ITSC XVI
Angra dos Reis, 7-13 May 2008
Midtropospheric CO2 Concentration derived from
infrared and microwave sounders.
Application to the TOVS, AIRS/AMSU, and
IASI/AMSU instruments.
Cyril Crevoisier, Alain Chédin, Noëlle A. Scott,
Gaelle Dufour, Raymond Armante and Virginie Capelle
Laboratoire de Météorologie Dynamique, CNRS, IPSL, Palaiseau
CO2 from infrared/microwave sounders
NOAA10/HIRS/MSU
1987-1991
Time coverage
NOAAk/HIRS/AMSU
1999-2005
AIRS/AMSU
NASA/Aqua
Since 2002
IASI/AMSU
ESA/MetOp
Since 2006
NOAA10
TOVS
NOAAk
ATOVS
Aqua
AIRS/AMSU
MetOp
IASI/AMSU
1987-1991
1999-2005
May 2002-…
Oct. 2006-…
0.5 - 2 cm-1
0.5 cm-1
(apodized)
Spectral
resolution
# IR/MW
channels
19/4
19/15
2378/15
(324/15)
8461/15
(421/15)
Local time
7.30
7.30
1.30
9.30
CO2 seasonal cycle - Northern tropics [0-20°N]
380
370
360
350
340
87
89
91
93
95
97
NOAA10
TOVS
99
01
03
05
NOAA15
ATOVS*
07
MetOp
IASI/AMSU
Aqua
AIRS/AMSU
•NOAA10: Chédin et al., JGR, 2003, 2008.
•NOAA15: Very preliminary results…
•AIRS: Crevoisier et al., GRL, 2004.
CO2 seasonal cycle - Northern tropics [0-20°N]
380
370
360
350
340
87
89
91
93
NOAA10
TOVS
Difference between
7.30 am/pm observations
95
97
99
01
03
05
NOAA15
ATOVS*
07
MetOp
IASI/AMSU
Aqua
AIRS/AMSU
Diurnal Tropospheric Excess of CO2
due to biomass burning emissions
See Poster B12 [Chédin et al.]
Spectrum and sensitivity to atmospheric components
Sensitivity of IASI TB to variations of atmospheric and
surface variables (simulations with the 4A RT model)
CO2 (1%)
H2O (20%)
O3 (20%)
CH4 (20%)
CO (40%)
N2O (2%)
Surface
surface
TBpert-TBref (K)
CH4
CO2
N2O
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
H2O
CO
O3
wavenumber (cm-1)
15 μm
10 μm
6 μm
4 μm
1 % of CO2 variation → 0.04% of TB variation
3ppmv → 0.3 K
The full information contained in the channels is needed to
extract the CO2 signal!
Spectrum and sensitivity to atmospheric components
Sensitivity of IASI TB to variations of atmospheric and
surface variables (simulations with the 4A RT model)
CO2 (1%)
H2O (20%)
O3 (20%)
CH4 (20%)
CO (40%)
N2O (2%)
Surface
surface
TBpert-TBref (K)
CH4
CO2
N2O
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
H2O
CO
O3
wavenumber (cm-1)
15 μm
10 μm
6 μm
4 μm
1 % of CO2 variation → 0.04% of TB variation
3ppmv → 0.3 K
The full information contained in the channels is needed to
extract the CO2 signal!
Spectrum and sensitivity to atmospheric components
Sensitivity of AIRS and IASI channels in the two CO2 bands
(simulations with the 4A RT model)
1.5
1
15 μm
4 μm
AIRS
TBpert-TBref (K)
0.5
0
-0.5
1.5
1
0.5
0
-0.5
650
H2O
IASI
noise
670
690
CO2
O3
710
730
750
surface T
CO
2220
noise
CO2
2260
2300
2340
wavenumber (cm-1)
CO2 (1%)
H2O (20%)
O3 (20%)
CO (40%)
Surface T (1%)
Surf. emissivity (5%)
At 4 μm: Non-LTE
Only nightime
retrieval
2380
Spectrum and sensitivity to atmospheric components
Jacobians of two “CO2” AIRS channels
Channel 261 - 4μm
Channel 80 - 15μm
0.1
CO2 Jacobian
T Jacobian
O3 Jacobian
1
10
100
1000
•Channels at 4μm peak lower in the atmosphere.
Spectrum and sensitivity to atmospheric components
Jacobians of two “CO2” AIRS channels
and AMSU weighting functions
Channel 264 - 4μm
Channel 80 - 15μm
0.1
CO2 Jacobian
T Jacobian
O3 Jacobian
1
10
AMSU 10
AMSU 9
100
AMSU 8
AMSU 7
AMSU 6
1000
•Channels at 4μm peak lower in the atmosphere.
•AMSU channels bring the information on temperature.
CO2 channel selection
•Aqua AIRS/AMSU:
-15 AIRS channels (8 in the 15 μm band - 7 in the 4 μm band).
-2 AMSU channels (6 and 8).
•MetOp IASI/AMSU:
-14 IASI channels (all in the 15 μm band).
-3 AMSU channels (6, 7, and 8).
IASI - CO2 channel selection
IASI sensitivity (K)
0.25
0.25
CO2 (1%)
H2O (20%)
O3 (20%)
10
IASI CO2 Jacobians
0.2
0.2
Sensitivity (K)
0.15
0.15
CH4 4%
AMSU 8
CO 20%
100
N2O 1%
0.1
0.1
O3 20%
CO2 1%
H2O 20%
0.05
0.05
00
-0.05
-0.05
AMSU 7
1
2
3
4
5
6
7
8
9
10
11
12
13
14
1000
AMSU 6
The level1b validation suite at LMD
See Poster B10 [Armante et al.]
Colocation of radiosoundings/re-analyses ERA40 with IR/MW observations
FTP
Radiosoundings
/Reanalysis
(ERA-40)
Quality control of
the Radiosoundings
ÎInter/extrapolation
UGAMP climatology
« Clean »
Radiosoundings
ECMWF
Radiative biases
between calculated
and observed BT
RT model
(Stransac, 4A)
Space and
Time
Colocation
(100 Km, 3h)
Fixed CO2=372 ppmv
- Radiosoundings «ERA40 »
(23 Go from 1979 to 2007 )
-Re-analyses ERA-40
(79 Mo / day, 2 days /month)
Example IASI/AMSU (MetOp)
Satellite data :14 orbits/day
900 Mo/day; 421 IR, 15 MW
L1B
Satellite
Data
(1979-2006)
Calc.-Obs. (K)
AIRS Radiative biases: Monthly evolution (5 years over the tropics)
0.8
AIRS 80 (15 μm)
1.6
0.6
1.4
0.4
1.2
0.2
1
0
0.8
-0.2
03
04
05
06
07
08
0.6
03
AIRS 264 (4 μm)
04
05
06
07
08
05
06
07
08
AMSU 6
1.3
1.1
0.9
0.7
~60 situations/month over sea
~30 situations/month over land
0.5
0.3
03
04
Calc.-Obs. (K)
AIRS Radiative biases: Monthly evolution (5 years over the tropics)
AIRS 80 (15 μm)
0.8
1.6
0.6
1.4
0.4
1.2
0.2
1
0
0.8
-0.2
03
04
05
06
07
08
“CO2” slopes (mean over 5 years):
AIRS 80: 2.16 ppmv.yr-1
AIRS 264: 2.39 ppmv.yr-1
Mauna Loa: 2.05
ppmv.yr-1
~60 situations/month over sea
~30 situations/month over land
0.6
03
AIRS 264 (4 μm)
04
05
06
07
08
05
06
07
08
AMSU 6
1.3
1.1
0.9
0.7
0.5
0.3
03
04
A stand-alone approach
General features of the CO2 retrieval scheme :
non-linear regressions
Training data
set (TIGR)
Selection of a set of CO2
channels
Off-line
Training of
Neural Networks
calc-obs
bias removal
Non-linear
inference scheme
« clear sky »
detection
qCO2
•Simultaneous use of IR and MW channels to decorrelate T/CO2.
IASI
AMSU
•Retrieval limited to the tropical region.
[Chédin et al., JGR, 2003; Crevoisier et al., GRL, 2004]
Evaluation of the inference scheme characteristics
We retrieve a mid-to-upper tropospheric integrated content of CO2.
Mean CO2 averaging kernel over TIGR
atmospheric dataset for nadir observation
Pressure (hPa)
10
100
5-15 km
1000
IASI/AMSU
NOAA15
AIRS/AMSU
CO2 distribution from AIRS and IASI - Monthly average
Evaluation of IASI CO2
JAL commercial airliners
between Australia and Japan
•Aircraft [Matsueda et al.]
-8-10 km
-1-2 points/month
-until March. 2007
10
IASI CO2 weighting function
altitude of
the aircraft
100
1000
•IASI CO2
-integrated content 5-15 km
-monthly mean
-period: July 2007-March 2008
Seasonal cycle
Detrended CO2 seasonal cycle as observed in situ by
JAL aircraft for 2003-2006
2
CO2 (ppmv)
1
0
-1
-2
Apr
Jun
Aug
Oct
Dec
Feb
Seasonal cycle
Detrended CO2 seasonal cycle as observed in situ by
JAL aircraft for 2003-2006
2
CO2 (ppmv)
1
IASI
(07/07-08/03)
0
-1
-2
Apr
Jun
Aug
Oct
Dec
Feb
Latitudinal variation
CO2 latitudinal variation in July
1 ppmv
20S-25S
15S-20S
10S-15S
05S-10S
EQ-05S
05N-EQ
10N-05N
15N-10N
20N-15N
25N-20N
30N-25N
2003
2004
JAL aircraft (10 km)
2005
2006
2007 IASI (5-15 km)
Conclusions
•We retrieve a mid-to-upper tropospheric integrated content of CO2 from
simultaneous IR/MW observations (TOVS, ATOVS, AIRS/AMSU,
IASI/AMSU).
•The CO2 signal is very low:
The full information contained in the channels is needed (that excludes
using PCA-like data).
•Good agreement of CO2 distribution between IASI and AIRS but lower
variability/uncertainty with IASI:
-Reducing radiometric noise is as important as improving spectral
resolution.
-A “good” AMSU instrument is important.
•General good agreement with in-situ observation in terms of seasonal cycle
and latitudinal gradients.