Validation of the remotely sensed nighttime sea surface temperature in the shallow waters at the Dongsha Atoll

Abstract

Fine scale temperature structures, which are commonly found in the top few meters of shallow water columns, may result in deviations of the remotely sensed night-time sea surface temperatures (SST) by the MODIS-Aqua sensor (SST sat ) from the bulk sea surface temperatures (SST bulk ) that they purport to represent. The discrepancies between SST sat and SST bulk recorded by temperature loggers at eight stations with bottom depths of 2 -20 m around the Dongsha Atoll (DSA) between June 2013 and May 2015 were examined. The SST sat had an average cool bias error of -0.43 ± 0.59°C. The bias error was larger in the warmer (> 26°C) waters which were presumably more strongly stratified. The root mean square error (RMSE) between SST sat and SST bulk , ±0.73°C, was 25% larger than that reported in the open northern South China Sea. An operational calibration algorithm was developed to increase the accuracy in the estimation of SST bulk from SST sat . In addition to removing the cool bias error, this algorithm also reduced the RMSE to virtually the same level as that found in the open northern South China Sea. With the application of the algorithm, in June 2015, the average SST in the lagoon of the DSA was raised by about 0.5°C to 31.1 ± 0.4°C, and the area of lagoon with SST bulk above 31°C, the median value of the physiological temperature threshold of reef organisms, was increased by 69% to about three quarters of the lagoon.

An enigmatic decoupling between heat stress and coral bleaching on the Great Barrier Reef

“…The key differences in heat stress histories among the satellite SST products demonstrate the need for validation with in situ temperature loggers (Pan et al, 2017; Fiedler et al, 2019). Using all available temperature loggers from the AIMS database (Australian Institute of Marine Science (AIMS), 2018), we show that OI-SSTv2 provides the most accurate representation, on average, of reef-water temperatures (Table 1) and heat stress (Table 2) during austral summer 2004 on the GBR.…”

Internal waves influence the thermal and nutrient environment on a shallow coral reef

“…Additionally, Level‐2 (11 μ m) swath sea surface temperature (SST) from the Moderate Resolution Imaging Spectroradiometer (MODIS) instrument aboard the Aqua and Terra satellites, with native spatial resolution of ∼ 1 × 1 km 2 , was used for the heat budget analysis. These data were obtained from the NASA Ocean Color Web (http://oceancolor.gsfc.nasa.gov/, accessed 02 July 2018) and have been observed to compare well to in situ observations at Dongsha Atoll (Pan et al ).…”

Patterns, Drivers, and Ecological Implications of Upwelling in Coral Reef Habitats of the Southern Red Sea

“…The median bias of OI‐SSTv2.1 was closer to zero than all other satellite products, although it was still −0.54°C. Our observed offsets are relatively large compared to satellite‐logger assessments in coral reef regions outside of the Red Sea (Aronson et al., 2002; Benthuysen et al., 2018; Castillo & Lima, 2010; Claar et al., 2019; DeCarlo & Harrison, 2019; Strong et al., 2002; Wellington et al., 2001), except for a few instances of larger biases in isolated embayments (DeCarlo et al., 2016), on shallow reef flats (Davis et al., 2011; DeCarlo et al., 2017; Pan et al., 2017), or on internal wave‐exposed reefs (DeCarlo et al., 2017; Wyatt et al., 2019). We found the largest negative biases for the shallowest loggers with high daily temperature ranges, but even loggers at 20 m depth were consistently warmer than satellite SST products (Figure 3).…”