5km Regional Virtual Stations
(Version 3.1, released July 31, 2019, experimental product)

NOTE: Alerts displayed on individual Regional Virtual Station (RVS) and Single-Pixel Virtual Station pages still use the heritage bleaching alert level system (which extended to Bleaching Alert Level 2). We are currently updating these systems to reflect the modified bleaching alert levels (now extending to Bleaching Alert Level 5). Until this update is complete, when a Station displays Alert Level 2, we suggest that users consult the Time Series data file that is linked directly below or to the right of the two-year time-series graph. This data file displays the underlying Coral Bleaching HotSpot and Degree Heating Week (DHW) values, from which a user can determine, on any day, what the new, corresponding Bleaching Alert Level should be, if higher than Alert Level 2.

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Daily 5km Regional Virtual Stations Product Description
(For a description of the Bleaching Heat Stress Gauges, see the Gauge and Time Series Product Description on each Gauge page.)

NOAA Coral Reef Watch (CRW) has developed a set of experimental daily 5km Regional Virtual Stations (219 total, with 5 duplicated Stations in overlapping regions). A Virtual Station is like having a temperature sensor in the water next to a coral reef, but data are completely based on satellite remote sensing measurements. The Regional Virtual Stations represent a change in the way we have looked at Virtual Station data in the past. They are now designed to take advantage of higher-resolution data while simultaneously providing comprehensive information on all coral reefs in a jurisdiction or predetermined sub-region. We realized early on that data from a single 5km pixel (satellite data grid point) provide much higher spatial detail but are less representative of a region's thermal conditions. Also, many coral reef ecosystem managers wanted to know what was happening across their entire jurisdiction. Rather than constructing Virtual Stations based on single 5km pixels as we did in our heritage twice-weekly 50km Virtual Stations, we created Regional Virtual Stations based on data from all of the 5km grids within each individual jurisdiction (e.g., Main Hawaiian Islands). An alert for a region is meant to inform users that they should look at the NOAA CRW map products for additional details/information.

The Regional Virtual Stations system now includes:

  • Regional Bleaching Heat Stress Gauges
  • Two-year time series graphics
  • Multi-year time series graphics
  • Virtual Stations map with data overlays in a Google Maps interface
  • Virtual Stations map with data overlays in a Google Earth file
  • Satellite Bleaching Alert Email System (free, automated, subscription-based; one alert per region; sent out up to two times per week for Stations that experienced heat stress level changes)

We use the data that fall within the boundary of each Regional Virtual Station to create a time series. Rather than provide the value of every 5km satellite pixel data point within a Station's boundary, we developed a new Regional Virtual Station algorithm. The algorithm is based on the daily 90th percentile Coral Bleaching HotSpot value among a Station's 5km pixels, and the other variables at the pixel where the 90th percentile HotSpot value locates. Daily Regional Virtual Station sea surface temperature (SST), SST Anomaly, and Coral Bleaching HotSpot values for a given day are the respective values from the satellite pixel where the 90th percentile Coral Bleaching HotSpot value occurs on that day. The Daily Regional Virtual Station Degree Heating Week (DHW) is then calculated (accumulated) from the Daily Regional Virtual Station HotSpots over a consecutive 84 days, following the DHW algorithm. The Daily Regional Virtual Station Bleaching Alert Area single-day value is derived from the Daily Regional Virtual Station Coral Bleaching HotSpot and DHW pair, and a rolling Bleaching Alert Area (7-day maximum) composite value is then produced.

We realize our approach has its costs. Some of the pros and cons we have identified in the switch to 5km Regional Virtual Stations are:

Pros of Regional Virtual Stations:

  • Utilization of higher resolution data
  • Quick guidance for an entire jurisdiction or sub-region
  • Better sense of regional impacts

Cons of Regional Virtual Stations:

  • Lower geographic specificity for individual islands and reefs
  • Less information on patterns within jurisdictions or sub-regions

However, as the alerts are meant to draw users to the maps, we think this will still provide the spatial pattern of the heat stress - now at 5km resolution.

NOAA CRW also expanded the geographic network of its daily 5km Regional Virtual Stations to include all coral reefs around the world, based on available references. These included the Millennium Coral Reef project maps, the International Union for Conservation of Nature's (IUCN) Coral Reefs of the World (Vol. 1, 2, and 3), the United Nations Environment Programme-World Conservation Monitoring Centre (UNEP-WCMC) World Atlas of Coral Reefs, several country scale atlas publications, and a few other resources. These references also were used to develop the outline (in black) for each 5km Regional Virtual Station. Each Station outline is based on a global 5km reef pixel mask developed by NOAA CRW, with the addition of a 20km buffer around each 5km reef mask. If we have missed a coral reef that you know of, please let us know the name and coordinates (latitude and longitude) of the missing reef.

***NOTE: NOAA CRW has begun development of single-pixel Virtual Stations for all U.S. and select international coral reef areas. Individual 5km x 5km data pixels are used to represent single reef sites. Currently, single-pixel Stations are established for Florida, Puerto Rico, and the US Virgin Islands.*** This major undertaking is the next phase of our Virtual Station implementation and will take a few years. Until this implementation phase is complete, should users wish to query individual pixels or groups of pixels, please use the netCDF files we have released for our 5km products. These are fully compatible with the NOAA CoastWatch Data Analysis Tool (CDAT) available from our website, ArcGIS, and many other tools.

We encourage you to look over these daily 5km Regional Virtual Stations and send us your comments at coralreefwatch@noaa.gov.