Evolution of the Daily Global 5km Satellite Coral Bleaching Heat Stress Product Suite
(Versions 1.0, 2.0, 3.0, and 3.1)


Version 1.0 Product Suite
(released July 5, 2012)

NOAA Coral Reef Watch's (CRW) Version 1.0 (or 1) experimental daily global 5km (0.05 degree spatial resolution exactly) satellite coral bleaching heat stress monitoring product suite was a next-generation version of the twice-weekly global 50km (0.5 degree spatial resolution exactly) monitoring product suite. It included sea surface temperature (SST), SST Anomaly, Coral Bleaching HotSpot, Degree Heating Week (DHW), and Bleaching Alert Area products, matching the core 50km satellite products. (5km versions of CRW's global 50km Virtual Stations and automated 50km Satellite Bleaching Alert Email System were not included in the Version 1 suite.)

The Version 1 5km products provided two major improvements over the 50km products (click here for a detailed description):

  1. New-generation SST Analysis for Deriving the 5km Product Suite

    1. Improved Data Density and Spatial and Temporal Resolutions.

    2. Improved SST Quality with New-Generation SST Algorithm.

  2. Improved Climatology

With the release of the Version 1 5km products, CRW significantly enhanced its capability for remotely monitoring in near real-time coral bleaching heat stress. Higher spatial and temporal resolution satellite coral bleaching heat stress products gave CRW the ability to provide service at or close to reef-scales.

Detailed Description of Version 1 5km Product Suite

CRW developed the Version 1 5km product suite in collaboration with the University of South Florida (USF), NASA-Ames, the UNEP World Conservation Monitoring Centre (WCMC), and the Cooperative Institute for Research in Environmental Science (CIRES), with funding support from the NASA Biodiversity and Ecological Forecasting (BEF) Program, the NOAA Coral Reef Conservation Program (CRCP), and the NOAA/National Environmental Satellite, Data, and Information Service (NESDIS) Ocean Remote Sensing (ORS) Program.



Version 2.0 Product Suite
(released May 5, 2014)

CRW's Version 2.0 (or 2) experimental daily global 5km (0.05 degree) satellite coral bleaching heat stress monitoring product suite was based on the NOAA/NESDIS operational daily global 5km geostationary-polar-orbiting (Geo-Polar) Blended Night-only SST Analysis. Products included SST, SST Anomaly, Coral Bleaching HotSpot, DHW, a 7-day maximum Bleaching Alert Area, and a 7-day SST Trend. On February 17, 2015, CRW added 212 5km Regional Virtual Stations/Bleaching Heat Stress Gauges. These were based on the Version 2 5km product suite and CRW's Coral Bleaching Heat Stress Outlook product and were much more comprehensive than the heritage 50km global Virtual Stations product. On October 24, 2016, CRW also released a free, automated 5km Bleaching Alert Email System based on the Version 2 5km products.

Improvements of the Version 2 5km products included the following:

  1. Next-generation SST Analysis

    1. Higher SST quality with a next-generation SST algorithm.

    2. Multiple satellites/sensors used for producing the blended SST analysis.

    3. Higher spatial and temporal resolutions and greater data density.

  2. New Climatology

    1. CRW produced 12 monthly mean climatologies and the Maximum Monthly Mean (MMM) climatology using night-only values for 1985-2012 from the 4km Advanced Very High Resolution Radiometer (AVHRR) Pathfinder Version 5.2 SST (PFV5.2) dataset, an official NOAA climate data record. Climatological average values were bias-adjusted to match the 5km SST data. They also were re-centered to the time-center of the 50km climatology (1985-1990 plus 1993), using the method described in Heron et al. (2015) and Liu et al. (2014), and were based on CRW's monitoring algorithm (also described in these articles). This maintained consistency with the heritage 50km products. (Note that, at the time, PFV5.2 was the highest quality historical daily global SST dataset available, with a spatial resolution (4km) close to CRW's desired 5km product resolution. However, we later learned the gappy daily PFV5.2 introduced warm bias in the resulting climatology, causing an underestimation of coral bleaching heat stress in many reef regions worldwide.)

    2. To preserve the interpretation of DHW values established by CRW's heritage 50km product suite, CRW faithfully recreated the 5km MMM climatology and HotSpot/DHW methodologies following the algorithm of the heritage 50km products. As a result, major differences between the Version 2 5km and 50km products existed in their different resolutions and in the methodologies used to create individual pixel SSTs. These differences were more obvious in some reef regions than others when detecting coral bleaching heat stress.

As with the Version 1 5km products, the Version 2 suite provided service at or near reef-scales, allowing direct monitoring of 95% of global coral reefs and significantly reducing data gaps caused by cloud cover.

Note that SST variability is often considerably higher at the much finer 5km spatial and daily temporal resolutions, when compared with the twice-weekly 50km SST. Due to resulting day-to-day fluctuations between stress levels in highly-variable locations, the Version 2 single-day 5km Bleaching Alert Area product did not consistently and adequately identify potentially harmful heat stress levels, especially with regard to accumulated heat stress impacts. Rather than requiring users to examine the Version 2 single-day 5km Bleaching Alert Area product over several days, CRW introduced a 7-day maximum Bleaching Alert Area composite product, which was updated daily. This 7-day composite product showed the maximum stress level that a pixel had experienced during the most recent seven (7) consecutive days. Data and images were dated on the last day of the 7-day period. Notably, it was compatible with CRW's twice-weekly 50km Bleaching Alert Area product, as the 50km Bleaching Alert Area is based on a half-week (3 or 4 days) composite of 50km SSTs (but with much less SST variability due to its much coarser spatial resolution).

With the Version 2 5km 7-day SST Trend product, updated daily, CRW provided information on the pace and direction of SST variation, and thus coral bleaching heat stress, if present, over the past seven days. Seven daily global SSTs were composited in the calculation. Pixels colored in green had insignificant trends, due either to small SST trends (within the range -0.2 to 0.2 °C) or trends that failed the statistical two-tailed Student's-t test for the 20% significance level with five degrees of freedom.

All other Version 2 products were single-day products, updated daily. Products were 1-2 days behind the current date, as data were processed in the early afternoon (U.S. Eastern Time) using data from the previous day. For example, data processed on a Wednesday afternoon included all observations made on Tuesday (independent of time zone) and carried Tuesday's date.

Read more about the Version 2 5km products in Liu et al. 2014.

CRW developed the Version 2 5km product suite in collaboration with USF, NASA-Ames, the UNEP WCMC, and CIRES, with funding support from the NASA BEF Program, the NOAA CRCP, and the NOAA/NESDIS ORS Program.



Version 3.0 Product Suite
(released May 4, 2017)

CRW's Version 3.0 (or 3) experimental daily global 5km (0.05 degree) satellite coral bleaching heat stress monitoring product suite introduced a significantly improved climatology. The climatology was derived from a combination of NOAA/NESDIS' 2002-2012 reprocessed daily global 5km Geo-Polar Blended Night-only SST Analysis and the 1985-2002 daily global 5km nighttime SST reanalysis, produced by the United Kingdom Met Office, on the Operational SST and Sea Ice Analysis (OSTIA) system.

Note that NESDIS switched its operational daily global 5km Geo-Polar Blended Night-only SST Analysis to use the near real-time OSTIA as the bias correction in September 2015. Hence, the 2002-2012 reprocessed 5km Geo-Polar Blended Night-only SST that became available in October 2016, extended with the 1985-2002 portion of the 5km OSTIA nighttime SST reanalysis, is the best historical 1985-2012 global nighttime SST dataset for deriving a climatology that is internally consistent and compatible with CRW's near real-time 5km products. Although NESDIS' reprocessed 5km Geo-Polar Blended SST Analysis is available to the end of 2016, to be consistent with CRW's Version 2 climatology, the Version 3 climatology was based on the same time period (1985-2012). It also was re-centered to the time-center of the 50km climatology (1985-1990 plus 1993) to maintain consistency with the Version 2 climatology and the heritage 50km products. Click here to learn more. CRW may incorporate more recent years in the climatology for future versions of its 5km products but potential impacts must be evaluated first.

CRW developed the Version 3 5km product suite with funding support from the NOAA CRCP.



Version 3.1 Product Suite
(initial release April 11, 2018 for 1985-2017 data; full release August 1, 2018 included 2018-present data)

CRW's current version of the daily global 5km (0.05 degree) satellite coral bleaching heat stress monitoring product suite, spanning January 1, 1985 to the present, is Version 3.1. It comprises the core of CRW's decision support system for coral reef management. Click here for more detailed information on the methodology behind the Version 3.1 5km products.

CRW developed the Version 3.1 5km product suite with funding support from the NOAA CRCP.



CRW's first-generation (heritage) coral bleaching heat stress monitoring products -- the aforementioned twice-weekly 50km (0.5-degree exactly) product suite -- served the U.S. and international coral reef communities for more than 20 years (1997-2020) as the only global early-warning system of coral reef ecosystem physical environmental changes. These products monitored and predicted all major mass coral bleaching events observed globally since 1997, while also providing other critical information to users, especially during times of high heat stress. While the 50km products no longer update in near real-time, as of their retirement on April 30, 2020, since they served as vital tools for our users for so many years, we still provide an archive of the 50km data and images on our website. As noted above, there are some differences between the 5km and 50km product suites in certain areas of the globe, and user discretion is advised. We have found the 5km product suite is more accurate due to our use of a next-generation, higher quality SST analysis; a next-generation SST algorithm based on multiple satellites/sensors; and an improved climatology.