SVP

This utility converts Surface Velocity Program (SVP) drifter data (SST + surface currents) into a DART observation sequence (obs_seq) file.

Overview

SVP drifters measure near-surface ocean temperature and currents. For the InaCAWO project, BMKG/Baron provide ASCII (CSV-like) files with:

• Header line of field names

• One row per surface observation time

The converter reads:

• dat – timestamp

• lat – latitude (degrees)

• lon – longitude (degrees)

• sea_temperature – SST (Kelvin; converted to C)

• u / v – eastward / northward surface velocity (m/s)

Each valid row becomes up to three DART observations at the surface (VERTISSURFACE): DRIFTER_TEMPERATURE, DRIFTER_U_CURRENT_COMPONENT, DRIFTER_V_CURRENT_COMPONENT

Note

Time handling: The converter reads the dat column, parses the timestamp, and constructs a DART time_type in the Gregorian calendar. Expected format: YYYY-MM-DDThh:mm:ssZ

Build & run

Build like other DART converters, then run with an input.nml that includes svp_to_obs_nml:

./svp_to_obs

The program writes a single output sequence defined by file_out.

Namelist

This namelist is added to input.nml:

&svp_to_obs_nml
   file_in          = ''                         ! single ASCII file (or '')
   file_list        = ''                         ! text file of paths (or '')
   file_out         = 'obs_seq.svp',             ! output obs_seq file
   obs_error_sst    = 0.20_r8,                   ! SST error (C)
   obs_error_vel    = 0.10_r8,                   ! U/V error (m/s)
   avg_obs_per_file = 500000,                    ! pre-allocation limit
   debug            = .true.
/

Namelist item	Type	Default	Description
file_in	character(len=256)	'' (empty)	Path to a single SVP ASCII input file. Mutually exclusive with file_list.
file_list	character(len=256)	'' (empty)	Text file listing SVP ASCII files, one per line. Use instead of file_in for batches.
file_out	character(len=256)	'obs_seq.svp'	Name of the DART output observation sequence file. Overwritten if it exists.
obs_error_sst	real(r8)	0.20_r8	Observation error standard deviation for SST (in °C).
obs_error_vel	real(r8)	0.10_r8	Observation error standard deviation for U and V (in m/s).
avg_obs_per_file	integer	500000	Estimated number of valid observations per input file. Used only for pre-allocation. Number of files times this number must be larger than the total number of output observations.
debug	logical	.true.	If true, prints detailed information for each file and observation.

Output

A new observation sequence file named according to file_out. Each observation record includes location (lat, lon), time, and one of the three kinds (SST, U, or V), with error variance set to the square of obs_error_sst or obs_error_vel.

With debug = .true., the converter prints a summary of accepted/filtered observations for each input file.

Output file: obs_seq.svp exists. Replacing it ...

Input file: #1 T_HCSV00_C_BMKG_20251006000000_SVP_300534064005670.csv
     * lat: 0.4730, lon: 43.3212, SST: 26.1200, U: -0.0062, V: -0.0061, date: 2025 Oct 06 00:00:00

Input file: #2 T_HCSV00_C_BMKG_20251006010000_SVP_300534064005670.csv
     * lat: 0.4732, lon: 43.3212, SST: 26.0100, U: 0.0000, V: 0.0061, date: 2025 Oct 06 01:00:00

Input file: #3 T_HCSV00_C_BMKG_20251006020000_SVP_300534064005670.csv
     * lat: 0.4730, lon: 43.3214, SST: 26.0400, U: 0.0062, V: -0.0061, date: 2025 Oct 06 02:00:00

Input file: #4 T_HCSV00_C_BMKG_20251006030000_SVP_300534064005670.csv
     * lat: 0.4732, lon: 43.3214, SST: 26.1400, U: 0.0000, V: 0.0061, date: 2025 Oct 06 03:00:00

Input file: #5 T_HCSV00_C_BMKG_20251006040000_SVP_300534064005670.csv
     * lat: 0.4730, lon: 43.3214, SST: 26.3300, U: 0.0000, V: -0.0061, date: 2025 Oct 06 04:00:00

...

> Ready to write 72 observations:
  write_obs_seq  opening formatted observation sequence file "obs_seq.svp"
  write_obs_seq  closed observation sequence file "obs_seq.svp"
  svp_to_obs Finished successfully.

Further reading

For background on the observing platform supported by this converter:

• Global Drifter Program (GDP): “SVP drifter overview” – NOAA and Scripps-maintained description of the standard SVP and SVP-B drifters used globally.

• Lumpkin & Pazos (2007): “Measuring surface currents with Surface Velocity Program drifters” – Classic technical paper detailing instrument design, calibration, and data characteristics.

• Ocean Observers: “Drifting buoys (DBCP)” – General introduction to the international drifter network and its coordination under WMO/IOC.