The ATSR Series, the SST Climate Record and Relevant Validation Programmes for the Future

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