Semiautomatic Detection of Artificial Terrestrial Targets for Remotely Sensed Image Georeferencing

Georeferencing of remote imagery with high spatial resolution can be achieved using the semiAUtomatic GEOreferencing (AUGEO) system which is based on artificial terrestrial targets (ATTs) and software AUGEO-2.0 for location and georeferencing. The aim of this letter is to describe the system and validate it. The ATTs consist of colored hexagonal tarps 0.25-1.0m in diameter, placed on the ground and georeferenced. The proposed software works as an add-on of Environment for Visualizing Images and was able to locate the ATTs (isolated or disposed in associated couples) in remote images based on its spectral band specificity. To validate the AUGEO system, ATTs were placed on the ground, and remote images were taken from airplanes and unmanned aerial vehicles several times throughout the year at two locations in Southern Spain in 2008. Three variables were considered to study ATT detection accuracy: 1) ATT size; 2) ATT color; and 3) distance between ATTs when they were coupled in pairs. The averaged accuracy for the coupled 1-m red ATTs (separated by 2.5 m) was 95.9%. As the ATT size decreased, the accuracy generally decreased, regardless of the color of the ATTs. Results from coupled analysis show that ATT detection increased as the distance between the ATTs decreased. The proposed system required less time than conventional georeferencing work and allowed the georeferencing of images that do not contain recognizable ground control points. This also contributed to the site-specific management of agricultural plots through remote sensing, which required high-spatial-resolution and accurate georeferenced images.