Retrieval of large volcanic SO2 columns from the Aura Ozone Monitoring Instrument: Comparison and limitations

To improve global measurements of atmospheric sulfur dioxide (SO2), we have developed a new technique, called the linear fit (LF) algorithm, which uses the radiance measurements from the Ozone Monitoring Instrument (OMI) at a few discrete ultraviolet wavelengths to derive SO2, ozone, and effective reflectivity simultaneously. We have also developed a sliding median residual correction method for removing both the along- and cross-track biases from the retrieval results. The achieved internal consistencies among the LF-retrieved geophysical parameters clearly demonstrate the success of this technique. Comparison with the results from the Band Residual Difference technique has also illustrated the drastic improvements of this new technique at high SO2 loading conditions. We have constructed an error equation and derived the averaging kernel to characterize the LF retrieval and understand its limitations. Detailed error analysis has focused on the impacts of the SO2 column amounts and their vertical distributions on the retrieval results. The LF algorithm is robust and fast; therefore it is suitable for near real-time application in aviation hazards and volcanic eruption warnings. Very large SO2 loadings (>100 DU) require an off-line iterative solution of the LF equations to reduce the retrieval errors. Both the LF and sliding median techniques are very general so that they can be applied to measurements from other backscattered ultraviolet instruments, including the series of Total Ozone Mapping Spectrometer (TOMS) missions, thereby offering the capability to update the TOMS long-term record to maintain consistency with its OMI extension. Copyright 2007 by the American Geophysical Union. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: D24S4

SO2 data from the ozone monitoring instrument

We discuss collection 2 SO2 data from the Dutch-Finnish Ozone Monitoring Instrument (OMI) on board NASA EOS/Aura spacecraft and show examples of detected volcanic and anthropogenic SO2 emissions. Quantification of anthropogenic SO2 emissions requires collection 3 reprocessing available in the fall 2007

Improving retrieval of volcanic sulphur dioxide from backscattered UV satellite observations

Existing algorithms that use satellite measurements of solar backscattered ultraviolet (BUV) radiances to retrieve sulfur dioxide (SO2) vertical columns underestimate the large SO2 amounts encountered in fresh volcanic eruption clouds. To eliminate this underestimation we have developed a new technique, named the Iterative Spectral Fitting (ISF) algorithm, for accurate retrieval of SO2 vertical columns in the full range of volcanic emissions. The ISF algorithm is applied to Ozone Monitoring Instrument (OMI) BUV measurements of the Sierra Negra eruption (Galàpagos Islands, Ecuador) in October 2005. The results represent major improvements over the operational OMI SO2 products. Based on the ISF data, we report the largest SO2 vertical column amount (>1000 Dobson Units (DU), where 1 DU = 2.69 × 1016 molecules/cm2) ever observed by a space borne instrument, implying that very high concentrations of SO2 can occur in the lower troposphere during effusive eruptions

Intra-seasonal variability in tropospheric ozone and water vapor in the tropics

Nearly two years of tropospheric O3 and H2O data from the Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) instruments are analyzed to study the characteristics of intra-seasonal oscillation (ISO) of 20–100 day periods. The analysis shows the presence of ISO signals in O3 and H2O throughout much of the tropics including the north Atlantic not shown in previous studies. ISO variability west of the dateline appears as a manifestation of eastward propagation of the Madden-Julian Oscillation (MJO). Time series of tropospheric O3 and H2O are negatively correlated throughout much of the tropics, and mostly over ocean. This suggests lofting of air from convection as a basic driving mechanism, with convection transporting low amounts of O3 and high amounts of H2O upwards from the boundary layer. ISO/MJO related changes in O3 and H2O are a major source of variability and often exceed 25% of background concentrations

In-flight validation of Aura MLS ozone with CAFS partial ozone columns

A comprehensive data set of partial ozone columns was derived from the charge-coupled device (CCD) Actinic Flux Spectroradiometer (CAFS) measurements taken during the Polar 2005, Houston 2005, and Costa Rica 2006 Aura Validation Experiments (AVE). It was used to validate the colocated daytime Aura Microwave Limb Sounder (MLS) partial ozone columns along the aircraft tracks over diverse geophysical conditions. Results show that the MLS v.1.5 and CAFS ozone columns agree to better than 3% at pressure levels of 100 and 146 hPa, and to better than 5% at 215 hPa level. The partial ozone column differences between the two systems were the largest during the Polar AVE (PAVE) 2005 campaign (polar region, ~250 hPa pressure level), and the smallest during the CRAVE 2006 campaign (tropics, ~100 hPa pressure level). Overall, the averaged bias between the MLS and CAFS partial ozone column is about 2%, and the standard deviation of the differences is about 2%. The v.2.2 update of the MLS data tends to reduce the bias to less than 1%. In addition, the AVE 2005 campaign uncovered an altitude-dependent bias, where the MLS partial ozone columns above 100 and 146 hPa pressure levels were about 1% higher than the CAFS derived columns, while the bias increased to about 3 % in partial columns integrated above 215 hPa. However, the MLS and CAFS data track each other closely over a wide range of atmospheric conditions, and the differences lie within the combined uncertainties of the two data sets

Aerosols and surface UV products form Ozone Monitoring Instrument observations: An overview

We present an overview of the theoretical and algorithmic aspects of the Ozone Monitoring Instrument (OMI) aerosol and surface UV algorithms. Aerosol properties are derived from two independent algorithms. The nearUV algorithm makes use of OMI observations in the 350-390 nm spectral region to retrieve information on the absorption capacity of tropospheric aerosols. OMI-derived information on aerosol absorption includes the UV Aerosol Index and absorption optical depth at 388 nm. The other algorithm makes use of the full UV-to-visible OMI spectral coverage to derive spectral aerosol extinction optical depth. OMI surface UV products include erythemally weighted daily dose as well as erythemal dose rate and spectral UV irradiances calculated for local solar noon conditions. The advantages and limitations of the current algorithms are discussed, and a brief summary of several validation and evaluation analysis carried out to assess the current level of uncertainty of these products is presented. Copyright 2007 by the American Geophysical Union. U7 - Export Date: 2 August 2010 U7 - Source: Scopus U7 - Art. No.: D24S4

Validation of the Aura Ozone Monitoring Instrument total column ozone product

This paper is an overview of the validation of the total column ozone data products from the Ozone Monitoring Instrument (OMI) on board the NASA EOS-Aura satellite. OMI is an imaging UV/visible spectrometer that maps global ozone on a daily basis. There are two ozone products from OMI, one derived using the traditional TOMS retrieval algorithm and another derived using a Differential Optical Absorption Spectroscopy algorithm that is being developed to take advantage of the hyperspectral capabilities of OMI. Validation is primarily performed through comparison with a network of Dobson and Brewer ground stations and secondarily through campaigns conducted specifically to validate Aura. Comparison with an ensemble of 76 Northern Hemisphere ground stations shows that OMI-TOMS total column ozone averages 0.4% higher than the station average, with station-to-station standard deviation of ±0.6%. The comparison shows that the OMI-TOMS ozone was stable over the 2-year period with no evidence of drift relative to the ground network. The OMI-DOAS product is also stable but with a 1.1% offset and a seasonal variation of ±2%. During four aircraft validation campaigns using the NASA DC-8 and WB-57 aircraft, ozone above the aircraft was measured using an actinic flux instrument and compared with OMI ozone. These comparisons showed agreement within 2% over a broad range of latitude and viewing conditions. Only during the high-latitude flights did the OMI-DOAS ozone show the effects of a solar zenith angle dependent error