multi-sensor daily MERGED, SNPP + NOAA-20, global, ~4 km (Level 3):
Ocean Color Level 3 VIIRS multi-sensor, daily, global, merge is produced through NOAA Multi-Sensor Level 1 to Level 2 processing system (MSL12). Parameters from this product suite include chlorophyll-a concentration (pictured above for 15 January 2020) and diffuse attenuation coefficients (Kd(490) and Kd(PAR) (not shown).
Ocean Color satellite sensors measure visible light at specific wavelengths which leaves the surface of the ocean and arrives at the top of the atmosphere where the sensor is located. From these visible spectral measurements, along with simultaneous measurements in the near infrared (NIR) and the short wave infrared (SWIR) wavelengths, the color of the ocean, or normalized water leaving radiances (nLw), can be calculated. Then, the nLws are used to derive other ocean properties such as the concentration of chlorophyll-a (chlor-a or sometimes chl, which is the green pigment responsible for photosynthesis and therefore an indicator of the amount of phytoplankton biomass in the ocean water) and the coefficient of extinction for downwelling irradiance (Kd(PAR) and Kd(490) which are related to water clarity).
The ocean color datasets described here are from the Visible and Infrared Imaging Radiometer Suite (VIIRS) sensor aboard the Suomi-NPP satellite (SNPP) which was launched in November 2011 and also aboard the NOAA-20 satellite launched in November 2017. NOAA ocean color data are processed using NOAA Multi-Sensor Level 1 to Level 2 processing system (MSL12) developed by the NOAA/STAR Ocean Color Team [Wang et al., 2013].
An excerpt from the EOS article by Mikelsons et al., 2019 explains the approach to the Level-3, multi-sensor merged, global, daily data product served here by CoastWatch at ~4 km spatial resolution in NetCDF format. "SNPP and NOAA-20 operate along the same Sun-synchronous polar orbit that crosses the equator at about 13:30 local time—both satellites travel around Earth from pole to pole in such a way that they observe the same areas at about the same time of day, no matter the season. There is about a 50-minute delay between the paths of NOAA-20 and SNPP, so NOAA-20’s path runs between two adjacent SNPP orbital paths and vice versa. Thus, the overlap of the spatial coverages in the two VIIRS sensors automatically fills each instrument’s data gaps [Mikelsons and Wang, 2019]. In addition, ocean color data from the VIIRS SNPP and NOAA-20 have the same spatial and temporal resolution, and these data are processed using the same algorithm and software package (i.e., MSL12). Therefore, the statistics of their ocean color products are very similar, and the data can be merged into a global 9-kilometer resolution data set directly without adjustment [Liu and Wang, 2019]."
Visible and InfraRed Imaging Radiometer Suite (VIIRS)
aboard Suomi NPP and NOAA-20 satellite missions
Afternoon orbit; ~13:30 equator crossing; phased at 50 minutes
Chlorophyll-a concentration (OCI algorithm) and diffuse attenuation coefficients (Kd(490), Kd(PAR))
|Processing Level|| |
Level-3: multi-sensor merged
|Spatial Coverage|| |
|Temporal Coverage|| |
Daily, generally 3-day delay
|Temporal Repeat|| |
~daily with small gaps
|Data Provider|| |
Creator: NOAA STAR and NOAA CoastWatch
Release Place: College Park, MD, USA
NOAA, MSL12, VIIRS, near real-time, chlorophyll, diffuse attenuation coefficient, Level-3, SNPP, NOAA-20, merged
Liu, X. and M. Wang, "Filling the gaps in ocean maps", EOS, 100 (2019). doi:10.1029/2019EO136548♦
Hu, C., Z. Lee, B.A. Franz, (2012) "Chlorophyll a algorithms for oligotrophic oceans: A novel approach based on three-band reflectance difference" Journal of Geophysical Research, 117 (2012) (C01011,doi:01010.01029/02011JC007395♦)
Alvera-Azcarate, A., et al. (2005), Reconstruction of incomplete oceanographic data sets using empirical orthogonal functions: Application to the Adriatic Sea, Ocean Model., 9, 325–346, doi:10.1016/j.ocemod.2004.08.001♦.
Beckers, J., and M. Rixen (2003), EOF calculations and data filling from incomplete oceanographic data sets, J. Atmos. Oceanic Technol., 20, 1,839–1,856, doi:10.1175/1520-0426(2003)020<1839:ECADFF>2.0.CO;2♦.
Algorithm Theoretical Basis Document (ATBD)
Wang, M., X. Liu, L. Jiang and S. Son, "The VIIRS Ocean Color Products", Algorithm Theoretical Basis Document Version 1.0, 68 pp., June 2017.
For more MSL12 processing documentation, please go to documentation tab here.
(♦ - non-government website)