Data Filtering and Masking Options
Science Team Recommended Values:
| Filtering Variables | Parameters | Min | Max |
|---|---|---|---|
| Viewing Zenith Angle | all | 0 | 70 |
| Solar Zenith Angle | Column Amount Ozone, Effective Surface Reflectivity |
0 | 84 |
| NO2 Total Vertical Column Density, NO2 Trop Vertical Column Density |
0 | 88 | |
| UV Aerosol Index | 0 | 70 | |
| Reflectivity | Column Amount Ozone, Effective Surface Reflectivity UV Aerosol Index |
0 | 100 |
| Cloud Fraction | NO2 Total Vertical Column Density | 0 | 100 |
| NO2 Trop Vertical Column Density | 0 | 30 | |
| Path Length Index | Column Amount Ozone, Effective Surface Reflectivity, NO2 Total Vertical Column Density, NO2 Trop Vertical Column Density |
3 | 14 |
| UV Aerosol Index | 3 | 7 | |
| Ocean Glint Angle | Column Amount Ozone, Effective Surface Reflectivity, NO2 Total Vertical Column Density, NO2 Trop Vertical Column Density |
0 | - |
| UV Aerosol Index | +/-20 | - |
| Masking Flags | Parameters | Flags |
|---|---|---|
| Snow/Ice | all | yes |
Snow Ice
The snow ice flag is used to mask out regions where the snow/ice coverage is greater than 50% (based on NISE climatology). When this box is checked it will include scenes containing snow or ice.
Viewing Zenith Angle
The angle between the local zenith and the line of sight to the spacecraft.
Solar Zenith Angle
The angle between the local zenith and the line of sight to the sun.
Reflectivity (OMTO3G Parameters)
The effective surface reflectivity is a proxy for clouds, providing the ability to filter clear sky (i.e. < 15%) versus cloudy scenes. The reflectivity used is at 360 nm.
Cloud Fraction (OMNO2G Parameters)
Cloud fraction provides the ability to filter clear sky (i.e. < 15%) versus cloudy scenes.
Path Length Index
The path length index gives an indication of the best viewing condition, giving more importance to the viewing zenith angle than on solar zenith angle, particularly at higher latitudes where solar zenith angles are large. The path length index is defined as
1/cos(SZA) + 2/cos(VZA).
where SZA = solar zenith angle, and VZA = viewing zenith angle
Ocean Glint Width Angle
The ocean glint width angle is twice the scattering angle over water when the Sun is near overhead. The scattering angle is defined as
cos-1 ( cos(SZA)*cos(VZA) + sin(SZA)*sin(VZA)*cos(RAA) )
where SZA = solar zenith angle, VZA = viewing zenith angle, and RAA = relative azimuth angle.
| Please NOTE: data are also screened to exclude scenes with the South Atlantic anomaly flag set (in the MeasurementQualityFlags field), and the solar eclipse flag set (in the GroundPixelQualityFlags field). Data from descending portion of orbit are excluded. |
| Ozone and Reflectivity: only data values where the QualityFlags is 0 or 1 are included. |
| UV Aerosol Index: only data values where the QualityFlags is less than 6 are included. The UV Aerosol Index data are adjusted with respect to TOMS by subtracting 0.5. |
| NO2 Total and Tropospheric Vertical Column Denisity: the Below Cloud NO2 values have been added. The values have been screened so only data where the vcdQualityFlags bit 0 is not set (i.e. good data) are used. |
You may obtain the original Level 2G (unfiltered) data by selecting the "Order Subsetted Daily L2G Data" button and downloading the data to your machine.
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