The AATSR sensor and its in-flight performance

1. Chris Mutlow(1), Gary Corlett(2) and Dave Smith(1) Earth Observation and Atmospheric Science Division,Rutherford Appleton Laboratory (2) Earth Observation Science, University of Leicester The AATSR sensor and its in-flight performance

2. The Along Track Scanning Radiometer (ATSR) Programme • Primary objective to measure Sea Surface Temperature (SST) with an accuracy of 0.3 K (±1σ limit) • Thermal and visible data for atmospheric and land studies (e.g. temperature, vegetation, aerosols, clouds) • Provision of a long-term dataset for global climate change studies • ATSR-1 (ERS-1) 09/1991 - 03/00 • ATSR-2 (ERS-2) 04/95 – Still working • AATSR (Envisat)03/02 - Operational

3. ATSR Programme Timeline

4. Long Term (A)ATSR Data Record • 14 year record of ATSR infrared data from 1991 when ATSR-1 was launched until today • This provides a traceable global SST record from 1991 to today • Sensors cross-calibrated • 10 year record of visible data available from the launch of ATSR-2 in 1995 until today • Calibrated using on-board VISCAL systems • Reprocessing is underway to put ATSR-1 and ATSR-2 data into a common AATSR “Envisat-style” format • See Matt Pritchard’s talk on Tuesday

5. What is (A)ATSR? Imaging infrared and visible radiometer on ENVISAT Similar channels to AVHRR & MODIS. Dual view (nadir and 55° to nadir) Along-track scanning, two views of same scene at different angles, for better atmospheric correction On-board calibration 2 on-board black bodies for IR calibration VISCAL unit for visible channel calibration (see first talk after coffee break) 500 km swath 1 km IFOV at nadir Stirling Cycle Coolers, cooling low noise detectors to 80K, for optimum signal-to-noise ratios

6. (A)ATSR Spectral Channels Red: ATSR-1,-2 and AATSR have these channels Blue: Only ATSR-2 and AATSR have these channels

7. Data Products from AATSR • Operational • Brightness temperatures and reflectances • Sea Surface Temperature (SST) • Land Surface Temperature (LST) • New product for AATSR • NDVI • Under development • Cloud parameters • Aerosol optical properties

8. AATSR On-board Calibration System Both blackbodies viewed every scan.

9. Blackbody Crossover Test • Test performed over 17th-19th May • All commands executed successfully • Data to be analysed -XBB BB temperatures +XBB Hot BB 11µm BB counts Cold BB

10. Scan Mechanism Trends

11. NEDT Trend

12. Cooler performance (1)

13. Cooler Performance (2)

14. FPA Temperatures

15. Visible Channel Signals

16. Contamination

17. Dynamic Range and Digitisation • Periodically (nominally every 6 Months) data are processed for one orbit. • Plots produced showing: • Max, mins and means for each scan over the orbit to evaluate dynamic range • Histograms of nadir view pixel counts to check for any missing/preferred states

18. Dynamic Range – IR Channels Daytime Night-time

19. Dynamic Range – Visible Channels Night-time Daytime

20. Digitisation States – IR channels Rounding off at 1024, 2048, 3072 Rounding off at 1024, 2048, 3072

21. Digitisation States – Visible Channels Rounding off at multiples of 1024

22. Dynamic Range & Digitisation Summary • IR Gain Offset Loop maintaining dynamic range of IR channels as expected • No saturation in visible channels – visible gains updated to maintain dynamic range. • Slight rounding off at 1024, 2048, 3072 counts – less than 1bit error (<20mK)

23. Example Validation Results • ATS_NR__2P (SST & LST) • Gridded 1km by 1km global product • Against in-situ radiometric measurements • ATS_AR__2P (SST only) • Spatially averaged products at various resolutions (30´; 10´; 50 km; 17 km) • Against in-situ buoy measurements • Further talks on data quality throughout the workshop

24. M-AERI and ISAR (Dual SST) From: Lizzie Noyes (University of Leicester), Werenfrid Wimmer (NOCS)

25. AATSR Compared to Buoy SST Sat “bulk” SST Sat “skin” SST From: Anne O’Carroll (Met Office)

26. Buoy Results 04/2003-03/2005 (Dual SST) From: Anne O’Carroll (Met Office)

27. Summary of LST Validation Results Vegetation cover not accounted for properly in the algorithm Actually a sea pixel to which LST retrieval has been applied in error From: Cesar Coll (University of Valencia), Jose Sobrino (University of Valencia), Fred Prata (CSIRO), Simon Hook (JPL)

28. Summary and Conclusions • AATSR is the third in a series of sensors providing a long-term data set of global SST since 1991. • Visible channel data available from 1995 • LST algorithm can be applied to data from 1991 • The sensor is performing extremely well • Geophysical validation results provide evidence of excellent data quality from both the SST and LST operational algorithms • Minor algorithm improvements are currently being assessed

29. Acknowledgements Co-authors Gary Corlett and Dave Smith for all their material Defra, the UK Department of Environment, Food and Rural Affairs, who funded AATSR to support their programme of climate prediction and research, which in turn provides inputs to their policy-making processes Funding agencies in Australia who made significant contributions The European Space Agency