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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.

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the aatsr sensor and its in flight performance
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

the along track scanning radiometer atsr programme
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
long term a atsr data record
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
what is a atsr
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

a atsr spectral channels
(A)ATSR Spectral Channels

Red: ATSR-1,-2 and AATSR have these channels

Blue: Only ATSR-2 and AATSR have these channels

data products from aatsr
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
aatsr on board calibration system
AATSR On-board Calibration System

Both blackbodies viewed

every scan.

blackbody crossover test
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

dynamic range and digitisation
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
digitisation states ir channels
Digitisation States – IR channels

Rounding off at 1024, 2048, 3072

Rounding off at 1024, 2048, 3072

digitisation states visible channels
Digitisation States – Visible Channels

Rounding off at multiples of 1024

dynamic range digitisation summary
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)
example validation results
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
m aeri and isar dual sst
M-AERI and ISAR (Dual SST)

From: Lizzie Noyes (University of Leicester), Werenfrid Wimmer (NOCS)

aatsr compared to buoy sst
AATSR Compared to Buoy SST

Sat “bulk” SST

Sat “skin” SST

From: Anne O’Carroll (Met Office)

buoy results 04 2003 03 2005 dual sst
Buoy Results 04/2003-03/2005 (Dual SST)

From: Anne O’Carroll (Met Office)

summary of lst validation results
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)

summary and conclusions
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
acknowledgements
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

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