VIIRS Ocean (color and SST)¶

Suomi NPP, NOAA-20 and NOAA-21 VIIRS Level-3 Global Mapped/Binned Ocean Color (CHL, RRS, KD, PAR, POC, PIC, IOP; version R2022.0 / NOAA-21 2025.0) and Sea Surface Temperature (SST, NSST, SST3) from the NASA Ocean Biology Processing Group

Available

At a glance¶

Note on period: Suomi NPP starts on 2012-01-02 (data delivery to end on 2026-11-02), NOAA-20 on 2017-11-29 and NOAA-21 on 2022-11-10 (CMR collection start dates). Standard SST runs to 2026-08-29 for Suomi NPP; for NOAA-20, Direct Data Access shows only NRT SST after early January 2026 (checked 2026-10-13; NRT runs to 2026-10-11).

Overview¶

Global Level-3 ocean color and sea surface temperature from VIIRS on Suomi NPP (launched 2011), NOAA-20 (formerly JPSS-1) and NOAA-21 (formerly JPSS-2), produced by NASA OBPG as the multi-satellite continuation of the MODIS ocean color record. Using the same processing system as MODIS, OBPG produces chlorophyll-a (chlor_a), remote sensing reflectance at five wavelengths, the diffuse attenuation coefficient at 490 nm (Kd_490), daily photosynthetically available radiation (par), particulate organic and inorganic carbon (poc, pic) and GIOP inherent optical properties, plus daytime and nighttime SST and an 8.6/11/12 µm triple-window SST (sst_triple). Daily, 8-day, monthly and annual composites are provided on 4 km and 9 km latitude–longitude grids in standard and NRT versions. With Suomi NPP delivery ending on 2026-11-02, NOAA-21 and NOAA-20 become the main records.

What changes with the successor¶

VIIRS ocean color R2022.0 (Suomi NPP) → VIIRS ocean color R2022.0.1 and R2022.0.2 (Suomi NPP mini-reprocessings)¶

Mini-reprocessings that removed a temporal drift left in the R2022 calibration, bringing Suomi NPP closer to NOAA-21 VIIRS and Aqua MODIS. A minor calibration error in late-2020 data was fixed at the same time, and data since 2020-08-01 were reprocessed.

Sources: OBPG — VIIRS-SNPP R2022.0.1 · OBPG — VIIRS-SNPP R2022.0.2

Suomi NPP VIIRS Ocean → NOAA-21 and NOAA-20 VIIRS Ocean Planned¶

Transition: 2026-11

Once NOAA ends Suomi NPP delivery at 13:00 UTC on 2026-11-02, the Suomi NPP version gets no new data. NOAA-21 (primary) and NOAA-20 (secondary) carry the same VIIRS sensor with the same OBPG processing, but their processing versions, band centres and product sets differ slightly.

Sources: NOAA NESDIS — Cessation of S-NPP data to users on/after November 2, 2026 · NASA Earthdata — Suomi NPP Data Product Delivery to Cease (2026-08-07) · OBPG — VIIRS-NOAA20 R2022.0 (cross-sensor Rrs differences)

Available variables¶

Variable names and units are taken from OB.DAAC OPeNDAP file attributes, Direct Data Access file listings (2026-10-11 daily files) and CMR collection descriptions. Each file holds one variable (e.g. JPSS2_VIIRS.20260601.L3m.DAY.CHL.chlor_a.4km.nc), and file names start with SNPP_VIIRS (Suomi NPP), JPSS1_VIIRS (NOAA-20) or JPSS2_VIIRS (NOAA-21). The wavelength numbers in Rrs and IOP names differ between satellites, so do not hard-code them.

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

Ocean color L3 (CHL, RRS, KD, POC, PIC files)¶

Photosynthetically available radiation (PAR files)¶

Inherent optical properties (IOP files, GIOP model — NOAA-20/21 wavelengths)¶

Sea surface temperature L3 (SST, NSST, SST3 files — Suomi NPP 2016.2, NOAA-20 2024.0)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA Earthdata Search (OB.DAAC portal) — Web search and download, earthaccess (Python; short_name e.g. VIIRSJ2_L3m_CHL, VIIRSJ1_L3m_RRS, VIIRSN_L3m_SST)
  • Collections are named VIIRSN_ (Suomi NPP), VIIRSJ1_ (NOAA-20) or VIIRSJ2_ (NOAA-21) + L3m_{CHL,RRS,KD,PAR,POC,PIC,IOP}, with L3b for binned files and an NRT suffix for NRT. SST collections are VIIRSN_L3m and VIIRSJ1_L3m_SST (on 2026-10-13 the latter had no granules registered in CMR — use Direct Data Access). A free NASA Earthdata Login is required.
• OB.DAAC Direct Data Access (Level-3 Mapped / NOAA21-VIIRS) — HTTPS directories by year and day, e.g. JPSS2_VIIRS.20260601_20260630.L3m.MO.CHL.chlor_a.4km.nc
  • NOAA-20 is under Level-3%20Mapped/NOAA20-VIIRS/ and Suomi NPP under Level-3%20Mapped/SNPP-VIIRS/. Standard and NRT (.NRT.nc) files sit side by side in each date folder. Earthdata Login is required.
• OB.DAAC OPeNDAP (L3 SMI) — OPeNDAP (year/MMDD folders, e.g. L3SMI/2026/0601/) for reading just the region you need
  • NOAA-20 is under /opendap/VIIRSJ1/L3SMI/ and Suomi NPP under /opendap/VIIRSN/L3SMI/.
• OB.DAAC File Search — Build file lists by name pattern and date range (for wget or curl)

Example code¶

Downloads NOAA-21 monthly 4 km chlorophyll with earthaccess and looks at the seas around Korea. Run earthaccess.login() once with a NASA Earthdata account.

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

earthaccess.login()
results = earthaccess.search_data(
    short_name="VIIRSJ2_L3m_CHL",           # NOAA-20: VIIRSJ1_L3m_CHL, Suomi NPP: VIIRSN_L3m_CHL
    granule_name="*.MO.CHL.chlor_a.4km*",   # daily: *.DAY.*, 8-day: *.8D.*  (NRT: the *_NRT collections)
    temporal=("2025-01-01", "2025-12-31"),
)
paths = earthaccess.download(results, "./viirs_chl")

ds = xr.open_mfdataset(paths, combine="nested", concat_dim="time")
ds = ds.sortby("lat")                                    # L3m latitude runs north to south
kr = ds["chlor_a"].sel(lat=slice(30, 42), lon=slice(117, 132))
print(float(10 ** np.log10(kr).mean()))                 # log-space mean for chlorophyll

Practical tips¶

• Time series built from Suomi NPP stop on 2026-11-02. NESDIS names NOAA-21 as the primary and NOAA-20 as the secondary replacement, so compare over the overlap (NOAA-21 from 2022-11) before switching.
• Rrs wavelengths differ between satellites (671 nm on Suomi NPP vs 667 nm on NOAA-20/21, etc.). OBPG reports that NOAA-20 Rrs(667) differs from Suomi NPP Rrs(671) by about 20%, so do not mix red-band values across satellites.
• NOAA-21 ocean color is R2025.0 while Suomi NPP and NOAA-20 are R2022.0 (with mini-reprocessings). NOAA-21's R2025.0 is a calibration-only reprocessing that redid the vicarious calibration with HyperNAV in situ radiometry.
• The CMR description and ATBD warn that chlor_a is less certain in sediment-rich waters such as the Yellow Sea and East China Sea coasts. Compare with GOCI-II or in situ data around Korea.
• OB.DAAC does not produce NOAA-21 SST (per the 2026-10-13 Direct Data Access listings). For NOAA-21 SST, look for NOAA STAR's GHRSST products.
• Standard NOAA-20 SST daily files do not appear on Direct Data Access after early January 2026; only NRT is there. The VIIRSJ1_L3m_SST collection in CMR has no granules either, so earthaccess may not find them.
• On the L3 mapped grid the same bin value repeats over several pixels at high latitudes. Compute area means from L3 binned files or with latitude weighting.
• Daytime SST is affected by diurnal warming, so nighttime SST (NSST) is safer for climatologies and trends.

Notices and change history¶

References for your paper¶

Dataset citation¶

NOAA-21 VIIRS L3 mapped chlorophyll R2025.0 (OB.DAAC) — DOI 10.5067/NOAA-21/VIIRS/L3M/CHL/2025.0

@misc{obpg2025viirsj2chl,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {{NOAA}-21 {VIIRS} Level-3 Global Mapped Chlorophyll ({CHL}) Data, version 2025.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/NOAA-21/VIIRS/L3M/CHL/2025.0}
}

NOAA-20 VIIRS L3 mapped chlorophyll R2022.0 (OB.DAAC) — DOI 10.5067/NOAA-20/VIIRS/L3M/CHL/2022.0

@misc{obpg2025viirsj1chl,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {{NOAA}-20 {VIIRS} Level-3 Global Mapped Chlorophyll ({CHL}) Data, version 2022.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/NOAA-20/VIIRS/L3M/CHL/2022.0}
}

Suomi NPP VIIRS L3 mapped chlorophyll R2022.0 (OB.DAAC) — DOI 10.5067/SUOMI-NPP/VIIRS/L3M/CHL/2022.0

@misc{obpg2025viirsnchl,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {Suomi-{NPP} {VIIRS} Level-3 Global Mapped Chlorophyll ({CHL}) Data, version 2022.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/SUOMI-NPP/VIIRS/L3M/CHL/2022.0}
}

Reference papers¶

OCx chlorophyll coefficients (used in R2022) — DOI 10.1016/j.rse.2019.04.021

@article{oreilly2019chl,
  author  = {O'Reilly, John E. and Werdell, P. Jeremy},
  title   = {Chlorophyll algorithms for ocean color sensors - {OC4}, {OC5} \& {OC6}},
  journal = {Remote Sensing of Environment},
  volume  = {229},
  pages   = {32--47},
  year    = {2019},
  doi     = {10.1016/j.rse.2019.04.021}
}

CI algorithm for low chlorophyll — DOI 10.1029/2011JC007395

@article{hu2012ci,
  author  = {Hu, Chuanmin and Lee, Zhongping and Franz, Bryan},
  title   = {Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference},
  journal = {Journal of Geophysical Research: Oceans},
  volume  = {117},
  number  = {C1},
  year    = {2012},
  doi     = {10.1029/2011JC007395}
}

OBPG chlorophyll-a ATBD v1.1 (2023) — DOI 10.5067/JCQB8QALDOYD

Acknowledgements¶

NASA asks users to cite the dataset DOI for each product and platform (Suomi NPP, NOAA-20, NOAA-21) actually used. Also state the processing version (R2022.0 or 2025.0; SST 2016.2 or 2024.0) and whether the files were NRT.

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¶

• OB.DAAC — VIIRS-SNPP data overview
• OBPG — VIIRS-NOAA21 R2025.0
• OBPG — VIIRS-NOAA20 R2022.0
• OBPG — VIIRS-SNPP R2022.0
• OBPG — Product Status (current version by sensor)
• NASA GES DISC alerts (S-NPP cessation re-announcement, 2026-10-07)
• Earthdata Forum — Suomi NPP Data Product Delivery To Cease (LP DAAC and LAADS replies)
• OBPG chlorophyll-a ATBD (PDF)
• This site — MODIS Ocean (predecessor; MODIS → VIIRS comparison)
• This site — PACE OCI (hyperspectral ocean color)
• This site — ESA OC-CCI (multi-sensor ocean colour climate record)
• This site — GOCI-II (geostationary ocean color around Korea)
• This site — VIIRS LST (same S-NPP cessation notice)