The S-NPP VIIRS ocean color products produced within NOAA STAR are undergoing a processing change (products produced in near real-time operationally within OSPO will remain unchanged). As a result, beginning February 20, 2018 the following changes are expected:

  • Improvements in data due to the update of the NOAA MSL12 processing (Level-2 / Level-3)
  • Changes in naming convention (Level-2)
  • Change in NetCDF structure (Level-2)
  • Change in location of data on CoastWatch servers (Level-2)
  • Change in retention of data to 1 year (Level-2 and Level-3 merges)

The CoastWatch VIIRS near-real-time ocean color Level-2 and Level-3 products will be produced from MSL12 v1.2x. The Algorithm Theoretical Basis Document (Wang, et al., 2017) details all processing and products for MSL12 v1.2x. In addition to processing updates, changes to products include:

  • New quality product: QA Score and I-band
  • Wavelength indication changed to nominal center-wavelength for VIIRS-SNPP normalized water-leaving radiances (nLw(λ))
  • NetCDF metadata changes for compatibility with CW
  • L2 flag changes (see ATBD for list)
  • High resolution 250 m landmask

Standard VIIRS SNPP ocean color data Level-2 products from MSL12 v1.2x (both near-real-time and science quality) include:

  • Normalized water-leaving (nLw(λ)) at 6 the VIIRS six visible bands (nominal center wavelengths)
  • M1 (410 nm)
  • M2 (443 nm)
  • M3 (486 nm)
  • M4 (551 nm)
  • M5 (671 nm)
  • I1 (638 nm)
  • Chlorophyll-a concentration
  • Diffuse attenuation coefficient at 490 nm (Kd(490)), and
  • Diffuse attenuation coefficient of photosynthetically available radiation (Kd(PAR))
  • QA Score (a quantitative assessment of VIIRS ocean color performance with respect to an empirical catalog of in situ spectra,see Wei et al., 2016.)

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.

Wei, J., Z. Lee, and S. Shang (2016), A system to measure the data quality of spectral remote-sensing reflectance of aquatic environments, J. Geophys. Res. Oceans, 121, 81898207, doi:10.1002/2016JC012126. (non-government website)

In addition to the data quality improvements, near real-time products will share a similar naming convention to the science quality data processed for S-NPP VIIRS:

Level-2 ocean color products are organized by Year and Day-of-the-Year. Filenames will appear as follows: V2018037003435_NPP_NRTNIR_L2.nc where:

  • V: Sensor VIIRS
  • 2017: Year of observation (YYYY)
  • 037: Day of year for the observation (DDD)
  • 003435: Hour, minutes, and seconds of the start of observation (hhmmss) in UTC
  • NPP: Spacecraft S-NPP
  • [NRT,SCI]NIR: Sensor data record source and environmental data record algorithm. Indicates Near Real-time or Science Quality output for distribution
  • L2: Processing level. L2 includes calibrated and geolocated geophysical products

Data files are in NetCDF4/CF but differ from past NOAA CoastWatch near real-time ocean color products in their use of hierarchical groups to store attributes, variables, variable naming, and dimensions. CoastWatch Utilities Software has been updated to work with these files. Additional metadata can be obtained using THREDDS services such as ISO or OPeNDAP to view the contents of a selected file.

These files will be available through the CoastWatch THREDDS server at the following URL:

https://www.star.nesdis.noaa.gov/thredds/catalog/swathNPPVIIRSL2WW00/catalog.html

Our website will be updated to reflect these new files. If you have questions, please submit them to coastwatch.info@noaa.gov. Thank you for your interest in NOAA CoastWatch.