Influence of sun angle differences in extracting surface area of water bodies

Galli, Gregory F.
Sensors used for collecting imagery (or data) record the amount of reflected radiation or light from Earth surface features. As the position of the Sun changes throughout the year the incident angle of the light also changes thus impacting the amount of reflected light. These variations influences the ability to distinguish and extract features such as water bodies in remotely sensed imagery. The objective of this research was to quantify the influence of sun angle in extracting surface areas of Pilot Butte, Keyhole, Fontenelle, and Bull Lake Reservoirs from Landsat Thematic Mapper images. Landsat images acquired in different months, i.e., different sun angle were obtained from USGS and were converted to Normalized Difference Wetness Index (NDWI) values ranging between -1 and +1. Surface areas of these water bodies were extracted based on the applying different thresholds on the NDWI values. Surface areas derived at different threshold values (0.0 – 0.2) were then analyzed for their sensitivity in comparison to the sun angle values.
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