March 21, ‘06 comp

May 5, ‘06 comp

Summary

• ~4% swath angle dependent difference• Up to 9% difference over clouds• Differences correlate with snow/ice maps• Known issue in OMTO3: O3 underestimation by up to 3%

at large SZAs due to straylight at 313 nm.

Comparison of OMTO3 v1, OMDOAO3 v0.9.42 and

OMDOAO3 v1 Zonal Means

Er-Woon ChiouAnd

Daniel KahnSSAI

Monthly Gridded Map Criteria

1 degree x 1 degree grid using all 60 pixels• OMTO3 screening criteria

(1) Total ozone > 0(2) Error flag = 1, 1, 2

• OMDOAO3 screening criteria(1) Total ozone > 20(2) Precision ÷ (total ozone) < 90%(3) Ascending part of the orbit

January 2005 Gridded Maps

March 2005 Gridded Maps

May 2005 Gridded Maps

July 2005 Gridded Maps

September 2005 Gridded Maps

November 2005 Gridded Maps

8-Weekly Zonal Means• Uses the nadir pixel only• 5-degree zones• 8-week period

– Week 1: 3/19 – 3/25– Week 8: 5/13 – 5/17

• OMTO3 screening criteria:1. 50 < total ozone < 7002. Error flag 0, 1, 2, 8, 9, 10

• OMDOAO3 screening criteria both versions:1. 50 < total ozone < 700

� DOAS v0.942 DOAS v1.01 OMTO3

� DOAS v0.942 DOAS v1.01 OMTO3

� DOAS v0.942 DOAS v1.01 OMTO3

Summary

• For 60 S through 60 N, OMDOAO3 v0.9.42 is larger than OMTO3 by about 8 ~ 9 DU

• For 50 S through 50 N, OMDOAO3 v1 is very close to OMTO3 for all 8 weeks with differences of 1 ~ 2 DU

• Differences between OMDOAO3 v1 and OMTO3 are larger during the first 4 weeks at 60 N and the last 2 weeks at 60 S

• For 30 S to 30 N, OMDOAO3 v1 is always slightly less than OMTO3

Cloud-top pressure climatology assumed by OMI Total O3 Products

OMTO3 January (R>0.6)

OMDOAS January ‘05 (fc>0.75)

Cloud hts are lower

Comparison of Cloud-top Pressures

Raman clouds are higher than O2-O2, but similar to THIR except in downwelling areas of the tropics.

THIR

O2-O2 Raman

Comparison of IR Cloud Heights

Nimbus-7 THIR (R>0.6) Note: color scales are different

Aqua MODIS Jan ‘05 (all R)

MODIS clouds are somewhat lower, particularly over water. Similar features were seen in THIR without R cutoff.

Summary

• O2-O2 derived cloud hts are generally too low compared to both IR and Raman.

• Raman values are similar to IR (after removing low reflecting clouds from the IR climatology) except in the downwelling areas of the tropics.

Possible Improvements to OMTO3

• Replace cloud climatology with OMI-”measured” cloud-top pressures.

• Fix (apparent) straylight related problem at large SZAs.• Improve O3 climatology using MLS data.• Improve Raman scattering table.• Improve profile correction scheme.

– optimal estimation using several wavelengths?• Degrade OMI resolution to 1-2 nm before doing retrieval.

– To reduce noise and Ring signal• Replace Bass & Paur (1981) with Malicet, Daumont et al. (1995)

O3 cross-section.