Gap-free SST analyses using satellite, and possibly in situ data, are the most widely used SST products for both operational and research applications. Currently more than thirty level 4 (L4) near real-time and reprocessed SST analyses are publicly available from organisations and operational agencies.


Compare the SST analyses and validation of the analyses, in order to provide information to producers to enable them to improve their analysis systems and to provide guidance to users in their particular applications.


COMPLETED Task 1: Inter-comparison of SST analyses for climate (Lead: Chunxue Yang, ISMAR-CNR)

The IC TT inter-compared SST analyses for climate studies (analyses of at least 15 years duration) in the framework of the Copernicus Climate Change Service (C3S). The work was led by Chunxue Yang, CNR/ISMAR.

  • The results of the study have been published in the Journal of Climate for peer review and publication: Yang, Chunxue, Francesca Elisa Leonelli, Salvatore Marullo, Vincenzo Artale, Helen Beggs, Bruno Buongiorno Nardelli, Toshio Michael Chin,
  • Vincenzo De Toma, Simon Good, Boyin Huang, Christopher J. Merchant, Toshiyuki Sakurai, Rosalia Santoleri, Jorge Vazquez-Cuervo, Huai-Min Zhang, Andrea Pisano (2020) Sea Surface Temperature intercomparison in the framework of the Copernicus Climate Change Service (C3S), J. Climate,
  • Preliminary results were reported to the GHRSST-XXI Science Team Meeting in 2020 (view the presentation here)
  • Final report to the Science Team was presented at GHRSST XXII Science Team Meeting in 2021 (view the presentation here).

Task 1 contributed to the Independent Assessment of Essential Climate Variables (C3S_511) Project for the Copernicus Climate Change Service (C3S).  The C3S_511 Project closed 30 June 2021.  Plans for intercomparison activities under the next phase of C3S are to be determined.

COMPLETED Task 2: Understanding the differences between SST analysis systems (Lead: Xu Li, NOAA/NCEP)

The number of drifting buoy observations used in an SST analysis system depends on many factors such as Quality Control, observation error, weighting relative to the background, and correlation length scale. The observation counts are system dependent even if the data received by the systems are the same. Results of a short study on the availability of drifting buoy observations in various operational SST analyses led by Xu Li (NOAA/NCEP) were presented in the Task Team session at the GHRSST-XXI Meeting (view the presentation here). The study compared four global SST analysis systems (NOAA/NCEP NSST, ECCC CMC 0.1 degree, ABoM GAMSSA and UKMO OSTIA) The numbers, total and used, of drifting buoy observations based on the 10-day daily average for 1-10 May 2020 were examined. As expected, the total number of drifting buoy observations ingested is different for each L4 product due to different quality control, data time windows, start times and cut-off times. CMC is the only L4 system to choose only one report per platform per day. GAMSSA is the only system to reject in situ data suspected of experiencing a diurnal signal.

The way in situ data are used in operational L4 systems (directly assimilated, quality control or bias correction of satellite data, etc.) is being investigated. The study will examine the impact of ingesting BUFR format ship SST data from the GTS and the impact of COVID-19 on the total number and type of in situ data ingested into operational SST analysis systems. Results will be reported to the Science Team at the GHRSST-XXII Science Team Meeting (2021).

If interested in contributing to Task 2 please contact Xu Li:

Task 3: Compare features in different L4 products (Lead: Jorge Vazquez, NASA/JPL)

If interested in contributing to Task 3 please contact Jorge Vazquez:

Task 3.1:  Validate L2, L3, and L4 SST gradients in highly variable regions using SailDrone and/or ship SST. An investigation examining SST gradients in SST analyses is led by Jorge Vazquez. SST gradients in L2, L3 and L4 SST products in highly variable regions are validated using SailDrone data; results are published in Vazquez-Cuervo, J.; Gomez-Valdes, J.; Bouali, M. (2020) Comparison of Satellite-Derived Sea Surface Temperature and Sea Surface Salinity Gradients Using the SailDrone California/Baja and North Atlantic Gulf Stream Deployments. Remote Sens.12

Task 3.2: Produce online visualization tool for L4 SST fronts. An online visualisation tool for L4 SST gradients has been deployed in the NOAA OceanView (OV) system (, and a visualisation tool for marine heatwaves is in development. OV displays the location of SST fronts derived from NOAA/SOCD Geo-Polar blended Level 4 SST, according to user specifications.  Characteristics of detected fronts such as average SST gradient magnitude and length are available and can be used to filter the displayed fronts.  OV also includes a profiler to see the value of SST gradients along a given front.

Task 3.3: Develop the science to calculate SST fronts and inter-compare. Marouan Bouali, Prasanjit Dash and Jorge Cuervo-Vazquez are comparing L4 ocean fronts in highly dynamic regions. Using OceanView, they are using a Sobel filter with a fixed threshold to extract fronts of interest and their characteristics i.e. mean gradient and length.  They aim to develop the science to calculate SST fronts by exploring other techniques and inter-compare, using various L4 datasets (Geo-Polar Blend, CMC, OSTIA and others) and Saildrone campaigns (see Vazquez et al., 2020).

Task 3.4: Validate SST gradients/fronts with other independent but related data. Aim to validate SST gradients/fronts with other independent but related data (e.g., sea surface salinity gradients or altimeter-derived currents), using OceanView.

Task 3.5: Compare feature resolution and spatial consistency of various L4 products across different marine regions. Explore methodologies other than spectral analysis to define a “resolution” metric in the spatial domain.

New areas to explore in 2021 and 2022 include:

  • ECOSTRESS SST gradient validation using Saildrones and ships (IMOS and ships4sst) (part of Task 3.1?);
  • Incorporation of ECOSTRESS SST into OceanView (part of Task 3.2?);
  • Compare SST gradients over seasonal and interannual time scales for various high-resolution L4 products (new Task 3.6?).

Task 3.6 Compare SST gradients over seasonal and interannual time scales for various high-resolution L4 products

Task 3.7: possible future task: SST fronts and Ocean Color Fronts.


  • June 2020: SST Climatology and Analysis Inter-Comparison Task Team Report 2020 by Beggs, Helen, Chunxue Yang, Vincenzo Artale, Bruno Buongiorno Nardelli, Vincenzo De Toma, Francesca Elisa Leonelli, Salvatore Marullo, Andrea Pisano, Rosalia Santoleri, Xu Li, Boyin Huang, Prasanjit Dash, Jorge Vazquez, Simon Good, Chongyuan Mao and the IC Task Team. Presented at the 21st GHRSST Science Team Meeting, 1– 4 June 2020


Co-Chairs: Daniele Ciani (CNR-ISMAR) and Jorge Vazquez (JPL/NASA)

Members: Daniele Ciani (CNR-ISMAR, Italy), Chongyuan Mao (Met Office, UK), Sheekela Baker-Yeboah, (NOAA, USA), Nico Weidberg (Uni. Vigo, Spain), Gary Wick (NOAA, USA), Andy Harris (NOAA, USA), Ioanna Karagali (DMI, Denmark), David S. Wethey (Univ. South Carolina, USA), Toshio M. Chin (JPL, USA), Pallavi Govekar (BOM, Australia), Dorina Surcel-Colan (ECCC, Canada), Christo Whittle (CSIR, South Africa), Yuwei Hu (ADFA, Australia), Marouan Bouali (Uni. San Paulo, Brazil), Huai-min Zhang, (NOAA, USA), Xungang Yin (NOAA, USA), Helen Beggs (BOM, Australia), Prasanjit Dash (NOAA, USA), Neeraj Agarwal (ISRO, India)



Please contact the co-chairs or the task leaders directly:

  • Daniele Ciani,
  • Jorge Vazquez,