Effects Of Topographic Corrections On Landsat-derived Phenology of Southern California Ecosystems

Abstract:

Topographic features such as elevation, slope, and aspect create local environmental conditions that can influence ecosystem characteristics and function in semi-arid regions. Topography also changes illumination conditions, creating light artifacts that affect satellite-measured reflectance. Before extracting semi-arid ecosystems properties from satellite measurements, topographic illumination artifacts need to be removed without altering the true topographic variability of such ecosystems. Many corrections techniques have been proposed, and their performance in reducing reflectance spatial variance have been extensively analysed and compared. Very little information is available on how topographic corrections affect the temporal variability of reflectance, although this type of information is critical when reflectance measurements are used to extract phenology or track recovery. We used the Google Earth Engine API to apply four different topographic corrections to a 10-years-long time series of Landsat TM images. The deviation of reflectance seasonality from known phenological information was then estimated and compared across vegetation classes and also correction methods. We will show our results using the Santa Ana Mountains as a study site, and will demonstrate the importance of topographic corrections in phenological studies.