Aviso+/CMEMS Observations
Overview
This short description of the SEALEVEL_GLO_SLA_L3_REP_OBSERVATIONS_008_018 product is repeated from the
INFORMATION tab from the Copernicus Marine Environment Monitoring
Service online catalogue (in April
2017).
For the Global Ocean- Mono altimeter satellite along-track sea surface heights computed with respect to a twenty-year mean. Previously distributed by Aviso+, no change in the scientific content. All the missions are homogenized with respect to a reference mission which is currently Jason-2. This product is computed with an optimal and centered computation time window (6 weeks before and after the date). Two kinds of datasets are proposed: filtered (nominal dataset) and unfiltered.
The main researcher for this project was Fred Castruccio.
The convert_aviso.f90 program is designed to read a netCDF file
containing the (Level 3) sea surface anomalies from any of the following platforms: “Jason-1”, “Envisat”, or
“Geosat Follow On”. One of those platforms must be listed in the netCDF file global attribute: platform
The data files have names like:
dt_global_j1_sla_vfec_20080101_20140106.nc,
dt_global_en_sla_vfec_20080101_20140106.nc, or
dt_global_g2_sla_vfec_20080101_20140106.nc
corresponding to the “Jason-1”, “Envisat”, and the “Geosat Follow On” platforms.
The DART observation TYPE corresponding to each of these platforms are J1_SEA_SURFACE_ANOMALY,
EN_SEA_SURFACE_ANOMALY, and GFO_SEA_SURFACE_ANOMALY, respectively and are defined in
obs_def_ocean_mod.f90.
Fred wrote a python script (shell_scripts/convert_aviso.py) to repeatedly call convert_aviso and decided it
was easiest to simply provide the input file name as a command line argument and always have the output file have the
name obs_seq.aviso. As such, there is no input namelist specifically for these parameters, but other DART modules
still require run-time crontrol specified by input.nml.
After creating a large number of output observation sequence files, it is usually necessary to consolidate the files
and subset them into files containing just the timeframe required for a single assimilation. NOTE: the
obs_sequence_tool is constructed for just this purpose.
The shell_scripts/makedaily.sh script attempts to consolidate all the SLA observations and those that may have
been (separately) converted from the World Ocean Database into 24-hour segments centered at midnight GMT. You will
have to modify the makedaily.sh script to suit your filesystem and naming convention. It is provided as a starting
point.
Reminder: (according to the data providers): In order to compute Absolute Dynamic Topography, the Mean Dynamic Topography (MDT) can be added. It is distributed by Aviso+ ( http://www.aviso.altimetry.fr/en/data/products/auxiliary-products/mdt.html ). Fred was using this product in assimilations with POP, so he chose a different source for MDT - consistent with POP’s behavior.
Data sources
The Copernicus Marine and Environment Monitoring Service (CMEMS) has taken over the processing and distribution of the
Ssalto/Duacs multimission altimeter products formerly administered by Aviso+. After a registration process, the
along-track sea level anomalies (SLA) may be downloaded from
http://marine.copernicus.eu/services-portfolio/access-to-products/
- search for the SEALEVEL_GLO_SLA_L3_REP_OBSERVATIONS_008_018 if it does not come up directly.
Programs
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does the actual conversion from netCDF to a DART observation sequence file, which may be ASCII or binary. |
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python script to convert a series of input files and datestamp the output files. |
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shell script to repeatedly call |
Namelist
There is no namelist for convert_aviso, but other namelists control aspects of the execution, namely
&obs_sequence_nml:write_binary_obs_sequence. see
MODULE obs_sequence_mod.
Modules used
assimilation_code/location/threed_sphere/location_mod.f90
assimilation_code/modules/assimilation/assim_model_mod.f90
assimilation_code/modules/io/dart_time_io_mod.f90
assimilation_code/modules/observations/obs_kind_mod.f90
assimilation_code/modules/observations/obs_sequence_mod.f90
assimilation_code/modules/utilities/ensemble_manager_mod.f90
assimilation_code/modules/utilities/null_mpi_utilities_mod.f90
assimilation_code/modules/utilities/random_seq_mod.f90
assimilation_code/modules/utilities/sort_mod.f90
assimilation_code/modules/utilities/time_manager_mod.f90
assimilation_code/modules/utilities/types_mod.f90
assimilation_code/modules/utilities/utilities_mod.f90
models/template/model_mod.f90
observations/forward_operators/obs_def_mod.f90
observations/obs_converters/AVISO/convert_aviso.f90
observations/obs_converters/utilities/obs_utilities_mod.f90