1. Outline: Method Preliminary results Future
Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels Caroline Poulsen,Tim Nightingale and Phil Watts
Outline:
Method
Preliminary results
Future
Point of contact:
co-PIs: Carsten Brockmann Ass(MERIS scene identification)., Dave Smith(calibration scientist), Anthony Baran(Ice particle phase functions)

2. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
Data products so far
5 scenes received from MERIS so far
10/21, 10/22, 10/23 ,11/16
2 colocated AATSR scenes
10/23 ,11/16
not all are suitable for analysis, no good stratus scene at present.
Data tools and analysis
LUTs have been generated for the baseline and error analysis cases.
Tools to read AATSR and MERIS developed and tested
Analysis routine has been adapted
Preliminary results

3. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
A 4 layer model has been developed to generated look up tables of atmospheric properties such as reflectance and transmittance as a function of cloud optical depth and particle size
Layer 1:Stratospheric aerosols
Layer 2:Rayleigh scattering
Layer 3:Cloud
Layer 4:Rayleigh scattering and aerosols
The Model which uses DISORT can be changed to vary the height of the cloud layer,
the concentration of aerosols or another cloud layer can be added to test the sensitivity
of the results to different factors

4. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
INTERCALIBRATION of visible
channels and The 1.6
channel cannot be calibrated this way
because it is sensitive to particle size
Method 1: Tropical (deep) convection
Optically thick, spectrally
‘neutral’ cloud Km
Cloud optical depth
not known, absolute
calibration not possible
(unless ‘saturation’
proves reliable).
Well defined spectral
characteristics allows
inter-channel calibration.
Optically thin atmosphere
above cloud
Non-reflecting
surface
Ocean

5. Scene pre-selection by Brockmann Ass.
(January-June shown)

6. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
Method 1: Tropical (deep) convection
AATSR 0.55/0.67 calibration 23/10
measurements
calculations
+ without ozone correction
With ozone correction derived from ECMWF profiles
 with ozone correction

7. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
Method 1: Tropical (deep) convection
AATSR 0.55/0.67 calibration 23/10
MERIS 0.55/0.67 calibration 23/10
Currently with ozone correction. This method has an accuracy of 1-2%

8. Method 2: Arctic Stratus + Dual view
Forward scattering
+ Oblique path =
High reflectance
Side scattering
+ nadir path =
Low reflectance
ABSOLUTE calibration of
visible channels
ATSR along-
track view
ATSR nadir
view
Stratus: homogeneous,
‘single layer’: not too thick!
Ocean: black
High Northern latitude, descending node
+90 secs
Rayleigh layer
+ aerosol?

9. Scene pre-selection by Brockmann Ass.
Solar geometry is very important in this case
May/Jun/Jul
Apr/Aug
Mar/Sept
Feb/Oct
Jan/Nov
Dec

10. ATSR-2 Method 2: Arctic Stratus + Dual view: 1.6 mm
calibration missing a 1.3 factor
Inc. CO2 absorption
DISORT reflectances
for t = 1-32, Re = 4-16

11. ATSR-2 Method 2: Arctic Stratus + Dual view : 1.6 mm
ATSR-2 Including missing 1.3 factor
Inc. CO2 absorption

12. ATSR-2 Method 2: Arctic Stratus + Dual view :- 0.55 mm

13. Inter- and Absolute-calibration of AATSR/ MERIS reflectance channels
Future
Proper error analysis.
More scenes, especially more stratus scenes.
Colocation with MERIS data.
Presentation of results.
Produce calibration figures.