Clouds and cloud shadows are common features of visible and infrared remotelysensed images collected from many parts of the world, particularly in humid and tropical regions. We have developed a simple and semiautomated method to mask clouds and shadows in Landsat ETM+ imagery, and have developed a recent cloud-free composite of multitemporal images for Puerto Rico and its adjacent islands that can be used for a variety of landscape analyses. Our assumption is that if clouds and shadows can be identified in a reference image, they can be replaced with data from other dates. We created cloud masks by using Landsat ETM+ band 1 (blue) and thermal band 6.1. Additionally, Landsat ETM+ band 4 (near infrared) and parameters of sun angle, topography, and cloud-shadow projection were used for directing and masking shadows. This methodology was applied to a set of 18 images from 1999 to 2003 to develop an island-wide image that is 96.5 percent cloud free. We considered the seasonality of the imagery when selecting reference images and building the mosaic in order to minimize variation in reflectance related to dry or wet season canopy characteristics. We developed a higher resolution data set by merging the 15-m resolution panchromatic band with the 30-m resolution Landsat ETM+ data. The methodology developed is simple and straightforward to use wherever obtaining cloud-free image data sets is desirable and can be integrated into other efforts that demand an accurate method for the identification of clouds and shadows.
Martinuzzi, Sebasti n; Gould, William A.; Ramos Gonzalez, Olga M. 2007. Creating cloud-free Landsat ETM+ data sets in tropical landscapes: cloud and cloud-shadow removal. U.S. Department of Agriculture, Forest Service, International Institute of Tropical Forestry. Gen. Tech. Rep. IITF-32.