Ocean Color Instrument

Other PACE Instruments: SPEXone | HARP2

PACE’s primary sensor, the Ocean Color Instrument (OCI), is a highly advanced optical spectrometer that measures properties of light over portions of the electromagnetic spectrum. It enables continuous measurement of light at finer wavelength resolution than previous NASA satellite sensors, extending key system ocean color data records for climate studies.

The color of the ocean is determined by the interaction of sunlight with substances or particles present in seawater such as chlorophyll, a green pigment found in most phytoplankton species. By monitoring global phytoplankton distribution and abundance with unprecedented detail, the OCI helps us to better understand the complex systems that drive ocean ecology. OCI data are also being used to better understand our atmosphere and land vegetation.

OCI allows us to identify phytoplankton types from space for the first time. Pink, green and blue colors indicate concentrations of specific groups of extremely tiny organisms known as “picophytoplankton.”
OCI allows us to identify phytoplankton types from space for the first time. Pink, green and blue colors indicate concentrations of specific groups of extremely tiny organisms known as “picophytoplankton.”
OCI allows us to identify phytoplankton types from space for the first time. Pink, green and blue colors indicate concentrations of specific groups of extremely tiny organisms known as “picophytoplankton.”
Each day, OCI provides 5-10X more data points than the largest dataset of picophytoplankton, allowing us to better understand, monitor and predict the key role they play in our ocean
Each day, OCI provides 5-10X more data points than the largest dataset of picophytoplankton, allowing us to better understand, monitor and predict the key role they play in our ocean
Each day, OCI provides 5-10X more data points than the largest dataset of picophytoplankton, allowing us to better understand, monitor and predict the key role they play in our ocean
OCI's ground-breaking, high spatial resolution data products reveal more fine details of nitrogen dioxide (NO₂) sources such as vehicle emissions and power plants
OCI's ground-breaking, high spatial resolution data products reveal more fine details of nitrogen dioxide (NO₂) sources such as vehicle emissions and power plants
OCI's ground-breaking, high spatial resolution data products reveal more fine details of nitrogen dioxide (NO₂) sources such as vehicle emissions and power plants
OCI's hyperspectral-enabled pigment indices provide new information about vegetation type, health status, productivity and leaf area. Only PACE can provide this information globally, every 1-2 days.
OCI's hyperspectral-enabled pigment indices provide new information about vegetation type, health status, productivity and leaf area. Only PACE can provide this information globally, every 1-2 days.
OCI's hyperspectral-enabled pigment indices provide new information about vegetation type, health status, productivity and leaf area. Only PACE can provide this information globally, every 1-2 days.
OCI data are being used to classify key factors related to ecosystem productivity of land vegetation. These environmental factors are important for humans and animals living in the region.
OCI data are being used to classify key factors related to ecosystem productivity of land vegetation. These environmental factors are important for humans and animals living in the region.
OCI data are being used to classify key factors related to ecosystem productivity of land vegetation. These environmental factors are important for humans and animals living in the region.
OCI hyperspectral information and AI synergy have been used to develop advanced tools for Gulf Coast phytoplankton monitoring and harmful algal bloom detection
OCI hyperspectral information and AI synergy have been used to develop advanced tools for Gulf Coast phytoplankton monitoring and harmful algal bloom detection
OCI hyperspectral information and AI synergy have been used to develop advanced tools for Gulf Coast phytoplankton monitoring and harmful algal bloom detection
Thanks to OCI's unique hyperspectral, visible and ultraviolet data, a red tide bloom was detected off the California coast during PACE-PAX satellite validation efforts
Thanks to OCI's unique hyperspectral, visible and ultraviolet data, a red tide bloom was detected off the California coast during PACE-PAX satellite validation efforts
Thanks to OCI's unique hyperspectral, visible and ultraviolet data, a red tide bloom was detected off the California coast during PACE-PAX satellite validation efforts

«»

1 2 3 4 5 6 7

The OCI was built at Goddard Space Flight Center (GSFC). It consists of a cross-track rotating telescope, thermal radiators, along with half-angle mirror and solar calibration mechanisms. The OCI’s tilt helps avoid sun glint and its single science detector design inhibits image striping. Its signal-to-noise ratios rivals or exceeds previous ocean color instruments. A detailed overview of OCI instrument design and prelaunch calibration is provided in Meister et al. (2024).

The OCI features:

Cross-track, 360° continuous rotating telescope
Two slit grating hyperspectral spectrographs (ultraviolet to visible & visible to near-infrared, NIR)
Fiber-coupled multiband filter spectrograph (NIR-to shortwave-infrared)

Recent Publications

Zheng, L., Lee, Z., Wang, Y., Yu, X., Lai, W., and Shang, S. (2025). Evaluation of near-blue UV remote sensing reflectance over the global ocean from SNPP VIIRS, PACE OCI, and GCOM-C SGLI, Opt. Express, 33, 40465-40488, doi: 10.1364/OE.568441.

Estep, R., Knuble, J., Gliese, U., and Chemerys, L. (2025). The PACE Ocean Color Instrument (OCI): From Concept to Commissioning, 2025 IEEE Aerospace Conference, pp. 1-8, doi: 10.1109/AERO63441.2025.11068421.

Lee, S., Patt, F., Eplee, R., McIntire, J. and Meister, G. (2025). PACE OCI straylight and crosstalk evaluation using Moon, Proc. SPIE 13267, Earth Observing Missions and Sensors: Development, Implementation, and Characterization VI, 132670E, doi: 10.1117/12.3039149.

Gliese, U., Kubalak, D., Meister, G., Chemerys, L., Knuble, Estep, R. and Werdell, P.J. (2025). Hyperspectral design of the Ocean Color Instrument on the NASA PACE mission and its significance for science, Proc. SPIE 13667, Sensors, Systems, and Next-Generation Satellites XXIX, 136670B, doi: 10.1117/12.3072749.

Knuble, J., Meister, G., McAndrew, B., Barsi, J., Kitchen-McKinley, S., Eplee, R., Gliese, U., Lee, S., McIntire, J., Sushkov, A., Bousquet, R., McCorkel, J., Cook, B., and Werdell, P.J. (2025). Hyperspectral calibration of OCI and on-orbit results, Proc. SPIE 13667, Sensors, Systems, and Next-Generation Satellites XXIX, 136670C, doi: 10.1117/12.3074926.

OCI Heritage

The OCI design is based on a long heritage of NASA technology development and flight programs. The OCI's operational concept, cross-track rotating telescope / half-angle mirror, system timing, and data processing infrastructure have been successfully used on previous and existing flight missions such as the Coastal Zone Color Scanner or CZCS (1978 to 1986), Sea-Viewing Wide Field-of-View Sensor or SeaWiFS (1997 to 2010), Suomi National Polar-orbiting Partnership (Visible Infrared Imaging Radiometer Suite or VIIRS), Aqua and Terra (Moderate Resolution Imaging Spectroradiometer or MODIS instrument). In addition, the OCI's avionics (communications, positioning) uses a significantly smaller electronics system developed by the iMUSTANG effort. OCI's functionality — rotating telescope (mechanism and timing), charged couple device (CCD) detector, optics — benefits from previous technology development efforts such as Ocean Radiometer for Carbon Assessment (ORCA).

Click to see full visualization

OCI is a hyperspectral imaging radiometer whose continuous coverage extends from 315 nm in the ultraviolet (UV) to 895 nm in the near infrared spectrum at 2.5 nm resolution (with bandwidths of 5 nm). At selected wavelength ranges across the chlorophyll-a fluorescence and oxygen A and B bands, the spectral steps are 1.25 nm (with bandwidth remaining at 5 nm). The prelaunch characterization of OCI focused on wavelengths above 340 nm, therefore the radiometric quality of spectral bands from 315 nm to 340 nm will be evaluated on-orbit. OCI also includes 7 discrete bands from 940 nm to 2260 nm in the shortwave infrared (SWIR) spectrum. Like SeaWiFS, OCI will perform a tilt maneuver every orbit at approximately the sub-solar point to avoid Sun glint reflected off the ocean, looking ~20° north (fore) in the northern hemisphere and ~20° south (aft) in the southern hemisphere.

The OCI telescope scans from west to east at a rotation rate of 5.77 Hz, acquiring Earth view data at a 1.2 km × 1.2 km ground sample footprint at the center of the scan (higher at the scan edges) and a ground swath width of ~2700 km. The OCI fore optics design follows that of SeaWiFS, with a rotating telescope, a half angle mirror, and a depolarizer that is transmissive (rather than reflective as with CZCS and SeaWiFS). Dichroics – material which splits visible light into distinct beams – direct the light to three different detection units: 1) a blue spectrograph (315-605 nm) with wavelength separation via grating and light detection using a CCD; 2) a red spectrograph (600-895 nm) using the same approach; and 3) SWIR detection assembly with wavelength separation using dichroics and bandpass filters, and with light detection via semiconductor devices that convert light into an electrical current, known as "photodiodes." The photodiodes use indium gallium arsenide (InGaAs) and mercury cadmium telluride (HgCdTe) as detector materials. The SWIR detection assembly guides light to individual detection units via fiber optic cables.

There are 3 on-board solar diffusers on OCI: 2 bright diffusers for radiometric gain trending, and 1 dim diffuser for linearity trending. Additionally, the Solar Pulse Calibration Assembly (SPCA) is used to monitor on-orbit changes of hysteresis in the SWIR bands. OCI will measure the lunar irradiance twice a month (for long-term radiometric gain trending), and use Fraunhofer lines and atmospheric absorption lines for spectral trending of the blue and red spectrographs.