GOCI (COMS)¶

Geostationary Ocean Color Imager (GOCI) on the Communication, Ocean and Meteorological Satellite (COMS, Chollian-1) — hourly ocean colour around Korea

Discontinued

At a glance¶

Note on period: COMS was launched on 27 June 2010 (Korean time). NASA CMR gives the L2 collection period as 2010-06-26 to 2021-03-31 and the L1B collection as 2011-04-01 to 2021-03-31, but as checked on 2026-10-14 the OB.DAAC L2 directories start on 2011-04-08 and end on 2021-03-31. From 2011 to 2017 only 21–56 days a year are present, whereas 2018 (274 days), 2019 (359), 2020 (366) and January–March 2021 (89) are nearly complete.

Overview¶

GOCI on COMS (Chollian-1) was the world's first geostationary ocean colour sensor, imaging a 2,500 km square of sea centred on Korea every hour in daylight, 8 times a day, at 500 m. Unlike polar orbiters that pass once or twice a day, it captured the daily evolution of the same waters (tidal sediment transport, spreading algal blooms, sea fog), and it was widely used for the Yellow Sea and East China Sea. KIOST's Korea Ocean Satellite Center operated and processed it, and NASA OBPG distributes through OB.DAAC its reprocessing (R2014.0), cross-calibrated to VIIRS, as L1B and L2 data (remote-sensing reflectance, chlorophyll, diffuse attenuation and more).

What changes with the successor¶

GOCI (COMS) → GOCI-II (GEO-KOMPSAT-2B)¶

Transition: 2021-03

GOCI-II raised the resolution from 500 m to 250 m and the spectral bands from 8 to 12, increased acquisitions around Korea from 8 to 10 a day and added a Full Disk acquisition. GOCI ended its mission in March 2021, and both sensors observed together from 2020-10 to 2021-03.

Sources: Choi et al. (2021), One Year of GOCI-II Launch — Korean Journal of Remote Sensing · NOSC — GK-2B GOCI-II · NASA OBPG — GOCI Ocean Color Reprocessing 2014.0

Compare the two side by side

Available variables¶

Variables named in the CMR description of the OB.DAAC GOCI L2 OC collection (GOCI_L2_OC, R2014.0). Units follow the NASA OBPG standard product descriptions; files are netCDF-4 with values in the geophysical_data group. Rrs is stored as one variable per band (Rrs_).

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 ocean colour (OB.DAAC, per acquisition)¶

The full variable list is in the official documentation.

How to get the data¶

• NASA OB.DAAC — GOCI L2 directory (direct download) — HTTPS direct download (netCDF-4, year/date folders, e.g. 2021/31-Mar-2021/G2021090001641.L2_COMS_OC.nc)
  • Requires a (free) NASA Earthdata Login. L1B files are in the Level-1B/GOCI/ folder with the same layout.
• NASA Earthdata Search — COMS GOCI Level-2 Regional OC (GOCI_L2_OC, 2014.0) — Earthdata Search / earthaccess / CMR API / AWS cloud (s3://ob-cumulus-prod-public/, us-west-2)
  • L1B is the GOCI_L1 collection (C1240264612-OB_DAAC). Requires a NASA Earthdata Login.

Example code¶

Finds and downloads OB.DAAC GOCI L2 files with earthaccess and reads chlorophyll. Run earthaccess.login() once with your NASA Earthdata account. L2 files are grouped: latitude and longitude are in navigation_data and values in geophysical_data.

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

earthaccess.login()
results = earthaccess.search_data(
    short_name="GOCI_L2_OC",
    temporal=("2020-08-01", "2020-08-01"),
)
files = earthaccess.download(results, "./goci")   # 8 files per day

f = sorted(files)[0]
geo = xr.open_dataset(f, group="geophysical_data")
nav = xr.open_dataset(f, group="navigation_data")
chl = geo["chlor_a"]                     # mg m-3
print(chl.shape, float(chl.median()))
print(float(nav["latitude"].min()), float(nav["latitude"].max()))

Practical tips¶

• OB.DAAC has only 21–56 days a year for 2011–2017 (checked 2026-10-14). For a continuous record in that period, look into the data held by KIOST's Korea Ocean Satellite Center (KOSC).
• OBPG applied a vicarious calibration cross-calibrating GOCI to VIIRS, which moved the chlorophyll ratio against MODIS-Aqua from about 0.6 to about 0.9. The KOSC processing (GDPS) and the OBPG version can differ, so do not mix them.
• OBPG lists a spectral artefact around clouds (Fukushima et al., 2015) and radiometric discontinuities between some slots due to stray light (Kim et al., 2015) as known issues not corrected in R2014.0. Treat values near cloud edges and slot boundaries with care.
• OBPG notes that GOCI L2 processing was at an early stage and that quality should improve as understanding matures. Check chlorophyll in turbid Yellow Sea coastal waters against in situ data before use.
• GOCI-II differs in resolution (500 m → 250 m), bands, acquisition times and processing. Before splicing the two, compare values for the same waters during the overlap (2020-10 to 2021-03).
• Gaps are especially frequent in the cloudy winter months. A study of missing GOCI chlorophyll reported an average missing ratio of about 80% for hourly images, so multi-day composites may be needed (Ocean and Polar Research, 2022).

Notices and change history¶

References for your paper¶

Dataset citation¶

COMS GOCI Level-2 Regional Ocean Color (OC) Data, version 2014.0 (OB.DAAC) — DOI 10.5067/COMS/GOCI/L2/OC/2014.0

@misc{obpg_goci_l2oc_2014,
  author    = {{NASA Ocean Biology Processing Group}},
  title     = {{COMS} {GOCI} Level-2 Regional Ocean Color ({OC}) Data, version 2014.0},
  publisher = {NASA Ocean Biology Distributed Active Archive Center (OB.DAAC)},
  doi       = {10.5067/COMS/GOCI/L2/OC/2014.0}
}

Reference papers¶

Overview of GOCI and its data processing system (GDPS) — DOI 10.1007/s12601-012-0024-4

@article{ryu2012goci,
  author  = {Ryu, Joo-Hyung and Han, Hee-Jeong and Cho, Seongick and Park, Young-Je and Ahn, Yu-Hwan},
  title   = {Overview of geostationary ocean color imager ({GOCI}) and {GOCI} data processing system ({GDPS})},
  journal = {Ocean Science Journal},
  volume  = {47},
  number  = {3},
  pages   = {223--233},
  year    = {2012},
  doi     = {10.1007/s12601-012-0024-4}
}

Acknowledgements¶

If you used OB.DAAC data, cite the dataset DOI above with your access date. If you used KOSC-processed data, credit the KIOST Korea Ocean Satellite Center, and state in the text which processing (OBPG R2014.0 or KOSC GDPS) you used.

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¶

• NASA OBPG — GOCI reprocessing R2014.0
• OB.DAAC — GOCI L2 directory
• OB.DAAC — GOCI L1B directory
• NASA Level-2 ocean colour file format
• WMO OSCAR — GOCI
• This site — successor GOCI-II (GEO-KOMPSAT-2B)
• This site — GK-2A (GEO-KOMPSAT-2A meteorological satellite)