OMI TOMS Total Ozone Column Validation Status April 2006

OMI total ozone column data retrieved with the TOMS algorithm and labeled OMTO3, was compared to total ozone column recordings by ground based Dobson and Brewer networks, and to SBUV total ozone column data. Based on 15 months of data we conclude that OMTO3 compares very well to the measurement by these correlative instruments. With respect to the worldwide Dobson network, a global average bias of 1% is found for OMTO3 if the tropics are excluded. When considering individual station averages, biases are within the 3% range, now with respect to both Brewer and Dobson instruments. Above 35 N, comparisons are considerably better, with differences within the 1% range. There is no significant dependence on solar zenith angle, or on total ozone column. With respect to Brewer instruments, which are almost all located in the Northern Hemisphere, a “global” average difference of -0.1% is found. Time series of globally averaged differences between OMTO3 and ground instruments show an annual variation with amplitude of 1.5% with respect to Dobson instruments, and no annual variation with respect to Brewer instruments. It should be noted that annual cycles in the recording by ground based instruments are expected and may contribute to the differences observed. Comparisons with SBUV reveal a positive bias of OMI data. When comparing the validation of OMI with that of EP-TOMS, validated against the same ground based instrument set, OMI clearly shows better results.