VIIRS Chlorophyll-a

Chlorophyll from satellite is an estimation of the concentration of the phytoplankton pigment, chlorophyll-a, in the ocean surface and is used as a proxy for the amount of phytoplankton in the surface water. This measurement has many applications in marine ecology, from ecosystem modeling, to fisheries management, and monitoring of water quality, to name only a few applications.

NOAA CoastWatch produces ocean color products, including chlorophyll, from the Visible Infrared Imaging Radiometer Suite (VIIRS) on-board the polar-orbiting Suomi-NPP and NOAA-20 satellites (Wang et al., 2017).

Atmospheric correction uses the near-infrared (NIR) approach of Jiang and Wang (2014), which is an iterative NIR approach combining the NIR approachs of Bailey et al. (2010), MUMM (or Ruddick et al. (2000)), and Wang et al. (2012), referred to as the BMW atmospheric correction (see Jiang and Wang, 2014, for detailed references). While short-wave infrared (SWIR) approaches, like that used for NOAA's MODIS ocean color products, generate more accurate results for coastal waters than NIR approaches, the improved BMW approach of Jiang and Wang (2014) was found to offer the most accurate results compared to other NIR approaches.

Chlorophyll is generated using the blue-green reflectance ratio empirical approach of O'Reilly et al. (1998), adjusting the algorithm for the VIIRS spectral bands. Specifically, the algorithm is a 3-band algorithm (OC3V, Ocean Chlorophyll 3-band algorithm for VIIRS) whose inputs are the water-leaving radiance at wavelengths of 443, 486, and 551 nm.

Data validation compared Suomi-NPP VIIRS chlorophyll values to in situ measurements from the NASA SeaBASS database, including both open ocean and coastal data (Wang et al., 2017). Results showed that VIIRS-derived chlorophyll data compared quite well with the in situ measurements with mean and median ratios of 1.299 and 1.142 respectively and standard deviation of 0.624 for a matchup time difference within 3-hours. Thus, errors in VIIRS-derived chlorophyll data are all within 30%. However, it should be particularly noted that for coastal water (e.g. CDOM-dominated water), satellite chlorophyll still has significant issues. For example, Le et al. (2013) point out a high chlorophyll bias in coastal water.

CoastWatch East Coast Node currently distributes mapped gridded VIIRS chlorophyll from the Suomi-NPP satellite for the U.S. east coast. Sensor nominal spatial resolution is 750 m. Data is science-quality (i.e., post-processed for increased accuracy) from the beginning of the Suomi-NPP/VIIRS mission (Jan 1, 2012) up to the current year. Current year data is of near-realtime quality (i.e., reduced accuracy for quick turn-around data within 24 hours).

• Filename pre-fix:
• VRSRCW: Science-Quality, 2012 - year prior to current year
• VRSUCW: Near-Realtime, current year