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MODMGGA Global Geolocation Angle

MODIS Global Geolocation Angle (MODMGGA) files contain information on solar and instrument angles. Variations in solar illumination and sensor viewing geometry are corrected by modeling the geometric relationship and distance between the area of the Earth's surface imaged, the sun, and the sensor. Such models are required to make accurate atmospheric corrections, and to convert and/or calibrate data to known (absolute) radiation or reflectance units. Doing so facilitates comparisons between data, or mosaicing multiple images from a single sensor while maintaining uniform illumination conditions from scene to scene.

MODIS Geolocation Angle files are used as input to higher level products such as Surface Reflectance. Geometry information for each sensor observation is stored on a geolocated grid with Level 2 geophysical parameters as Level 2G (gridded) products. The multiple observations stored in the L2G structure are examined by the Level 3 processes to extract only the most relevant observations falling over each grid cell.

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