VIIRS single-sensor S-NPP and NOAA-20 Anomaly products

Updated: March 8, 2021

Data are available through the following servers:
Service	Resource Locator
HTTPS	S-NPP NRT Anomaly Difference in Data Portal S-NPP NRT Anomaly Ratio (proportional difference) in Data Portal NOAA-20 NRT Anomaly Difference in Data Portal NOAA-20 NRT Anomaly Ratio (proportional difference) in Data Portal
ERDDAP
THREDDS	S-NPP: https://www.star.nesdis.noaa.gov/thredds/socd/coastwatch/catalog_viirs_npp_global_chloranom_daily.html NOAA-20: https://www.star.nesdis.noaa.gov/thredds/socd/coastwatch/catalog_viirs_n20_global_chloranom_daily.html

Near-real-time (NRT) global daily chlorophyll-a (Chl-a) anomaly products that can be used to detect and identify algae blooms from satellite ocean color measurements such as those from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership (SNPP) and NOAA-20. Specifically, the production of the two Chl-a anomaly products, one for the Chl-a anomaly in difference and another for the Chl-a anomaly ratio (actually, the proptional difference or relative difference; product is labelled "pdif" in the files) compared to the 61-day Chl-a median value from the previous time period (as a Chl-a reference), has been implemented in the daily global NRT satellite data processing. These two Chl-a anomaly products represent the global ocean and coastal/inland water Chl-a abnormal condition for a given location and can provide more complete characteristics for the daily phytoplankton (or algae) biomass status by comparing to the normal condition.

Key	Description
Platform/Sensor	S-NPP/VIIRS NOAA-20/VIIRS
Measurement/Products	chlorophyll-a anomaly difference chlorophyll-a aonomaly ratio (proportional difference)
DOI	https://doi.org/10.1016/j.jag.2020.102288
Short Name	NOAA VIIRS Chlorophyll Anomaly
Sample Filename	V2021008_D1_NRT_WW00_chloradiff.nc V2021007_D1_NRT_WW00_chlorapdif.nc
Dataset Type	NetCDF-4
Processing Level	Level-4
Spatial Coverage	Global
Temporal Coverage	Daily; computed by difference or ratio of a 61 day mean
Latency	48 hours
Resolution	2km (2.3163 km or 0.02°)
Projection	Geographic/WGS84 (EPSG:4326)
Swath Width	N/A
Sample Frequency	N/A
Temporal Repeat	daily
Orbital Period	N/A
Orbit	N/A
Data Provider	NOAA
Formats	NetCDF-4
Keywords	NOAA, JPSS, VIIRS, Chlorophyll, Anomaly, CoastWatch, NOAA National Environmental Satellite, Data, and Information Service, Center for Satellite Applications and Research, STAR, global, daily, 4km

Documentation:

Wang M., L. Jiang, K. Mikelsons, X. Liu, Satellite-derived global chlorophyll-a anomaly products, International Journal of Applied Earth Observation and Geoinformation, Volume 97, 2021, 102288, https://doi.org/10.1016/j.jag.2020.102288.