# Presentation: 185918

## Status OMI Ozone Profile Algorithm

- Ben Veihelmann on behalf of:
- Johan de Haan and Pepijn Veefkind
- KNMI, de Bilt, The Netherlands

## OMI Ozone Profile Product

**along track pixel number**

**across track pixel number**

**layer number**

-  complementary to O3-profile data from limb sounders
-  ~15 profiles / second
-  high spatial resolution

## Ozone profile algorithm

- Optimal estimation (Rodgers)
- A-priori: Fortuin & Kelder climatology
- Forward model:  on-line radiative transfer (6 stream Lidort-a)
- Non-linear => iterative solution (start with a-priori)
- Use O2-O2 cloud product for cloud pressure and (initial) fraction
- Wavelength region: 270 – 330 nm (UV1 & UV2)
- Output: ozone layer column for 18 layers, a-priori,averaging kernel, DFS, error covariance, diagnostics, meta-data

## Software

- Software developed by SSF under KNMI guidance,except for the radiative transfer module
- Tests of software using prototype software developed by Roeland van Oss, Olaf Tuinder and Johan de Haan (OPERA, developed for GOME-2 and applied to GOME)
- Software nearly finished, some minor fixes required
- Integration in ODPS in progress
- Converges in about 4-5 iteration steps
- Initially, not all pixels will be processed. Pixels in the cross-track and flight direction can be skipped.

## Features

- Optional fit parameters:surface albedo, cloud fraction, NO2 column, SO2 column,aerosol optical thickness (at 400 nm) [not yet cloud albedo]
- Use Cabannes-Raman scattering to account for Ring effect
- Use absorption cross-section based interpolation => less wavelengths for forward calculations (about 100)
- Use polarization correction LUT
- Use Chebyshev expansion of reflectance=> convolution of radiance with slit function partly stored in LUT

## Example: SAUNA validation campaign

- Atmospheric Pressure [hPa]

- OMI

-  balloon-borne sonde
-  3 collocated MLS profiles v1.5

## Orbit 9235, 10 April 2006

- MLS

- OMI

## Plans

- Complete inter-comparison with prototype softwarewrite test report
- Prepare for QA, inter-comparison MLS, SBUV, and validation- validation: focus on campaigns
- Improve efficiency/accuracy of radiative transfer module- Layer Based Orders of Scattering (LABOS) (nearly completed)- factor 2.5 - 5 faster than Lidort-a
- Other improvements- depends on QA, inter-comparison, and validation- e.g. replace F&K climatology, polarization correction LUT
- provisional release: October 2006
- public release: in collection 3

## Conclusions

- Based on experience with GOME an improved O3 profile algorithm has been developed (e.g. account for rot. Raman scattering)
- Complex algorithm => extensive testing with a proven code
- Initial results for OMI data look mostly OK
- Integration in ODPS in progress
- Further improvements depend on QA, inter-comparisons, validation results, and further research:- replace radiative transfer module to improve efficiency- fit cloud albedo for thick clouds

## Backup Material

## Cross-Section Based Wavelength-Interpolation

- known on fine grid

- calculate on coarse grid

## Chebyshev-Expansion convolution of sunspectra F0 with slitfunction S precomputed  LUT

- Chebyshev-Expansion convolution of sunspectra *F**0* with slitfunction *S* precomputed  LUT

## Comparison MLS v1.5volume mixing ratio

- Comparison MLS v1.5volume mixing ratio

- Pixels nearSodankula

- atmospheric pressure (hPa)

- mixing ratio

- Ozone profile

## Example: SAUNA validation campaign

- Figure: E. Brinksma, M. Kroon

- balloon-borne sonde
- OMI

- Ozone profile

## Slide 15

## Relative change

- in reflectance
- if 1 DU ozone
- is removed from
- an atmospheric later
- p = midlevel pressure
- NOTE: isothermal

- As = 0.05

- As = 0.80

## Zoomed for As = 0.80

## Normalized for As = 0.05