Full Resolution – Reduced Resolution

differences

E. Papandrea, M. Carlotti, M. Ridolfi, E. Arnone

DCFI, University of Bologna, Italy

B.M. Dinelli

ISAC-CNR, Bologna, Italy

QWG# 18

Frascati, 3-5 Dec 2008

Outline

- Significant systematic differences exist between products retrieved from MIPAS Full Resolution (FR) and Reduced Resolution (RR) measurements

-Few test retrievals were carried-out using MIPAS measurements of orbit 10798 to characterize these differences.

-Orbit 10798 was acquired at full spectral resolution with the “old” scan pattern (17 sweeps). The measurements were then artificially degraded to the new reduced resolution by BOMEM, therefore two versions of the L1B files (FR and RR) relative to the same measurements are available.

-Here are the names of the two L1B files used in the tests:

- MIP_NL__1P_10798_SIM_HIGH_REPROCESS2 (FR)

- MIP_NL__1P_10798_FULL_8.0cm_threshold_5 (RR)

Solid black lines: average differences between profiles (RR-FR).

Dashed lines: average differences calculated by interpolating linearly in log(p) one profile to the pressure grid of the other.

ESDs: red for FR and blue for RR.

Retrievals performed with ORM on the RR and the FR measurements show a systematic difference around 30-40 km in both pressure and temperature.

RR-FR REFERENCE

RR-FR REFERENCE --- RR-FR REFERENCE (2081)

NLTE Problems?

At last QWG meeting Manuel Lopes Puertas has pointed out that the CO2 laser band (at 900 cm-1) shows night – day differences at 30 km due to NLTE effects.

Two of the MWs used in the retrieval of PT for the RR observations are in the CO2 laser band region. The two MWs are used only at low altitudes, below 30 km.

-Are the CO2 lines inside the MWs affected by NLTE at the used altitudes?

-Are the spectral points that show NLTE differences masked out?

MWs: PT_363 PT_364

Simulated spectrum for MWs PT_0363, PT_0364 at respectively 22 and 26 km. The blue dots show the unmasked spectral points. The green lines show the position of the CO2 lines inside the MW.

Possible NLTE in PT MWs (FR)

The microwindows used in the retrieval of PT for the RR observations that are in the CO2 laser band region are:

PT__0363 937.500 – 940.500 used below 23 km

PT__0364 942.313 – 944.625 used below 27 km

Upper panel: measured spectra for MW PT_0363 at about 24 km for scans 15 (black - day) and 63 (blue -night). Lower panel: day minus night difference between the two spectra.

FR-2081

Possible NLTE in PT MWs (FR)

Upper panel: measured spectra for MW PT_0364 at about 24 km for scans 15 (black - day) and 63 (blue - night). Lower panel: day minus night difference between the two spectra.

The microwindows used in the retrieval of PT for the RR observations that are in the CO2 laser band region are:

PT__0363 937.500 – 940.500 used below 23 km

PT__0364 942.313 – 944.625 used below 27 km

FR-2081

Possible NLTE in PT MWs (RR)

Upper panel: measured spectra for MW PT_0363 at about 24 km for scans 61 (black - day) and 89 (blue - night). Lower panel: day minus night difference between the two spectra

The microwindows used in the retrieval of PT for the RR observations that are in the CO2 laser band region are:

PT__0363 937.500 – 940.500 used below 23 km

PT__0364 942.313 – 944.625 used below 27 km

RR-27214

Possible NLTE in PT MWs (RR)

Upper panel: measured spectra for MW PT_0364 at about 24 km for scans 61 (black - day) and 89 (blue - night). Lower panel: day minus night difference between the two spectra.

The microwindows used in the retrieval of PT for the RR observations that are in the CO2 laser band region are:

PT__0363 937.500 – 940.500 used below 23 km

PT__0364 942.313 – 944.625 used below 27 km

RR-27214

MWs: PT_363 PT_364

Red circle: points masked by hand -> No differences in the retrieval

RR-FR REFERENCE --- RR-FR DAY

RR-FR REFERENCE --- RR-FR NIGHT

RR-FR REFERENCE --- RR-FR CONT 60 km

RR-FR REFERENCE --- RR-RR CONT 60 km

RR-FR REFERENCE --- FR-FR CONT 60 km

RR-FR REFERENCE --- RR-FR OFFSET ALT. DEP.

RR-FR REFERENCE --- RR-FR GMTR

RR-FR REFERENCE --- RR-FR GMTR (MTR MWs)

Conclusions / 1

• MWs PT__0363 and PT__0364 are affected by NLTE at altitudes that are included in the PT retrieval Occupation Matrix for reduced resolution.

• The large systematic differences observed between temperatures and pressures retrieved from RR and FR measurements (outside the ESDs boundaries) seem to be concentrated in the diurnal part of the orbit (due to NLTE ?).

• Masking out the central part of the CO2 lines affected by NLTE doesn’t reduce the differences.

• Extending the retrieval of the continuum from 20 km up to 60 km makes large differences in the RR retrievals and small differences in the FR retrievals. The difference between FR and RR retrievals globally decreases, showing that the continuum is able to compensate (at least partially) for some effect that is badly modeled by the forward model.

Conclusions / 2

• The use of an altitude dependent offset does not reduce the differences.

• The horizontal variability of the atmosphere (not modeled by ORM) is not the cause of the observed bias.

• The bias decreases significantly if the MWs selected for the GMTR joint p,T, H2O, O3 retrieval are used.

POSSIBLE ACTIONS:

• Select different MWs for the RR.• Fit the continuum up to 60 km (check pressure broadening

parameters to explain pressure bias when continuum is fitted up to 60 km).