Topographyc Shadow Influence on Optical Image Acquired by Satellite in the Southern Hemisphere

Abstract

During image acquisition, is usually chosen scenes with a lesser cloud cover to avoid loss of spectral information. However, when training samples are collected for image classification, the user finds shadowed areas. Such situation is similar to the presence of clouds since spectral information of these classes is the same in all optical bands of the sensor. This fact becomes more pronounced in mountainous relief areas due to shadow projection on the terrain, which can vary among all seasons during the solar year. With the goal to obtain images with a lower presence of shadow, it was simulated, under the same relief conditions, shading variation in function of latitude (0º to 40º S). Solar radiation models were processed for the days and times passages of the Landsat TM and ETM+ satellite on the Southern Hemisphere. It was verified that over 30º S and 40º S latitudes, a loss of shading area varying between 27% to 91 % and that images should be preferentially taken between October and February. For latitudes comprising 0º and 10º S, the loss was considered negligible, when we set a 10% threshold of loss in the total valid area in an image. According to the amount of radiation in a terrain, South and West areas received less direct solar radiation over the year for all analyzed latitudes in the modeling.

AgroShadow: A New Sentinel-2 Cloud Shadow Detection Tool for Precision Agriculture

“…Many discrimination methods and approaches were developed in the past years both for low and high-resolution remote sensing images [11][12][13]. Some of them are focused on shadows casted by ground features as building or trees (especially for high resolution images) [14,15], other on topographic shadows [16,17], lastly on clouds classification [18][19][20][21].…”