A method to build cloud free images from CBERS-4 AWFI sensor using median filtering

Abstract. Cloud free images are useful for applications where the user is more interested in the visual identification of variability of a phenomenon than in the actual values. The presence of clouds and their shadows hinder the visual interpretation in these applications. Median values in data sets are a better representation of the true value than the average when the data set is contaminated with unusual high or low values. Since clouds and their shadows are these unusual values, the median value of a pixel from images gathered in different conditions could provide true representation of the pixel value. To test this hypothesis, images from CBERS-4 AWFI sensor covering an area of 70 Km by 60 km around Brasília in Brazil and acquired from 2017/July/20th to 2017/August/24th were processed using data sets with 3, 5 and 6 images. The results indicate that the smaller set is enough to build a cloud free image where a pixel has at least 2 cloud free data. In more general cases, 6 images are enough to build a cloud free data.