KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Performances of the KLIMA-IASI Accelerated RM

S. Del Bianco

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

These tests have been carried out to evaluate the performances of the KLIMA-IASI Accelerated Retrieval Model. All tests have been performed using simulated IASI measurements and selecting as retrieval target the temperature profile, the water vapour profile, the total and partial columns of carbon dioxide and ozone and the Earth skin temperature.

A quantitative assessment of the quality of the retrieval products has been derived by computing:• the retrieval error on the target parameters (including the random and the systematic components);• the bias between the retrieved and the true value of the target parameters due the approximations of the accelerated retrieval code.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

A series of 5 retrieval tests was conducted, by combining different options for the set up of the FMs used to generate the simulated measurements and to perform retrieval calculations.

FM of simulated measurements

FM of the retrieval

A priori VCM including FM errors

Spectral band selection

TEST 1 Reference FM Reference FM NO NO

TEST 2 Reference FM Accelerated FM NO NO

TEST 3 Reference FM Accelerated FM YES NO

TEST 4 Reference FM Accelerated FM NO YES

TEST 5 Reference FM Accelerated FM YES YES

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

The basic features of the inverse model implemented in all retrieval tests can be summarised as follows:

Multi Target Retrieval;

Pressure retrieval grid for temperature: equal to the retrieval grid of IASI L2 operational products for the first 21 levels from 1050.0 hPa to 478.54 hPa (0-6 km); for the levels above only one every third pressure level is maintained. The total number of levels of the retrieval grid for temperature is 44;

Pressure retrieval grid for H2O: equal to the retrieval grid of IASI L2 operational products for the first 21 levels from 1050.0 hPa to 478.54 hPa (0-6 km); for the levels above only one every third pressure level is maintained. The total number of levels of the retrieval grid for temperature is 44;

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Pressure retrieval grid for CO2: equal to the retrieval grid of IASI L2 operational products for the first 4 levels from 1050.0 hPa to 978.98 hPa; for the levels above only one every second pressure level is maintained up to 499.54 hPa (~ 5.6 km). The total number of levels of the retrieval grid for temperature is 12;

Pressure retrieval grid for O3: one every third pressure level of the retrieval grid of IASI L2 operational products is taken from 1050.0 hPa to 759.16 hPa (~2.4 km). The total number of levels of the retrieval grid for temperature is 4;

Marquardt parameters: 0.01 for all targets;

Marquardt and Gauss dumping factor: 3;

Use of the optimal estimation.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

The target parameter of the retrieval are:

The profile of temperature;

The profiles of water vapour, carbon dioxide, and ozone;

The band dependent earth surface temperature.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

The atmospheric scenario (true atmospheric state and a priori values) selected for all the retrieval tests were taken from the IG2 climatology developed by University of Leicester for the operational analysis of MIPAS-ENVISAT data (Remedios et al. 2007).

True atmospheric state – IG2 profiles, October 2008 at Northern mid-latitude [20°N - 65°N].

A-priori atmospheric state – IG2 profiles, October 2007 at Northern mid-latitude [20°N - 65°N]. These IG2 profiles were used for the retrieved gases and temperature and pressure profiles.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

A priori errors and correlation length used for the retrieval tests

Target Parameter

A Priori Error

Error Correlation Length

Temperature 4 K 3 km

Water Vapour 100 – 120 % 5 km

Carbon Dioxide 10 % 5 km

Ozone 100 % 5 km

Surface Temperature 20 K N.A.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Temperature retrieval

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Temperature retrieval

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Water vapour retrieval

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Water vapour retrieval

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Ozone retrieval

Total Column PBL Column

Retr. Error [%]

(Retr. - True) [%]

Retr. Error [%]

(Retr. - True) [%]

TEST 1 0.7 -3.2 47.5 -14.0

TEST 2 0.7 -3.2 47.2 120.4

TEST 3 0.7 -2.9 47.4 54.2

TEST 4 2.1 -12.2 49.7 -5.6

TEST 5 2.2 -10.2 49.7 -3.2

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Carbon dioxide retrieval

Total Column PBL Column

Retr. Error [%]

(Retr. - True) [%]

Retr. Error [%]

(Retr. - True) [%]

TEST 1 1.3 -1.9 5.3 -1.3

TEST 2 1.2 -2.3 5.3 -1.8

TEST 3 1.2 -2.4 5.3 -2.6

TEST 4 1.5 -1.5 5.8 0.4

TEST 5 1.4 -1.7 5.7 -0.3

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Conclusion (1)

Using the VCM of the FM in the T5 test the performance of the water vapour retrieval and in the T3 the performance of thePBL O3 column retrieval have been improved wrt T4 and T2 respectively.

The spectral band selection increases the temperature error of about 0.25 K and the water vapour error of about 5% above 1 km and of 10% above 5 km.

A bias of 0.5% has been observed in the CO2 retrieval in T2 and T3. This bias has not been observed in T4 and T5 where the band selection reduces the systematic errors.

KLIMA – IASI Phase 1 Final Meeting ESA-ESRIN, 2 March 2009

Conclusion (2)

A better assessment of the CO2 bias needs of a statistical reduction of the random retrieval error.These tests may be done using the actual measurement NESR.

The results of these tests show that the total CO2 column can be retrieved with the target accuracy of 0.3% averaging 25 observations corresponding to 100 x 100 km pixel.