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:

eohelp@esa.int

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