Esri has launched a hub that will serve as the collection point for free remote sensing and imagery materials. The purpose of the hub is to help with the development of university-level instructional aids for introductory remote sensing and imagery classes.
The first materials on the hub are focused on hands-on learning labs as well as slide decks that introduce fundamental imagery and remote sensing concepts.
More materials will be added to the hub over the coming months. In the meantime, the available materials are:
Visit: Introduction to Remote Sensing and Imagery