1. OMI Soft Calibration P. K. Bhartia, Glen Jaross, Steve Taylor, Xiong Liu, Tom Kelly, Changwoo Ahn, Dave Haffner NASA GSFC, Maryland, USA

2. What is Soft Calibration? Instrument parameters that are derived by checking consistency against radiative transfer models or by using external data Which OMI products are most sensitive to instrument calibration?*** Aerosol index (AI) Aerosol Absorption Optical Thickness (AAOT) Trop O 3 profile *** DOAS algorithms “soft calibrate” during fitting

3. -dep of Aerosol Absorption  abs=0.05 BC OCDust Assume 10% abs at 410 nm

4. Detection of Absorbing Aerosols from UV Measurements Solar ZA: 45˚-55˚ Satellite ZA: 0˚-60˚ Azimuth= ~90˚ Points shifts up/down & left/right due to aerosol absorption Sky brightness color Saturation color Saturation blue gray Solar ZA: 45˚-55˚ Satellite ZA: 0˚-60˚ Azimuth= ~90˚ Nimbus/7 TOMS data  -independent instrument change will shift points left or right  - dependent change will shift them up or down

5. Effect of Swath Angle Anomaly on OMI UV Aerosol Index Pos 41 Pos 54

6. Effect of Error in Radiance on O 3 profile Assumed error: 0% at 329 nm, 1% at 270 nm, linear with

7. Straylight error in Col 3 OMI UV1 radiances estimated using MLS O 3 profiles f c >80% f c <10% 60˚ SZA, Swath Pos 16 Increases with SZA

8. Straylight error without any correction

9. Conclusions  OMI UV-AI, AAOT and trop O 3 products are very sensitive to instrumental errors.  There are significant calibration (multiplicative) and straylight (additive) errors in OMI UV1 data. MLS O 3 profiles can be used to estimate these errors. Since the errors vary with SZA, swath position and cloud fraction, the correction is complicated.  To improve OMI aerosol products we need to analyze errors in UV-AI at locations where there are no (absorbing) aerosols (S. Pacific). Fresnel reflection and water-leaving radiances from oceans have large effect on UV-AI. These effects must be corrected to estimate instrumental errors.