Enhanced usability of satellite sea surface temperature data
Submitting InstitutionUniversity of Southampton
Unit of AssessmentEarth Systems and Environmental Sciences
Summary Impact TypeEnvironmental
Research Subject Area(s)
Physical Sciences: Astronomical and Space Sciences
Engineering: Geomatic Engineering
Technology: Communications Technologies
Summary of the impact
Satellite measurements of sea surface temperature (SST) make a much
greater impact on weather forecasting and climate change detection since
University of Southampton (UoS) research revolutionised the way SST data
are processed. Multiple satellite observations can now be combined into
the more complete and detailed SST maps needed by fine resolution
meteorological models and used for marine industry operations. Pioneering
methodology using a new shipborne radiometer tests the quality of SST maps
more rigorously than was previously possible. It provides the first
traceable validation of data from the UK's AATSR sensor, confirming their
fundamental reliability for observing climate change.
During 1991-2012 a series of UK-designed Along-Track Scanning Radiometers
(ATSR, ATSR-2 and AATSR) measured SST from European Space Agency (ESA)
satellites. These observe the ocean skin, the top millimetre, whereas
conventional thermometers on buoys measure temperature a few metres deep.
The difference between these, ΔT, reaches 5K because of wind
cooling and solar heating, and is difficult to characterise. This creates
uncertainty >0.3K when comparing individual satellite and buoy data,
hindering confirmation of ATSR's high accuracy for climate monitoring.
Moreover, ATSR was overlooked for operational applications (e.g. weather
forecasting) because of its poorer coverage. Thus despite the inherent
high quality and low noise of the sensor, the ATSR datasets were largely
ignored for 15 years.
This prompted Professor Ian Robinson's (UoS 1976 - present) research
group to study sea surface thermal processes, seeking to improve the
applicability of satellite SST data. Craig Donlon (UoS PhD 1990-94, UoS
postdoc 1994-97, visiting fellow 2004-08) sought ways to measure skin SST
from ships. In 1995, comparing observations from an early ship radiometer
to conventional thermometry, he obtained evidence that the cool skin
component of ΔT is quantifiable to accuracies better than 0.1K [3.1],
and attempted direct validations of satellite SST using ship radiometers.
Subsequently Alice Stuart-Menteth (UoS PhD 2000-04) identified the diurnal
warming factors contributing to ΔT [3.2].
In 1996 Robinson and Donlon drew together other SST experts from space
and meteorological agencies, including ESA, NASA, UK Met Office, Eumetsat,
RAL and Météo-France, to participate in the EU-funded Concerted Action
project for the Study of the Ocean's Thermal Skin (CASOTS). They developed
strategies for better determination of ΔT and for reliable
shipborne radiometry, discovering that the quality of each SST measurement
from satellites must be evaluated in relation to the coincident ocean
conditions, such as time of day, wind and sunshine. These insights led in
2002 to the formation of the Group for High Resolution Sea Surface
Temperature (GHRSST) [3.3]. Donlon convened the first Science Team
(ST) meeting, was elected ST Chair in 2002, and employed as Executive
Director 2004-09. Robinson is a ST member (2003-13), joined by Southampton
colleagues A.Stuart-Menteth, D.Poulter and W.Wimmer for periods.
In 2004 Donlon and Robinson helped to formulate the GHRSST protocols for
producing usable SST datasets. These combine information from diverse
satellite sensors to achieve SST maps with fine space-time resolution,
full coverage and quantifiable accuracy. Robinson led the ESA- funded
Medspiration project (2004-2008) which developed the prototype GHRSST data
processing system, at last enabling AATSR data to underpin the evolution
of new classes of global SST datasets [3.4].
Concurrently Donlon designed the first infrared SST autonomous radiometer
(ISAR) for unattended ship deployment, building the prototype at
Southampton in 2001 [3.5]. ISAR measures in situ skin SST
with uncertainty <0.1K, inter-calibrated against Système
International d'unités (SI) standards. From 2004 to the present,
funded by a £1 million+ contract from DECC, UoS researcher Werenfrid
Wimmer developed ship radiometry as a tool for validating AATSR data with
uncertainty <0.1K, using many thousands of match-up data from
continuous monitoring by ISAR along UK-Spain ferry routes [3.6].
References to the research
(the best 3 illustrating quality of work are starred)
*[3.1] Donlon, C.J., T.J. Nightingale, T. Sheasby, J. Turner, I.S.
Robinson and W.J. Emery, Implications of the oceanic thermal skin
temperature deviation at high wind speed, Geophys. Res. Letters, 26
(16), 2505-2508, 1999.
*[3.2] Stuart-Menteth, A. C., Robinson, I. S. and Challenor, P., A
global study of diurnal warming using satellite derived SST. J.
Geophys. Res., 108 (C5), 3155 doi:10.1029/20025C001534,
*[3.3] Donlon,C.J., Robinson, I.S., Casey, K. S. and 23 others.
The Global Ocean Data Assimilation Experiment (GODAE) High Resolution Sea
Surface Temperature Pilot Project (GHRSST-PP). Bull. Am. Meteorol. Soc.,
88 (8), 1197-1213, 2007 (doi: 10.1175/BAMS-88-8- 1197).
[3.4] Robinson, I.S., J.-F. Piollé, P. Le Borgne, D.J.S. Poulter,
C. J. Donlon and O. Arino, Widening the application of AATSR SST data to
operational tasks through the Medspiration Service. Remote Sensing of
Environment. 116, 126-139, 2012.
[3.5] Donlon C, Robinson I S, Reynolds M, Wimmer W, Fisher G,
Edwards R, Nightingale T J An Infrared Sea Surface Temperature Autonomous
Radiometer (ISAR) for Deployment aboard Volunteer Observing Ships (VOS). Journal
of Atmospheric and Oceanic Technology, 25 (1): 93-113, 2008.
[3.6] Wimmer, W., Robinson, I.S and Donlon, C. J. Long-term
Validation of AATSR SST data products using shipborne radiometry in the
Bay of Biscay and English Channel. Remote Sensing of Environment.
116, 17-31, 2012. doi:10.1016/j.rse.2011.03.022.
Grants and Awards
Research Studentships: 1990-1993 C J Donlon (NERC); 1995-1998 S Keogh
(NERC); 2000-2003 A Stuart-Menteth (Southampton funded).
1996-1997: ~ €80,000. from EU Environment Programme . CASOTS —
Concerted Action for Study of the Ocean's Thermal Skin. PI: I S
1999-2000: £18,000 from Southampton Instrument development fund. Constructing
a prototype autonomous shipborne radiometer (ISAR). PIs: C J Donlon
and I S Robinson,
2004-2008: €1,100,000 (of which ~€300,000 to Southampton) contract from
European Space Agency (Data Utilisation Envelope Programme). Medspiration
— European regional contribution to GHRSSST-PP. Project manager: I S
2004-2014: £1,317,254 Contract from Defra/DECC to UoS extended through
five phases. Validation of AATSR Sea Surface Temperature Products
using the shipborne ISAR Radiometer. Project Manager: I.S. Robinson,
ISAR Scientist: W. Wimmer.
Details of the impact
Two major impacts can be traced from the Southampton SST research group:
A) The new capability to produce high-resolution blended SST datasets
through the Group for High Resolution Sea Surface Temperature (GHRSST) [5.1].
Such datasets have rapidly become an essential link in the data chain by
which ocean satellites improve the operational forecasting of
environmental conditions on land and at sea. They are used by US,
European, Japanese and Australian agencies to improve the reliability of
daily SST maps and hence weather forecasts.
B) The new use of shipborne radiometry to establish the absolute accuracy
of satellite SST measurements, traceable to international references,
allows global time series to be used with enhanced confidence for
monitoring the changes in spatial and temporal patterns of SST in response
to climate change.
A) Southampton's SST research activities contributed directly to the
creation of the GHRSST in 2002 through having trained its founding
director, Craig Donlon, and by supplying several Science Team members.
Their role in the successful evolution of GHRSST was to provide the
scientific understanding of temperature structure near the ocean surface.
This understanding was needed to underpin the procedures in the GHRSST
Data Specification which is the "recipe" for successfully blending data
from different satellites. Donlon et al. [3.3] describes the
challenge of persuading several major agencies to agree to a common
protocol for processing SST measurement from satellites. The newly
specified GHRSST products were first prototyped by the Medspiration
project [3.4] led from Southampton (2004-2008), that confirmed the
effectiveness of the GHRSST approach. Until this point global SST data
from individual satellite sensors had been inadequate for operational
applications requiring daily SST at fine spatial resolution. By 2008,
Medspiration data products, including AATSR data, were used routinely by
agencies around the world as the primary source for creating their own SST
analysis products. In 2009, the AATSR Exploitation Board acknowledged
"During the past two years, the operational use of (A)ATSR data has
taken a major step forward as a result of the ESA-funded Medspiration
project, the European backbone of GHRSST-PP". "A consensus view
is emerging that (A)ATSR data, although offering less coverage than
other sensors, are the most accurate available and can be used in
multi-sensor analysis schemes as the benchmark against which data from
other sensors can be bias-corrected" [5.2]. Since 2008 the
UK Met Office has been producing their own daily global SST analysis,
OSTIA, that first grew from the availability of Medspiration products. The
Met Office operational Numerical Weather Prediction system switched to use
OSTIA after rapid melting of Arctic ice in 2007 had revealed problems in
their previous SST analysis. This change has measurably reduced errors [5.3]
and improved the quality of weather forecasts.
GHRSST is now a truly international collaboration with over US$18 million
invested across all of the project activities [5.4]. It provides
the framework within which all satellite SST data can be shared, indexed,
processed, quality controlled, analysed and documented. Global and
regional SST products are now produced by GHRSST regional data assembly
centres in Australia, Japan, USA and Europe. SST products are passed in
near real time to operational GHRSST global data assembly centres where
they are integrated together into reliable, error-quantified, analysed SST
maps, irrespective of cloud or weather.
High resolution SST maps based on GHRSST principles have become essential
inputs to local weather forecasting models in many parts of the world
making routine forecasts for many sectors of society. Meteorological
agencies aim, for example, to issue flood warnings, predict the extent of
ice on highways, or forecast rain probabilities in sufficient local detail
that users as diverse as water companies, road gritters or farmers at
harvest time can depend on them. The same SST maps are also needed by
ocean forecasting systems for offshore industry and military operations,
validation and forcing of ocean and atmospheric models, ecosystem
assessment, tourism and fisheries research, amongst many others. [5.5].
B) Southampton's development of the autonomous ship radiometer (ISAR)
introduced a significant improvement to the quality assessment of
satellite SST data. Comparison between satellite and ISAR measurements,
which both observe the skin SST, completely eliminates the ~0.3K
uncertainty from estimating ΔT when using buoy measurements in
conventional validation. ISAR's calibration to better than 0.1K allows
validation of AATSR data to an equivalent precision for each individual
match-up between satellite and in situ observations. The high
quality of AATSR data confirmed by ISAR [3.6] has encouraged
widespread use of AATSR. It justifies the use of AATSR for bias adjustment
of inferior SST datasets when producing analysed SST maps [5.2]
with reliably estimated uncertainties. This is particularly valuable for
operational forecasting applications where quantification of forecasting
uncertainty is critical such as search and rescue or route-planning for
sea transport of large structures [5.5].
The Global Climate Observing System (GCOS) is the international body
established to ensure that the observations and information needed to
address climate-related issues are obtained and made available to all
potential users. It has defined 50 Essential Climate Variables (ECV), of
which SST is one, that are necessary to support the work of the United
Nations Framework Convention on Climate Change and the Intergovernmental
Panel on Climate Change (IPCC). Because ISAR is subjected to validation
against an infrared radiation source before and after each autonomous
deployment, every SST measurement is traceable to the S.I. reference
standards against which the radiation source is tested. Thus accumulated
ISAR observations can be treated as a SST "reference dataset", meeting the
strict traceability requirements of the GCOS and are therefore useful for
independent validation of other SST ECVs. The policy impact of this unique
capability, contrasting with conventional SST measurements, is now
acknowledged by Professor David Mackay, Department for Energy and Climate
Change (DECC) Chief Scientific Advisor:
"We recognise...in-situ measurement using radiometers traceable to
international reference standards is highly desirable to ensure
climate-quality datasets" [5.6].
The ESA Climate Change Initiative programme, overseen by Dr Craig Donlon
[5.7], has the task of producing a new SST dataset to the GCOS
specification of an Essential Climate Variable, which requires that
satellite SST validation must provide traceability to international
reference standards. Using ISAR to validate AATSR SST data now provides
the SI traceability needed to establish AATSR as the key input to the new
global SST time series. ISAR-type sensors are specified by ESA as
essential for validation of the AATSR successor instrument, SLSTR. This is
further evidence of the impact of Southampton's ship radiometry work on
ESA validation policy for climate quality satellite SST datasets [5.8].
The published success of ISAR deployments created a demand from agencies
around the world wishing to use shipborne radiometers. Since 2009, six
ISARs have been sold by UoS to Institutes in USA (2), Japan, China,
Denmark and UK, producing a turnover of £250,000, supporting a technician
for two years and demonstrating a modest commercial and employment impact.
The Southampton group's major impact on operational applications of
satellite oceanography has been recognized by the presentation of the
prestigious 2011 Remote Sensing and Photogrammetry Society Award to
Professor Robinson [5.9].
Sources to corroborate the impact
[5.1] GHRSST web site home page : https://www.ghrsst.org/
[5.2] These excerpts are from section 4.2.1. (see pp. 49-50) of
the (A)ATSR Exploitation Plan, Volume 1, (A)ATSR Project Overview.
Document reference ERSE-DTEX-EOPG-PL09-0003, Issue 1, 15 May 2009.
Exploitation Plan Volume 1 (Revised Issue 1).pdf Can be accessed
and selecting the link to: ATSR Exploitation Plan (AEP)
[5.3] Figure 11 in section 5.3 Impact of OSTIA on ocean
forecasting and NWP system, in: Donlon, C. J., M. Martin, J. D.
Stark, J. Roberts-Jones, E. Fiedler and W. Wimmer (2011). The Operational
Sea Surface Temperature and Sea Ice analysis (OSTIA) system. Remote
Sensing of the Environment. http://dx.doi.org/10.1016/j.rse.2010.10.017
[5.4] GHRSST information page https://www.ghrsst.org/ghrsst-science/what-is-ghrsst/
[5.5] GHRSST applications web page at https://www.ghrsst.org/users-partners/applications/
[5.6]. DECC Chief Scientific Advisor. The quotation comes from a
letter outlining DECC's position on the importance of SST to climate
policy and the role of satellite SST validation in the production of
[5.7] Principal Scientist for Oceans and Ice at the European Space
Agency/ESTEC. He can confirm the crucial importance of ship radiometry to
ensure compliance with GCOS requirements and can also corroborate many of
the other impacts being claimed.
[5.8]. The "Sentinel-3 Calibration and Validation Plan", produced
jointly by ESA and Eumetsat in preparation for the 2014 launch of the Sea
and Land Surface Temperature (SLSTR) sensor on the Sentinel-3
satellite for the EU Copernicus Programme, explicitly states the
importance of shipborne radiometers for SST product validation:
"SSTskin measurements from in situ ship mounted radiometers in
regional deployments shall complement the drifter data as they provide
independent and SI standards-traceable measurements of SSTskin (i.e.
exactly the same quantity measured by SLSTR). They also provide a method
of "bridging the gap" between AATSR and SLSTR."
[ESA document reference: S3-PL-ESA-SY-0265, Issue 0, Revision 12, Date of
Issue 21-9-2012] (Quotation is from bulleted list of Methodology on page
159/246, within section 126.96.36.199. "SST product validation"). The content of
this document can be confirmed by Optical Sensors Performance, Products
and Algorithm Manager at ESA.
[5.9] Remote Sensing and Photogrammetry Society Award to Professor