1. Comparison of AATSR SST with other sensors
David Ridley
Marianne Edwards
Space Research Centre
University of Leicester
I’d like to talk to you about some work we have been setting up at Leicester, looking at the comparison of AATSR SST with other sensors.
This work had been carried out with David Ridley. David Ridley is an undergraduate physics student at Leicester and a very able programmer.

2. Comparison with global datasets
Comparison of global monthly mean AATSR SST data with:-
ATSR-2
AVHRR
MODIS
ECMWF
TMI
To date, comparisons performed between AATSR data and MODIS, ECMWF and TMI for September 2002
Data compared are monthly means, at half degree resolution
AATSR data used: spatially averaged product, dual view SST retrieval, all available data
We have set up IDL routines to compare AATSR SST data with SST data from ATSR-2, AVHRR, MODIS, ECMWF analysis fields and TMI data. To date, comparisons have been performed between AATSR data and MODIS, ECMWF and TMI for September 2002.
Data are compared at monthly means, half degree resolution.
The AATSR data used are the AST product, SST taken using the dual view and all available data for the month – so both night-time and day-time.

3. Methodology
Difference images produced to find areas of discrepancy for more detailed analysis.
Time series analysis.
This slide shows the output from the routines – difference images. You can go in and specify a smaller area.

4. AATSR vs ECMWF Sept 2002 ECMWF: 2.5 degree
Mean global difference: deg K
Mean absolute difference: 0.88 deg K
Standard deviation: 1.43 deg K
Tropical region (+/- 30 degrees)
Mean difference: deg K
Standard deviation: 0.88 deg K
Percentage of values between +/- 0.6 deg K: 54.82
Comparisons with ECMWF show that AATSR and SST from ECMWF analysis fields are generally negligible.
Expect skin to be slightly cooler – the fact that they are the same indicating that maybe AATSR is marginally too warm. Same results as Lisa’s results.
ECMWF poor at the poles.
Poor edge matching – due to 2.5 degree binning? No land mask given.

5. AATSR vs TMI Sept 2002 TMI data: 0.25 degree Binned to half degree
for comparison
Mean global difference: deg K (TMI warmer)
Mean absolute difference: 0.50 deg K
Standard deviation: 0.55 deg K
Tropical region (+/- 30 degrees)
Mean difference: deg K
Standard deviation: 0.50 deg K
Percentage of values between +/- 0.6 deg K: 68.48
The comparison of AATSR and TMI shows that TMI is slightly warmer – generally half a degree difference
Kelvin-Helmholtz wave instability – waves seen in the East Pacific ??
Get waves in the ocean of SST – TMI and AATSR measuring at different points?? Out of phase?? Possibly??
African aerosol anomaly not seen – problem with MODIS? Or same correction by TMI + MODIS (different methods).
Done some comparisons with nadir only SST’s from AATSR – distribution with other instruments is much more similar. AATSR takes dual view – TMI doesn’t – are other instruments all out by ~0.5K?
No poles

6. SST from 11 micron day/night
AATSR vs MODIS Sept 2002
MODIS: 36km,
SST from 11 micron day/night
Mean global difference: deg K (MODIS warmer)
Standard deviation: 0.75 deg K
Tropical region (+/- 30 degrees)
Mean difference: deg K
Standard deviation: 0.51 deg K
Percentage of values between +/- 0.6 deg K: 65.63
This slide shows AATSR versus MODIS for September 2002.
The mean global difference is –0.41 degrees indicating that MODIS is generally reading warmer than AATSR. There is quite a large standard deviation of 0.75 degrees.
If you just take the tropical region (half the total number of pixels), the mean difference is the same as the global difference.
Lisa’s results – AATSR slightly too warm – these indicated AATSR slightly too cool.
Interesting to compare these on a regional basis.
Early results – need more than one month to see any patterns.
Regional variations – aerosol off the coast of West Africa
Dual/nadir comparison picks up this region suggesting the dual view is correcting for the aerosol and thus MODIS is incorrect ??
Poor correlation in polar regions.
Mean absolute difference: 0.64 deg K

7. Further investigations needed.
Conclusions
Preliminary results - comparisons performed for AATSR data and SST from ECMWF analyses, MODIS and TMI data, for September 2002
Difficult to see patterns with one month’s data. More data and processing needed, including comparisons with AVHRR and ATSR-2.
Further investigations needed.
How accurate are TMI and MODIS against buoy data?
Spot checks using precision radiometers