Through a satellite darkly: night views of European seas improveESA ocean heat map (Forwarded)

ESA News
http://www.esa.int

20 March 2006

Through a satellite darkly: night views of European seas improve ESA ocean
heat map

The Mediterranean looks better in the dark -- at least in the view of an
ESA-led effort to use satellites to take the daily temperature of Europe's
seas. A switch to data acquired at night is one of several improvements
undertaken to enhance reliability and reach of Medspiration project
outputs.

With sea surface temperature (SST) an important variable for weather and
ocean forecasting -- and increasingly seen as a key indicator of climate
change -- the concept behind Medspiration is to combine data from multiple
satellite systems to produce a robust set of sea surface data for the
waters around Europe and also the whole of the Atlantic Ocean.

Medspiration products are designed for near-real time ingestion into
numerical ocean forecasting models to keep their outputs 'coupled' to
reality, in the same way as numerical weather prediction (NWP) atmospheric
models ingest satellite and in-situ results to enhance the overall
accuracy of weather forecasts.

An ultra high-resolution sea surface temperature map focused on the
Mediterranean Sea with an accuracy of less than 0.3 C is being made
available daily.

Medspiration products have been available to users since November 2004,
but significant quality enhancements came about in January 2006, including
two sq. km coverage being extended out into the Atlantic to match the grid
of a major ocean forecasting model run by Italy's National Institute for
Geophysics and Volcanology (INGV) and funded by the European Commission,
known as the Mediterranean Forecasting System Towards Environmental
Predictions (MFSTEP).

New Medspiration product is also now available on a same-day basis: the
daily analysis is now centred on the start of the current day instead of
midday of the previous day, with the daily generation time being stretched
back to 18:00 instead of 07:00 UTC.

And significantly, only satellite data acquired during local night are now
being utilised for the product. Satellite instruments can only measure the
'skin' SST -- the top ten to 20 microns of water -- rather than the 'bulk'
SST beneath, which is the value that oceanographers are most interested
in, the one that has the greatest influence on climate.

During the daytime, incoming solar radiation can heat the topmost water
layers, setting up steep temperature gradients which can mislead satellite
instruments. Such gradients dissipate during the night, minimising at dawn
which is when heat-measuring satellite sensors such as radiometers get
closest to taking the temperature of deeper water layers. Switching to
night acquisitions only also means that there is no longer a wind
threshold in the data selection -- in the past a certain level of wind
speed was necessary to stir up waters to reduce temperature gradients.

These improved results from the Medspiration project also feed into an
even more ambitious scheme to combine all available SST data into a
worldwide high-resolution product, known as the Global Ocean Data
Assimilation Experiment (GODAE) High-Resolution Sea Surface Temperature
Pilot Project (GHRSST-PP).

Its aim is to deliver to the user community a new generation of highly
accurate worldwide SST products with a space resolution of less than ten
kilometres every six hours. In support of that larger goal, since December
Medspiration has made a new global product available: SST measured by the
Advanced Along Track Scanning Radiometer (AATSR) aboard ESA's Envisat
satellite. The product is available for users worldwide, including other
operational groups in the USA, Australia and Japan contributing to the
GHRSST-PP system.

ESA has not only initiated Medspiration as the European contribution to
the overall GHRSST-PP effort, but also funds a GHRSST International
Project Office, located at the Hadley Centre for Climate Prediction and
Research, part of the UK Met Office located in Exeter.

"Medspiration now provides ultra-high resolution SST products covering
nearly all the European seas in addition to a substantial part of the
north-east Atlantic," said Craig Donlon, head of the GHRSST-PP Office.
"This should help European NWP and ocean forecasting systems improve their
services in the coming months.

"The extension of the Medspiration area is a direct response to requests
from the user community made at a consultation meeting at Brest in
December. The Medspiration project -- and indeed the international
GHRSST-PP -- considers such regular user consultations as one of the
primary feedback mechanisms. By federating European efforts across R&D
laboratories, operational NWP agencies, universities and the user
communities, Medspiration is now providing cutting edge products that
allow us to think about new possibilities."

Scientific and operational needs for ocean heating data

The temperature of the ocean surface helps 'make the weather': it is a
strong influence on the exchange of heat, momentum, water and gases
between the ocean and the air. Besides assessing such atmospheric inputs,
accurate wide-area measurements of SST and its variations over time are
also essential for forecasting sea state and currents, monitoring algal
blooms and marine pollution, and predicting the movement of oil spills.

The availability of such accurate daily SST maps covering almost all
European waters also create potential for plenty of more localised uses,
including meteorology and tourism applications -- and even steering
fishermen towards better catches.

The products will also have plenty of value in the longer term. Because
water takes a long time to warm up or cool down the sea surface functions
as an enormous reservoir of heat: the top two metres of ocean alone store
all the equivalent energy contained in the atmosphere. The whole of their
waters store more than a thousand times this same value -- climatologists
sometimes refer to the oceans as the 'memory' of the Earth's climate, and
measuring SST on a long-term basis is the most reliable way to establish
the rate of global warming.

Like thermometers in the sky, a number of different satellites measure SST
on an ongoing basis. For example, AATSR aboard ESA's Envisat uses infrared
wavelengths to acquire SST for a square kilometre of ocean to an accuracy
of 0.2 C. In fact, thanks to its high accuracy, AATSR is helping to
calibrate other sensors employed by the Medspiration project.

As well as AATSR, Medspiration also employs data from the Spinning
Enhanced Visible and Infra-Red Imager (SEVIRI) on Meteosat-8, two Advanced
Very High Resolution Radiometer (AVHRR) sensors on US NOAA polar orbiters,
and a pair of Japanese-built instruments, the Advanced Microwave Scanning
Radiometer (AMSR) and TRMM TRMM Microwave Imager (TMI) instruments, aboard
NASA's Aqua and the JAXA-NASA Tropical Rainfall Measuring Mission (TRMM)
spacecraft respectively.

Other satellites may have decreased accuracy or resolution, but
potentially make up for it with cloud-piercing microwave abilities or much
larger measuring 'footprints'. Combine all available satellite data
together -- along with localised measurements from buoys and research
ships -- and you can achieve daily monitoring of the temperature of all
the oceans covering 71% of the Earth's surface. This information is then
prepared for input into the relevant 'virtual ocean' -- a sophisticated
computer model of the genuine article.

The combination of satellite and also available in-situ observations with
numerical modelling -- a technique known as 'data assimilation' -- is an
extremely powerful one. It has revolutionised atmospheric weather
forecasting and is now being applied to the oceans.

Near real time observational inputs keep an ocean model from diverting too
much from reality, while the outputs from the model make up for any gaps
in coverage. With maximised coupling between actual observations and the
numerical model, output data can be credibly used for operational tasks.
And these models can also be used to look deeper than just the ocean
surface.

Medspiration and MARCOAST

The Medspiration project is being supported through ESA's Data User
Element of the Earth Observation Envelope Programme-2 (EOEP-2). As well as
ESA, CLS and CNR, the Medspiration team comprises the Southampton
Oceanography Centre, the UK-based VEGA company, Meteo-France's Centre for
Space Meteorology, the French Research Institute for Exploitation of the
Sea (IFREMER), the France-based Actimar firm and the Norwegian
Meteorological Institute.

Medspiration is being run as a demonstration project up until the end of
2007, with user consultations taking place every six months -- the next
being scheduled for June. The project will then be extended to cover
requirements coming from the MARCOAST initiative to deliver a range of
operational services in the marine environment including water quality and
algal bloom reporting as well as oil-spill related services.

Related news

* Plunge into warmer waters this summer with ESA's Mediterranean heat map
http://www.esa.int/esaEO/SEMRVT5TI8E_index_0.html
* Satellites plus software equal best-ever Mediterranean heat map
http://www.esa.int/esaCP/SEMG9L2AR2E_index_0.html
* Proof of a warming world is written on water
http://www.esa.int/esaCP/SEM9V567ESD_Protecting_0.html

Related missions

* Envisat
http://www.esa.int/esaEO/SEMWYN2VQUD_index_0_m.html
* MSG overview
http://www.esa.int/esaEO/SEMLFM2VQUD_index_0_m.html

In depth

* Data User Programme
http://dup.esrin.esa.it/

Related links

* Medspiration
http://www.soc.soton.ac.uk/lso/medspiration/
* GODAE
http://www.bom.gov.au/bmrc/ocean/GODAE/
* GHRSST-PP
http://www.ghrsst-pp.org/

[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEM1XXNVGJE_index_0.html ]