Remote sensing is observing or measuring phenomena without direct physical contact, often from a distance.  In order to do this, sensors are very important.  Sensors measure physical quantities and convert them into a signal that can be read by an observer or by an electronic instrument.  There are two types of platforms that we can place sensors on to observe the earth.  They are:

1.  Orbital platforms which include satellites

2.  Sub-orbital platforms which include aircraft, drones, balloons, and kites.