Sensor Types
Active vs. Passive
Passive Sensors
The most common remote sensing imagery comes from passive multispectral sensors. These sensors “pick up” the natural light from the sun and its reflectance from the Earth’s surface. The images are similar to an ordinary photograph with a digital camera and consist of different channels for particular wavelengths. Most multispectral platforms have at least three spectral channels (red, green, blue; aka RGB) and a maximum of twelve spectral channels. Hyperspectral sensors take this to the next level and consist of > 100 channels for different wavelengths.
Active Sensors
Active sensors emit their radiation by themselves. Therefore, they are less dependent on environmental conditions like e.g. the angle of the sun. The long wavelengths of a radar sensor e.g. can penetrate through clouds making imagery more consistent. In future units we will see how LiDAR data works and what information can be retrieved from it.