single file. Only one of the two namelist items that specify input files can have a valid value, so to use a single filename set the list name ‘wod_input_filelist’ to the empty string (’ ‘).
wod_input_filelist	character(len=128)	To convert one or more files in a single execution create a text file which contains each input filename, in ascii, one filename per line. Set this item to the name of that file, and set ‘wod_input_file’ to the empty string (’ ‘).
wod_out_file	character(len=128)	The output file to be created. Note that unlike earlier versions of some converters, this program will overwrite an existing output file instead of appending to it. The risk of replicated observations, which are difficult to detect since most of the contents are floating point numbers, outweighed the possible utility.
avg_obs_per_file	integer	The code needs an upper limit on the number of observations generated by this program. It can be larger than the actual number of observations converted. The total number of obs is computed by multiplying this number by the number of input files. If you get an error because there is no more room to add observations to the output file, increase this number. Do not make this an unreasonably huge number, however, since the code does preallocate space and will be slow if the number of obs becomes very large.
print_every_nth_cast	integer	If a value greater than 0, the program will print a message after processing every N casts. This allows the user to monitor the progress of the conversion.
print_qc_summary	logical	If .TRUE. the program will print out a summary of the number of casts which had a non-zero quality control values (current files appear to use values of 1-9).
debug	logical	If .TRUE. the program will print out debugging information.
timedebug	logical	If .TRUE. the program will print out specialized time-related debugging information.
max_casts	integer	If a value greater than 0 the program will only convert at most this number of casts from each input file. Generally only expected to be useful for debugging. A negative value will convert all data from the input file.
no_output_file	logical	If .TRUE. the converter will do all the work needed to convert the observations, count the number of each category of QC values, etc, but will not create the final obs_seq file. Can be useful if checking an input file for problems, or for getting QC statistics without waiting for a full output file to be constructed, which can be slow for large numbers of obs. Only expected to be useful for debugging.
temperature_error	real(r8)	The combined expected error of temperature observations from all sources, including instrument error, model bias, and representativeness error (e.g. larger or smaller grid box sizes affecting expected accuracy), in degrees Centigrade. Values in output file are error variance, which will be this value squared.
salinity_error	real(r8)	The combined expected error of salinity observations from all sources, including instrument error, model bias, and representativeness error (e.g. larger or smaller grid box sizes affecting expected accuracy) in g/kg (psu). Values in output file are error variance, and use units of msu (kg/kg), so the numbers will be this value / 1000.0, squared.

Modules used

types_mod
time_manager_mod
utilities_mod
location_mod
obs_sequence_mod
obs_def_mod
obs_def_ocean_mod
obs_kind_mod

Errors and known bugs

The code for setting observation error variances is using fixed values, and we are not certain if they are correct. Incoming QC values larger than 0 are suspect, but it is not clear if they really signal unusable values or whether there are some codes we should accept.

Future Plans

• This converter is currently being used on WOD09 data, but the standard files generally stop with early 2009 data. There are subsequent additional new obs files available from the download site.

• The fractional-time field, and sometimes the day-of-month field in a small percentage of the obs have bad values. The program currently discards these obs, but it may be possible to recover the original good day number and/or time of day. There is a subroutine at the end of the wod_to_obs.f90 file which contains all the reject/accept/correction information for the year, month, day, time fields. To accept or correct the times on more obs, edit this subroutine and make the necessary changes.

References

[1]

Boyer, T.P., J. I. Antonov, O. K. Baranova, C. Coleman, H. E. Garcia, A. Grodsky, D. R. Johnson, R. A. Locarnini, A. V. Mishonov, T.D. O’Brien, C.R. Paver, J.R. Reagan, D. Seidov, I. V. Smolyar, and M. M. Zweng, 2013: World Ocean Database 2013, NOAA Atlas NESDIS 72, S. Levitus, Ed., A. Mishonov, Technical Ed.; Silver Spring, MD, 209 pp., doi:10.7289/V5NZ85MT.

[2]

Johnson, D.R., T.P. Boyer, H.E. Garcia, R.A. Locarnini, O.K. Baranova, and M.M. Zweng, 2009. World Ocean Database 2009 Documentation. Edited by Sydney Levitus. NODC Internal Report 20, NOAA Printing Office, Silver Spring, MD, 175 pp., http://www.nodc.noaa.gov/OC5/WOD09/pr_wod09.html.