Daily Global 5km Satellite Coral Bleaching Thermal Stress Monitoring Products
NOAA Coral Reef Watch (CRW) has been providing near-real-time 50 km (0.5 degree exactly) global satellite coral bleaching monitoring to the U.S. and international coral reef communities since 1997. Our current operational 50 km monitoring products, including Coral Bleaching HotSpots, Degree Heating Weeks (DHW), and Bleaching Alert Area, derived from NOAA's Polar-orbiting Operational Environmental satellites (POES) Advanced Very High Resolution Radiometer (AVHRR) nighttime sea surface temperature (SST) have been very successful in detecting and monitoring thermal stress typically associated with mass coral bleaching.
During most mass bleaching events, sea temperature anomalies usually occur in-phase or nearly in-phase over a broad area that includes both coral reefs and their adjacent open ocean waters. This allows CRW's 50 km products to work well in detecting mass bleaching caused by large-scale thermal stresses from offshore waters adjacent to coral reef areas. However, since coastal water temperatures over reefs often exceed those seen in adjacent offshore pixels and have greater temperature gradients during bleaching seasons, CRW's 50 km products may underestimate the thermal stress associated with a bleaching event or miss small-scale features found right over the reefs.
In addition to providing limited information regarding warming in coastal regions, especially over patchy coral reefs, CRW's current operational 50 km product suite is based on the NOAA/NESDIS heritage twice-weekly 50 km SST analyses developed in the 1970s. It uses a very limited subset of SST measurements from a single satellite sensor, an old-generation cloud screening algorithm, and primitive gap-filling technique.
Advances in coral reef management practices have driven the need for higher resolution monitoring at reef or near-reef scales. Higher spatial resolution products enable monitoring of bleaching thermal stress at relatively small scales specific to coral reefs and subject to localized effects (e.g., shallow water, tidal mixing, and coastal runoff). Higher resolution products allow CRW to more accurately predict mass coral bleaching events, as well as more accurately account for episodes of minor or no coral bleaching.
To address the growing demand for high-resolution coral bleaching thermal stress monitoring products, research and development of these products have been underway with support from NASA and NOAA/NESDIS. CRW is using NESDIS' new-generation near-real-time daily global 5 km SST analysis and reprocessed Pathfinder Version 5.2 AVHRR SST dataset to develop the higher resolution coral bleaching monitoring product suite.
CRW's experimental daily global 5 km (0.05 degree exactly) satellite coral bleaching thermal stress monitoring product suite, released in June 2012, is a new-generation version of the current operational twice-weekly 50 km (0.5 degree exactly) monitoring product suite based on the NOAA/NESDIS 5 km SST analysis that provides highest possible resolution currently feasible for global monitoring. The high resolution 5 km suite currently includes sea surface temperature (SST), SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks (DHW), and Bleaching Alert Area products, matching to the core operational 50 km satellite products. High-resolution (5 km) versions of CRW's other operational products, such as Virtual Stations and the automated bleaching e-mail alerts, will come soon after the final determination of representative satellite pixel locations for select reef sites in the global tropical oceans is made. The 5 km product suite provides two major improvements over the current operational 50 km product suite:
New-generation SST Analysis for Deriving the Product Suite: CRW's new-generation 5 km coral bleaching product suite is based on the operational global daily 5 km geostationary-polar-orbiting day-night blended SST analysis recently made available at NOAA's National Environmental Satellite, Data, and Information Service (NESDIS).
Improved Data Density and Spatial and Temporal Resolutions: NOAA/NESDIS' 5 km SST analysis is at a much higher spatial resolution, is updated daily, and uses an order of magnitude more satellite observations from multiple operational satellites operated by NOAA, the Japan Meteorological Agency (JMA), and the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Compared to CRW's current operational 50 km SST analysis, based on only a single sensor onboard a polar-orbiting satellite (currently NOAA-19), the inclusion of SST data from multiple geostationary satellites (e.g., NOAA's GOES-east and GOES-west, EUMETSAT's Meteosat Second Generation (MSG) satellite, and JMA's MTSAT), as well as multiple polar-orbiting satellites (e.g., NOAA-19 and EUMETSAT's MetOp-A) in the 5 km SST analysis increases the frequency of observations for a particular coral reef site from no more than one per day to over 20 per day. Sub-daily observations by each geostationary satellite for an observed location drastically reduces cloud-caused data gaps in daily SST analysis.
Improved SST Quality with New-Generation SST Algorithm: New algorithms for deriving SST analyses from raw satellite measured radiance data are used in producing the new-generation 5 km SST analysis, including a new cloud screening algorithm, SST retrieval algorithm, and gap filling algorithm. As a result, the 5 km SST analysis retains many more valid SST observations (that would otherwise have been discarded in the 50 km SST analysis for CRW's current operational products) and provides a gap-filled SST analysis with much higher quality.
Improved Climatology: CRW's SST Anomaly, Coral Bleaching HotSpots, DHW, and Bleaching Alert Area products are very sensitive to the quality and compatibility of the climatology (long-term average conditions) used in the analysis. A new climatology at 5 km resolution, matching NESDIS' 5 km SST analysis, was implemented for CRW's 5 km product suite. The new-generation 5 km climatology is derived based on the 1985-2006 data from the Version 5.2 Pathfinder 4 km Advanced Very High Resolution Radiometer (AVHRR) SSTs. Major steps in developing the climatology included (1) gap-filling of a high-quality subset of the original global daily Pathfinder SST data, (2) adjusting the statistical characteristics of the Pathfinder SST based on the difference between the gap-filled daily Pathfinder SST and the NESDIS 5 km operational SST analysis, and (3) detrending the 1985-2006 Pathfinder SST time series to the center of the pre-determined baseline time period for the operational 50 km product suite (1985-1993, excluding 1991-1992), to avoid the influence of long-term SST trends present in the data after 1993. The new 5 km climatology also addresses known errors in the operational 50 km climatology that cause overestimation of bleaching thermal stress in certain areas, such as the regions around the Gulf of Panama and Gulf of Oman.
Sample figures below compare the current operational twice-weekly 50 km (for the twice-weekly period of June 8-10, 2012) and new-generation daily 5 km (for June 11, 2012) SST, SST Anomaly, HotSpot, DHW, and Bleaching Alert Area products for the Pacific region. Note the finer features present in the 5 km product images, which are the result of the improvements listed above.
Users are referred to the methodology of CRW's operational twice-weekly 50 km product suite for the algorithms used to derive the SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks (DHW), and Bleaching Alert Area. The new-generation 5 km products presently use the same algorithms as the 50 km products.
This daily 5 km global coral bleaching thermal stress monitoring product suite, released experimentally in June 2012, significantly advances CRW's capability for near-real-time satellite coral bleaching thermal stress monitoring. The new 5 km products will comprise the core of CRW's new-generation Decision Support System (DDS) for coral reef management. With higher spatial and temporal resolution products, CRW can now provide service at or close to reef-scales. After further testing and evaluation of the 5 km product suite, CRW's decades-old operational 50 km product suite, which has provided pioneer service to global coral reef communities, will be retired.
Development of the new-generation 5 km product suite has been accomplished through a collaboration of CRW, the University of South Florida, NASA-Ames, the UNEP World Conservation Monitoring Centre, and the Cooperative Institute for Research in Environmental Science, with funding support from the NASA Biodiversity and Ecological Forecasting program and the NOAA Coral Reef Conservation Program. The 5 km product suite will undergo continuous improvements over the next few years to reduce bias caused by daytime solar heating in the sea surface skin layer; to apply physical retrieval algorithms to account for local atmospheric influence; to resolve remaining issues caused by cloud cover (perhaps through addition of microwave-SST data); and to apply more sophisticated and accurate algorithms for coral bleaching thermal stress monitoring.
CRW will continue to produce the current operational product suite until the 5 km product suite becomes operational. There will be some differences between the two product suites in certain areas, and user discretion is advised. The expectation is that the 5 km high-resolution product suite will be more accurate in general, due to the improved data quality, density, and spatial and temporal resolutions.
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