Highlights of AATSR Commissioning

1. Highlights of AATSR Commissioning David Llewellyn-Jones AATSR Principal Investigator Space Research Centre University of Leicester including contributions provided by Dave Smith, Jack Abolins (RAL) Lisa Horrocks (Met Office), and Marianne Edwards (Leicester)

3. AATSR on ENVISAT • Imaging radiometer • Thermal Infrared, near infrared and visible wavelength channels • Third in a series, designed to measure Global Sea-surface temperature (SST) for climate applications • accuracies better than 0.5C • High radiometric performance required (better than 0.1C accuracy) and achieved

5. Why is AATSR such a good thermal radiometer? • High signal-to-noise ratio detectors - active cooling system (Stirling cycle coolers) • Stable calibration system - two black-bodies, spanning essential dynamic range - viewing black bodies with same optical path as scene - viewing each-body each scan - stable thermal environment for each black-body

6. Some highlights of Commissioning results. . • Radiometric Noise • Black-body temperatures • Compare & contrast with AVHRR • Overall thermal performance of instrument • Geophysical Validation • Comparisons with MERIS and ATSR2

7. Radiometric Noise Note: For thermal channels, NET specification is 0.05K

8. AATSR Black-body Temperature recordsshowing variations over one daywith near-sinusoidal orbital variations superimposed

9. A single orbit record of AVHRR Black-body temperaturepassing the terminator

10. Black-Body Crossover test • Exchange roles of AATSR black-bodies - ie heat the cooler BB and allow heated BB to cool, monitoring BB temperatures as function of time • At ‘crossover’ point, both black bodies are nominally at same temperature and should give same detector signal • This test would reveal problems with prt sensors or in emissive surfaces of the black-bodies • Results show discrepancies of less than 30mK

11. AATSR Black-body ‘crossover’ test This plot identifies the time at which both sets of black-body temp sensors indicate the same temperature. At this time both BB’s give same signal to within <30mkK

12. Overall thermal performance • Blackbodies • Orbital variation ~ ±0.1°C • Rate of change <0.015°C per two minutes (reqt. <0.02°C) • Fore-Optics • Orbital variation ~ ±0.5°C • Rate of change <0.04°C per two minutes (reqt. <0. 2°C) • FPA Baffle Tube • Orbital variation ~ ±0.5°C • Rate of change <0.04°C per two minutes (reqt. <0. 2°C)

13. Comparison with ATSR2 (first shown at SODAP review)Same-day Thermal images – Gulf of Oman

14. Geophysical Validation • Over 15 validation projects in progress worldwide. 7 have already collected in situ data • Comparisons at UK Met Office between AATSR METEO SST and in situ buoy data show promising results • For Vis/NIR channels, good comparison with MERIS (better than 5%)

15. the ESA Near-real-time skin SSTs for the period 19th - 29th August (except 25th August )

16. First AATSR-Buoy SST comparisons(A O’Carroll & L. Horrocks, UK Met Office) • For the period 19-21st August 2002: mean ESA skin - buoy SST difference = 0.039 (=0.348) • For the period 22-27th August 2002: mean ESA skin - buoy SST difference = -0.096 (=0.583) • Some minor anomalies in polar regions • Bearing in mind skin-bulk temperature differences and known uncertainties in buoy data, this is a very satisfactory starting-point for the AATSR validation programme, indicating that AATSR is already very close to meeting its geophysical performance specifications.

17. Summary and Conclusions • Next presentation (Dave Smith) will show detailed results • In the essential areas of radiometric noise and BB performance AATSR is comfortably within specification • In all other respects AATSR is within specification • Excellent comparisons with ATSR2 and MERIS • First Validation results (Lisa Horrocks and Anne O’Carroll) extremely promising, details in later presentation from Marianne Edwards • Stable operation – only one unavailability notice so far