A Short History of the GHRSST-PP

In the last decade, satellite measurements of SST have matured considerably and today, several instruments provide unprecedented daily views of the structure and dynamics of the ocean surface with astonishing accuracy (e.g. AATSR). New microwave instruments (e.g., AMSR-E) are now providing global measurements that are free from the corrupting influence of clouds and stratospheric aerosols - contaminants that have perpetually frustrated infrared measurements from space. Global networks of moored and drifting buoys report in situ SST in real time via satellite link and the Global Telecommunications System (GTS). In situ radiometer systems (e.g., ISAR), providing precise measurements of the surface skin temperature, capable of autonomous deployment aboard commercial ships for extended periods are emerging, promising for the first time, the possibility of an extensive data resource for the proper validation of sea surface temperatures from infrared satellite sensors.

In 1997, the Ocean Observing Panel for Climate (OOPC) proposed the Global Data Assimilation Experiment (GODAE) as an experiment in which a comprehensive, integrated observing system would be established and held in place for several years. GODAE now provides a global system of observations, communications, modeling and assimilation, and is delivering regular, comprehensive information on the state of the oceans, in a way that will promote and engender wide utility and availability of this resource for maximum benefit to the community.

Sea surface temperature is fundamental for many GODAE activities. It contains information about climate conditions that directly affect human health, economy, and enterprise. It is an ocean parameter that is widely used for describing ocean circulation and dynamics, in the study of upper-ocean physical and biogeochemical processes, as a boundary condition for oceanographic and meteorological models, as a central factor in studies of air sea fluxes, and as an indicator for climate change and variability.

While the measurement of SST, arguably one of the most basic yet important oceanographic parameters, represents a fine example of operational oceanography, fundamental challenges still remain to reconcile difference. Satellite sea surface temperature products are of varied heritage, assembled using many different approaches and algorithms, often with considerable duplication of effort in different countries. Extensive data sets are derived from multiple sensors sampling at different times of the day introducing regional and temporal biases associated with diurnal stratification of the upper ocean. In some cases, precessive satellite orbits compound this problem although little progress has been made to address these effects. In practice, the accuracy, sensitivity, and sampling resolution of global SST products is far from optimal.

GODAE rapidly realized that current SST data sets are not able to fulfill its requirements and in March 2000, the International GODAE Steering Team (IGST) issued a Prospectus for a GODAE SST project that established the broad scientific rationale for the development of an operational high-resolution SST data product. This product would address the needs of GODAE and the wider oceanographic community. By November 2000, an International Workshop was convened at the European Commission Joint Research Center in Italy to develop the prospectus.

Rather than improving individual satellite data streams, a fresh approach emerged based on the fusion and combined analysis of complementary satellite and in situ measurements. The combination of satellite and in situ SST data sets is one of great significance. Only by careful reference to in situ observations can satellite measurements attain the quality and accuracy required to confidently reveal the small signals associated with climate change and variability. A new generation of global SST products would be derived harnessing the unique strengths of separate data streams to alleviate the weakness of others. High-resolution products would be generated in real time by a demonstration system and would be freely and widely available. From this Workshop, the GODAE High Resolution Sea Surface Temperature Pilot Project (GHRSST-PP) was born.