Optical Remote Sensing
"Optical remote sensing is obtaining information about an area or phenomenon through a device that does not touch the area or phenomenon under study. Your eyes are a good example of remote sensing instruments. Many remote sensing devices are onboard satellites that monitor the Earth from space. Remote sensing allows mapping of vegetation, climate and atmospheric composition over large regions and to repeat the measurements consistently over many years. In this way remote sensing provides planetary-scale measurements of our climate system helping us develop and validate new theories. It also allows for monitoring the effectiveness of various solutions to reduce greenhouse gas emissions." (NASA 2014)
NASA 2014. “Remote Sensing.” 2014. https://www.nasa.gov/content/remote-sensing/.