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The ATSR Series, the SST Climate Record and Relevant Validation Programmes for the Future. David Llewellyn-Jones C J Merchant*, O Embury*, G K Corlett Space Research Centre Department of Physics & Astronomy University of Leicester, UK *University of Edinburgh. - PowerPoint PPT Presentation
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Earth Observation Science www.leos.le.ac.uk
The ATSR Series, the SST Climate Record
and Relevant Validation Programmes
for the FutureDavid Llewellyn-Jones
C J Merchant*, O Embury*, G K Corlett Space Research Centre
Department of Physics & AstronomyUniversity of Leicester, UK
*University of Edinburgh
AATSR, Climate Record and Validation
• AATSR and its Data• ATSR Re-processing for Climate
(ARC Project)• Recent Validation Results• Validation Priorities for the
Future
ATSR Viewing GeometryATSR Viewing Geometry
ATSR Scan sequence –showing on-board Calibration System
Nadir View
Along-Track View
Hot Blackbody Cold Blackbody
VISCAL
Scan Direction
Blackbodies viewedevery scan.
An ATSR on-
board Black Body
Peering into the Void - How
Black is Black?
ATSR Main Characteristics• 7 spectral channels (like AVHRR, or MODIS
– 3 thermal IR: at 3.7 μm, 11 μm, 12 μm– 4 Vis/NIR: at 0.55 μm, 0.67 μm, 0.87 μm, 1.6
μm)- provides basic SST information
• Dual view – Nadir and 55° to nadir – Gives a direct measurement of atmospheric
effects– Very effective for dealing with aerosol
contamination• On board calibration
– 2 on-board black bodies for IR calibration– VISCAL unit for visible channel calibration
ATSR Characteristics - 2
• AATSR (ATSR-3) Currently flying on ESA’s Envisat
• Swath-width - 500 km– Dual view less effective at wider swath-
widths• Field-of-view - 1 km at nadir
– Same as AVHRR• Stirling Cycle Coolers, cooling low noise
detectors to 80K– Gives optimum detector performance
and exceptional image clarity
ATSR DataStandard Products:-• SST data produced at 1km resolution,
– also gridded at 0.5˚ and 10 arc-min long-lat
– ToA BTs also available (L1b)• Full range of Level 1b, Level 2 Products and
Browse products available from ESA– Revised Data Policy
• To gain access, please contact:
ATSR Re-processing for Climate (ARC)• Consortium with Relevant
experience/Skills– U Edinburgh – (Retrievals)– U Leicester – (Validation, incl overlap
analysis– Southampton Oceanography Centre –
Assessment with in situ data– (K Met Office/Hadley Centre – assessment
for climate purposes• Objective: to generate Climate-
standard (GCOS-compliant) SST data-set from standard ATSR level L1b data
• Analogous to AVHRR Pathfinder teams
ARC Project
ARC Procedures• Made record homogeneous at
BT level (Overlap periods, drift effects etc)• ARC Algorithms:• Cloud Detection
– ‘Obvious’ Clouds: some image pre-processing– ‘Marginal’ Clouds: Bayesian probability-of-
clear calculation• SST Retrieval
– coefficients– includes adjustments to coefficients to
compensate for inter-satellite calibration discrepancies
Skin to Depth Adjustmentskin effect and stratification: 20 cm, 1 mfor AATSR also 30 min orbit time adjustmentUncertainty model
ARC SSTs - Assessments of accuracy
• Dependencies on TCWV, wind etc also within +/- 0.1 K target
Accuracy (Lack of Bias) Assessment: AATSR
Accuracy (Lack of Bias) Assessment: ATSR-1
Assessments of precision
Precision estimates (0.1 deg data)• AATSR “drifter depth” SSTs from ARC have
lower uncertainty than drifting buoy SSTs
– Independent 3-way analysis by Katie Lean, UKMO
Assessment of stabilityARC - Tropical Moored Buoys
Stability: 0.03 K/dec for 1993-2009*
*in the tropics – which is the only place we can make an assessment
ARC D2 – in situ (drifter + GTMBA)
HadSST3 vs ARC SST0.2m, 1991-2006: global mean anomaly, co-located
Pinatubo
geolocdodgy atsr2
atsr1 det.temp. drift
Comparison by Nick Rayner
Read all About it!• Journal:
• Special Issue on AATSR• Special Issue on AATSR• Now Online; Due for Publication 2012• 19 Articles• Covers whole range of Applications• Acknowledgments due to:
– John Remedios and Roger Saunders– (Co-editors)– Editorial staff of JRSE– Not forgetting PJ Minnett, Deputy Editor!
Reference for much of this Material:-
Please cite this article as: Embury, O., et al., Remote Sensing of Environment (2011), doi:10.1016/j.rse.2011.02.028 O. Embury et al. / Remote Sensing of Environment xxx (2011) xxx–xxx
Paper version available in 2012
Now available online to JRSE subscribers
The Future for ARC
• Programme of updates planned• ARC Methods to be used to
generate Standard Products for ESA
• ARC Data are the Foundation for SST Element in ESA’s Climate Change Initiative (CCI)
Get ARC Data!• From NEODC (Part of BADC)
• URL is
• If you browse datasets, ARC is at the top of the list (under AATSR).
• Need to get a BADC registration and password
• If all else fails, contact Chris Merchant• Netcdf files• Readme and Briefing Doc• Will collect user e-mails
wwww.neodc.rl.ac.uk
Validation Issues• Objectives of a Validation
programme include:1) Provide Basic Quality Control
Information2) Provide in situ Reference
Measurements which are calibrated to recognised standards
3) Establish achievable limits of accuracy and Precision
What is needed?• ‘Generic validation’
– Concentrate on variable, not the mission– Essential during Data-gaps
• Use Traceable Calibration for Reference Data– For SST at this time, this means
Radiometers
Science MuseumLondon
Science Museum London
Wow!
New Gallery:“Atmosphere - Exploring Climate
Science”
, launched March 2002Sun-synchronous orbit, 1030 local time daylight descending
AATSR
EENVISATEurope’s largest satellite
Against US coastal moorings
-0.04 K stepsame time as ECMWF upgrade from 60 to 91 model levels
ARC SSTs• Final period of ARC involved assessment
of ARC SSTs at UoE, UoL, NOCS and Met Office
• At final team meeting in June, prime focus was a synthesis of these results
• Outcome was the briefing document, which aims to summarize our main conclusions about the characteristics of the ARC SSTs
L3C netcdf files• sst_skin
– radiometric skin temperature at time of observation
• sst_depth– SST adjusted for skin and diurnal effects for
nominal depths of 0.2, 1.0 m– Adjusted to consistent satellite overpass time
(10:30 LECT)• uncertainty
– Estimated retrieval uncertainty based on theoretical algorithm performance, sensitivity to radiometric noise, number of clear-sky pixels
• time• number_of_pixels
Planned upgrade: v1.1• Expected before end 2011
Planned upgrade: v1.2• Expected before end 2012, and will:
Summary of ARC improvements - 1
Summary of ARC improvements - 2
ENVISAT,
People
and the
AATSR
Made record homogeneous at BT level
• 3.7 & 11 only (D2*) reference retrieval
• N2, N3, D2, D3 offsets adj’d to D2* AATS
R
• D2* for ATSR-2 is then consistent with AATSR
• N2, N3, D2, D3 offsets adj’d to D2*
ATSR-2 • No 3.7, so ATSR-2
D2* is ref. for offsets at end
• ATSR-1 D2* (untied) is ref. at start
• Detector temp. trendATSR-
1AATSR-ATSR2 overlapAdjusted BT calibration for 3.7 & 11(accounting for spectral responses)
ATSR-2-ATSR-1 overlapReconcile 11 & 12 BTs