Remote Sensing Equipment is used to obtain information about an object from a distance, and, almost always, with no contact with the object. The term is widely used for earth observation data from aircraft and satellites. The sensing technology may detect available light, sound, infrared, magnetic, gravity or other signals, or actively scan with radar, lidar or ultrasound. A few applications require contact with the object being measured, for example, sea temperature at depth usually needs a submerged sensor in contact with the water.