that 1998 turned out to be the most significant year for mass coral bleaching in known
history.
The HotSpot product gained widespread recognition when, in early 1998,
Dr. Strong announced that the Great Barrier Reef (NE Australia) was bleaching before
either the Great Barrier Reef Marine Park Authority (GBRMPA) or the Australian
Institute of Marine Science (AIMS) knew about it. Out of the realization that this
product was potentially a very powerful satellite tool for coral reef management, a
formal agreement was signed between NOAA, AIMS and the GBRMPA to work
together on the development of new and improved satellite products for monitoring
coral reef health. As a result of this agreement, and a series of workshops, the HotSpot
product suite has grown and the understanding of the mechanisms and management
actions associated with coral bleaching have vastly improved.
This chapter will describe the operational HotSpot product suite and each of its
derivations.
2. Sea Surface Temperature Data
NOAA has been producing sea surface temperatures from satellite data since
1972. Monitoring SST from earth-orbiting infrared radiometers has had a wide impact
on oceanographic science. Currently, one of the principal sources of infrared data for
SST measurement is the Advanced Very High Resolution Radiometer (AVHRR),
which has been carried on NOAA’s Polar Orbiting Environmental Satellites (POES)
since 1978. It is a broad-band, four or five channel (depending on the model) scanner,
with sensors in the visible, near-infrared, and thermal infrared portions of the
electromagnetic spectrum (http://www.ngdc.noaa.gov/seg/globsys/avhrr.shtml). The
POES satellite system offers the advantage of daily global coverage, by making nearpolar orbits roughly 14.1 times every 24 hours. In situ SSTs, from buoys (drifting and
moored) are used operationally for calibration purposes to maintain accuracy, removing
any biases, and compiling statistics with time (McClain, 1985; Strong, 1991; and
Strong, et al., 2000).
The composite AVHRR-SST products have a resolution of 50km and are produced
twice-weekly in near real-time. On Tuesdays data from the previous three days
(Saturday through Monday) are used, and on Saturdays data from the previous four
days (Tuesday through Friday). Since the AVHRR is limited to a temporal resolution of six
hours (when combining data from both operational satellites), it is not possible to accurately
characterize the diurnal variation in SST caused by the cyclic heating of the sea surface as the
sun changes it’s angle during the day and its absence during the night. While some of
NOAA’s operational SST products use blended day and night retrievals, nighttime-only
observations are used in many SST products in an effort to minimize the effects
of diurnal variation. Nighttime SST products compare most favorably with
in-situ buoy SSTs at 1 meter depths (Montgomery and Strong, 1995). An example of the
global nighttime composite AVHRR-SST product can be seen in Figure 1.
The nighttime AVHRR-SST products were primarily developed for NOAA’s Coral Reef
Watch (CRW) Program for both monitoring and assessment of coral bleaching. CRW’s other
satellite monitoring and assessment products include SST anomalies, coral bleaching
HotSpots, Degree Heating Weeks (DHW) , Tropical Coral Bleaching Indices, and SST time
series, including on-line animations. The development and production of these
CRW products takes place within the NOAA National Environmental Satellite,
Data, and Information Service (NESDIS). This NESDIS team is comprised of
12
Skirving, Strong, Liu, Arzayus, Liu and Sapper
history.
The HotSpot product gained widespread recognition when, in early 1998,
Dr. Strong announced that the Great Barrier Reef (NE Australia) was bleaching before
either the Great Barrier Reef Marine Park Authority (GBRMPA) or the Australian
Institute of Marine Science (AIMS) knew about it. Out of the realization that this
product was potentially a very powerful satellite tool for coral reef management, a
formal agreement was signed between NOAA, AIMS and the GBRMPA to work
together on the development of new and improved satellite products for monitoring
coral reef health. As a result of this agreement, and a series of workshops, the HotSpot
product suite has grown and the understanding of the mechanisms and management
actions associated with coral bleaching have vastly improved.
This chapter will describe the operational HotSpot product suite and each of its
derivations.
2. Sea Surface Temperature Data
NOAA has been producing sea surface temperatures from satellite data since
1972. Monitoring SST from earth-orbiting infrared radiometers has had a wide impact
on oceanographic science. Currently, one of the principal sources of infrared data for
SST measurement is the Advanced Very High Resolution Radiometer (AVHRR),
which has been carried on NOAA’s Polar Orbiting Environmental Satellites (POES)
since 1978. It is a broad-band, four or five channel (depending on the model) scanner,
with sensors in the visible, near-infrared, and thermal infrared portions of the
electromagnetic spectrum (http://www.ngdc.noaa.gov/seg/globsys/avhrr.shtml). The
POES satellite system offers the advantage of daily global coverage, by making nearpolar orbits roughly 14.1 times every 24 hours. In situ SSTs, from buoys (drifting and
moored) are used operationally for calibration purposes to maintain accuracy, removing
any biases, and compiling statistics with time (McClain, 1985; Strong, 1991; and
Strong, et al., 2000).
The composite AVHRR-SST products have a resolution of 50km and are produced
twice-weekly in near real-time. On Tuesdays data from the previous three days
(Saturday through Monday) are used, and on Saturdays data from the previous four
days (Tuesday through Friday). Since the AVHRR is limited to a temporal resolution of six
hours (when combining data from both operational satellites), it is not possible to accurately
characterize the diurnal variation in SST caused by the cyclic heating of the sea surface as the
sun changes it’s angle during the day and its absence during the night. While some of
NOAA’s operational SST products use blended day and night retrievals, nighttime-only
observations are used in many SST products in an effort to minimize the effects
of diurnal variation. Nighttime SST products compare most favorably with
in-situ buoy SSTs at 1 meter depths (Montgomery and Strong, 1995). An example of the
global nighttime composite AVHRR-SST product can be seen in Figure 1.
The nighttime AVHRR-SST products were primarily developed for NOAA’s Coral Reef
Watch (CRW) Program for both monitoring and assessment of coral bleaching. CRW’s other
satellite monitoring and assessment products include SST anomalies, coral bleaching
HotSpots, Degree Heating Weeks (DHW) , Tropical Coral Bleaching Indices, and SST time
series, including on-line animations. The development and production of these
CRW products takes place within the NOAA National Environmental Satellite,
Data, and Information Service (NESDIS). This NESDIS team is comprised of
12
Skirving, Strong, Liu, Arzayus, Liu and Sapper