MODIS Ocean (color and SST)¶

Aqua and Terra MODIS Level-3 Global Mapped/Binned Ocean Color (CHL, RRS, KD, PAR, POC, PIC, IOP, FLH; version R2022.0) and Sea Surface Temperature (SST, NSST, SST4; version R2019.0) from the NASA Ocean Biology Processing Group

Being replaced

At a glance¶

Note on period: Terra starts on 2000-02-24 and Aqua on 2002-07-04 (CMR collection start dates). On 2026-10-13 both Aqua and Terra NRT daily files were available through 2026-10-12. Standard files run to 2026-05-30 for Aqua ocean color (monthly 2026-04), 2025-11-30 for Terra ocean color, 2026-08-31 for Aqua SST and 2026-09-01 for Terra SST. OBPG has deferred the next MODIS Aqua ocean color reprocessing until after the mission ends.

Overview¶

Global Level-3 ocean color and sea surface temperature from MODIS on Terra (launched 1999) and Aqua (launched 2002), produced by NASA OBPG. It continues the SeaWiFS record and has been a workhorse satellite ocean dataset for more than 20 years. Ocean color products include chlorophyll-a (chlor_a), remote sensing reflectance at ten wavelengths (Rrs_412 to Rrs_678), the diffuse attenuation coefficient at 490 nm (Kd_490), daily photosynthetically available radiation (par), particulate organic and inorganic carbon (poc, pic), fluorescence line height (nflh) and GIOP inherent optical properties. SST comes as 11/12 µm daytime and nighttime SST and the night-only 3.95/4.05 µm SST4. Daily, 8-day, monthly and annual composites are provided on 4 km and 9 km latitude–longitude grids in standard and NRT versions. With Terra and Aqua drifting and nearing end of mission, NASA points users to VIIRS and PACE OCI.

What changes with the successor¶

MODIS ocean color R2018.0 → MODIS ocean color R2022.0¶

Transition: 2022-10

A multi-mission reprocessing covering SeaWiFS through VIIRS and OLCI. It updated instrument calibration and vicarious calibration (MOBY), ancillary meteorology and ozone, chlorophyll coefficients and the land/water mask, while keeping product formats and suites as in R2014.0 (the file naming did change). SST was not part of this reprocessing and stays at R2019.0.

Sources: OBPG — Reprocessing 2022.0 General Description · OBPG — MODIS-Aqua R2022.0 · OBPG — MODIS-Terra R2022.0

MODIS ocean color R2022.0 → MODIS ocean color R2022.0.1 to R2022.0.3 (mini-reprocessings)¶

Mini-reprocessings to fix calibration problems after the orbits began drifting. R2022.0.1 revised the temporal calibration of Aqua data since 2021-07-01; R2022.0.2 cross-calibrated Aqua to NOAA-20 VIIRS after the second yaw maneuver in August 2024 degraded quality, and cross-calibrated Terra to Aqua. On 2026-10-13 the latest Aqua standard files carry the attribute R2022.0.3.

Sources: OBPG — MODIS-Aqua R2022.0.1 · OBPG — MODIS-Aqua R2022.0.2 · OBPG — MODIS-Terra R2022.0.2

MODIS Ocean (Aqua and Terra; ocean color R2022.0, SST R2019.0) → VIIRS Ocean (Suomi NPP, NOAA-20, NOAA-21) Planned¶

NASA advises moving to comparable VIIRS products as Terra and Aqua end. OBPG produces VIIRS ocean color L3 with the same processing system (l2gen, OCI chlorophyll, GIOP) and reports that VIIRS (Suomi NPP and NOAA-20) and Aqua chlorophyll and Rrs agree within 10% over global deep water. VIIRS has fewer bands, though, so some products such as fluorescence and 4 µm SST have no VIIRS counterpart.

Sources: OBPG — VIIRS-NOAA20 R2022.0 (cross-sensor comparison) · OBPG — VIIRS-SNPP R2022.0 · Transition from MODIS to VIIRS (Earthdata, 2025-05-02)

Compare the two side by side

Available variables¶

Variable names and units are taken from OB.DAAC OPeNDAP file attributes, Direct Data Access file listings and CMR collection descriptions. Each file holds one variable (e.g. AQUA_MODIS.20260530.L3m.DAY.CHL.chlor_a.4km.nc), and Terra files (TERRA_MODIS…) use the same names. SST is stored as Int16 with scale_factor 0.005, while some ocean color L3m variables are stored as float (xarray handles both).

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 and fluorescence (PAR, FLH files)¶

Inherent optical properties (IOP files, GIOP model)¶

Sea surface temperature L3 (SST, NSST, SST4 files, R2019.0)¶

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. MODISA_L3m_CHL, MODISA_L3m_RRS, MODIST_L3m_CHL, MODISA_L3m_SST, MODISA_L3m_SST4)
  • Collections are named MODISA_L3m_{CHL,RRS,KD,PAR,POC,PIC,IOP,FLH} (Aqua) and MODIST_L3m_… (Terra), with L3b for binned files and an NRT suffix for NRT. SST collections are MODISA_L3m (R2019.0). A free NASA Earthdata Login is required.
• OB.DAAC Direct Data Access (Level-3 Mapped / Aqua-MODIS) — HTTPS directories by year and day, e.g. AQUA_MODIS.20260601_20260630.L3m.MO.SST4.sst4.4km.nc
  • Terra is under Level-3%20Mapped/Terra-MODIS/ and binned files under Level-3%20Binned/. 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/2026/0530/) for reading just the region you need
  • Terra is under /opendap/MODIST/L3SMI/.
• OB.DAAC File Search — Build file lists by name pattern and date range (for wget or curl)
• NASA PO.DAAC — MODIS L3 SST mirror (e.g. MODIS_AQUA_L3_SST_THERMAL_DAILY_4KM_DAYTIME_V2019.0) — Earthdata Search / earthaccess / OPeNDAP / Harmony / podaac-data-subscriber
  • There is a separate collection for each combination of Thermal IR (11 µm) or MID-IR (4 µm), day or night, daily/8-day/monthly/annual and 4 or 9 km (Terra collections start with MODIS_TERRA_L3_SST_…).

Example code¶

Downloads Aqua monthly 4 km chlorophyll with earthaccess and looks at the seas around Korea. Run earthaccess.login() once with a NASA Earthdata account. The granule_name pattern follows the OB.DAAC tutorial.

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

earthaccess.login()
results = earthaccess.search_data(
    short_name="MODISA_L3m_CHL",          # Terra: MODIST_L3m_CHL, SST: MODISA_L3m_SST / MODISA_L3m_NSST
    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, "./modis_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))
log_mean = np.log10(kr).mean("time")                    # chlorophyll is usually averaged in log space
print(float(10 ** log_mean.mean()))

Practical tips¶

• OBPG said in December 2025 that orbit changes and calibration problems may not be fully correctable, so post-2022 Aqua ocean color is of lower reliability for long-term change. Cross-check recent years with VIIRS or PACE OCI.
• The CMR description and ATBD warn that chlor_a is less certain in optically complex waters rich in sediment and dissolved organic matter, such as the Yellow Sea and East China Sea coasts (the open-ocean accuracy goal is ±35%). Validate against in situ data or compare with GOCI-II for Korean coastal work.
• Terra standard ocean color stops at 2025-11-30 and only NRT exists after that (checked 2026-10-13). If you use Terra ocean color from December 2025 on, say it is NRT or use Aqua or VIIRS instead.
• Daytime SST (11 µm) is affected by diurnal warming and glint, so nighttime SST (NSST) or SST4 is safer for climatologies and trends. SST4 is valid only at night.
• On the L3 mapped grid, several pixels share one bin at high latitudes, so values repeat (OBPG bin description). Compute area means and statistics from L3 binned files or with latitude weighting.
• With the R2022 release the file names changed to the AQUA_MODIS.YYYYMMDD.L3m.… pattern and OPeNDAP folders moved from three-digit day of year to four-digit MMDD. Old scripts that build names like A2020001… no longer work.
• OBPG reports R2022 Terra and Aqua chlorophyll and Rrs within 10% of each other, and R2022.0.2 re-cross-calibrated Terra to Aqua, but their morning and afternoon overpasses differ and both are drifting, so do not merge them into one series.
• Standard and NRT files are calibrated differently. The latest months exist only as NRT, so state the version in papers (the .NRT in the file name and the processing_version attribute).

Notices and change history¶

References for your paper¶

Dataset citation¶

Aqua MODIS L3 mapped chlorophyll R2022.0 (OB.DAAC) — DOI 10.5067/AQUA/MODIS/L3M/CHL/2022.0

@misc{obpg2025modisachl,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {Aqua {MODIS} Level-3 Global Mapped Chlorophyll ({CHL}) Data, version 2022.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/AQUA/MODIS/L3M/CHL/2022.0}
}

Aqua MODIS L3 mapped remote sensing reflectance R2022.0 (OB.DAAC) — DOI 10.5067/AQUA/MODIS/L3M/RRS/2022.0

@misc{obpg2025modisarrs,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {Aqua {MODIS} Level-3 Global Mapped Remote-Sensing Reflectance ({RRS}) Data, version 2022.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/AQUA/MODIS/L3M/RRS/2022.0}
}

Terra MODIS L3 mapped chlorophyll R2022.0 (OB.DAAC) — DOI 10.5067/TERRA/MODIS/L3M/CHL/2022.0

@misc{obpg2025modistchl,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {Terra {MODIS} Level-3 Global Mapped Chlorophyll ({CHL}) Data, version 2022.0},
  year      = {2025},
  publisher = {NASA Ocean Biology Distributed Active Archive Center},
  doi       = {10.5067/TERRA/MODIS/L3M/CHL/2022.0}
}

Aqua MODIS L3 daytime SST, daily 4 km, R2019.0 (PO.DAAC) — DOI 10.5067/MODSA-1D4D9

@misc{jpl2020modisasst,
  author    = {{NASA/JPL}},
  title     = {{MODIS} Aqua Level 3 {SST} Thermal {IR} Daily 4km Daytime V2019.0},
  year      = {2020},
  publisher = {NASA Physical Oceanography Distributed Active Archive Center},
  doi       = {10.5067/MODSA-1D4D9}
}

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}
}

A decade of MODIS SST — DOI 10.1016/j.rse.2015.04.023

@article{kilpatrick2015modissst,
  author  = {Kilpatrick, K. A. and Podest{\'a}, G. and Walsh, S. and Williams, E. and Halliwell, V. and Szczodrak, M. and Brown, O. B. and Minnett, P. J. and Evans, R.},
  title   = {A decade of sea surface temperature from {MODIS}},
  journal = {Remote Sensing of Environment},
  volume  = {165},
  pages   = {27--41},
  year    = {2015},
  doi     = {10.1016/j.rse.2015.04.023}
}

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

Acknowledgements¶

NASA asks users to cite the dataset DOI for each product (CHL, RRS, SST, …) and platform (Aqua, Terra) actually used. Also state the version (R2022.0, or R2019.0 for SST) 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¶

• OBPG — Reprocessing history
• OBPG — Product Status (current version by sensor)
• OBPG — File naming convention
• OBPG — Level-3 binning scheme
• OBPG chlorophyll-a ATBD (PDF)
• OBPG — SST quality flags
• Earthdata alert — Aqua MODIS Mini-reprocessing R2022.0.3
• Oceandata Help Hub (tutorials and notebooks)
• This site — VIIRS Ocean (successor)
• This site — PACE OCI (hyperspectral successor)
• This site — ESA OC-CCI (multi-sensor ocean colour climate record including MODIS)
• This site — GOCI-II (geostationary ocean color around Korea)
• This site — MODIS LST (orbit drift of the same satellites)