Search - GOME_DAILY |
Data DescriptionGlobal Ozone Monitoring Experiment-2 (GOME-2) Total Ozone Daily Data - The GOME-2 total ozone retrieval algorithm is based on OMI/TOMS (Ozone Monitoring Instrument / Total Ozone Mapping Spectrometer) V8 algorithm, which is a three-step process of successive estimation improvement. The algorithm uses a pair of wavelengths 331nm and 318nm (340nm and 331nm for high solar zenith angle) to derive total ozone and surface reflectivity. It first calculates N-value at the pair of wavelengths using input radiance/irradiance from GOME-2 level 1b data. With its geo-reference information, such as latitude, longitude, solar zenith angle, etc., the measured N-value is compared with pre-calculated N-value to derive the step-one total ozone and reflectivity. The pre-calculated N-value is generated by using OTMRAD forward radiative transfer model. In order to obtain step-two ozone, the profiles of ozone and temperature climatologies are then applied at all levels to account for seasonal and latitudinal variations in profile shape. In the last step, the step-two ozone estimation is modified to correct for wavelength dependent effects (tropospheric aerosol and sun glint) and local upper level profile shape effects. The algorithm writes out all the retrieval variables and corresponding geo-referenced information to PMF at the end of each scan process. Each day, the granules are accumulated to create the level 3 gridded map in ASCII and GRIB2 format. The Level 3 products are created by computing weighted averages of the Level 2 products with Fields of View intersecting each 1.25 degrees Longitude by 1.00 degree Latitude grid cell. (In polar regions the cells increase to 5.00 degrees Longitude.) The weights scale as the reciprocal of the relative path lengths (one divided by the sum of the secant of view angle plus secant of solar zenith angle) for each observation. The Magnesium II information is extracted daily from the GOME-2 1B granules, as soon as new solar radiance measurements are available. The product includes a 61-wavelength subset of the daily solar spectrum and a Mg II core-to-wing ratio for the spectrum. Our Mg II Index value is a simple ratio of the average of the irradiance measurements near three core wavelengths to the average of the irradiance measurements near four wavelengths at the wings, two at each wing. Each irradiance value is computed by interpolation of the pair of values for GOME-2 surrounding the following positions: 276.82, 276.97, 279.78, 279.92, 280.07, 283.03, and 283.17 nm. The daily gridded total ozone and Magnesium II products are available in ASCII format.
|
