SWOT KaRIn (L2 LR SSH · L3)¶

Surface Water and Ocean Topography (SWOT) KaRIn Low Rate Sea Surface Height — PO.DAAC SWOT_L2_LR_SSH Version D (Basic, Expert, WindWave, Unsmoothed) and AVISO SWOT_L3_LR_SSH (wide-swath interferometric altimeter sea surface height and significant wave height)

Available

At a glance¶

Note on period: Launched on 2022-12-16. The KaRIn calibration phase on the 1-day repeat orbit began on 2023-03-30 and lasted until 2023-07-10; after the orbit transition, the 21-day science orbit started on 2023-07-21 (cycle 1). KaRIn data from 2023-07-21 to 07-26 are missing or suspect because the instrument was not yet configured for the science orbit. PO.DAAC Version D files start on 2023-03-27 (cycle 473). Release history — beta (pre-validated) in December 2023, Version C public release in March 2024, Version D in May 2025.

Overview¶

SWOT, launched by NASA and the French space agency CNES in December 2022, carries KaRIn, a Ka-band radar interferometer that maps a 120 km wide swath in one pass. It resolves two-dimensional sea surface structure below a few tens of kilometres (submesoscale eddies, fronts, internal tides) that conventional nadir altimeters miss. The low-rate (LR) L2 ocean product comes as Basic for general users, Expert with every correction term, WindWave with significant wave height and wind speed (all on a 2 km grid), and Unsmoothed on a 250 m grid; AVISO and DUACS produce a separate L3 with cross-calibration, noise filtering and geostrophic currents. KaRIn's high-rate (HR) mode also feeds river and lake products (PIXC, RiverSP, LakeSP, Raster), which this page does not cover.

What changes with the successor¶

SWOT KaRIn Version C → SWOT KaRIn Version D¶

Transition: 2025-05

A release that fixes known Version C issues through updated processing algorithms, calibration parameters and some geophysical models. Tide models, the mean sea surface and the MDT were replaced, a geoid error of order 10 cm was fixed, and the whole record since 2023-03 was reprocessed as Version D.

Sources: PO.DAAC — Version C to D transition complete (2025-05-21) · PO.DAAC — Version C to D transition announcement (2025-04-24) · SWOT Version D KaRIn Products Release Note (2025-12-19) · Major Changes to SWOT Products from Version C to D (2025-05-19)

Available variables¶

L2 variable names follow the PO.DAAC dataset pages (Basic and Expert variable lists) and NASA CMR variable definitions; L3 names follow the AVISO SWOT_L3_LR_SSH handbook (issue 3.1, v3.0). In L2, the variables with the _2 suffix (ssh_karin_2 and so on) use the currently recommended set of corrections, and the Expert file contains every Basic and WindWave variable.

instantaneous mean accumulated maximum minimum static — instantaneous: value at the time stamp · mean/accumulated/maximum/minimum: over the indicated interval · static: does not change with time

L2 sea surface height (Basic and Expert, 2 km)¶

L2 waves and wind (WindWave and Expert, 2 km)¶

L2 Unsmoothed (250 m)¶

AVISO L3 (Basic and Expert, 2 km)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA PO.DAAC — SWOT L2 KaRIn LR SSH Version D (SWOT_L2_LR_SSH_D) — Earthdata Search / earthaccess / podaac-data-subscriber (netCDF-4, one file per pass)
  • The sub-collections SWOT_L2_LR_SSH_BASIC_D, SWOT_L2_LR_SSH_EXPERT_D, SWOT_L2_LR_SSH_WINDWAVE_D and SWOT_L2_LR_SSH_UNSMOOTHED_D can be downloaded separately. A free NASA Earthdata login is required. Version C remains available in the SWOT_L2_LR_SSH_2.0 collections.
• AVISO+ — SWOT L3 LR SSH (SWOT_L3_LR_SSH) — FTP/SFTP at ftp-access.aviso.altimetry.fr (path /swot_products/l3_karin_nadir/l3_lr_ssh), THREDDS (tds-odatis.aviso.altimetry.fr)
  • AVISO+ account required. Basic, Expert and Technical v3.0 (2 km) and Unsmoothed v2.0.1 (250 m) are the latest versions.
• AVISO+ — SWOT ocean data access (L2, L3 and L3 Wind Wave) — FTP/SFTP — L2 LR SSH at /swot_products/l2_karin/l2_lr_ssh, L3 Wind Wave at /swot_products/l3_karin/l3_lr_wind_wave
  • CNES-side L2 distribution and the L3 wave product (SWOT_L3_LR_WIND_WAVE v3.0) are also available here. AVISO+ account required.

Example code¶

Downloads L2 Basic files from PO.DAAC with earthaccess. Run earthaccess.login() once with your NASA Earthdata account first.

# pip install earthaccess xarray netCDF4
import earthaccess
import xarray as xr

earthaccess.login()
results = earthaccess.search_data(
    short_name="SWOT_L2_LR_SSH_BASIC_D",       # Expert: SWOT_L2_LR_SSH_EXPERT_D
    temporal=("2025-06-01", "2025-06-21"),      # one science-orbit cycle (~21 days)
    bounding_box=(120, 30, 135, 42),            # around Korea (west, south, east, north)
)
files = earthaccess.download(results[:5], "./swot")

ds = xr.open_dataset(files[0])
ssha = ds["ssha_karin_2"] + ds["height_cor_xover"]   # crossover correction must be added by the user
ssha = ssha.where(ds["ssha_karin_2_qual"] == 0)      # keep values with no flag bits set
print(files[0], float(ssha.std()))

Practical tips¶

• height_cor_xover (the crossover correction) is not applied to the ssh_karin and ssha_karin variables. Add it yourself to remove long-wavelength errors such as cross-swath tilts and offsets, or use AVISO L3, which includes it.
• The Version D release note says the ice and rain flags are not fully reliable. ssha_karin_qual can be 0 even when rain_flag or dynamic_ice_flag is non-zero, so check both flags separately.
• Near-coast data are not well validated and can have large errors, and unflagged cross-track stripes (from Doppler centroid jumps) can appear near coasts. Take particular care along the intricate southern and western coasts of Korea.
• Ships and icebergs may not be flagged. Treat isolated spikes in busy waters such as the Korea Strait and the East China Sea with suspicion.
• Versions C and D differ in tide model (FES2014 to FES2022b), mean sea surface, MDT, sigma0 calibration (about 2.5 dB lower) and a geoid fix, so do not mix them. Download the Version D reprocessing (PGD0) for 2023-03 to 2025-05 as well.
• The release note reports residual errors in swh_karin on roughly 78-day timescales linked to the satellite beta angle. For long-term wave statistics, compare with nadir-altimeter records such as ESA Sea State CCI.
• The calibration phase (2023-03-30 to 07-10, 1-day repeat orbit) revisits narrow stripes every day, which suits studies of fast variability, but leaves everything outside them empty. Its sampling is entirely different from the 21-day science orbit, so do not pool the two periods into one statistic.
• Unsmoothed (250 m) runs to about 40 GB per day and 15 TB per year. Select only the cycles and passes you need; 2 km Basic or Expert is enough for most mesoscale work.
• When checked on 2026-10-13, a search of the PO.DAAC sub-collection SWOT_L2_LR_SSH_BASIC_D returned nothing for 2025-04-08 to 05-02, while the parent collection SWOT_L2_LR_SSH_D held Basic files (PGD0) for that period. If a period looks empty, search the parent collection too.
• The operational Copernicus Marine DUACS L4 maps have used SWOT nadir altimeter (SWOT-Nadir) measurements since November 2023, but not the KaRIn wide-swath data. An L4 that merges KaRIn has been available since November 2025 only as a demonstration dataset.

Notices and change history¶

References for your paper¶

Dataset citation¶

SWOT L2 KaRIn LR SSH Version D (PO.DAAC) — DOI 10.5067/SWOT-SSH-D

@misc{swot2025lrsshD,
  author    = {{Surface Water Ocean Topography (SWOT)}},
  title     = {{SWOT} Level 2 {KaRIn} Low Rate Sea Surface Height Data Product, Version {D}},
  year      = {2025},
  publisher = {NASA Physical Oceanography Distributed Active Archive Center},
  version   = {D},
  doi       = {10.5067/SWOT-SSH-D}
}

AVISO SWOT L3 KaRIn LR SSH Basic v3.0 — DOI 10.24400/527896/A01-2023.017

@misc{avisoduacs2024swotl3basic,
  author    = {{AVISO/DUACS}},
  title     = {{SWOT} Level-3 {KaRIn} Low Rate {SSH} Basic (v3.0)},
  year      = {2024},
  publisher = {CNES},
  doi       = {10.24400/527896/A01-2023.017}
}

AVISO SWOT L3 KaRIn LR SSH Expert v3.0 — DOI 10.24400/527896/A01-2023.018

@misc{avisoduacs2024swotl3expert,
  author    = {{AVISO/DUACS}},
  title     = {{SWOT} Level-3 {KaRIn} Low Rate {SSH} Expert (v3.0)},
  year      = {2024},
  publisher = {CNES},
  doi       = {10.24400/527896/A01-2023.018}
}

Reference papers¶

SWOT mission overview — DOI 10.1029/2023GL107652

@article{fu2024swot,
  author  = {Fu, Lee-Lueng and Pavelsky, Tamlin and Cretaux, Jean-Francois and Morrow, Rosemary and Farrar, J. Thomas and Vaze, Parag and Sengenes, Pierre and Vinogradova-Shiffer, Nadya and Sylvestre-Baron, Annick and Picot, Nicolas and Dibarboure, Gerald},
  title   = {The Surface Water and Ocean Topography Mission: A Breakthrough in Radar Remote Sensing of the Ocean and Land Surface Water},
  journal = {Geophysical Research Letters},
  volume  = {51},
  number  = {4},
  pages   = {e2023GL107652},
  year    = {2024},
  doi     = {10.1029/2023GL107652}
}

Acknowledgements¶

For L3, AVISO asks users to include "The SWOT L3_LR_SSH product, derived from the L2 SWOT KaRIn low rate ocean data products (NASA/JPL and CNES), is produced and made freely available by AVISO and DUACS teams as part of the DESMOS Science Team project" together with the product DOI. PO.DAAC asks for a data citation with authors, title, publisher and DOI in the reference list.

Information on the datasets used in this study was compiled with the help of the Korean Climate Data Navigator (KCDN) (Sim, 2026; https://doi.org/10.5281/zenodo.23300923).

Links¶

• PO.DAAC — SWOT mission page (documents and release notes)
• PO.DAAC — SWOT mission events (data gaps and manoeuvres)
• SWOT User Handbook (D-109532 Rev A, PDF)
• L2_LR_SSH Product Description Document (D-56407 Rev C, PDF)
• AVISO SWOT L3 handbook (issue 3.1, PDF)
• NASA JPL — SWOT mission overview
• This site — DUACS multi-mission altimetry L4 sea level
• This site — ESA Sea State CCI altimeter significant wave height