Evaluating Operational AVHRR Sea Surface Temperature Data at the Coastline Using Benthic Temperature Loggers

Abstract

Abstract:The nearshore coastal ocean is one of the most dynamic and biologically productive regions on our planet, supporting a wide range of ecosystem services. It is also one of the most vulnerable regions, increasingly exposed to anthropogenic pressure. In the context of climate change, monitoring changes in nearshore coastal waters requires systematic and sustained observations of key essential climate variables (ECV), one of which is sea surface temperature (SST). As temperature influences physical, chemical and biological processes within coastal systems, accurate monitoring is crucial for detecting change. SST is an ECV that can be measured systematically from satellites. Yet, owing to a lack of adequate in situ data, the accuracy and precision of satellite SST at the coastline are not well known. In a prior study, we attempted to address this by taking advantage of in situ SST measurements collected by a group of surfers. Here, we make use of a three year time-series (2014-2017) of in situ water temperature measurements collected using a temperature logger (recording every 30 min) deployed within a kelp forest (∼3 m below chart datum) at a subtidal rocky reef site near Plymouth, UK. We compared the temperature measurements with three other independent in situ SST datasets in the region, from two autonomous buoys located ∼7 km and ∼33 km from the coastline, and from a group of surfers at two beaches near the kelp site. The three datasets showed good agreement, with discrepancies consistent with the spatial separation of the sites. The in situ SST measurements collected from the kelp site and the two autonomous buoys were matched with operational Advanced Very High Resolution Radiometer (AVHRR) EO SST passes, all within 1 h of the in situ data. By extracting data from the closest satellite pixel to the three sites, we observed a significant reduction in the performance of AVHRR at retrieving SST at the coastline, with root mean square differences at the kelp site over twice that observed at the two offshore buoys. Comparing the in situ water temperature data with pixels surrounding the kelp site revealed the performance of the satellite data improves when moving two to three pixels offshore and that this improvement was better when using an SST algorithm that treats each pixel independently in the retrieval process. At the three sites, we related differences between satellite and in situ SST data with a suite of atmospheric variables, collected from a nearby atmospheric observatory, and a high temporal resolution land surface temperature (LST) dataset. We found that differences between satellite and in situ SST at the coastline (kelp site) were well correlated with LST and solar zenith angle; implying contamination of the pixel by land is the principal cause of these larger differences at the coastline, as opposed to issues with atmospheric correction. This contamination could be either from land directly within the pixel, potentially impacted by errors in geo-location, or possibly through thermal adjacenc...

Projected Marine Heatwaves in the 21st Century and the Potential for Ecological Impact

“…Their spatial scale extends over hundreds to thousands of kilometers, which are resolved by global ocean and climate models. A similar correspondence can be seen in coarse resolution satellite SST products where studies have used remotely sensed satellite, surfer-captured and kelp forest temperature logger data showing a good correspondence across the data sources (Brewin et al, 2018), as well as a general consistency between satellite and benthic/coastal temperature loggers (Stobart et al, 2016), and between satellite SSTs and in situ benthic temperatures (Smale and Wernberg, 2009). While there certainly would be many empirical and theoretical exceptions to this correspondence, these studies indicate that there is utility in these global products at inferring coastal temperatures and ecosystem impacts.…”

An Evaluation of Autonomous In Situ Temperature Loggers in a Coastal Region of the Eastern Mediterranean Sea for Use in the Validation of Near-Shore Satellite Sea Surface Temperature Measurements

“…Previous use of satellite SST to monitor the coastal ocean have been carried out in different regions worldwide, e.g., the English Channel [21], Canada [22], Caribbean Sea [23], Argentina [24], South Africa [18], China [7], Western Australia [25][26][27][28], the Mediterranean Sea [29,30], and the Gulf of California [31]. The aforementioned studies used several satellite SST products including Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua [22][23][24]26,30,31], MODIS Terra [18,22,23,26,30] and Advanced Very High Resolution Radiometer (AVHRR) [7,18,21,[25][26][27][28][29]31]. Some studies performed in the coastal zones are close to places of anthropogenic infrastructures such as aquaculture [22] or nuclear power stations [7].…”

“…This is a result both of the variable natural characteristics of the coastal zone [33] and of the poor network of near-shore coastal ocean instruments [18] when compared to the platforms in the open ocean [34]. Recently, Brewin et al [21] used AVHRR data of high temporal resolution in the coastal zone of Plymouth to evaluate operational SST data at the coastline. They matched their in situ data within 1 h of the satellite overpasses and they chose the closest 1 km pixel from their in situ logger's location.…”

Editorial for the Special Issue “Remote Sensing in Coastal Zone Monitoring and Management—How Can Remote Sensing Challenge the Broad Spectrum of Temporal and Spatial Scales in Coastal Zone Dynamic?”

“…In this special issue the capability of using multi-mission/airborne data and their combination with field measurements to study coastal, estuarine and marine environments has been addressed [1][2][3][4][5].…”

“…Hilton et al [4] quantify polychlorinated biphenyl concentrations in San Francisco Bay using multi-mission satellite imagery. And finally using benthic temperature loggers, Brewin et al [5] evaluate the operational retrieval of sea surface temperature at the coastline from Advanced Very High Resolution Radiometer satellite data.…”