The U.S. National Oceanic and Atmospheric Administration’s (NOAA) Coral Reef Watch (CRW) operates a global Four-Month Coral Bleaching Outlook system for shallow-water coral reefs in collaboration with NOAA’s National Centers for Environmental Prediction (NCEP). The Outlooks are generated by applying the algorithm used in CRW’s operational satellite coral bleaching heat stress monitoring, with slight modifications, to the sea surface temperature (SST) predictions from NCEP’s operational Climate Forecast System Version 2 (CFSv2). Once a week, the probability of heat stress capable of causing mass coral bleaching is predicted for four months in advance. Each day, CFSv2 generates an ensemble of 16 forecasts, with nine runs out to 45 days, three runs out to three months, and four runs out to nine months. This results in 28-112 ensemble members produced each week. A composite for each predicted week is derived from daily predictions within each ensemble member. The probability of each of four heat stress ranges (Watch and higher, Warning and higher, Alert Level 1 and higher, and Alert Level 2) is determined from all the available ensemble members for the week to form the weekly probabilistic Outlook. The probabilistic Four-Month Outlook is the highest weekly probability predicted among all the weekly Outlooks during a four-month period for each of the stress ranges. An initial qualitative skill analysis of the Outlooks for 2011-2015, compared with CRW’s satellite-based coral bleaching heat stress products, indicated the Outlook has performed well with high hit rates and low miss rates for most coral reef areas. Regions identified with high false alarm rates will guide future improvements. This Outlook system, as the first and only freely available global coral bleaching prediction system, has been providing critical early warning to marine resource managers, scientists, and decision makers around the world to guide management, protection, and monitoring of coral reefs since 2012. This has been especially valuable during the third global coral bleaching event that started in mid-2014 and extended into mid-2017. The Outlook system is an integrated component of CRW’s global decision support system for coral bleaching. Recent management actions taken in light of this system are discussed.

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The National Oceanic and Atmospheric Administration's Coral Reef Watch program developed and operates several global satellite products to monitor bleaching-level heat stress. While these products have a proven ability to predict the onset of most mass coral bleaching events, they occasionally miss events; inaccurately predict the severity of some mass coral bleaching events; or report false alarms. These products are based solely on temperature and yet coral bleaching is known to result from both temperature and light stress. This study presents a novel methodology (still under development), which combines temperature and light into a single measure of stress to predict the onset and severity of mass coral bleaching. We describe here the biological basis of the Light Stress Damage (LSD) algorithm under development. Then by using empirical relationships derived in separate experiments conducted in mesocosm facilities in the Mexican Caribbean we parameterize the LSD algorithm and demonstrate that it is able to describe three past bleaching events from the Great Barrier Reef (GBR). For this limited example, the LSD algorithm was able to better predict differences in the severity of the three past GBR bleaching events, quantifying the contribution of light to reduce or exacerbate the impact of heat stress. The new Light Stress Damage algorithm we present here is potentially a significant step forward in the evolution of satellite-based bleaching products.

Satellite monitoring of thermal stress on coral reefs has become an essential component of reef management practice around the world. A recent development by the U.S. National Oceanic and Atmospheric Administration's Coral Reef Watch (NOAA CRW) program provides daily global monitoring at 5 km resolutionat or near the scale of most coral reefs. In this paper, we introduce two new monitoring products in the CRW Decision Support System for coral reef management: Regional Virtual Stations, a regional synthesis of thermal stress conditions, and Seven-day Sea Surface Temperature (SST) Trend, describing recent changes in temperature at each location. We describe how these products provided information in support of management activities prior to, during and after the 2014 thermal stress event in the Commonwealth of the Northern Mariana Islands (CNMI). Using in situ survey data from this event, we undertake the first quantitative comparison between 5 km satellite monitoring products and coral bleaching observations. Analysis of coral community characteristics, historical temperature conditions and thermal stress revealed a strong influence of coral biodiversity in the patterns of observed bleaching. This resulted in a model based on thermal stress and generic richness that explained 97% of the variance in observed bleaching. These findings illustrate the importance of using local benthic characteristics to interpret the level of impact from thermal stress exposure. In an era of continuing climate change, accurate monitoring of thermal stress and prediction of coral bleaching are essential for stakeholders to direct resources to the most effective management actions to conserve coral reefs.

Coral reefs are in decline worldwide and monitoring activities are important for assessing the impact of disturbance on reefs and tracking subsequent recovery or decline. Monitoring by field surveys provides accurate data but at highly localised scales and so is not cost-effective for reef scale monitoring at frequent time points. Remote sensing from satellites is an alternative and complementary approach. While remote sensing cannot provide the level of detail and accuracy at a single point than a field survey, the statistical power for inferring large scale patterns benefits in having complete areal coverage. This review considers the state of the art of coral reef remote sensing for the diverse range of objectives relevant for management, ranging from the composition of the reef: physical extent, benthic cover, bathymetry, rugosity; to environmental parameters: sea surface temperature, exposure, light, carbonate chemistry. In addition to updating previous reviews, here we also consider the capability to go beyond basic maps of habitats or environmental variables, to discuss concepts highly relevant to stakeholders, policy makers and public communication: such as biodiversity, environmental threat and ecosystem services. A clear conclusion of the review is that advances in both sensor technology and processing algorithms continue to drive forward remote sensing capability for coral reef mapping, particularly with respect to spatial resolution of maps, and synthesis across multiple data products. Both trends can be expected to continue.

The U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) program has developed a daily global 5-km product suite based on satellite observations to monitor thermal stress on coral reefs. These products fulfill requests from coral reef managers and researchers for higher resolution products by taking advantage of new satellites, sensors and algorithms. Improvements of the 5-km products over CRW’s heritage global 50-km products are derived from: (1) the higher resolution and greater data density of NOAA’s next-generation operational daily global 5-km geo-polar blended sea surface temperature (SST) analysis; and (2) implementation of a new SST climatology derived from the Pathfinder SST climate data record. The new products increase near-shore coverage and now allow direct monitoring of 95% of coral reefs and significantly reduce data gaps caused by cloud cover. The 5-km product suite includes SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks and Bleaching Alert Area, matching existing CRW products. When compared with the 50-km products and in situ bleaching observations for 2013–2014, the 5-km products identified known thermal stress events and matched bleaching observations. These near reef-scale products significantly advance the ability of coral reef researchers and managers to monitor coral thermal stress in near-real-time.

For the past decade remote sensing products provided by NOAA's Coral Reef Watch (CRW) have used satellite-derived sea surface temperature (SST) measurements to inform coral reef managers, scientists, and the public about thermal stress events throughout the tropics. These products, tailored primarily for managers, have become well-accepted as they provide a cost-effective means of conducting near-real-time monitoring of changes in SSTs that impact coral reef ecosystems over broad spatial scales. While satellite-based measurements of SSTs on and around coral reef ecosystems can describe part of what is occurring in reef environments, incorporating additional remotely-sensed environmental variables will provide a more complete assessment of changing environmental conditions and corals' responses. Non-SST-based satellite product development areas include ocean color to track land-based sources of pollution; synthetic aperture radar to detect oil spills and possibly coral spawning events; insolation to measure coral photosystem health; ocean surface vector winds to model biological connectivity via wind currents; and satellite altimetry to measure and track long-term trends in sea-level rise and short-term storm surge and wave damage. These product development areas hold great promise for improving the effectiveness of coral reef management in the United States' coastal marine jurisdictions and internationally . This presentation introduces a newly produced report describing NOAA's recent and forthcoming remote sensing products and correlates their applicability to U.S. jurisdictional coral reef management priorities and NOAA Coral Reef Conservation Program (Coral Program) Goals & Objectives. Targeting development of these high-priority remote sensing products will significantly contribute to addressing the Coral Program's identified three top threats to coral reef ecosystems.

Coral disease events are emerging as a significant threat to coral reefs in a changing climate. Over the past few years, several modelling studies have derived empirical relationships linking white syndrome (WS) disease outbreaks on Pacific coral reefs with unusual temperatures in summer and winter, and host density. These relationships have informed development of a series of predictive tools – maps of outbreak likelihood for Australia's Great Barrier Reef and the Hawaiian archipelago. These tools are key to strategic regional frameworks to respond to coral disease outbreaks. They inform both the targeted monitoring that can improve our understanding of coral disease dynamics and trials of experimental management actions that may mitigate disease impacts. Early research suggests that water quality could be another key driver of coral disease prevalence on reefs, as poor water quality has been correlated with increased susceptibility of corals to diseases and bleaching. Therefore we plan to test the inclusion of water quality measurements as a means of increasing the predictive capacity of these management-directed tools. By reducing the number of false positives and negatives, we aim to refine and improve the accuracy of tools developed to assess disease outbreak likelihood. Ongoing and future work also includes testing for links between environmental parameters and other coral diseases; expanding this work spatially, including a specific focus on coral disease dynamics in the Caribbean; and combining the learned relationships with climate predictions to examine potential future disease scenarios.

The NOAA Coral Reef Watch (CRW) program uses near-real-time satellite measurements of sea surface temperature (SST) to monitor thermal stress of the coral reefs. These data provide up-to-date measurements pinpointing areas that are currently at risk for thermally induced coral bleaching. All of CRW's products can be accessed through CRW's Web portal at http://coralreefwatch.noaa.gov. Ongoing examination of tropical SSTs reveal regionally diverse but changing SST patterns and trends. In 2005 and 2010, two record-breaking thermal stress events occurred throughout much of the eastern Caribbean (Wilkinson and Souter 2008. Status of Caribbean coral reefs after bleaching and hurricanes in 2005. Townsville, Australia: Global Coral Reef Monitoring Network, and Reef and Rainforest Research Centre, 152; Eakin et al. 2010. Caribbean corals in crisis: record thermal stress, bleaching, and mortality in 2005. PLoS One, 5, e13969). In 1998 and 2010, record-breaking bleaching occurred in all tropical oceans (Wilkinson 2000. Status of coral reefs of the world 2000, Townsville, Australia: Australian Institute of Marine Science, 375). With global satellite SSTs spanning more than two decades, we now have sufficient data to examine global- and basin-scale trends. The development and production of these CRW products takes place within National Oceanic and Atmospheric Administration's National Environmental Satellite, Data, and Information Service (NESDIS). This NESDIS team is comprised of scientists from the Marine Ecosystem & Climate Branch in the Satellite Oceanography & Climatology Division of the Center for Satellite Applications & Research and from personnel within NESDIS' Office of Satellite Products and Operations.

This paper proposes an experimental methodology toward describing and quantifying coral reef bleaching using very high spatial resolution optical satellite imagery. Sea surface temperature-based bleaching alerts issued by NOAA's Coral Reef Watch triggered image acquisition and served as an indication for high bleaching probability. Images of suspected coral reef bleaching events and reference images of the same reefs during previous unbleached conditions were coregistered and radiometrically normalized for change detection. An experimental methodology was developed to describe the severity and extent of the bleaching. The methodology hinges on the creation of the Coral Bleaching Index (CBI), constructed from change detected in the green, blue, and red wavelength bands. Results are provided in the form of colorized difference images showing areas of observed bleaching in gold, as well as CBI images, visualizing varying bleaching intensities. Comparison of the CBI with available field validation data yielded a correlation, however additional reference data would be needed for more detailed quality assessment. This technique is seen as a step toward the routine detection and long-term monitoring of coral reef bleaching from space and serves as a proposed tool for detecting bleaching in remote areas where observers cannot be deployed. (C) 2011 Society of Photo-Optical Instrumentation Engineers (SPIE). [DOI:10.1117/1.3595300]

Techniques for deriving estimated bathymetry from satellite data are well established; however, use of this product in complex terrains is limited. Accurate bathymetry is essential in the construction of hydrodynamic models and satellite-derived bathymetry is a strong candidate for use in coastal and shallow waters. A case study of Palau is presented which uses satellite-derived bathymetry as input to a hydrodynamic model. Palau underwent widespread coral bleaching during 1998, thought to be due to thermal stress, and existing satellite products observed anomalous increases in temperature. The numerical model is used to evaluate sea surface temperature patterns during such a bleaching event. Comparisons between the model and thermal indicators derived from satellite data are made, and the results used to suggest improvements for satellite monitoring of thermal stress events. INTRODUCTION Coral bleaching is the process by which a coral polyp, under environmental stress, expels its symbiotic zooxanthellae. The affected coral colony appears bleached. Severe bleaching can cause death of the coral colony. In September 1998, coral reefs across Palau were observed to be severely affected by bleaching (Wilkinson, 1998). A large proportion of the region (70-80%) underwent widespread bleaching and incurred high mortality rates; however, other regions appeared less affected. One of the major environmental stresses that causes bleaching of corals is heightened water temperature (Berkelmans & Willis, 1999). Increased water temperatures, and hence bleaching events, are linked to weather events, which in turn may or may not be linked to climate events (e.g., El Niño). Mass bleaching occurs when there is an extended summer period of calm, sunny conditions that coincide with weak currents. Over 98% of solar radiation energy is absorbed within the top 4 metres of the water column. This heat remains at the top of the water column unless there is a mechanism to mix it with the cooler water below. Vertical mixing occurs in regions of relatively strong horizontal currents, which can be associated with surface winds, large scale currents (e.g., North Equatorial Current) and tides. Therefore, extended periods of sustained cloudless summer days with low winds and low currents will likely induce bleaching events. Hydrodynamic models can be used to describe oceanographic currents and from these predict SST patterns for future, severe, mass coral bleaching events. Hydrodynamic modelling can also assist in the investigation of other issues that relate to the coral reef ecosystem; connectivity with biological events (e.g., coral/fish spawning) and anthropogenic interactions (e.g., sewage outfall, pollution accidents) can be monitored and/or predicted. One of the most important inputs to a high resolution hydrodynamic model is the bathymetry. The effect of incorrect bathymetry on computational fluid dynamic models can be significant and, as such, the accuracy of bathymetry can be crucial to the success of the numerical model (a detailed discussion is given in Gille et al., 2004). For remote geographic locations, where in situ data are limited, remote sensing techniques can provide such bathymetry. Lyzenga (1978) developed a theoretical basis for describing water depth by passive remote sensing upon which many others have expanded. Stumpf et al. (2003) applied this knowledge to investigate shallow regions with low bottom-albedo and variable bottom-types (e.g., sand, coral, algae, seagrass) using satellite data and developed a new algorithm for estimating water depths to 25 m and beyond. In this work, satellite-derived bathymetry data are used as input for a numerical model to study the surface currents near Palau. From the model output, regions of vertical mixing are identified and the subsequent reduction in surface temperature for these waters is calculated. Patterns in the modelled temperature distribution are compared with satellite-derived Sea Surface Temperature (SST) data. METHOD Historical bathymetric data for Palau were measured primarily by Japanese ships prior to the Second World War; however, little in-situ data has been published since 1969. Newhall & Rohmann (2003) derived estimated-depths for the region surrounding Palau from LandSat imagery to use in classifying benthic habitat. The method used followed that described in Stumpf et al. (2003), an algorithm which is accurate to an approximate depth of 25 metres. The estimated-depth values were determined at the grid resolution of the LandSat image; i.e., 28.5 m. As the desired resolution for the numerical model was approximately 250 m, the estimated depth values were averaged across 99 points to produce a 256.5 m resolution data set. To describe the bathymetry beyond the depth-scope of the LandSat data (~20 m), the two-arc-minute-resolution data of Smith & Sandwell (1997) were interpolated to a 256.5 m grid aligned with the LandSat-derived data. Some smoothing was undertaken to combine the datasets. In addition, corrections were made to the data near to land, known coral reefs and in regions of obvious discrepancy, determined by comparison of the data with nautical charts and depth soundings (C. McLean, unpublished data). The corrections were incorporated by removing incorrect values, inserting replacement values where available and krigeing the data to fill any remaining gridpoints. Initial output from the computational model gave further indications of short-comings in the bathymetry, deduced by the presence/absence of observed currents, and further corrections were made. The numerical study was undertaken using the Princeton Ocean Model (POM) as described by Blumberg & Mellor (1987). POM is a terrain-following (s-coordinate) model that has been used in a variety of oceanic and coastal applications (e.g., Chang & Isobe, 2003). The surface currents around Palau were modelled on a two-dimensional rectangular grid of 764328 points at 256.5 m resolution. Model land was defined by a 2.5 m isobath. Surface current velocities were defined at the open boundaries according to Heron et al. (in prep.) for the December to March season. The sea-surface elevations at these boundaries were defined as a function of tide gauge data collected in the Palau lagoon (Malakal Harbour). The boundary conditions were defined so as to reproduce the recorded elevations at the nearest model gridpoint as closely as possible. No wind stress was applied in the model, as per the conditions for mass coral bleaching events. The model was ramped to the stated boundary conditions for 0.5 days and then run for 29.5 days. Model validation was performed using data collected during Aug 2002 Jan 2003, described in Steinberg et al. (in prep.). The currents output from the computational model can be used to determine whether there is vertical mixing, due to bottom friction, throughout the water column. Simpson & Hunter (1974) examined the energy required for full vertical mixing and deduced a parameter to describe the position of fronts between mixed and stratified waters in the Irish Sea. This parameter (h/u, where h is the water depth and u is the surface velocity) was determined at each model timestep across the numerical domain. The value suggested by Simpson et al. (1982) for complete vertical mixing was employed here; i.e. log10[ h/u ] < 2.7 As mass bleaching events are related to temperature stress, an estimate of temperature variations, due to vertical mixing, was calculated. A vertical profile of the water temperature was determined by modelling the diurnal insolation of an initially uniform-temperature water column for a period of two weeks. The profile was then mixed from the surface to a specified depth to determine the reduction in temperature at the sea surface for a fully-mixed water column of that depth. This temperature-reduction was calculated for the range of water depths observed in the Palau lagoon, thus providing an indication of the temperature of the water column for any regions that are fully mixed. Advection of cooled waters is not presented here but will likely expand any areas cooled by the mixing mechanism. The temperature distribution across the Palau lagoon due to mixing was compared with satellite-derived Sea Surface Temperature (SST) data acquired during the widespread bleaching event in late 1998. SST values from the Pathfinder 4km SST database for the period 01 May 1998 28 Feb 1999 were examined to compare with the results from the model output. The daily data selected were for the night-time descending pass of the satellite so as to eliminate diurnal heating effects. For the region corresponding to the model domain, the quality tests imposed upon the 4km SST data discounted more than 80% of the values. The analysis of Kilpatrick et al. (2001) uses two tests to determine if an SST value is of sufficient quality. The first test compares the SST value with a value derived from the weekly SST data described by Reynolds & Smith (1994). Kilpatrick et al. (2001) indicate that this comparison may be biased in coastal zones and in regions with large SST gradients (spatial or temporal). The second discriminaton identifies pixels contaminated with cloud. Failure to meet the conditions of either of these tests causes the data to be considered as poor quality. Due to the coastal location and variable-temperature nature of this study, the "poor-quality" pixel data were also considered. RESULTS Surface currents derived in the Palau model during the advent of the highest high-tide of the 30-day modelled period are shown in Figure 1. The surface currents in the lagoon exceeded 1.4 m/s during the spring tides. The surface currents in the Palau region are tidally-dominated (Heron et al., in prep.). As such, the currents, and therefore the vertical mixing, are maximised during times of greatest tidal range. Figure 2 illustrates the minimum value of the Simpson-Hunter parameter across the domain, corres

An air-water interaction study was performed near Waukegan, Ill., to determine the effect of the cold waters of Lake Michigan on warm air flowing over them. Four days in late May and early June were chosen to analyze the physical nature of the interaction. Many times during spring and early summer, a cold temperate-latitude lake produces intense inversions that limit vertical turbulent energy transfers. Typically these inversions average 1 km in thickness. Coupled with such an inversion there often develops a shallow overwater mesoscale high pressure system, the lake anticyclone. The observations of the cold lake's effect on the atmosphere were taken on an east-west line through Waukegan for a distance 5 km inland (west) and ranging as far as 40 km over the lake (east). Hourly wind soundings to a height of approximately 1500 m were made and air and dew point temperature profiles were measured by wiresonde from the R/V (research vessel) Mysis. Pilot balloon observations at the shoreline and 5 km inland were analyzed together with balloon soundings over the water to depict the diurnal development of the lake's effect on the gradient wind near the shoreline. The low-level wind near the lake was always altered by the prevailing regional wind above the inversion. This lake influence was observed on every sunny day. The major orthogonal gradient winds and their interaction with the lake anticyclones were compared with results from Estoque's numerical model of “sea effect”. The most dramatic effect occurred when a warm offshore wind moved out over a developing inversion above the lake. As the air approached the shoreline it experienced a pronounced upward component of motion, followed by strong subsidence as it moved out over the lake. Parallel-to-shore wind data from Waukegan demonstrated increased vertical motions from the balancing forces of the northerly gradient wind and the lake high over the reverse case of the southerly gradient wind and the lake high. Results under onshore gradient winds, while least dramatic in vertical motion induced by this lake, demonstrated low-level cloud suppression for several tens of kilometers over land downwind.

Coral reefs are one of the world’s most biologically diverse and productive ecosystems. However, these valuable resources are highly threatened by human activities. Satellite remotely sensed observations enhance our understanding of coral reefs and some of the threats facing them by providing global spatial and time-series data on reef habitats and the environmental conditions influencing them in near-real time. This review highlights many of the ways in which satellites are currently used to monitor coral reefs and their threats, and provides a look toward future needs and capabilities.