Validation of the OMI Surface UV product OMI Science Team Meeting #11 De Bilt, June 20-23, 2006 Aapo Tanskanen

OMI Surface UV Algorithm N. Krotkov /GEST Center, University of Maryland J. Herman /NASA GSFC A. Tanskanen, A. Arola /FMI paper: ”Surface Ultraviolet Irradiance from OMI”, IEEE TGRS Aura Special Issue, May 2006 Validation of the OMI Surface UV Data A. Määttä, A. Tanskanen, J. Kaurola, T. Koskela, A. Karpetchko /FMI V. Fioletov / MSC Environment Canada G. Bernhard / Biospherical Instruments poster: ”Validation of the OMI surface UV data” in the AGU fall meeting, 5-9 Dec, 2005 R. McKenzie / NIWA Y. Kondo / University of Tokyo OMI is a contribution of NIVR in collaboration with FMI to the EOS Aura mission of NASA. Scientific use of OMI data is coordinated by KNMI, NASA and FMI.

UV radiation affects Human health: skin cancer, cataracts, immune system, vitamin D synthesis Aquatic and terrestrial ecosystems Materials Additionally, UV is involved in various atmospheric and other processes by photochemical reactions Surface UV depends on Solar zenith angle Total column ozone Clouds Aerosols Surface albedo Topography Some Background Information about UV There is a need for UV forecasts and longterm monitoring of UV. These services are being developed for example within the PROMOTE GSE of ESA.

OMI Surface UV Algorithm and Surface UV Products Inherits from the TOMS UV algorithm based on look-up-tables made with various radiative transfer models. 1.Calculate clear-sky surface UV irradiance 2.Define cloud optical depth  that gives the measured TOA radiance 3.Make cloud correction using the obtained  4.Absorbing aerosol correction to be added in the future Input: OMI Level 2 total ozone column data from NASA Products: Erythemal dose rate at local solar noon (UV Index) Erythemal daily dose Irradiances at 305, 310, 324 and 380 nm at local solar noon Processing, archiving and dissemination of the OMI surface UV data are performed at FMI’s Satellite Data Centre in Sodankylä. The OMI surface UV algorithm is implemented in two separate processing systems: OMI-VFD and Global OMUVB.

OMI Very-Fast-Delivery has been operational since March 2006 OMI data is received by Direct Broadcast in Sodankylä and is processed immediately after each overpass of the Aura satellite. Distribution plots for total column ozone, UV Index and Erythemal daily dose are published within 30 minutes after the overpass at

Global OMUVB product is based solely on the L2 OMTO3 data, The rest of the presentation corresponds to this data product

Currently, some 6886 granules out of the total ECS Collection 2 OMTO3 granules have been processed, which corresponds to a time period from August 17, 2004 to March 24, The L2 OMI Surface UV data (OMUVB) are archived locally in Sodankylä and have been submitted to the Aura Validation Data Center. AVDC provides overpass data for some 80 sites for OMI validation teams. There are plans to reprocess all the data as a reprocessed version of the OMTO3 data becomes available. Processing Status Data Dissemination AVDC provides L2 OMUVB overpass data, new sites can be added as requested FMI provides a website for online plotting and download of L3 OMUVB images Additionally, both L2 (HDF5-EOS) and L3 (1x1 degrees TOMS) data are available at FMI’s ftp site for registered users

Validation of the OMI UV data with Ground-Based Spectral UV Measurements Comparison of the daily erythemal doses Ground-based reference data Brewers in Jokioinen and Sodankylä SUV100 network data by National Science Foundation Canadian Brewer network data from Meteorological Service of Canada Spectral UV data from Palmer and Tokyo

Please note that the scatterogram for Jokioinen does not correspond to the latest validation results!

Brewer data provided by MSC/Environment Canada Preliminary data: calibration errors up to 5% are possible

SUV-100 data provided by NSF UV Monitoring Network, operated by Biospherical Instruments Inc. under a contract from the US National Science Foundation’s Office of Polar Programs via Raytheon Polar Services Company. Preliminary Version 0 data: no cosine correction, Version 2 data will be higher by 4-10%

Preliminary results. Ground-based data provided by NIWA and University of Tokyo

Validation Statistics for Daily Doses [kJ/m 2 ] Validation instrumentnBias%BiasRMS%RMSr Jokioinen Brewer Mk-III # %0.2233%0.99 Sodankylä Brewer Mk-II # % %0.97 Toronto Brewer Mk-II # % %0.98 Toronto Brewer Mk-III # % %0.97 San Diego SUV % %0.95 Ushuaia SUV % %0.97 Barrow SUV % %0.94 Palmer %0.5124%0.97 Tokyo %1.0075%0.92

Conclusions Analog to the TOMS total column ozone time-series the surface UV time-series are continued with the OMI measurement data applying an algorithm that is similar to the TOMS UV algorithm First validation results imply anticipated accuracy of the OMI surface UV data: it’s time to publish the data Results imply that there is a need to introduce a correction for absorbing aerosols in order to get better agreement with reference data in sites affected by urban pollution or aerosols from natural sources. The validation effort continues: use more reference data from ground-based instruments, validate also spectral irradiances, elaborate the statistical analysis of validation results

I will be out of office from July 3rd till August 15th See you in Boulder!