Contents

This chapter gives examples of the content for each dataset and format. They are presented as an HTML representation of xarray Dataset, so it is possible to directly consult the fields metadata by uncollapse the Data variables Section of the widget, and clicking on to display the attribute of a variable

Getting knowledgeable about the different Level-3 Sea Level Anomalies and their associated corrections can be tricky. The following table is a good start for differenciating the calibrated, edited and filtered fields. An X in the column indicates that the process is applied to the field.

SLA field (netcdf)	calibrated	edited	filtered
ssha_unedited	X
ssha_unfiltered	X	X
ssha_filtered	X	X	X

Netcdf

V3.0.0V2.0.1

BasicExpertTechnical

<xarray.Dataset> Size: 27MB
Dimensions:          (num_nadir: 1379, num_lines: 9860, num_pixels: 69)
Coordinates:
    latitude         (num_lines, num_pixels) float64 5MB ...
    longitude        (num_lines, num_pixels) float64 5MB ...
Dimensions without coordinates: num_nadir, num_lines, num_pixels
Data variables:
    i_num_line       (num_nadir) int16 3kB ...
    i_num_pixel      (num_nadir) int8 1kB ...
    mdt              (num_lines, num_pixels) float64 5MB ...
    ssha_filtered    (num_lines, num_pixels) float64 5MB ...
    ssha_unfiltered  (num_lines, num_pixels) float64 5MB ...
    time             (num_lines) datetime64[ns] 79kB ...
Attributes: (12/43)
    Conventions:                     CF-1.9
    Metadata_Conventions:            Unidata Dataset Discovery v1.0
    cdm_data_type:                   Swath
    comment:                         Sea Surface Height measured by Altimetry
    data_used:                       SWOT KaRIn L2_LR_SSH PGC0/PIC0/PIC2/PID0...
    doi:                             https://doi.org/10.24400/527896/A01-2023...
    ...                              ...
    geospatial_lon_max:              208.702964
    date_modified:                   2025-11-05T16:23:49Z
    history:                         2025-11-05T16:23:49Z: Created by DUACS K...
    date_created:                    2025-11-05T16:23:49Z
    date_issued:                     2025-11-05T16:23:49Z
    temporality:                     reproc

xarray.Dataset

• Dimensions:
  • num_nadir: 1379
  • num_lines: 9860
  • num_pixels: 69
• Coordinates: (2)
  • latitude
    (num_lines, num_pixels)
    float64
    ...

    comment :

    Latitude of measurement [-80,80]. Positive latitude is North latitude, negative latitude is South latitude.

    long_name :

    latitude (positive N, negative S)

    standard_name :

    latitude

    units :

    degrees_north

    [680340 values with dtype=float64]

  • longitude
    (num_lines, num_pixels)
    float64
    ...

    comment :

    Longitude of measurement. East longitude relative to Greenwich meridian.

    long_name :

    longitude (degrees East)

    standard_name :

    longitude

    units :

    degrees_east

    [680340 values with dtype=float64]

• Data variables: (6)
  • i_num_line
    (num_nadir)
    int16
    ...

    comment :

    alongtrack indice of the nearest karin pixel from the nadir data

    long_name :

    alongtrack indice of the nearest karin pixel from the nadir data

    units :

    count

    [1379 values with dtype=int16]

  • i_num_pixel
    (num_nadir)
    int8
    ...

    comment :

    acrosstrack indice of the nearest karin pixel from the nadir data

    long_name :

    acrosstrack indice of the nearest karin pixel from the nadir data

    units :

    count

    [1379 values with dtype=int8]

  • mdt
    (num_lines, num_pixels)
    float64
    ...

    comment :

    The mean dynamic topography is the sea surface height above geoid; it is used to compute the absolute dynamic topography adt=ssha+mdt. A -5cm bias is added to the MDT for consistency with DUACS nadir products. This bias is inherited from the change of reference period implemented in 2014 when DUACS products went from a 7-year reference [1993, 1997] to a 20-year reference [1993, 2012]

    long_name :

    HYBRID-CNES-CLS22-CMEMS2020 Mean Dynamic Topography

    source :

    HYBRID-CNES-CLS22-CMEMS2020 (https://doi.org/10.24400/527896/a01-2024.010)

    standard_name :

    sea_surface_height_above_geoid

    units :

    m

    [680340 values with dtype=float64]

  • ssha_filtered
    (num_lines, num_pixels)
    float64
    ...

    comment :

    Height of the sea surface anomaly with all corrections applied and with calibration, data selection and noise reduction (using Unet model) applied; see the product user manual for details.

    long_name :

    sea surface height anomaly calibrated, edited and filtered

    standard_name :

    sea_surface_height_above_mean_sea_level

    units :

    m

    disclaimer :

    Experimental algorithm. This parameter is the noise-mitigated counterpart of the ‘ssha_unfiltered’ variable. The noise was mitigated through a machine-learning algorithm (Treboutte et al., 2024). Caution is advised because the algorithm validation is still ongoing: some of the ocean features less than 50km in wavelength may also be affected by the de-noising algorithm

    [680340 values with dtype=float64]

  • ssha_unfiltered
    (num_lines, num_pixels)
    float64
    ...

    comment :

    Height of the sea surface anomaly with all corrections applied and with calibration and data selection applied; It is equivalent to the Sea Level Anomaly (SLA) distribued in the nadir DUACS products; see the product user manual for details.

    long_name :

    sea surface height anomaly calibrated and edited

    standard_name :

    sea_surface_height_above_mean_sea_level

    units :

    m

    [680340 values with dtype=float64]

  • time
    (num_lines)
    datetime64[ns]
    ...

    comment :

    Time of measurement in seconds in the UTC time scale since 1 Jan 2000 00:00:00 UTC. [tai_utc_difference] is the difference between TAI and UTC reference time (seconds) for the first measurement of the data set. If a leap second occurs within the data set, the attribute leap_second is set to the UTC time at which the leap second occurs.

    leap_second :

    0000-00-00T00:00:00Z

    long_name :

    time in UTC

    standard_name :

    time

    tai_utc_difference :

    37.0

    [9860 values with dtype=datetime64[ns]]

• Attributes: (43)

  Conventions :

  CF-1.9

  Metadata_Conventions :

  Unidata Dataset Discovery v1.0

  cdm_data_type :

  Swath

  comment :

  Sea Surface Height measured by Altimetry

  data_used :

  SWOT KaRIn L2_LR_SSH PGC0/PIC0/PIC2/PID0 (NASA/CNES). DOI associated: https://doi.org/10.24400/527896/a01-2023.015

  doi :

  https://doi.org/10.24400/527896/A01-2023.017

  geospatial_lat_units :

  degrees_north

  geospatial_lon_units :

  degrees_east

  geospatial_vertical_max :

  0

  geospatial_vertical_min :

  0

  geospatial_vertical_positive :

  down

  geospatial_vertical_resolution :

  point

  geospatial_vertical_units :

  m

  institution :

  CLS, CNES

  keywords :

  Oceans > Ocean Topography > Sea Surface Height

  keywords_vocabulary :

  NetCDF COARDS Climate and Forecast Standard Names

  platform :

  Swot

  processing_level :

  L3

  product_version :

  3.0

  project :

  SSALTO/DUACS

  reference_altimeter :

  S6

  references :

  Handbook: https://www.aviso.altimetry.fr/fileadmin/documents/data/tools/handbook_duacs_SWOT_L3.pdf

  source :

  Altimetry measurements

  ssalto_duacs_comment :

  The reference mission used for the altimeter inter-calibration processing is Sentinel-6A

  standard_name_vocabulary :

  NetCDF Climate and Forecast (CF) Metadata Convention Standard Name Table v37

  time_coverage_resolution :

  PT0.3S

  title :

  NRT SWOT KaRIn & nadir Global Ocean swath SSALTO/DUACS Sea Surface Height L3 product

  contact :

  aviso@altimetry.fr

  creator_email :

  aviso@altimetry.fr

  creator_name :

  DUACS - Data Unification and Altimeter Combination System

  creator_url :

  https://aviso.altimetry.fr

  license :

  https://www.aviso.altimetry.fr/fileadmin/documents/data/License_Aviso.pdf

  time_coverage_start :

  2023-07-01T00:23:16Z

  time_coverage_end :

  2023-07-01T01:14:22Z

  geospatial_lat_min :

  -78.272196

  geospatial_lat_max :

  78.272247

  geospatial_lon_min :

  41.756995

  geospatial_lon_max :

  208.702964

  date_modified :

  2025-11-05T16:23:49Z

  history :

  2025-11-05T16:23:49Z: Created by DUACS KaRIn prototype

  date_created :

  2025-11-05T16:23:49Z

  date_issued :

  2025-11-05T16:23:49Z

  temporality :

  reproc