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
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.
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.