OMTO3 Release Specific Information

Software Version

The current release of OMTO3 is version 0.9.45.

ECS Collection Number 2

OMTO3 v0.9.45 is the second release of the Software designed to produce total ozone from the OMI data. Changes from the previous version (v0.9.41 are listed below, in the Release History.

Known Issue List

This section describes significant issues unique to the OMTO3 v0.9.45 product relative to the TOMS ozone product.

1. The OMTO3 software applies adjustments to the radiance measurements for 317.5 nm, 331.2 nm, and 360 nm, the wavelengths used by the OMTO3 product. These adjustments are derived using a refinement of the procedure used to correct the cross-track problems with Earth Probe (EP) TOMS after 1999. The OMTO3 orbital output file stores the wavelengths and their corresponding adjustments for each scan or cross-track position in the additional file attributes section of the HDF metadata. The wavelength values are in "WavelengthOfAdjustment", and the values of the adjustments are in "NVXAdjustment."
   


2. Compared to TOMS, OMI's smaller field-of-view results in a larger "sea-glint" per unit field-of-view and a corresponding larger error in derived ozone under these conditions. The ozone error  typically manifests itself as a cross-track dependence over water that is not corrected by the adjustments described in the previous item.  This uncorrected error in the ozone can be up to 3%.
   


3. The OMTO3 Aerosol Index (AI) is not valid for solar zenith angles greater than approximately 60 degrees. Because the OMI solar zenith angles are typically higher than the solar zenith angles for TOMS at the same latitude, the OMI AI become invalid at somewhat lower latitudes than TOMS. This may show up as a cross-track dependence in the OMI AI, and is not corrected by the radiance measurement adjustments. This uncorrected error in the AI can be up to 4%.


4. Compared to TOMS, the OMTO3 Aerosol Index is 0.5 NVALUE high. Users of the Aerosol Index are advised to make this correction, for consistency with the TOMS data record.

Release History

1. V0.9.45m calculates radiance residuals at  12 wavelengths (listed below), which include the six EP/TOMS wavelengths used in the v0.9.41 release, plus six additional wavelengths. The residuals at the additional wavelengths are used to check instrument calibration and also serve as input for deriving the SO2 column. The SO2 data will be released later as a separate product. Note, that the algorithm for deriving total ozone remains the same as in v0.9.41.

308.70nm,  310.80nm,  311.85nm,  312.61nm,  313.20nm,  314.40nm,

317.62nm,  322.42nm,  331.34nm,  345.40nm,  360.15nm,  372.80nm


2. The OMTO3 algorithm uses the solar irradiances measured by OMI on a single day (orbit 3725 on March 28, 2005), and assumes that neither the true solar irradiance (at 1 AU) nor the instrument calibration change with time. However, the solar irradiance needs to be corrected for the Sun-Earth distance effect. This was inadvertently left out in Version 0.9.41 for orbits 3709 through 4794. Version 0.9.45 makes the necessary adjustment. Orbits 3709 through 4794 have been reprocessed with v0.9.45 and the data replaced. Please ensure you are using the reprocessed data for these orbits by verifying in the metadata the value of REPROCESSINGACTUAL is "processed 2 times" and the value of PGEVERSION is "0.9.45" .